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Massimo GASPARI

Professore Ordinario
Dipartimento di Scienze Fisiche, Informatiche e Matematiche sede ex-Fisica

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Pubblicazioni

2024 - CHEX-MATE: Characterization of the intra-cluster medium temperature distribution [Articolo su rivista]
Lovisari, L.; Ettori, S.; Rasia, E.; Gaspari, M.; Bourdin, H.; Campitiello, M. G.; Rossetti, M.; Bartalucci, I.; De Grandi, S.; De Luca, F.; De Petris, M.; Eckert, D.; Forman, W.; Gastaldello, F.; Ghizzardi, S.; Jones, C.; Kay, S.; Kim, J.; Maughan, B. J.; Mazzotta, P.; Pointecouteau, E.; Pratt, G. W.; Sayers, J.; Sereno, M.; Simonte, M.; Tozzi, P.
abstract

Context. Galaxy clusters grow through the accretion of mass over cosmic time. Their observed properties are then shaped by how baryons distribute and energy is diffused. Thus, a better understanding of spatially resolved, projected thermodynamic properties of the intra-cluster medium (ICM) may provide a more consistent picture of how mass and energy act locally in shaping the X-ray observed quantities of these massive virialized or still collapsing structures. Aims. We study the perturbations in the temperature (and density) distribution to evaluate and characterize the level of inhomogeneities and the related dynamical state of the ICM. Methods. We obtain and analyze the temperature and density distribution for 28 clusters (2.4 × 1014Mo˙ < M500 < 1.2 × 1015Mo˙; 0.07 < z < 0.45) selected from the CHEX-MATE sample. We use these spatially resolved two-dimensional distributions to measure the global and radial scatter and identify the regions that deviate the most from the average distribution. During this process, we introduce three dynamical state estimators and produce "clean"temperature profiles after removing the most deviant regions. Results. We find that the temperature distribution of most of the clusters is skewed towards high temperatures and is well described by a log-normal function. There is no indication that the number of regions deviating more than 1σ from the azimuthal value is correlated with the dynamical state inferred from morphological estimators. The removal of these regions leads to local temperature variations up to 10- 20% and an average increase of ∼5% in the overall cluster temperatures. The measured relative intrinsic scatter within R500, σ T,int/T, has values of 0.17-0.05+0.08, and is almost independent of the cluster mass and dynamical state. Comparing the scatter of temperature and density profiles to hydrodynamic simulations, we constrain the average Mach number regime of the sample to M3D = 0.36-0.09+0.16. We infer the ratio between the energy in turbulence and the thermal energy, and translate this ratio in terms of a predicted hydrostatic mass bias b, estimating an average value of b ∼ 0.11 (covering a range between 0 and 0.37) within R500. Conclusions. This study provides detailed temperature fluctuation measurements for 28 CHEX-MATE clusters which can be used to study turbulence, derive the mass bias, and make predictions on the scaling relation properties.

2024 - Deep Chandra Observations of A2495: A Possible Sloshing-regulated Feedback Cycle in a Triple-offset Galaxy Cluster [Articolo su rivista]
Rosignoli, L.; Ubertosi, F.; Gitti, M.; Brighenti, F.; Pasini, T.; O'Sullivan, E.; Gastaldello, F.; Gaspari, M.; Temi, P.
abstract

We present the analysis of new, deep Chandra observations (130 ks) of the galaxy cluster A2495. This object is known for the presence of a triple offset between the peaks of the intracluster medium (ICM), the brightest cluster galaxy (BCG), and the warm gas glowing in Hα line. The new Chandra data confirm that the X-ray emission peak is located at a distance of ∼6.2 kpc from the BCG, and at ∼3.9 kpc from the Hα emission peak. Moreover, we identify two generations of X-ray cavities in the ICM, likely inflated by the central radio galaxy activity. Through a detailed morphological and spectral analysis, we determine that the power of the active galactic nucleus (AGN) outbursts (P cav = 4.7 ± 1.3 × 1043 erg s−1) is enough to counterbalance the radiative losses from ICM cooling (L cool = 5.7 ± 0.1 × 1043 erg s−1). This indicates that, despite a fragmented cooling core, A2495 still harbors an effective feedback cycle. We argue that the offsets are most likely caused by sloshing of the ICM, supported by the presence of spiral structures and a probable cold front in the gas at ∼58 kpc east of the center. Ultimately, we find that the outburst interval between the two generations of X-ray cavities is of the order of the dynamical sloshing timescale, as already hinted from the previous Chandra snapshot. We thus speculate that sloshing may be able to regulate the timescales of AGN feedback in A2495, by periodically fueling the central AGN.

2024 - Feeding and feedback processes in the Spiderweb proto-intracluster medium [Articolo su rivista]
Lepore, M.; Di Mascolo, L.; Tozzi, P.; Churazov, E.; Mroczkowski, T.; Borgani, S.; Carilli, C.; Gaspari, M.; Ginolfi, M.; Liu, A.; Pentericci, L.; Rasia, E.; Rosati, P.; Rottgering, H. J. A.; Anderson, C. S.; Dannerbauer, H.; Miley, G.; Norman, C.
abstract

Context. We present a detailed analysis of the thermal, diffuse emission of the proto-intracluster medium (proto-ICM) detected in the halo of the Spiderweb Galaxy at z=2.16, within a radius of ~150 kpc. Aims. Our main goal is to derive the thermodynamic profiles of the proto-ICM, establish the potential presence of a cool core and constrain the classical mass deposition rate (MDR) that may feed the nuclear and the star formation (SF) activity, and estimate the available energy budget of the ongoing feedback process. Methods. We combined deep X-ray data from Chandra and millimeter observations of the Sunyaev-Zeldovich (SZ) effect obtained by the Atacama Large Millimeter/submillimeter Array (ALMA). Results. Thanks to independent measurements of the pressure profile from the ALMA SZ observation and the electron density profile from the available X-ray data, we derived, for the first time, the temperature profile in the ICM of a z> 2 protocluster. It reveals the presence of a strong cool core (comparable to local ones) that may host a significant mass deposition flow, consistent with the measured local SF values. We also find mild evidence of an asymmetry in the X-ray surface brightness distribution, which may be tentatively associated with a cavity carved into the proto-ICM by the radio jets. In this case, the estimated average feedback power would be in excess of ~1043 erg s-1. Alternatively, the asymmetry may be due to the young dynamical status of the halo. Conclusions. The cooling time of baryons in the core of the Spiderweb protocluster is estimated to be ~0.1 Gyr, implying that the baryon cycle in the first stages of protocluster formation is characterized by a high-duty cycle and a very active environment. In the case of the Spiderweb protocluster, we are witnessing the presence of a strongly peaked core that is possibly hosting a cooling flow with a MDR up to 250-1000 M⊙ yr-1, responsible for feeding both the central supermassive black hole (SMBH) and the high star formation rate (SFR) observed in the Spiderweb Galaxy. This phase is expected to be rapidly followed by active galactic nucleus (AGN) feedback events, whose onset may have already left an imprint in the radio and X-ray appearance of the Spiderweb protocluster, eventually driving the ICM into a self-regulated, long-term evolution in less than one Gyr.

2023 - Astrophysics with the Laser Interferometer Space Antenna [Articolo su rivista]
Amaro-Seoane, P.; Andrews, J.; Arca Sedda, M.; Askar, A.; Baghi, Q.; Balasov, R.; Bartos, I.; Bavera, S. S.; Bellovary, J.; Berry, C. P. L.; Berti, E.; Bianchi, S.; Blecha, L.; Blondin, S.; Bogdanovic, T.; Boissier, S.; Bonetti, M.; Bonoli, S.; Bortolas, E.; Breivik, K.; Capelo, P. R.; Caramete, L.; Cattorini, F.; Charisi, M.; Chaty, S.; Chen, X.; Chruslinska, M.; Chua, A. J. K.; Church, R.; Colpi, M.; D'Orazio, D.; Danielski, C.; Davies, M. B.; Dayal, P.; De Rosa, A.; Derdzinski, A.; Destounis, K.; Dotti, M.; Dutan, I.; Dvorkin, I.; Fabj, G.; Foglizzo, T.; Ford, S.; Fouvry, J. -B.; Franchini, A.; Fragos, T.; Fryer, C.; Gaspari, M.; Gerosa, D.; Graziani, L.; Groot, P.; Habouzit, M.; Haggard, D.; Haiman, Z.; Han, W. -B.; Istrate, A.; Johansson, P. H.; Khan, F. M.; Kimpson, T.; Kokkotas, K.; Kong, A.; Korol, V.; Kremer, K.; Kupfer, T.; Lamberts, A.; Larson, S.; Lau, M.; Liu, D.; Lloyd-Ronning, N.; Lodato, G.; Lupi, A.; Ma, C. -P.; Maccarone, T.; Mandel, I.; Mangiagli, A.; Mapelli, M.; Mathis, S.; Mayer, L.; Mcgee, S.; Mckernan, B.; Miller, M. C.; Mota, D. F.; Mumpower, M.; Nasim, S. S.; Nelemans, G.; Noble, S.; Pacucci, F.; Panessa, F.; Paschalidis, V.; Pfister, H.; Porquet, D.; Quenby, J.; Ricarte, A.; Ropke, F. K.; Regan, J.; Rosswog, S.; Ruiter, A.; Ruiz, M.; Runnoe, J.; Schneider, R.; Schnittman, J.; Secunda, A.; Sesana, A.; Seto, N.; Shao, L.; Shapiro, S.; Sopuerta, C.; Stone, N. C.; Suvorov, A.; Tamanini, N.; Tamfal, T.; Tauris, T.; Temmink, K.; Tomsick, J.; Toonen, S.; Torres-Orjuela, A.; Toscani, M.; Tsokaros, A.; Unal, C.; Vazquez-Aceves, V.; Valiante, R.; van Putten, M.; van Roestel, J.; Vignali, C.; Volonteri, M.; Wu, K.; Younsi, Z.; Yu, S.; Zane, S.; Zwick, L.; Antonini, F.; Baibhav, V.; Barausse, E.; Bonilla Rivera, A.; Branchesi, M.; Branduardi-Raymont, G.; Burdge, K.; Chakraborty, S.; Cuadra, J.; Dage, K.; Davis, B.; de Mink, S. E.; Decarli, R.; Doneva, D.; Escoffier, S.; Gandhi, P.; Haardt, F.; Lousto, C. O.; Nissanke, S.; Nordhaus, J.; O'Shaughnessy, R.; Portegies Zwart, S.; Pound, A.; Schussler, F.; Sergijenko, O.; Spallicci, A.; Vernieri, D.; Vigna-Gomez, A.
abstract

The Laser Interferometer Space Antenna (LISA) will be a transformative experiment for gravitational wave astronomy, and, as such, it will offer unique opportunities to address many key astrophysical questions in a completely novel way. The synergy with ground-based and space-born instruments in the electromagnetic domain, by enabling multi-messenger observations, will add further to the discovery potential of LISA. The next decade is crucial to prepare the astrophysical community for LISA’s first observations. This review outlines the extensive landscape of astrophysical theory, numerical simulations, and astronomical observations that are instrumental for modeling and interpreting the upcoming LISA datastream. To this aim, the current knowledge in three main source classes for LISA is reviewed; ultra-compact stellar-mass binaries, massive black hole binaries, and extreme or interme-diate mass ratio inspirals. The relevant astrophysical processes and the established modeling techniques are summarized. Likewise, open issues and gaps in our understanding of these sources are highlighted, along with an indication of how LISA could help making progress in the different areas. New research avenues that LISA itself, or its joint exploitation with upcoming studies in the electromagnetic domain, will enable, are also illustrated. Improvements in modeling and analysis approaches, such as the combination of numerical simulations and modern data science techniques, are discussed. This review is intended to be a starting point for using LISA as a new discovery tool for understanding our Universe.

2023 - CHEX-MATE: A non-parametric deep learning technique to deproject and deconvolve galaxy cluster X-ray temperature profiles [Articolo su rivista]
Iqbal, A.; Pratt, G. W.; Bobin, J.; Arnaud, M.; Rasia, E.; Rossetti, M.; Duffy, R. T.; Bartalucci, I.; Bourdin, H.; De Luca, F.; De Petris, M.; Donahue, M.; Eckert, D.; Ettori, S.; Ferragamo, A.; Gaspari, M.; Gastaldello, F.; Gavazzi, R.; Ghizzardi, S.; Lovisari, L.; Mazzotta, P.; Maughan, B. J.; Pointecouteau, E.; Sereno, M.
abstract

Temperature profiles of the hot galaxy cluster intracluster medium (ICM) have a complex non-linear structure that traditional parametric modelling may fail to fully approximate. For this study, we made use of neural networks, for the first time, to construct a data-driven non-parametric model of ICM temperature profiles. A new deconvolution algorithm was then introduced to uncover the true (3D) temperature profiles from the observed projected (2D) temperature profiles. An auto-encoder-inspired neural network was first trained by learning a non-linear interpolatory scheme to build the underlying model of 3D temperature profiles in the radial range of [0.02- 2] R500, using a sparse set of hydrodynamical simulations from the THREE HUNDRED PROJECT. A deconvolution algorithm using a learning-based regularisation scheme was then developed. The model was tested using high and low resolution input temperature profiles, such as those expected from simulations and observations, respectively. We find that the proposed deconvolution and deprojection algorithm is robust with respect to the quality of the data, the morphology of the cluster, and the deprojection scheme used. The algorithm can recover unbiased 3D radial temperature profiles with a precision of around 5% over most of the fitting range. We apply the method to the first sample of temperature profiles obtained with XMM-Newton for the CHEX-MATE project and compared it to parametric deprojection and deconvolution techniques. Our work sets the stage for future studies that focus on the deconvolution of the thermal profiles (temperature, density, pressure) of the ICM and the dark matter profiles in galaxy clusters, using deep learning techniques in conjunction with X-ray, Sunyaev Zel'Dovich (SZ) and optical datasets.

2023 - CHEX-MATE: Constraining the origin of the scatter in galaxy cluster radial X-ray surface brightness profiles [Articolo su rivista]
Bartalucci, I.; Molendi, S.; Rasia, E.; Pratt, G. W.; Arnaud, M.; Rossetti, M.; Gastaldello, F.; Eckert, D.; Balboni, M.; Borgani, S.; Bourdin, H.; Campitiello, M. G.; De Grandi, S.; De Petris, M.; Duffy, R. T.; Ettori, S.; Ferragamo, A.; Gaspari, M.; Gavazzi, R.; Ghizzardi, S.; Iqbal, A.; Kay, S. T.; Lovisari, L.; Mazzotta, P.; Maughan, B. J.; Pointecouteau, E.; Riva, G.; Sereno, M.
abstract

We investigate the statistical properties and the origin of the scatter within the spatially resolved surface brightness profiles of the CHEXâ MATE sample, formed by 118 galaxy clusters selected via the SZ effect. These objects have been drawn from the Planck SZ catalogue and cover a wide range of masses, M500â =â [2â â â 15]à - 1014â Mâ , and redshift, zâ =â [0.05,â 0.6]. We derived the surface brightness and emission measure profiles and determined the statistical properties of the full sample and sub-samples according to their morphology, mass, and redshift. We found that there is a critical scale, Râ â ¼â 0.4R500, within which morphologically relaxed and disturbed object profiles diverge. The median of each sub-sample differs by a factor of â ¼10 at 0.05R500. There are no significant differences between mass- and redshift-selected sub-samples once proper scaling is applied. We compare CHEXâ MATE with a sample of 115 clusters drawn from the THE THREE HUNDRED suite of cosmological simulations. We found that simulated emission measure profiles are systematically steeper than those of observations. For the first time, the simulations were used to break down the components causing the scatter between the profiles. We investigated the behaviour of the scatter due to object-by-object variation. We found that the high scatter, approximately 110%, at Râ <â 0.4R500YSZ is due to a genuine difference between the distribution of the gas in the core of the clusters. The intermediate scale, R500YSZâ =â [0.4â 0.8], is characterised by the minimum value of the scatter on the order of 0.56, indicating a region where cluster profiles are the closest to the self-similar regime. Larger scales are characterised by increasing scatter due to the complex spatial distribution of the gas. Also for the first time, we verify that the scatter due to projection effects is smaller than the scatter due to genuine object-by-object variation in all the considered scales.

2023 - Compton-Thick AGN in the NuSTAR Era X: Analysing seven local CT-AGN candidates [Articolo su rivista]
Sengupta, D.; Marchesi, S.; Vignali, C.; Torres-Alba, N.; Bertola, E.; Pizzetti, A.; Lanzuisi, G.; Salvestrini, F.; Zhao, X.; Gaspari, M.; Gilli, R.; Comastri, A.; Traina, A.; Tombesi, F.; Silver, R.; Pozzi, F.; Ajello, M.
abstract

Context. We present the broad-band X-ray spectral analysis (0.6a-50 keV) of seven Compton-Thick active galactic nuclei (CT-AGN; line-of-sight (LOS) column density > 1024 cma-2) candidates selected from the Swift-BAT 100 month catalogue using archival NuSTAR data. Aims. We aim to obtain a complete census of the heavily obscured AGN in the local Universe (za-0.05). Methods. This work is in continuation of the ongoing research of the Clemson-INAF group to classify CT-AGN candidates at redshift za-0.05 using physically motivated torus models. Results. Our results confirm that three out of seven targets are bona fide CT-AGN. Adding our results to the previously analysed sources using NuSTAR data, we increase the population of bona fide CT-AGN by a9%, bringing the total number to 35 out of 414 AGN. We also performed a comparative study using MYTorus and borus02 on the spectra in our sample, finding that both physical models are strongly consistent in the parameter space of LOS column density and photon index. Furthermore, we also investigate the clumpiness of the torus clouds by separately computing the LOS and average torus column densities in each of the seven sources. Adding our results to all the previous 48 CT-AGN candidates analysed by the Clemson-INAF research team for which NuSTAR observations are available, we find that 78% of the sources are likely to have a clumpy distribution of the obscuring material surrounding the accreting supermassive black hole.

2023 - Does absorption against AGN reveal supermassive black hole accretion? [Articolo su rivista]
Rose, T.; Mcnamara, B. R.; Combes, F.; Edge, A. C.; Fabian, A. C.; Gaspari, M.; Russell, H.; Salome, P.; Tremblay, G.; Ferland, G.
abstract

Galaxies often contain large reservoirs of molecular gas that shape their evolution. This can be through cooling of the gas - which leads to star formation, or accretion on to the central supermassive black hole - which fuels active galactic nucleus (AGN) activity and produces powerful feedback. Molecular gas has been detected in early-type galaxies on scales of just a few tens to hundreds of solar masses by searching for absorption against their compact radio cores. Using this technique, ALMA has found absorption in several brightest cluster galaxies, some of which show molecular gas moving towards their galaxy's core at hundreds of km s-1. In this paper, we constrain the location of this absorbing gas by comparing each galaxy's molecular emission and absorption. In four galaxies, the absorption properties are consistent with chance alignments between the continuum and a fraction of the molecular clouds visible in emission. In four others, the properties of the absorption are inconsistent with this scenario. In these systems, the absorption is likely produced by a separate population of molecular clouds in close proximity to the galaxy core and with high inward velocities and velocity dispersions. We thus deduce the existence of two types of absorber, caused by chance alignments between the radio core and: (i) a fraction of the molecular clouds visible in emission, and (ii) molecular clouds close to the AGN, in the process of accretion. We also present the first ALMA observations of molecular emission in S555, Abell 2390, RXC J1350.3+0940, and RXC J1603.6+1553 - with the latter three having Mmol > 1010 Mθ.

2023 - GBT/MUSTANG-2 900 resolution imaging of the SZ effect in MS0735.6+7421: Confirmation of the SZ cavities through direct imaging (Corrigendum) [Articolo su rivista]
Orlowski-Scherer, J.; Haridas, S. K.; Di Mascolo, L.; Sarmiento, K. P.; Romero, C. E.; Dicker, S.; Mroczkowski, T.; Bhandarkar, T.; Churazov, E.; Clarke, T. E.; Devlin, M.; Gaspari, M.; Lowe, I.; Mason, B.; Sarazin, C. L.; Sievers, J.; Sunyaev, R.
abstract

2023 - Inferences from Surface Brightness Fluctuations of Zwicky 3146 via the Sunyaev-Zel’dovich Effect and X-Ray Observations [Articolo su rivista]
Romero, C. E.; Gaspari, M.; Schellenberger, G.; Bhandarkar, T.; Devlin, M.; Dicker, S. R.; Forman, W.; Khatri, R.; Kraft, R.; Di Mascolo, L.; Mason, B. S.; Moravec, E.; Mroczkowski, T.; Nulsen, P.; Orlowski-Scherer, J.; Sarmiento, K. P.; Sarazin, C.; Sievers, J.; Su, Y.
abstract

The galaxy cluster Zwicky 3146 is a sloshing cool-core cluster at z = 0.291 that in Sunyaev-Zel’dovich (SZ) imaging does not appear to exhibit significant pressure substructure in the intracluster medium. We perform a surface brightness fluctuation analysis via Fourier amplitude spectra on SZ (MUSTANG-2) and X-ray (XMM-Newton) images of this cluster. These surface brightness fluctuations can be deprojected to infer pressure and density fluctuations from the SZ and X-ray data, respectively. In the central region (Ring 1, r < 100″ = 440 kpc, in our analysis), we find fluctuation spectra that suggest injection scales around 200 kpc (∼140 kpc from pressure fluctuations and ∼250 kpc from density fluctuations). When comparing the pressure and density fluctuations in the central region, we observe a change in the effective thermodynamic state from large to small scales, from isobaric (likely due to the slow sloshing) to adiabatic (due to more vigorous motions). By leveraging scalings from hydrodynamical simulations, we find an average 3D Mach number ≈0.5. We further compare our results to other studies of Zwicky 3146 and, more broadly, to other studies of fluctuations in other clusters.

2023 - Multiple Shock Fronts in RBS 797: The Chandra Window on Shock Heating in Galaxy Clusters [Articolo su rivista]
Ubertosi, F.; Gitti, M.; Brighenti, F.; Mcdonald, M.; Nulsen, P.; Donahue, M.; Brunetti, G.; Randall, S.; Gaspari, M.; Ettori, S.; Calzadilla, M.; Ignesti, A.; Feretti, L.; Blanton, E. L.
abstract

Using ∼427 ks of Chandra observations, we present a study of shock heating and intracluster medium (ICM) cooling in the galaxy cluster RBS 797. We discover three nested pairs of weak shocks at roughly 50, 80, and 130 kpc from the center. The total energy associated with the shocks is ∼6 × 1061 erg, with the central active galactic nucleus (AGN) driving a pair of weak shocks every 20-30 Myr with a power P sh ≈ 1046 erg s−1. Based on its morphology and age (∼30 Myr), the inner cocoon shock is associated with the four equidistant X-ray cavities previously discovered. From the thermodynamic analysis of the inner 30 kpc, we find evidence for ICM condensation into colder gas between and behind the X-ray cavities. The total AGN mechanical power (cavities and shocks) of 3.4 × 1046 erg s−1 can balance the ICM radiative losses, estimated as L cool = 2.3 × 1045 erg s−1. By building plots of P cav versus L cool, P shock versus L cool, and P tot versus L cool for RBS 797 and 14 other galaxy clusters, galaxy groups, and elliptical galaxies where both cavities and shocks are detected, we verify that the most powerful outbursts are found in the strongest cooling systems. Ultimately, we observe that the mechanical power of the AGN exceeds the gas radiative losses by a factor that is different for FR I and FR II radio galaxies, being less than a few tens for FR Is (as RBS 797) and more than roughly 100 for FR IIs.

2023 - Physical cool-core condensation radius in massive galaxy clusters [Articolo su rivista]
Wang, Lei; Tozzi, Paolo; Yu, Heng; Gaspari, Massimo; Ettori, Stefano
abstract

We investigate the properties of cool cores in an optimally selected sampleof 37 massive and X-ray-bright galaxy clusters, with regular morphologies,observed with Chandra. We measured the density, temperature, and abundanceradial profiles of their intracluster medium (ICM). From these independentquantities, we computed the cooling (tcool) free-fall (tff), and turbulence(teddy) timescales as a function of radius. By requiring the profile-crossingcondition, tcool=teddy=1, we measured the cool-core condensation radius Rccc,within which the balancing feeding and feedback processes generate theturbulent condensation rain and related chaotic cold accretion (CCA). We alsoconstrained the complementary (quenched) cooling flow radius Rqcf, obtained viathe condition tcool=25Xtff, that encompasses the region of thermally unstablecooling. We find that in our cluster sample and in the limited redshift rangeconsidered (1.3E14<16.6E14 Msun, 0.03<0.29), the distribution of Rcccpeaks at 0.01r500 and the entire range remains below 0.07r500, with a very weakincrease with redshift and no dependence on the cluster mass. We find that Rqcfis typically 3 times larger than Rccc, with a wider distribution, and growingmore slowly along Rccc, according to an average relation Rqcf~Rccc^(0.46), witha large intrinsic scatter. We suggest that this sublinear relation can beunderstood as an effect of the micro rain of pockets of cooled gas flickeringin the turbulent ICM, whose dynamical and thermodynamical properties arereferred to as "macro weather". Substituting the classical cool-core radiusR(7.7Gyr), we propose that Rqcf is an indicator of the size of the global corestied to the long-term macro weather, with the inner Rccc closely tracing theeffective condensation rain and chaotic cold accretion (CCA) zone that feedsthe central supermassive black hole.

2023 - Still alive and kicking: A significant outburst in changing-look AGN Mrk 1018 [Articolo su rivista]
Brogan, R.; Krumpe, M.; Homan, D.; Urrutia, T.; Granzer, T.; Husemann, B.; Neumann, J.; Gaspari, M.; Vaughan, S. P.; Croom, S. M.; Combes, F.; Perez Torres, M.; Coil, A.; Mcelroy, R.; Winkel, N.; Singha, M.
abstract

Context. Changing-look active galactic nuclei (AGN) have been observed to change their optical spectral type. Mrk 1018 is particularly unique: First classified as a type 1.9 Seyfert galaxy, it transitioned to being a type 1 Seyfert galaxy a few years later before returning to its initial classification as a type 1.9 Seyfert galaxy after ∼30 years. Aims. We present the results of a high-cadence optical monitoring programme that caught a major outburst in 2020. Due to sunblock, only the decline could be observed for ∼200 days. We studied X-ray, UV, optical, and infrared data before and after the outburst to investigate the responses of the AGN structures. Methods. We derived a u'-band light curve of the AGN contribution alone. The flux increased by a factor of ∼13. We confirmed this in other optical bands and determined the shape and speed of the decline in each waveband. The shapes of Hβ and Hα were analysed before and after the event. Two XMM-Newton observations (X-ray and UV) from before and after the outburst were also exploited. Results. The outburst is asymmetric, with a swifter rise than decline. The decline is best fit by a linear function, ruling out a tidal disruption event. The optical spectrum shows no change approximately eight months before and 17 months after. The UV flux is increased slightly after the outburst but the X-ray primary flux is unchanged. However, the 6.4 keV iron line has doubled in strength. Infrared data taken 13 days after the observed optical peak already show an increased emission level as well. Conclusions. Calculating the distance of the broad-line region and inner edge of the torus from the supermassive black hole can explain the multi-wavelength response to the outburst, in particular: I) the unchanged Hβ and Hα lines, ii) the unchanged primary X-ray spectral components, iii) the rapid and extended infrared response, as well as iv) the enhanced emission of the reflected 6.4 keV line. The outburst was due to a dramatic and short-lasting change in the intrinsic accretion rate. We discuss different models as potential causes.

2023 - Supermassive Black Hole Winds in X-rays: SUBWAYS: I. Ultra-fast outflows in quasars beyond the local Universe [Articolo su rivista]
Matzeu, G. A.; Brusa, M.; Lanzuisi, G.; Dadina, M.; Bianchi, S.; Kriss, G.; Mehdipour, M.; Nardini, E.; Chartas, G.; Middei, R.; Piconcelli, E.; Gianolli, V.; Comastri, A.; Longinotti, A. L.; Krongold, Y.; Ricci, F.; Petrucci, P. O.; Tombesi, F.; Luminari, A.; Zappacosta, L.; Miniutti, G.; Gaspari, M.; Behar, E.; Bischetti, M.; Mathur, S.; Perna, M.; Giustini, M.; Grandi, P.; Torresi, E.; Vignali, C.; Bruni, G.; Cappi, M.; Costantini, E.; Cresci, G.; De Marco, B.; De Rosa, A.; Gilli, R.; Guainazzi, M.; Kaastra, J.; Kraemer, S.; La Franca, F.; Marconi, A.; Panessa, F.; Ponti, G.; Proga, D.; Ursini, F.; Baldini, P.; Fiore, F.; King, A. R.; Maiolino, R.; Matt, G.; Merloni, A.
abstract

We present a new X-ray spectroscopic study of 22 luminous (2 × 1045 ≲ Lbol/erg s-1 ≲ 2 × 1046) active galactic nuclei (AGNs) at intermediate redshifts (0.1 ≲ z ≲ 0.4), as part of the SUpermassive Black hole Winds in the x-rAYS (SUBWAYS) sample, mostly composed of quasars and type 1 AGNs. Here, 17 targets were observed with XMM-Newton in 2019- 2020, and the remaining 5 are from previous observations. The aim of this large campaign (1.45 Ms duration) is to characterise the various manifestations of winds in the X-rays driven from supermassive black holes in AGNs. In this paper we focus on the search for and characterisation of ultra-fast outflows (UFOs), which are typically detected through blueshifted absorption troughs in the Fe K band (E > 7 keV). By following Monte Carlo procedures, we confirm the detection of absorption lines corresponding to highly ionised iron (e.g. Fe XXV Hα and Fe XXVI Lyα) in 7 out of 22 sources at the ≳95% confidence level (for each individual line). The global combined probability of such absorption features in the sample is > 99.9%. The SUBWAYS campaign, based on XMM-Newton, extends to higher luminosities and redshifts than previous local studies on Seyferts. We find a UFO detection fraction of ∼30% of the total sample, which is in agreement with previous findings. This work independently provides further support for the existence of highly ionised matter propagating at mildly relativistic speeds (≳0.1c) in a considerable fraction of AGNs over a broad range of luminosities, which is believed to play a key role in the self-regulated AGN feeding-feedback cycle, as also supported by hydrodynamical multi-phase simulations.

2023 - Supermassive Black Hole Winds in X-rays: SUBWAYS: II. HST UV spectroscopy of winds at intermediate redshifts [Articolo su rivista]
Mehdipour, M.; Kriss, G. A.; Brusa, M.; Matzeu, G. A.; Gaspari, M.; Kraemer, S. B.; Mathur, S.; Behar, E.; Bianchi, S.; Cappi, M.; Chartas, G.; Costantini, E.; Cresci, G.; Dadina, M.; De Marco, B.; De Rosa, A.; Dunn, J. P.; Gianolli, V. E.; Giustini, M.; Kaastra, J. S.; King, A. R.; Krongold, Y.; La Franca, F.; Lanzuisi, G.; Longinotti, A. L.; Luminari, A.; Middei, R.; Miniutti, G.; Nardini, E.; Perna, M.; Petrucci, P. -O.; Piconcelli, E.; Ponti, G.; Ricci, F.; Tombesi, F.; Ursini, F.; Vignali, C.; Zappacosta, L.
abstract

We present a UV spectroscopic study of ionized outflows in 21 active galactic nuclei (AGN), observed with the Hubble Space Telescope (HST). The targets of the Supermassive Black Hole Winds in X-rays (SUBWAYS) sample were selected with the aim to probe the parameter space of the underexplored AGN between the local Seyfert galaxies and the luminous quasars at high redshifts. Our targets, spanning redshifts of 0.1- 0.4 and bolometric luminosities (Lbol) of 1045- 1046 erg s-1, have been observed with a large multi-wavelength campaign using XMM-Newton, NuSTAR, and HST. Here, we model the UV spectra and look for different types of AGN outflows that may produce either narrow or broad UV absorption features. We examine the relations between the observed UV outflows and other properties of the AGN. We find that 60% of our targets show a presence of outflowing H I absorption, while 40% exhibit ionized outflows seen as absorption by either C IV, N V, or O VI. This is comparable to the occurrence of ionized outflows seen in the local Seyfert galaxies. All UV absorption lines in the sample are relatively narrow, with outflow velocities reaching up to -3300 km s-1. We did not detect any UV counterparts to the X-ray ultra-fast outflows (UFOs), most likely due to their being too highly ionized to produce significant UV absorption. However, all SUBWAYS targets with an X-ray UFO that have HST data demonstrate the presence of UV outflows at lower velocities. We find significant correlations between the column density (N) of the UV ions and Lbol of the AGN, with NH I decreasing with Lbol, while NO VI is increasing with Lbol. This is likely to be a photoionization effect, where toward higher AGN luminosities, the wind becomes more ionized, resulting in less absorption by neutral or low-ionization ions and more absorption by high-ionization ions. In addition, we find that N of the UV ions decreases as their outflow velocity increases. This may be explained by a mechanical power that is evacuating the UV-absorbing medium. Our observed relations are consistent with multiphase AGN feeding and feedback simulations indicating that a combination of both radiative and mechanical processes are in play.

2023 - The Close AGN Reference Survey (CARS): A parsec-scale multi-phase outflow in the super-Eddington NLS1 Mrk 1044 [Articolo su rivista]
Winkel, N.; Husemann, B.; Singha, M.; Bennert, V. N.; Combes, F.; Davis, T. A.; Gaspari, M.; Jahnke, K.; Mcelroy, R.; O' Dea, C. P.; Perez-Torres, M. A.
abstract

Context. The interaction between active galactic nuclei (AGNs) and their host galaxies is scarcely resolved. Narrow-line Seyfert 1 (NLS1) galaxies are believed to represent AGN at early stages of their evolution and to allow one to observe feeding and feedback processes at high black hole accretion rates. Aims. We aim to constrain the properties of the ionised gas outflow in Mrk 1044, a nearby super-Eddington accreting NLS1. Based on the outflow energetics and the associated timescales, we estimate the outflow' s future impact on the ongoing host galaxy star formation on different spatial scales. Methods. We applied a spectroastrometric analysis to observations of Mrk 1044' s nucleus obtained with the adaptive-optics-assisted narrow field mode of the VLT/MUSE instrument. This allowed us to map two ionised gas outflows traced by [O III], which have velocities of-560 ± 20 km s-1 and-144 ± 5 km s-1. Furthermore, we used an archival spectrum from the Space Telescope Imaging Spectrograph on HST to identify two Ly-α absorbing components that escape from the centre with approximately twice the velocity of the ionised gas components. Results. Both [O III] outflows are spatially unresolved and located close to the AGN (< 1 pc). They have gas densities higher than 105 cm-3, which implies that the BPT diagnostic cannot be used to constrain the underlying ionisation mechanism. We explore whether an expanding shell model can describe the velocity structure of Mrk 1044' s multi-phase outflow. In the ionised gas emission, an additional outflowing component, which is spatially resolved, is present. It has a velocity of-211 ± 22 km s-1 and a projected size of 4.6 ± 0.6 pc. Our kinematic analysis suggests that significant turbulence is present in the interstellar medium around the nucleus, which may lead to a condensation rain, potentially explaining the efficient feeding of Mrk 1044' s AGN. Within the innermost 0.5′ (160 pc), we detect modest star formation hidden by the beam-smeared emission from the outflow. Conclusions. We estimate that the multi-phase outflow was launched < 104 yr ago. Together with the star formation in the vicinity of the nucleus, this suggests that Mrk 1044' s AGN phase started only recently. The outflow carries enough mass and energy to impact the host galaxy star formation on different spatial scales, highlighting the complexity of the AGN feeding and feedback cycle in its early stages.

2023 - The Close AGN Reference Survey (CARS): An Interplay between Radio Jets and AGN Radiation in the Radio-quiet AGN HE0040-1105 [Articolo su rivista]
Singha, M.; Winkel, N.; Vaddi, S.; Torres, M. P.; Gaspari, M.; Smirnova-Pinchukova, I.; O'Dea, C. P.; Combes, F.; Omoruyi, O.; Rose, T.; Mcelroy, R.; Husemann, B.; Davis, T. A.; Baum, S. A.; Lawlor-Forsyth, C.; Neumann, J.; Tremblay, G. R.
abstract

We present a case study of HE 0040-1105, an unobscured radio-quiet active galactic nucleus (AGN) at a high accretion rate of λ Edd = 0.19 ± 0.04. This particular AGN hosts an ionized gas outflow with the largest spatial offset from its nucleus compared to all other AGNs in the Close AGN Reference Survey. By combining multiwavelength observations from the Very Large Telescope/MUSE, Hubble Space Telescope/Wide Field Camera 3, Very Large Array, and European VLBI Network, we probe the ionization conditions, gas kinematics, and radio emission from host galaxy scales to the central few parsecs. We detect four kinematically distinct components, one of which is a spatially unresolved AGN-driven outflow located within the central 500 pc, where it locally dominates the interstellar medium conditions. Its velocity is too low to escape the host galaxy’s gravitational potential, and may be re-accreted onto the central black hole via chaotic cold accretion. We detect compact radio emission in HE 0040-1105 within the region covered by the outflow, varying on a timescale of ∼20 yr. We show that neither AGN coronal emission nor star formation processes wholly explain the radio morphology/spectrum. The spatial alignment between the outflowing ionized gas and the radio continuum emission on 100 pc scales is consistent with a weak jet morphology rather than diffuse radio emission produced by AGN winds. >90% of the outflowing ionized gas emission originates from the central 100 pc, within which the ionizing luminosity of the outflow is comparable to the mechanical power of the radio jet. Although radio jets might primarily drive the outflow in HE 0040-1105, radiation pressure from the AGN may contribute to this process.

2023 - The evolving cluster cores: Putting together the pieces of the puzzle [Articolo su rivista]
Molendi, S.; De Grandi, S.; Rossetti, M.; Bartalucci, I.; Gastaldello, F.; Ghizzardi, S.; Gaspari, M.
abstract

2023 - The Fraction and Kinematics of Broad Absorption Line Quasars across Cosmic Time [Articolo su rivista]
Bischetti, M.; Fiore, F.; Feruglio, C.; D'Odorico, V.; Arav, N.; Costa, T.; Zubovas, K.; Becker, G.; Bosman, S. E. I.; Cupani, G.; Davies, R.; Eilers, A. -C.; Farina, E. P.; Ferrara, A.; Gaspari, M.; Mazzucchelli, C.; Onoue, M.; Piconcelli, E.; Zanchettin, M. V.; Zhu, Y.
abstract

Luminous quasars are powerful targets to investigate the role of feedback from supermassive black holes (BHs) in regulating the growth phases of BHs themselves and of their host galaxies, up to the highest redshifts. Here we investigate the cosmic evolution of the occurrence and kinematics of BH-driven outflows, as traced by broad absorption line (BAL) features, due to the C iv ionic transition. We exploit a sample of 1935 quasars at z = 2.1-6.6 with bolometric luminosity log(L bol/erg s−1) ≳ 46.5, drawn from the Sloan Digital Sky Survey and from the X-Shooter legacy survey of Quasars at the Reionization Epoch (XQR-30). We consider rest-frame optical bright quasars to minimize observational biases due to quasar selection criteria. We apply a homogeneous BAL-identification analysis, based on employing composite template spectra to estimate the quasar intrinsic emission. We find a BAL quasar fraction close to 20% at z ∼ 2-4, while it increases to almost 50% at z ∼ 6. The velocity and width of the BAL features also increase at z ≳ 4.5. We exclude the possibility that the redshift evolution of the BAL properties is due to differences in terms of quasar luminosity and accretion rate. These results suggest significant BH feedback occurring in the 1 Gyr old universe, likely affecting the growth of BHs and, possibly, of their host galaxies, as supported by models of early BH and galaxy evolution.

2023 - The NuSTAR and Chandra View of CL 0217+70 and Its Tell-tale Radio Halo [Articolo su rivista]
Tumer, A.; Wik, D. R.; Zhang, X.; Hoang, D. N.; Gaspari, M.; van Weeren, R. J.; Rudnick, L.; Stuardi, C.; Mernier, F.; Simionescu, A.; Rojas Bolivar, R. A.; Kraft, R.; Akamatsu, H.; Plaa, J. D.
abstract

Mergers of galaxy clusters are the most energetic events in the universe, driving shock and cold fronts, generating turbulence, and accelerating particles that create radio halos and relics. The galaxy cluster CL 0217+70 is a remarkable late-stage merger, with a double peripheral radio relic and a giant radio halo. Chandra detects surface brightness (SB) edges that correspond to radio features within the halo. In this work, we present a study of this cluster with Nuclear Spectroscopic Telescope Array and Chandra data using spectro-imaging methods. The global temperature is found to be kT = 9.1 keV. We set an upper limit for the inverse Compton (IC) flux of ∼2.7 × 10−12 erg s−1 cm−2, and a lower limit to the magnetic field of 0.08 μG. Our local IC search revealed a possibility that IC emission may have a significant contribution at the outskirts of the radio halo emission and on/near shock regions within ∼0.6 r 500 of clusters. We detected a “hot spot” feature in our temperature map coincident with an SB edge, but our investigation on its origin is inconclusive. If the “hot spot” is the downstream of a shock, we set a lower limit of kT > 21 keV to the plasma that corresponds to ∼2. We found three shock fronts within 0.5 r 500. Multiple weak shocks within the cluster center hint at an ongoing merger activity and continued feeding of the giant radio halo. CL 0217+70 is the only example hosting these secondary shocks in multiple form.

2023 - Unraveling baroclinicity in black hole weather storms [Articolo su rivista]
Wittor, D.; Gaspari, M.
abstract

In the intracluster, intragroup, and circumgalactic medium (ICM, IGrM, CGM), turbulence plays a vital role in the self-regulated feedback and feeding cycle of central supermassive black holes (SMBHs). Here, we continue our systematic dissection of the turbulent 'weather' in high-resolution hydrodynamical simulations of feedback driven by active galactic nuclei (AGN). In non-barotropic and stratified atmospheres, baroclinicity is expected to generate fresh turbulence via misaligned gradients of density and pressure - such as in cyclonic storms on Earth. In this work, we dissect for the first time baroclinicity and its components in the astrophysical halo weather. Over the macro-scale galaxy cluster, baroclinicity tends to be dynamically subdominant for the enstrophy amplification. However, at and below the meso scale near the SMBH (r < 10 kpc; t < 20 Myr), baroclinicity is important to seed the initial enstrophy during active periods of AGN jet feedback. We find that baroclinicity shows stronger correlation with the density rather than pressure gradients. Despite the density-pressure gradient misalignment being often below 45°, their amplitudes boosted by mechanical AGN feedback are sufficient to enable key enstrophy/turbulence generation. Our study provides a novel step forward in understanding astrophysical atmospheres toward a unified BlackHoleWeather framework, akin to the complexity of Earth's weather.

2023 - X-Ray Cavity Dynamics and Their Role in the Gas Precipitation in Planck Sunyaev-Zeldovich (SZ) Selected Clusters [Articolo su rivista]
Olivares, V.; Su, Y.; Forman, W.; Gaspari, M.; Andrade-Santos, F.; Salome, P.; Nulsen, P.; Edge, A.; Combes, F.; Jones, C.
abstract

We study active galactic nucleus (AGN) feedback in nearby (z < 0.35) galaxy clusters from the Planck Sunyaev-Zeldovich sample using Chandra observations. This nearly unbiased mass-selected sample includes both relaxed and disturbed clusters and may reflect the entire AGN feedback cycle. We find that relaxed clusters better follow the one-to-one relation of cavity power versus cooling luminosity, while disturbed clusters display higher cavity power for a given cooling luminosity, likely reflecting a difference in cooling and feedback efficiency. Disturbed clusters are also found to contain asymmetric cavities when compared to relaxed clusters, hinting toward the influence of the intracluster medium (ICM) "weather"on the distribution and morphology of the cavities. Disturbed clusters do not have fewer cavities than relaxed clusters, suggesting that cavities are difficult to disrupt. Thus, multiple cavities are a natural outcome of recurrent AGN outbursts. As in previous studies, we confirm that clusters with short central cooling times, t cool, and low central entropy values, K 0, contain warm ionized (10,000 K) or cold molecular (<100 K) gas, consistent with ICM cooling and a precipitation/chaotic cold accretion scenario. We analyzed archival Multi-Unit Spectroscopic Explorer observations that are available for 18 clusters. In 11/18 of the cases, the projected optical line emission filaments appear to be located beneath or around the cavity rims, indicating that AGN feedback plays an important role in forming the warm filaments by likely enhancing turbulence or uplift. In the remaining cases (7/18), the clusters either lack cavities or their association of filaments with cavities is vague, suggesting alternative turbulence-driven mechanisms (sloshing/mergers) or physical time delays are involved.

2022 - CHEX-MATE: Morphological analysis of the sample [Articolo su rivista]
Campitiello, M. G.; Ettori, S.; Lovisari, L.; Bartalucci, I.; Eckert, D.; Rasia, E.; Rossetti, M.; Gastaldello, F.; Pratt, G. W.; Maughan, B.; Pointecouteau, E.; Sereno, M.; Biffi, V.; Borgani, S.; De Luca, F.; De Petris, M.; Gaspari, M.; Ghizzardi, S.; Mazzotta, P.; Molendi, S.
abstract

A classification of the galaxy clustera's dynamical state is crucial when dealing with large samples. The identification of the most relaxed and most disturbed objects is necessary for both cosmological analysis, focused on spherical and virialised systems, and astrophysical studies, centred around all those micro-physical processes that take place in disturbed clusters (such as particle acceleration or turbulence). Among the most powerful tools for the identification of the dynamical state of clusters is the analysis of their intracluster medium (ICM) distribution. In this work, we performed an analysis of the X-ray morphology of the 118 (Cluster HEritage project with XMM-Newton -Mass Assembly and Thermodynamics at the Endpoint of structure formation) CHEX-MATE clusters, with the aim of providing a classification of their dynamical state. To investigate the link between the X-ray appearance and the dynamical state, we considered four morphological parameters: the surface brightness concentration, the centroid shift, and the second- and third-order power ratios. These indicators result to be strongly correlated with each other, powerful in identifying the disturbed and relaxed population, characterised by a unimodal distribution, and not strongly influenced by systematic uncertainties. In order to obtain a continuous classification of the CHEX-MATE objects, we combined these four parameters in a single quantity, M, which represents the grade of relaxation of a system. On the basis of the M value, we identified the most extreme systems of the sample, finding 15 very relaxed and 27 very disturbed galaxy clusters. From a comparison with previous analysis on X-ray selected samples, we confirmed that the Sunyaev-Zeldovich (SZ) clusters tend to be more disturbed. Finally, by applying our analysis to a simulated sample, we found a general agreement between the observed and simulated results, with the only exception being the concentration. This latter behaviour is partially related to the presence of particles with a high smoothed-particle-hydrodynamics density in the central regions of the simulated clusters due to the action of the idealised isotropic thermal active galactic nucleus (AGN) feedback.

2022 - Compton-thick AGN in the NuSTAR Era. VIII. A joint NuSTAR-XMM-Newton Monitoring of the Changing-look Compton-thick AGN NGC 1358 [Articolo su rivista]
Marchesi, S.; Zhao, X.; Torres-Alba, N.; Ajello, M.; Gaspari, M.; Pizzetti, A.; Buchner, J.; Bertola, E.; Comastri, A.; Feltre, A.; Gilli, R.; Lanzuisi, G.; Matzeu, G.; Pozzi, F.; Salvestrini, F.; Sengupta, D.; Silver, R.; Tombesi, F.; Traina, A.; Vignali, C.; Zappacosta, L.
abstract

We present the multi-epoch monitoring with NuSTAR and XMM-Newton of NGC 1358, a nearby Seyfert 2 galaxy whose properties made it a promising candidate X-ray changing-look active galactic nucleus (AGN), i.e., a source whose column density could transition from its 2017 Compton-thick (having LOS hydrogen column density NH,LOS> 1024cm−2) state to a Compton-thin (NH,LOS< 1024cm−2) one. The multi-epoch X-ray monitoring confirmed the presence of significant NH,LOSvariability over timescales of weeks to years, and allowed us to confirm the changing-look nature of NGC 1358, which has most recently been observed in a Compton-thin status. Multi-epoch monitoring with NuSTAR and XMM-Newton is demonstrated to be highly effective in simultaneously constraining three otherwise highly degenerate parameters: the torus average column density and covering factor, and the inclination angle between the torus axis and the observer. We find a tentative anticorrelation between column density and luminosity, which can be understood under the framework of chaotic cold accretion clouds driving recursive AGN feedback. The monitoring campaign of NGC 1358 has proven the efficiency of our newly developed method to select candidate NH,LOS-variable, heavily obscured AGN, which we plan to soon extend to a larger sample to better characterize the properties of the obscuring material surrounding accreting supermassive black holes, as well as to constrain AGN feeding models.

2022 - Directly Tracing Cool Filamentary Accretion over >100 kpc into the Interstellar Medium of a Quasar Host at z = 1 [Articolo su rivista]
Johnson, S. D.; Schaye, J.; Walth, G. L.; Li, J. I.; Rudie, G. C.; Chen, H. -W.; Chen, M. C.; Epinat, B.; Gaspari, M.; Cantalupo, S.; Kollatschny, W.; Liu, Z. (.; Muzahid, S.
abstract

We report the discovery of giant (50−100 kpc) [O ii] emitting nebulae with MUSE in the field of TXS 0206−048, a luminous quasar at z = 1.13. “Down-the-barrel” UV spectra of the quasar show absorption at velocities coincident with those of the extended nebulae, enabling new insights into inflows and outflows around the quasar host. One nebula exhibits a filamentary morphology extending over 120 kpc from the halo toward the quasar and intersecting with another nebula surrounding the quasar host with a radius of 50 kpc. This is the longest cool filament observed to date and arises at higher redshift and in a less massive system than those in cool-core clusters. The filamentary nebula has line-of-sight velocities >300 km s−1 from nearby galaxies but matches that of the nebula surrounding the quasar host where they intersect, consistent with accretion of cool intergalactic or circumgalactic medium or cooling hot halo gas. The kinematics of the nebulae surrounding the quasar host are unusual and complex, with redshifted and blueshifted spiral-like structures. The emission velocities at 5−10 kpc from the quasar match those of inflowing absorbing gas observed in UV spectra of the quasar. Together, the extended nebulae and associated redshifted absorption represent a compelling case of cool, filamentary gas accretion from halo scales into the extended interstellar medium and toward the nucleus of a massive quasar host. The inflow rate implied by the combined emission and absorption constraints is well below levels required to sustain the quasar’s radiative luminosity, suggesting anisotropic or variable accretion.

2022 - Gas condensation in brightest group galaxies unveiled with MUSE: Morphology and kinematics of the ionized gas [Articolo su rivista]
Olivares, V.; Salome, P.; Hamer, S. L.; Combes, F.; Gaspari, M.; Kolokythas, K.; O'Sullivan, E.; Beckmann, R. S.; Babul, A.; Polles, F. L.; Lehnert, M.; Loubser, S. I.; Donahue, M.; Gendron-Marsolais, M. -L.; Lagos, P.; Pineau Des Forets, G.; Godard, B.; Rose, T.; Tremblay, G.; Ferland, G.; Guillard, P.
abstract

The origin of the cold gas in central galaxies in groups is still a matter of debate. We present Multi-Unit Spectroscopic Explorer (MUSE) observations of 18 optically selected local (z ≤ 0:017) brightest group galaxies (BGGs) to study the kinematics and distribution of the optical emission-line gas. MUSE observations reveal a distribution of gas morphologies including ten complex networks of filaments extending up to ∼10 kpc to two compact (<3 kpc) and five extended (>5 kpc) disk-dominated structures. Some rotating disks show rings and elongated structures arising from the central disk. The kinematics of the stellar component is mainly rotationdominated, which is very different from the disturbed kinematics and distribution found in the filamentary sources. The ionized gas is kinematically decoupled from the stellar component for most systems, suggesting an external origin for the gas. We also find that the Hα luminosity correlates with the cold molecular gas mass. By exploring the thermodynamical properties of the X-ray atmospheres, we find that the filamentary structures and compact disks are found in systems with small central entropy values, K, and tcool=teddy ratios. This suggests that, similar to brightest cluster galaxies (BCGs) in cool core clusters, the ionized filaments and the cold gas associated to them are likely formed from hot halo gas condensations via thermal instabilities, which is consistent with the chaotic cold accretion simulations (as shown via the C ratio, Tat, and k plot). We note that the presence of gaseous rotating disks is more frequent than in BCGs. An explanation for the origin of the gas in those objects is a contribution to gas fueling by wet mergers or group satellites, as qualitatively hinted at by some sources of the present sample. Nonetheless, we discuss the possibility that some extended disks could also be a transition stage in an evolutionary sequence including filaments, extended disks, and compact disks, as described by hot gas condensation models of cooling flows.

2022 - GBT/MUSTANG-2 9' resolution imaging of the SZ effect in MS0735.6+7421: Confirmation of the SZ cavities through direct imaging [Articolo su rivista]
Orlowski-Scherer, J.; Haridas, S. K.; Di Mascolo, L.; Sarmiento, K. P.; Romero, C. E.; Dicker, S.; Mroczkowski, T.; Bhandarkar, T.; Churazov, E.; Clarke, T. E.; Devlin, M.; Gaspari, M.; Lowe, I.; Mason, B.; Sarazin, C. L.; Sievers, J.; Sunyaev, R.
abstract

Context. Mechanical feedback from active galactic nuclei is thought to be the dominant feedback mechanism quenching cooling flows and star formation in galaxy cluster cores. It, in particular, manifests itself by creating cavities in the X-ray emitting gas, which are observed in many clusters. However, the nature of the pressure supporting these cavities is not known. Aims. Using the MUSTANG-2 instrument on the Green Bank Telescope (GBT), we aimed to measure thermal Sunyaev-Zeldovich (SZ) effect signals associated with the X-ray cavities in MS0735.6+7421, a moderate-mass cluster that hosts one of the most energetic active galactic nucleus outbursts known. We used these measurements to infer the level of nonthermal sources of pressure that support the cavities, such as magnetic fields and turbulence, as well as relativistic and cosmic ray components. Methods. We used the preconditioned gradient descent method to fit a model for the cluster, cavities, and central point source directly to the time-ordered data of the MUSTANG-2 signal. We used this model to probe the thermodynamic state of the cavities. Results. We show that the SZ signal associated with the cavities is suppressed compared to the expectations for a thermal plasma with temperatures of a few tens of keV. The smallest value of the suppression factor, f, that is consistent with the data is 0.4, lower than what has been inferred in earlier work. Larger values of f are possible once the contribution of the cocoon shock surrounding the cavities is taken into account. Conclusions. We conclude that in the 'thermal' scenario, when half of the pressure support comes from electrons with a Maxwellian velocity distribution, the temperature of these electrons must be greater than 100 keV at 2.5 confidence. Alternatively, electrons with nonthermal momentum distribution could contribute to the pressure, although existing data do not distinguish between these two scenarios. The baseline model with cavities located in the sky plane yields a best-fitting value of the thermal SZ signal suppression inside cavities of 0.5, which, at face value, implies a mix of thermal and nonthermal pressure support. Larger values of f (up to 1, i.e., no thermal SZ signal from the cavities) are still possible when allowing for variations in the line-of-sight geometry.

2022 - Multi-scale feedback and feeding in the closest radio galaxy Centaurus A [Articolo su rivista]
Mckinley, B.; Tingay, S. J.; Gaspari, Massimo; Kraft, R. P.; Matherne, C.; Offringa, A. R.; Mcdonald, M.; Calzadilla, M. S.; Veilleux, S.; Shabala, S. S.; Gwyn, S. D. J.; Bland-Hawthorn, J.; Crnojević, D.; Gaensler, B. M.; Johnston-Hollitt, M.
abstract

Supermassive black holes and supernova explosions at the centres of active galaxies power cycles of outflowing and inflowing gas that affect galactic evolution and the overall structure of the Universe. While simulations and observations show that this must be the case, the range of physical scales (over ten orders of magnitude) and paucity of available tracers make both the simulation and observation of these effects difficult. By serendipity, there lies an active galaxy, Centaurus A (NGC 5128), at such a close proximity as to allow its observation over this entire range of scales and across the entire electromagnetic spectrum. In the radio band, however, details on scales of 10-100 kpc from the supermassive black hole have so far been obscured by instrumental limitations. Here we report low-frequency radio observations that overcome these limitations and show evidence for a broad, bipolar outflow with velocity of 1,100 km/s and mass-outflow rate of 2.9 M⊙/yr on these scales. We combine our data with the plethora of multiscale, multi-wavelength, historical observations of Centaurus A to probe a unified view of feeding and feedback, which we show to be consistent with the chaotic cold accretion self-regulation scenario.

2022 - Particle re-acceleration and diffuse radio sources in the galaxy cluster Abell 1550 [Articolo su rivista]
Pasini, T.; Edler, H. W.; Bruggen, M.; De Gasperin, F.; Botteon, A.; Rajpurohit, K.; Van Weeren, R. J.; Gastaldello, F.; Gaspari, M.; Brunetti, G.; Cuciti, V.; Nanci, C.; Di Gennaro, G.; Rossetti, M.; Dallacasa, D.; Hoang, D. N.; Riseley, C. J.
abstract

Context. Radio observations of galaxy clusters reveal a plethora of diffuse, steep-spectrum sources related to the re-acceleration of cosmic-ray electrons, such as halos, relics, and phoenices. In this context, the LOw Frequency ARray Low-Band Antenna (LOFAR-LBA) Sky Survey (LoLSS) provides the most sensitive images of the sky at 54 MHz to date, allowing us to investigate re-acceleration processes in a poorly explored frequency regime. Aims. We study diffuse radio emission in the galaxy cluster Abell 1550, with the aim of constraining particle re-acceleration in the intra-cluster medium. Methods. We exploited observations at four different radio frequencies: 54, 144, 400, and 1400 MHz. To complement our analysis, we made use of archival Chandra X-ray data. Results. At all frequencies we detect an ultra-steep spectrum radio halo (Sν ν1.6) with an extent of 1.2 Mpc at 54 MHz. Its morphology follows the distribution of the thermal intra-cluster medium inferred from the Chandra observation. West of the centrally located head-tail radio galaxy, we detect a radio relic with a projected extent of 500 kpc. From the relic, a 600 kpc long bridge departs and connects with the halo. Between the relic and the radio galaxy, we observe what is most likely a radio phoenix, given its curved spectrum. The phoenix is connected to the tail of the radio galaxy through two arms, which show a nearly constant spectral index for 300 kpc. Conclusions. The halo could be produced by turbulence induced by a major merger, with the merger axis lying in the NE-SW direction. This is supported by the position of the relic, whose origin could be attributed to a shock propagating along the merger axis. It is possible that the same shock has also produced the phoenix through adiabatic compression, while we propose that the bridge could be generated by electrons which were pre-accelerated by the shock, and then re-accelerated by turbulence. Finally, we detect hints of gentle re-energisation in the two arms that depart from the tail of the radio galaxy.

2022 - Probing Multiphase Gas in Local Massive Elliptical Galaxies via Multiwavelength Observations [Articolo su rivista]
Temi, P.; Gaspari, Massimo; Brighenti, F.; Werner, N.; Grossova, R.; Gitti, Myriam; Sun, M.; Amblard, A.; Simionescu, A.
abstract

We investigate the cold and warm gas content, kinematics, and spatial distribution of six local massive elliptical galaxies to probe the origin of the multiphase gas in their atmospheres. We report new observations, including Stratospheric Observatory for Infrared Astronomy [C II], Atacama Large Millimeter/submillimeter Array CO, Multi Unit Spectroscopic Explorer (MUSE) Hα+[N II], and Very Large Array (VLA) radio observations. These are complemented by a large suite of multiwavelength archival data sets, including thermodynamical properties of the hot gas and radio jets, which are leveraged to investigate the role of active galactic nucleus (AGN) feeding/feedback in regulating the multiphase gas content. Our galactic sample shows a significant diversity in cool gas content, spanning filamentary and rotating structures. In our noncentral galaxies, the distribution of such gas is often concentrated, at variance with the more extended features observed in central galaxies. Misalignment between the multiphase gas and stars suggest that stellar mass loss is not the primary driver. A fraction of the cool gas might be acquired via galaxy interactions, but we do not find quantitative evidence of mergers in most of our systems. Instead, key evidence supports the origin via condensation out of the diffuse halo. Comparing with chaotic cold accretion (CCA) simulations, we find that our cool gas-free galaxies are likely in the overheated phase of the self-regulated AGN cycle, while for our galaxies with cool gas, the k-plot and AGN power correlation corroborate the phase of CCA feeding in which the condensation rain is triggering more vigorous AGN heating. The related C-ratio further shows that central/noncentral galaxies are expected to generate an extended/inner rain, consistent with our sample.

2022 - Testing the Limits of AGN Feedback and the Onset of Thermal Instability in the Most Rapidly Star-forming Brightest Cluster Galaxies [Articolo su rivista]
Calzadilla, M. S.; Mcdonald, M.; Donahue, M.; Mcnamara, B. R.; Fogarty, K.; Gaspari, M.; Gitti, M.; Russell, H. R.; Tremblay, G. R.; Voit, G. M.; Ubertosi, F.
abstract

We present new, deep, narrow- and broadband Hubble Space Telescope observations of seven of the most star-forming brightest cluster galaxies (BCGs). Continuum-subtracted [OII] maps reveal the detailed, complex structure of warm (T ∼ 104 K) ionized gas filaments in these BCGs, allowing us to measure spatially resolved star formation rates (SFRs) of ∼60-600 M ⊙yr−1. We compare the SFRs in these systems and others from the literature to their intracluster medium cooling rates ( M ̇ cool ), measured from archival Chandra X-ray data, finding a best-fit relation of log ( SFR ) = ( 1.66 ± 0.17 ) log ( M ̇ cool ) + (−3.22 ± 0.38) with an intrinsic scatter of 0.39 ± 0.09 dex. This steeper-than-unity slope implies an increasingly efficient conversion of hot (T ∼ 107 K) gas into young stars with increasing M ̇ cool , or conversely a gradual decrease in the effectiveness of AGN feedback in the strongest cool cores. We also seek to understand the physical extent of these multiphase filaments that we observe in cluster cores. We show, for the first time, that the average extent of the multiphase gas is always smaller than the radii at which the cooling time reaches 1 Gyr, the t cool/t ff profile flattens, and that X-ray cavities are observed. This implies a close connection between the multiphase filaments, the thermodynamics of the cooling core, and the dynamics of X-ray bubbles. Interestingly, we find a one-to-one correlation between the average extent of cool multiphase filaments and the radius at which the cooling time reaches 0.5 Gyr, which may be indicative of a universal condensation timescale in cluster cores.

2022 - The Close AGN Reference Survey (CARS): IFU survey data and the BH mass dependence of long-term AGN variability [Articolo su rivista]
Husemann, B.; Singha, M.; Scharwächter, J.; Mcelroy, R.; Neumann, J.; Smirnova-Pinchukova, I.; Urrutia, T.; Baum, S. A.; Bennert, V. N.; Combes, F.; Croom, S. M.; Davis, T. A.; Fournier, Y.; Galkin, A.; Gaspari, Massimo; Enke, H.; Krumpe, M.; O'Dea, C. P.; Pérez-Torres, M.; Rose, T.; Tremblay, G. R.; Walcher, C. J.
abstract

Context. Active galactic nuclei (AGN) are thought to be intimately connected with their host galaxies through feeding and feedback processes. A strong coupling is predicted and supported by cosmological simulations of galaxy formation, but the details of the physical mechanisms are still observationally unconstrained.Aims: Galaxies are complex systems of stars and a multiphase interstellar medium (ISM). A spatially resolved multiwavelength survey is required to map the interaction of AGN with their host galaxies on different spatial scales and different phases of the ISM. The goal of the Close AGN Reference Survey (CARS) is to obtain the necessary spatially resolved multiwavelength observations for an unbiased sample of local unobscured luminous AGN.Methods: We present the overall CARS survey design and the associated wide-field optical integral-field unit (IFU) spectroscopy for all 41 CARS targets at z < 0.06 randomly selected from the Hamburg/ESO survey of luminous unobscured AGN. This data set provides the backbone of the CARS survey and allows us to characterize host galaxy morphologies, AGN parameters, precise systemic redshifts, and ionized gas distributions including excitation conditions, kinematics, and metallicities in unprecedented detail.Results: We focus our study on the size of the extended narrow-line region (ENLR) which has been traditionally connected to AGN luminosity. Given the large scatter in the ENLR size-luminosity relation, we performed a large parameter search to identify potentially more fundamental relations. Remarkably, we identified the strongest correlation between the maximum projected ENLR size and the black hole mass, consistent with an RENLR,max ∼ MBH^0.5 relationship. We interpret the maximum ENLR size as a timescale indicator of a single black hole (BH) radiative-efficient accretion episode for which we inferred = (0.45 ± 0.08)log(MBH/[M⊙]) + 1.78−0.67+0.54 using forward modeling. The extrapolation of our inferred relation toward higher BH masses is consistent with an independent lifetime estimate from the He II proximity zones around luminous AGN at z ∼ 3.Conclusions: While our proposed link between the BH mass and AGN lifetime might be a secondary correlation itself or impacted by unknown biases, it has a few relevant implications if confirmed. For example, the famous AGN Eigenvector 1 parameter space may be partially explained by the range in AGN lifetimes. Also, the lack of observational evidence for negative AGN feedback on star formation can be explained by such timescale effects. Further observational tests are required to confirm or rule out our BH mass dependent AGN lifetime hypothesis.

2022 - The Close AGN Reference Survey (CARS): Locating the [O III] wing component in luminous local Type 1 AGN [Articolo su rivista]
Singha, M.; Husemann, B.; Urrutia, T.; O'Dea, C. P.; Scharwächter, J.; Gaspari, Massimo; Combes, F.; Nevin, R.; Terrazas, B. A.; Pérez-Torres, M.; Rose, T.; Davis, T. A.; Tremblay, G. R.; Neumann, J.; Smirnova-Pinchukova, I.; Baum, S. A.
abstract

Context. The strong asymmetry in the optical [O III] λ5007 emission line is one of the best signatures of active galactic nuclei (AGN) driven warm (∼10^4 K) ionized gas outflows on host galaxy scales. While large spectroscopic surveys such as the sloan digital sky survey (SDSS) have characterized the kinematics of [O III] for large samples of AGN, estimating the associated energetics requires spatially resolving these outflows with, for example, integral field unit (IFU) studies.Aims: As part of the Close AGN Reference Survey, we obtained spatially resolved IFU spectroscopy for a representative sample of 39 luminous type 1 AGN at 0.01 < z < 0.06 with the multi unit spectroscopic explorer and the visible multi object spectrograph IFUs at the very large telescope to infer the spatial location of the ionized gas outflows.Methods: We compared the 2D light distributions of the [O III] wing to that of the Hβ broad emission line region, a classical point source (PSF). We then used the PSF to distinguish between the unresolved and resolved [O III] wing emission. We further determined its location using spectro-astrometry for the point-like sources.Results: The [O III] wing is spatially unresolved in 23 out of the 36 AGN with >80% of the flux associated with a point-like source. We measured < 100 pc offsets in the spatial location of the outflow from the AGN nucleus using the spectro-astrometry technique for these sources. For the other 13 AGN, the [O III] wing emission is resolved and possibly extended on several kiloparsec scales.Conclusions: We conclude that [O III] wing emission can be compact or extended in an unbiased luminous AGN sample, where both cases are likely to appear. Electron density in the compact [O III] wing regions (median ne ∼ 1900 cm^−3) is nearly a magnitude higher than in the extended ones (median ne ∼ 500 cm^−3). The presence of spatially extended and compact [O III] wing emission is unrelated to the AGN bolometric luminosity and to inclination effects, which means other features such as time delays, or mechanical feedback (radio jets) may shape the ionized gas outflow properties.

2022 - The Close AGN Reference Survey (CARS). No obvious signature of AGN feedback on star formation, but subtle trends [Articolo su rivista]
Smirnova-Pinchukova, I.; Husemann, B.; Davis, T. A.; Smith, C. M. A.; Singha, M.; Tremblay, G. R.; Klessen, R. S.; Powell, M.; Connor, T.; Baum, S. A.; Combes, F.; Croom, S. M.; Gaspari, Massimo; Neumann, J.; O'Dea, C. P.; Pérez-Torres, M.; Rosario, D. J.; Rose, T.; Scharwächter, J.; Winkel, N.
abstract

Context. Active galactic nuclei (AGN) are thought to be responsible for the suppression of star formation in massive ∼10^10 M⊙ galaxies. While this process is a key feature in numerical simulations of galaxy formation, it has not been unambiguously confirmed in observational studies yet.Aims: The characterization of the star formation rate (SFR) in AGN host galaxies is challenging as AGN light contaminates most SFR tracers. Furthermore, the various SFR tracers are sensitive to different timescales of star formation from approximately a few to 100 Myr. We aim to obtain and compare SFR estimates from different tracers for AGN host galaxies in the Close AGN Reference Survey (CARS) to provide new observational insights into the recent SFR history of those systems.Methods: We constructed integrated panchromatic spectral energy distributions to measure the far infrared (FIR) luminosity as a tracer for the recent (< 100 Myr) SFR. In addition we used the integral-field unit observation of the CARS targets to employ the Hα luminosity decontaminated by AGN excitation as a proxy for the current (< 5 Myr) SFR.Results: We find that significant differences in specific SFR of the AGN host galaxies as compared with the larger galaxy population disappear once cold gas mass, in addition to stellar mass, is used to predict the SFR for a specific AGN host. Only a tentative trend with the inclination of the host galaxy remains, such that SFR appears slightly lower than expected when the galaxies of unobscured AGN appear more edge-on along our line-of-sight, particular for dust-insensitive FIR-based SFRs. We identify individual galaxies with a significant difference in their SFR which can be related to a recent enhancement or decline in their SFR history that might be related to various processes including interactions, gas consumption, outflows, and AGN feedback.Conclusions: AGN can be present in various stages of galaxy evolution which makes it difficult to relate the SFR solely to the impact of the AGN. Our study shows that stellar mass alone is an insufficient parameter to estimate the expected SFR of an AGN host galaxy compared to the underlying non-AGN galaxy population. We do not find any strong evidence for a global positive or negative AGN feedback in the CARS sample. However, there is tentative evidence that (1) the relative orientation of the AGN engine with respect to the host galaxies might alter the efficiency of AGN feedback and that (2) the recent SFH is an additional tool to identify rapid changes in galaxy growth driven by the AGN or other processes.

2022 - The Close AGN Reference Survey (CARS): Tracing the circumnuclear star formation in the super-Eddington NLS1 Mrk 1044 [Articolo su rivista]
Winkel, N.; Husemann, B.; Davis, T. A.; Smirnova-Pinchukova, I.; Bennert, V. N.; Combes, F.; Gaspari, M.; Jahnke, K.; Neumann, J.; O'Dea, C. P.; Perez-Torres, M.; Singha, M.; Tremblay, G. R.; Rix, H. W.
abstract

Context. The host galaxy conditions for rapid supermassive black hole growth are poorly understood. Narrow-line Seyfert 1 (NLS1) galaxies often exhibit high accretion rates and are hypothesized to be prototypes of active galactic nuclei (AGN) at an early stage of their evolution. Aims. We present adaptive optics (AO) assisted VLT MUSE NFM observations of Mrk 1044, the nearest super-Eddington accreting NLS1. Together with archival MUSE WFM data, we aim to understand the host galaxy processes that drive Mrk 1044 s black hole accretion. Methods. We extracted the faint stellar continuum emission from the AGN-deblended host and performed spatially resolved emission line diagnostics with an unprecedented resolution. Combining both MUSE WFM and NFM-AO observations, we used a kinematic model of a thin rotating disk to trace the stellar and ionized gas motion from 10 kpc galaxy scales down to 30 pc around the nucleus. Results. Mrk 1044 s stellar kinematics follow circular rotation, whereas the ionized gas shows tenuous spiral features in the center. We resolve a compact star-forming circumnuclear ellipse (CNE) that has a semi-minor axis of 306 pc. Within this CNE, the gas is metal-rich and its line ratios are entirely consistent with excitation by star formation. With an integrated star formation rate of 0.19 ± 0.05 M- yr 1, the CNE contributes 27% of the galaxy-wide star formation. Conclusions. We conclude that Mrk 1044 s nuclear activity has not yet affected the circumnuclear star formation. Thus, Mrk 1044 is consistent with the idea that NLS1s are young AGN. A simple mass budget consideration suggests that the circumnuclear star formation and AGN phase are connected and the patterns in the ionized gas velocity field are a signature of the ongoing AGN feeding.

2022 - The NuSTAR, XMM-Newton, and Suzaku View of A3395 at the Intercluster Filament Interface [Articolo su rivista]
Tumer, A.; Wik, D. R.; Gaspari, M.; Akamatsu, H.; Westergaard, N. J.; Tombesi, F.; Ercan, E. N.
abstract

Galaxy clusters are the largest virialized objects in the universe. Their merger dynamics and their interactions with the cosmic filaments that connect them are important for our understanding of the formation of large-scale structure. In addition, cosmic filaments are thought to possess the missing baryons in the universe. Studying the interaction of galaxy clusters and filaments therefore has the potential to unveil the origin of the baryons and the physical processes that occur during merger stages of galaxy clusters. In this paper, we study the connection between A3395 and the intercluster filament with NuSTAR, XMM-Newton, and Suzaku data. Since the NuSTAR observation is moderately contaminated by scattered light, we present a novel technique developed for disentangling this background from the emission from the intracluster medium. We find that the interface of the cluster and the intercluster filament connecting A3395 and A3391 does not show any signs of heated plasma, as was previously thought. This interface has low temperature, high density, and low entropy, thus we suggest that the gas is cooling, being enhanced by the turbulent or tidal "weather"driven during the early stage of the merger. Furthermore, our temperature results from the NuSTAR data are in agreement with those from XMM-Newton and from joint NuSTAR and XMM-Newton analysis for a region with ∼25% scattered light contamination within 1σ. We show that the temperature constraint of the intracluster medium is valid even when the data are contaminated up to ∼25% for ∼5 keV cluster emission.

2021 - AGN feeding and feedback in Fornax A: kinematical analysis of the multi-phase ISM [Articolo su rivista]
Maccagni, FILIPPO MARCELLO; Serra, Paolo; Gaspari, Massimo; Kleiner, D.; Morokuma-Matsui, K.; Oosterloo, T. A.; Onodera, M.; Kamphuis, P.; Loi, F.; Thorat, K.; Ramatsoku, M.; Smirnov, O.; White, S. V.
abstract

We present a multi-wavelength study of the gaseous medium surrounding the nearby active galactic nucleus (AGN), Fornax A. Using MeerKAT, ALMA, and MUSE observations, we reveal a complex distribution of the atomic (H I), molecular (CO), and ionised gas in its centre and along the radio jets. By studying the multi-scale kinematics of the multi-phase gas, we reveal the presence of concurrent AGN feeding and feedback phenomena. Several clouds and an extended 3 kpc filament - perpendicular to the radio jets and the inner disk (r ≲ 4.5 kpc) - show highly-turbulent kinematics, which likely induces non-linear condensation and subsequent chaotic cold accretion (CCA) onto the AGN. In the wake of the radio jets and in an external (r ≳ 4.5 kpc) ring, we identify an entrained massive (∼10^7 M⊙) multi-phase outflow (vOUT ∼ 2000 km s^−1). The rapid flickering of the nuclear activity of Fornax A (∼3 Myr) and the gas experiencing turbulent condensation raining onto the AGN provide quantitative evidence that a recurrent, tight feeding and feedback cycle may be self-regulating the activity of Fornax A, in agreement with CCA simulations. To date, this is one of the most in-depth probes of such a mechanism, paving the way to apply these precise diagnostics to a larger sample of nearby AGN hosts and their multi-phase inter stellar medium.

2021 - An H α/X-ray orphan cloud as a signpost of intracluster medium clumping [Articolo su rivista]
Ge, C.; Luo, R.; Sun, M.; Yagi, M.; Jachym, P.; Boselli, A.; Fossati, M.; Nulsen, P. E. J.; Sarazin, C.; Edge, T.; Gavazzi, G.; Gaspari, M.; Koda, J.; Komiyama, Y.; Yoshida, M.
abstract

Recent studies have highlighted the potential significance of intracluster medium (ICM) clumping and its important implications for cluster cosmology and baryon physics. Many of the ICM clumps can originate from infalling galaxies, as stripped interstellar medium (ISM) mixing into the hot ICM. However, a direct connection between ICM clumping and stripped ISM has not been unambiguously established before. Here, we present the discovery of the first and still the only known isolated cloud (or orphan cloud [OC]) detected in both X-rays and H α in the nearby cluster A1367. With an effective radius of 30 kpc, this cloud has an average X-ray temperature of 1.6 keV, a bolometric X-ray luminosity of -3.1 × 1041 erg s−1, and a hot gas mass of -1010 M☉. From the Multi-Unit Spectroscopic Explorer (MUSE) data, the OC shows an interesting velocity gradient nearly along the east-west direction with a low level of velocity dispersion of -80 km s−1, which may suggest a low level of the ICM turbulence. The emission line diagnostics suggest little star formation in the main H α cloud and a low-ionization (nuclear) emission-line regions like spectrum, but the excitation mechanisms remain unclear. This example shows that stripped ISM, even long after the initial removal from the galaxy, can still induce ICM inhomogeneities. We suggest that the magnetic field can stabilize the OC by suppressing hydrodynamic instabilities and thermal conduction. This example also suggests that at least some ICM clumps are multiphase in nature and implies that the ICM clumps can also be traced in H α. Thus, future deep and wide-field H α surveys can be used to probe the ICM clumping and turbulence.

2021 - Erratum: Dissecting the turbulent weather driven by mechanical AGN feedback (MNRAS (2020) 498: 4 (4983-5002) DOI: 10.1093/mnras/staa2747) [Articolo su rivista]
Wittor, D.; Gaspari, M.
abstract

This is an Erratum to the paper entitled ‘Dissecting the turbulent weather driven by mechanical AGN feedback’, which is published in MNRAS, 498(4), 4983–5002 (2020). We found and corrected two errors in the post-processing analysis code involved in the calculation of baroclinic and advective source term in the Eulerian analysis, which is only a minor part of the main paper (section 3; most of the paper is indeed focused on the Lagrangian analysis). (Figure Presented).

2021 - Feedback from active galactic nuclei in galaxy groups [Articolo su rivista]
Eckert, D.; Gaspari, M.; Gastaldello, F.; Le Brun, A. M. C.; O'Sullivan, E.
abstract

The co-evolution between supermassive black holes and their environment is most directly traced by the hot atmospheres of dark matter halos. The cooling of the hot atmosphere supplies the central regions with fresh gas, igniting active galactic nuclei (AGN) with long duty cycles. Outflows from the central engine tightly couple with the surrounding gaseous medium and provide the dominant heating source preventing runaway cooling by carving cavities and driving shocks across the medium. The AGN feedback loop is a key feature of all modern galaxy evolution models. Here, we review our knowledge of the AGN feedback process in the specific context of galaxy groups. Galaxy groups are uniquely suited to constrain the mechanisms governing the cooling-heating balance. Unlike in more massive halos, the energy that is supplied by the central AGN to the hot intragroup medium can exceed the gravitational binding energy of halo gas particles. We report on the state-of-the-art in observations of the feedback phenomenon and in theoretical models of the heating-cooling balance in galaxy groups. We also describe how our knowledge of the AGN feedback process impacts galaxy evolution models and large-scale baryon distributions. Finally, we discuss how new instrumentation will answer key open questions on the topic.

2021 - Iron in X-COP: Tracing enrichment in cluster outskirts with high accuracy abundance profiles [Articolo su rivista]
Ghizzardi, Simona; Molendi, Silvano; Remco van der, Burg; DE GRANDI, Sabrina; Bartalucci, Iacopo; Gastaldello, Fabio; Rossetti, Mariachiara; Biffi, Veronica; Borgani, Stefano; Dominique, Eckert; Ettori, Stefano; Gaspari, Massimo; Ghirardini, Vittorio; Rasia, Elena
abstract

We present the first metal abundance profiles for a representative sample ofmassive clusters. Our measures extend to $R_{500}$ and are corrected for asystematic error plaguing previous outskirt estimates. Our profiles flatten outat large radii, admittedly not a new result, however the radial range andrepresentative nature of our sample extends its import well beyond previousfindings. We find no evidence of segregation between cool-core andnon-cool-core systems beyond $\sim 0.3 R_{500}$, implying that, as was foundfor thermodynamic properties (Ghirardini et al, 2019), the physical state ofthe core does not affect global cluster properties. Our mean abundance within$R_{500}$ shows a very modest scatter, $< $15%, suggesting the enrichmentprocess must be quite similar in all these massive systems. This is a newfinding and has significant implications on feedback processes. Together withresults from thermodynamic properties presented in a previous X-COP paper, itaffords a coherent picture where feedback effects do not vary significantlyfrom one system to another. By combing ICM with stellar measurements we havefound the amount of Fe diffused in the ICM to be about ten times higher thanthat locked in stars. Although our estimates suggest, with some strength, thatthe measured iron mass in clusters is well in excess of the predicted one,systematic errors prevent us from making a definitive statement. Furtheradvancements will only be possible when systematic uncertainties, principallythose associated to stellar masses, both within and beyond $R_{500}$, can bereduced.

2021 - Iron in X-COP: Tracing enrichment in cluster outskirts with high accuracy abundance profiles (Corrigendum) [Articolo su rivista]
Ghizzardi, Simona; Molendi, Silvano; Van der Burg, Remco; DE GRANDI, Sabrina; Bartalucci, Iacopo; Gastaldello, Fabio; Rossetti, Mariachiara; Biffi, Veronica; Borgani, Stefano; Eckert, Dominique; Ettori, Stefano; Gaspari, Massimo; Ghirardini, Vittorio; Rasia, Elena
abstract

We discovered a conversion error in deriving the expected iron yield YFe for Maoz &Graur (2017) values (see gold shaded area in our Fig. 19 in the original paper). Expected yields are evaluated through equation 12 and converted to solar units (see Eq. 11). We adopt the solar abundance measurements by Asplund et al. (2009); under this assumption, the solar iron abundance is Zm; = 0:00124; this is the solar iron abundance by mass fraction with respect to the gas mass, namely (Fe=gas). This is the value reported in our Sect. 5.1 and used throughout the paper. However, when we derived YFe using the yIa, kIa, yCC, and kCC estimates from Maoz &Graur (2017), we erroneously used Zm; = 0:00174, which is the solar iron abundance by mass fraction with respect to the hydrogen mass, (Fe=H), leading to a wrong expected range for the iron yield. The correct estimate for YFe is YFe; = 3:65+-1 1:30 30Z. In the meantime, Freundlich &Maoz (2021) published updated values for Type-Ia supernova (SNIa) rates. Their new estimates provide kIa = 3:1+1:1-1:0 × 10-3M-1, which leads to YFe; = 2:34+0:63-0:56Z. By chance, the new updated value is not very different from the wrong value reported in Ghizzardi et al. (2021), leaving our discussion and main conclusions unchanged. The last paragraph in Sect. 5.2 should be replaced with: "Recently, it has been shown (see Maoz &Graur 2017 and Friedmann &Maoz 2018) that type Ia SN explosions in galaxy (Figure Presented) clusters are more frequent than in the field. If, following Maoz &Graur (2017), we assume a SNIa rate per unit mass of kIa = (5:4 ± 2:3) × 10-3M-1, we derive YFe; = 3:65+-1 1:3 3 Z. More recently, Freundlich &Maoz (2021) published updated values for SNIa rates in clusters, kIa = 3:1+1:1-1:0 ×10-3 M-1, which lead to YFe; = 2:34+0:63-0:56Z (gold shaded region in Fig. 19). This revised SN rate brings the expected effective yield closer, but it is still well below the measured ones." Figure 19 should be replaced with the one reported here.

2021 - Multiphase Powerful Outflows Detected in High-z Quasars [Articolo su rivista]
Chartas, G.; Cappi, Massimo; Vignali, C.; Dadina, Mauro; James, V.; Lanzuisi, Giorgio; Giustini, M.; Gaspari, Massimo; Strickland, S.; Bertola, E.
abstract

We present results from a comprehensive study of ultrafast outflows (UFOs) detected in a sample of 14 quasars, 12 of which are gravitationally lensed, in a redshift range of 1.41-3.91, near the peak of the active galactic nucleus (AGN) and star formation activity. New XMM-Newton observations are presented for six of them, which were selected to be lensed and contain a narrow absorption line (NAL) in their UV spectra. Another lensed quasar was added to the sample, albeit already studied because it was not searched for UFOs. The remaining seven quasars of our sample are known to contain UFOs. The main goals of our study are to infer the outflow properties of high-z quasars, constrain their outflow induced feedback, study the relationship between the outflow properties and the properties of the ionizing source, and compare these results to those of nearby AGN. Our study adds six new detections (>99% confidence) of UFOs at z >1.4, almost doubling the current number of cases. Based on our survey of six quasars selected to contain a NAL and observed with XMM-Newton, the coexistence of intrinsic UV NALs and UFOs is found to be significant in >83% of these quasars suggesting a link between multiphase AGN feedback properties of the meso- and microscale. The kinematic luminosities of the UFOs of our high-z sample are large compared to their bolometric luminosities (median of L K/L Bol ⪆ 50%). This suggests they provide efficient feedback to influence the evolution of their host galaxies and that magnetic driving may be a significant contributor to their acceleration.

2021 - Observational Evidence for Enhanced Black Hole Accretion in Giant Elliptical Galaxies [Articolo su rivista]
Mcdonald, Michael; Mcnamara, Brian R.; Calzadilla, Michael S.; Chen, Chien-Ting; Gaspari, Massimo; Hickox, Ryan C.; Kara, Erin; Korchagin, Ilia
abstract

We present a study of the relationship between black hole accretion rate (BHAR) and star formation rate (SFR) in a sample of giant elliptical galaxies. These galaxies, which live at the centers of galaxy groups and clusters, have star formation and black hole activity that is primarily fueled by gas condensing out of the hot intracluster medium. For a sample of 46 galaxies spanning five orders of magnitude in BHAR and SFR, we find a mean ratio of log10(BHAR/SFR)=−1.45±0.2 , independent of the methodology used to constrain both SFR and BHAR. This ratio is significantly higher than most previously published values for field galaxies. We investigate whether these high BHAR/SFR ratios are driven by high BHAR, low SFR, or a different accretion efficiency in radio galaxies. The data suggest that the high BHAR/SFR ratios are primarily driven by boosted black hole accretion in spheroidal galaxies compared to their disk counterparts. We propose that the angular momentum of the cool gas is the primary driver in suppressing BHAR in lower-mass galaxies, with massive galaxies accreting gas that has condensed out of the hot phase on nearly radial trajectories. Additionally, we demonstrate that the relationship between specific BHAR and SFR (sBHAR and sSFR) has much less scatter over six orders of magnitude in both parameters, due to competing dependence on morphology between the M_BH-M_star and BHAR-SFR relations. In general, active galaxies selected by typical techniques have sBHAR/sSFR ∼ 10, while galactic nuclei with no clear AGN signatures have sBHAR/sSFR ∼ 1, consistent with a universal M_BH-M_spheroid relation.

2021 - Radio galaxies in galaxy groups: Kinematics, scaling relations, and AGN feedback [Articolo su rivista]
Pasini, T.; Finoguenov, A.; Bruggen, M.; Gaspari, M.; De Gasperin, F.; Gozaliasl, G.
abstract

We investigate the kinematic properties of a large (N = 998) sample of COSMOS spectroscopic galaxy members distributed among 79 groups. We identify the Brightest Group Galaxies (BGGs) and cross-match our data with the VLA-COSMOS Deep survey at 1.4 GHz, classifying our parent sample into radio/non-radio BGGs and radio/non-radio satellites. The radio luminosity distribution spans from $L_R\sim 2\times 10^{21}$ W Hz$^{-1}$ to $L_R\sim 3\times 10^{25}$ W Hz$^{-1}$. A phase-space analysis, performed by comparing the velocity ratio (line-of-sight velocity divided by the group velocity dispersion) with the galaxy-group centre offset, reveals that BGGs (radio and non-radio) are mostly ($\sim$80 per cent) ancient infallers. Furthermore, the strongest ($L_R\gt 10^{23}$ W Hz$^{-1}$) radio galaxies are always found within 0.2$R_{\rm vir}$ from the group centre. Comparing our samples with HORIZON-AGN, we find that the velocities and offsets of simulated galaxies are more similar to radio BGGs than to non-radio BGGs, albeit statistical tests still highlight significant differences between simulated and real objects. We find that radio BGGs are more likely to be hosted in high-mass groups. Finally, we observe correlations between the powers of BGG radio galaxies and the X-ray temperatures, $T_{\rm x}$, and X-ray luminosities, $L_{\rm x}$, of the host groups. This supports the existence of a link between the intragroup medium and the central radio source. The occurrence of powerful radio galaxies at group centres can be explained by Chaotic Cold Accretion, as the AGN can feed from both the galactic and intragroup condensation, leading to the observed positive $L_{\rm R}-T_{\rm x}$ correlation.

2021 - Scaling Properties of Galaxy Groups [Articolo su rivista]
Lovisari, Lorenzo; Ettori, Stefano; Gaspari, Massimo; Giles, Paul A.
abstract

Galaxy groups and poor clusters are more common than rich clusters, and host the largest fraction of matter content in the Universe. Hence, their studies are key to understand the gravitational and thermal evolution of the bulk of the cosmic matter. Moreover, because of their shallower gravitational potential, galaxy groups are systems where non-gravitational processes (e.g., cooling, AGN feedback, star formation) are expected to have a higher impact on the distribution of baryons, and on the general physical properties, than in more massive objects, inducing systematic departures from the expected scaling relations. Despite their paramount importance from the astrophysical and cosmological point of view, the challenges in their detection have limited the studies of galaxy groups. Upcoming large surveys will change this picture, reassigning to galaxy groups their central role in studying the structure formation and evolution in the Universe, and in measuring the cosmic baryonic content. Here, we review the recent literature on various scaling relations between X-ray and optical properties of these systems, focusing on the observational measurements, and the progress in our understanding of the deviations from the self-similar expectations on groups' scales. We discuss some of the sources of these deviations, and how feedback from supernovae and/or AGNs impacts the general properties and the reconstructed scaling laws. Finally, we discuss future prospects in the study of galaxy groups.

2021 - The Cluster HEritage project with XMM-Newton: Mass Assembly and Thermodynamics at the Endpoint of structure formation. I. Programme overview [Articolo su rivista]
CHEX-MATE, Collaboration; Arnaud, M.; Ettori, Stefano; Pratt, G. W.; Rossetti, Mariachiara; Eckert, D.; Gastaldello, Fabio; Gavazzi, R.; Kay, S. T.; Lovisari, L.; Maughan, B. J.; Pointecouteau, E.; Sereno, Mauro; Bartalucci, Iacopo; Bonafede, Annalisa; Bourdin, H.; Cassano, Rossella; Duffy, R. T.; Iqbal, A.; Maurogordato, S.; Rasia, Elena; Sayers, J.; Andrade-Santos, F.; Aussel, H.; Barnes, D. J.; Barrena, R.; Borgani, Stefano; Burkutean, Sandra; Clerc, N.; Corasaniti, P. -S.; Cuillandre, J. -C.; DE GRANDI, Sabrina; De Petris, M.; Dolag, K.; Donahue, M.; Ferragamo, A.; Gaspari, Massimo; Ghizzardi, Simona; Gitti, Myriam; Haines, C. P.; Jauzac, M.; Johnston-Hollitt, M.; Jones, C.; Kéruzoré, F.; Le Brun, A. M. C.; Mayet, F.; Mazzotta, P.; Melin, J. -B.; Molendi, Silvano; Nonino, Mario; Okabe, N.; Paltani, S.; Perotto, L.; Pires, S.; Radovich, Mario; Rubino-Martin, J. -A.; Salvati, L.; Saro, Alexandro; Sartoris, Barbara; Schellenberger, G.; Streblyanska, A.; Tarrío, P.; Tozzi, Paolo; Umetsu, K.; van der Burg, R. F. J.; Vazza, Franco; Venturi, Tiziana; Yepes, G.; Zarattini, S.
abstract

The Cluster HEritage project with XMM-Newton - Mass Assembly and Thermodynamics at the Endpoint of structure formation (CHEX-MATE) is a three-mega-second Multi-Year Heritage Programme to obtain X-ray observations of a minimally-biased, signal-to-noise-limited sample of 118 galaxy clusters detected by Planck through the Sunyaev-Zeldovich effect. The programme, described in detail in this paper, aims to study the ultimate products of structure formation in time and mass. It is composed of a census of the most recent objects to have formed (Tier-1: 0.05 < z < 0.2; 2 × 10^14 M⊙ < M500 < 9 × 10^14 M⊙), together with a sample of the highest mass objects in the Universe (Tier-2: z < 0.6; M500 >7.25 × 10^14 M⊙). The programme will yield an accurate vision of the statistical properties of the underlying population, measure how the gas properties are shaped by collapse into the dark matter halo, uncover the provenance of non-gravitational heating, and resolve the major uncertainties in mass determination that limit the use of clusters for cosmological parameter estimation. We will acquire X-ray exposures of uniform depth, designed to obtain individual mass measurements accurate to 15 − 20% under the hydrostatic assumption. We present the project motivations, describe the programme definition, and detail the ongoing multi-wavelength observational (lensing, SZ, radio) and theoretical effort that is being deployed in support of the project.

2021 - The Clusters Hiding in Plain Sight (CHiPS) Survey: CHIPS1911+4455, a Rapidly Cooling Core in a Merging Cluster [Articolo su rivista]
Somboonpanyakul, Taweewat; Mcdonald, Michael; Bayliss, Matthew; Voit, Mark; Donahue, Megan; Gaspari, Massimo; Dahle, Håkon; Rivera-Thorsen, Emil; Stark, Antony
abstract

We present high-resolution optical images from the Hubble Space Telescope, X-ray images from the Chandra X-ray Observatory, and optical spectra from the Nordic Optical Telescope for a newly discovered galaxy cluster, CHIPS1911+4455, at z = 0.485 ± 0.005. CHIPS1911+4455 was discovered in the Clusters Hiding in Plain Sight survey, which sought to discover galaxy clusters with extreme central galaxies that were misidentified as isolated X-ray point sources in the ROSAT All-Sky Survey. With new Chandra X-ray observations, we find the core (r = 10 kpc) entropy to be 17_-9^2 keV cm^2 , suggesting a strong cool core, which is typically found at the centers of relaxed clusters. However, the large-scale morphology of CHIPS1911+4455 is highly asymmetric, pointing to a more dynamically active and turbulent cluster. Furthermore, the Hubble images reveal a massive, filamentary starburst near the brightest cluster galaxy (BCG). We measure the star formation rate for the BCG to be 140-190 M⊙/yr, which is one of the highest rates measured in a central cluster galaxy to date. One possible scenario for CHIPS1911+4455 is that the cool core was displaced during a major merger and rapidly cooled, with cool, star-forming gas raining back toward the core. This unique system is an excellent case study for high-redshift clusters, where such phenomena are proving to be more common. Further studies of such systems will drastically improve our understanding of the relation between cluster mergers and cooling, and how these fit in the bigger picture of active galactic nuclei feedback.

2021 - The Clusters Hiding in Plain Sight (CHiPS) Survey: Complete Sample of Extreme BCG Clusters [Articolo su rivista]
Somboonpanyakul, Taweewat; Mcdonald, Michael; Gaspari, Massimo; Stalder, Brian; Stark, Antony A.
abstract

We present optical follow-up observations for candidate clusters in the Clusters Hiding in Plain Sight survey, which is designed to find new galaxy clusters with extreme central galaxies that were misidentified as bright isolated sources in the ROSAT All-Sky Survey catalog. We identify 11 cluster candidates around X-ray, radio, and mid-IR-bright sources, including six well-known clusters, two false associations of foreground and background clusters, and three new candidates, which are observed further with Chandra. Of the three new candidates, we confirm two newly discovered galaxy clusters: CHIPS 1356-3421 and CHIPS 1911+4455. Both clusters are luminous enough to be detected in the ROSAT All-Sky Survey data if not because of their bright central cores. CHIPS 1911+4455 is similar in many ways to the Phoenix cluster, but with a highly disturbed X-ray morphology on large scales. We find the occurrence rate for clusters that would appear to be X-ray-bright point sources in the ROSAT All-Sky Survey (and any surveys with similar angular resolution) to be 2% ± 1%, and the occurrence rate of clusters with runaway cooling in their cores to be <1%, consistent with predictions of chaotic cold accretion. With the number of new groups and clusters predicted to be found with eROSITA, the population of clusters that appear to be point sources (due to a central QSO or a dense cool core) could be around 2000. Finally, this survey demonstrates that the Phoenix cluster is likely the strongest cool core at z < 0.7—anything more extreme would have been found in this survey.

2021 - The Deepest Chandra View of RBS 797: Evidence for Two Pairs of Equidistant X-ray Cavities [Articolo su rivista]
Ubertosi, F.; Gitti, Myriam; Brighenti, F.; Brunetti, Gianfranco; Mcdonald, M.; Nulsen, P.; Mcnamara, B.; Randall, S.; Forman, W.; Donahue, M.; Ignesti, Alessandro; Gaspari, Massimo; Ettori, Stefano; Feretti, L.; Blanton, E. L.; Jones, C.; Calzadilla, M.
abstract

We present the first results of a deep Chandra observation of the galaxy cluster RBS 797 whose previous X-ray studies revealed two pronounced X-ray cavities in the east-west (E-W) direction. Follow-up VLA radio observations of the central active galactic nucleus (AGN) uncovered different jet and lobe orientations, with radio lobes filling the E-W cavities and perpendicular jets showing emission in the north-south (N-S) direction over the same scale (≍30 kpc). With the new ~427 ks total exposure, we report the detection of two additional, symmetric X-ray cavities in the N-S direction at nearly the same radial distance as the E-W ones. The newly discovered N-S cavities are associated with the radio emission detected at 1.4 and 4.8 GHz in archival VLA data, making RBS 797 the first galaxy cluster found to have four equidistant, centrally symmetric, radio-filled cavities. We derive the dynamical and radiative ages of the four cavities from X-ray and radio data, respectively, finding that the two outbursts are approximately coeval, with an age difference of ⪅10 Myr between the E-W and N-S cavities. We discuss two scenarios for the origin of the two perpendicular, equidistant cavity systems: either the presence of a binary AGN that is excavating coeval pairs of cavities in perpendicular directions or a fast (<10 Myr) jet reorientation event that produced subsequent, misaligned outbursts.

2021 - The Metal Content of the Hot Atmospheres of Galaxy Groups [Articolo su rivista]
Gastaldello, Fabio; Simionescu, Aurora; Mernier, Francois; Biffi, Veronica; Gaspari, Massimo; Sato, Kosuke; Matsushita, Kyoko
abstract

Galaxy groups host the majority of matter and more than half of all the galaxies in the Universe. Their hot (10^7 K), X-ray emitting intra-group medium (IGrM) reveals emission lines typical of many elements synthesized by stars and supernovae. Because their gravitational potentials are shallower than those of rich galaxy clusters, groups are ideal targets for studying, through X-ray observations, feedback effects, which leave important marks on their gas and metal contents. Here, we review the history and present status of the chemical abundances in the IGrM probed by X-ray spectroscopy. We discuss the limitations of our current knowledge, in particular due to uncertainties in the modeling of the Fe-L shell by plasma codes, and coverage of the volume beyond the central region. We further summarize the constraints on the abundance pattern at the group mass scale and the insight it provides to the history of chemical enrichment. Parallel to the observational efforts, we review the progress made by both cosmological hydrodynamical simulations and controlled high-resolution 3D simulations to reproduce the radial distribution of metals in the IGrM, the dependence on system mass from group to cluster scales, and the role of AGN and SN feedback in producing the observed phenomenology. Finally, we highlight future prospects in this field, where progress will be driven both by a much richer sample of X-ray emitting groups identified with eROSITA, and by a revolution in the study of X-ray spectra expected from micro-calorimeters onboard XRISM and ATHENA.

2021 - WISDOM project - VIII. Multiscale feedback cycles in the brightest cluster galaxy NGC 0708 [Articolo su rivista]
North, E. V.; Davis, T. A.; Bureau, M.; Gaspari, M.; Cappellari, M.; Iguchi, S.; Liu, L.; Onishi, K.; Sarzi, M.; Smith, M. D.; Williams, T. G.
abstract

We present high-resolution (synthesized beam size 0${-{.}{\prime\prime}}$088 × 0${-{.}{\prime\prime}}$083 or 25 × 23 pc2) Atacama Large Millimetre/submillimetre Array 12CO(2-1) line and 236 GHz continuum observations, as well as 5 GHz enhanced Multi-Element Radio Linked Interferometer Network (e-MERLIN) continuum observations, of NGC 0708; the brightest galaxy in the low-mass galaxy cluster Abell 262. The line observations reveal a turbulent, rotating disc of molecular gas in the core of the galaxy, and a high-velocity, blueshifted feature ≈0${-{.}{\prime\prime}}$4 (≈113 pc) from its centre. The submillimetre continuum emission peaks at the nucleus, but extends towards this anomalous CO emission feature. No corresponding elongation is found on the same spatial scales at 5 GHz with e-MERLIN. We discuss potential causes for the anomalous blueshifted emission detected in this source, and conclude that it is most likely to be a low-mass in-falling filament of material condensing from the hot intracluster medium via chaotic cold accretion, but it is also possible that it is a jet-driven molecular outflow. We estimate the physical properties this structure has in these two scenarios, and show that either explanation is viable. We suggest future observations with integral field spectrographs will be able to determine the true cause of this anomalous emission, and provide further evidence for interaction between quenched cooling flows and mechanical feedback on both small and large scales in this source.

2021 - X-ray obscuration from a variable ionized absorber in PG 1114+445 [Articolo su rivista]
Serafinelli, Roberto; Braito, Valentina; Severgnini, Paola; Tombesi, Francesco; Giani, G; Piconcelli, Enrico; DELLA CECA, Roberto; Vagnetti, Fausto; Gaspari, Massimo; Saturni, FRANCESCO GABRIELE; Middei, Riccardo; Tortosa, Alessia
abstract

Photoionized absorbers of outflowing gas are commonly found in the X-ray spectra of active galactic nuclei. While most of these absorbers are seldom significantly variable, some ionized obscurers have increasingly been found to substantially change their column density on a wide range of timescales. These NHvariations are often considered as the signature of the clumpy nature of the absorbers. Here we present the analysis of a new Neil Gehrels Swift Observatory campaign of the type 1 quasar PG 1114+445, which was observed to investigate the time evolution of the multiphase outflowing absorbers previously detected in its spectra. The analyzed dataset consists of 22 observations with a total exposure of ∼90 ks that spans about 20 months. For the whole campaign, we report an unusually low flux state with respect to all previous X-ray observations of this quasar. From the analysis of the stacked spectra, we find a fully covering absorber with a column density log(NH/cm−2) = 22.9−0.1+0.3. This is an order of magnitude higher than the column density measured in the previous observations. This is either due to a variation of the known absorbers or to a new one that eclipses the X-ray emitting source. We also find an ionization parameter of log(ξ/erg cm s−1) = 1.4−0.2+0.6. Assuming that the obscuration lasts for the whole duration of the campaign, that is, more than 20 months, we estimate the minimum distance of the ionized clump, which is located at r ≳ 0.5 pc.

2020 - A molecular absorption line survey towards the AGN of Hydra-A [Articolo su rivista]
Rose, Tom; Edge, A. C.; Combes, F.; Hamer, S.; Mcnamara, B. R.; Russell, H.; Gaspari, Massimo; Salomé, P.; Sarazin, C.; Tremblay, G. R.; Baum, S. A.; Bremer, M. N.; Donahue, M.; Fabian, A. C.; Ferland, G.; Nesvadba, N.; O'Dea, C.; Oonk, J. B. R.; Peck, A. B.
abstract

We present Atacama Large Millimeter/submillimeter Array observations of the brightest cluster galaxy Hydra-A, a nearby (z=0.054) giant elliptical galaxy with powerful and extended radio jets. The observations reveal CO(1-0), CO(2-1), 13CO(2-1), CN(2-1), SiO(5-4), HCO+(1-0), HCO+(2-1), HCN(1-0), HCN(2-1), HNC(1-0) and H2CO(3-2) absorption lines against the galaxy's bright and compact active galactic nucleus. These absorption features are due to at least 12 individual molecular clouds which lie close to the centre of the galaxy and have velocities of approximately −50 to +10 km/s relative to its recession velocity, where positive values correspond to inward motion. The absorption profiles are evidence of a clumpy interstellar medium within brightest cluster galaxies composed of clouds with similar column densities, velocity dispersions and excitation temperatures to those found at radii of several kpc in the Milky Way. We also show potential variation in a ∼10 km/s wide section of the absorption profile over a two year timescale, most likely caused by relativistic motions in the hot spots of the continuum source which change the background illumination of the absorbing clouds.

2020 - Constraining the origin and models of chemical enrichment in galaxy clusters using the Athena X-IFU [Articolo su rivista]
Mernier, F.; Cucchetti, E.; Tornatore, L.; Biffi, V.; Pointecouteau, E.; Clerc, N.; Peille, P.; Rasia, E.; Barret, D.; Borgani, Stefano; Bulbul, E.; Dauser, T.; Dolag, K.; Ettori, Stefano; Gaspari, M.; Pajot, F.; Roncarelli, M.; Wilms, J.; Noûs, C.
abstract

The chemical enrichment of the Universe at all scales is related to stellarwinds and explosive supernovae phenomena. Metals produced by stars and laterspread at the mega-parsec scale through the intra-cluster medium (ICM) become afossil record of the chemical enrichment of the Universe and of the dynamicaland feedback mechanisms determining their circulation. As demonstrated by theresults of the soft X-ray spectrometer onboard Hitomi, high resolution X-rayspectroscopy is the path to to differentiate among the models that considerdifferent metal production mechanisms, predict the outcoming yields, and arefunction of the nature, mass, and/or initial metallicity of their stellarprogenitor. Transformational results shall be achieved through improvements inthe energy resolution and effective area of X-ray observatories to detect raremetals (e.g. Na, Al) and constrain yet uncertain abundances (e.g. C, Ne, Ca,Ni). The X-ray Integral Field Unit (X-IFU) instrument onboard thenext-generation European X-ray observatory Athena is expected to deliver suchbreakthroughs. Starting from 100 ks of synthetic observations of 12 abundanceratios in the ICM of four simulated clusters, we demonstrate that the X-IFUwill be capable of recovering the input chemical enrichment models at both low($z = 0.1$) and high ($z = 1$) redshifts, while statistically excluding morethan 99.5% of all the other tested combinations of models. By fixing theenrichment models which provide the best fit to the simulated data, we alsoshow that the X-IFU will constrain the slope of the stellar initial massfunction within $\sim$12%. These constraints will be key ingredients in ourunderstanding of the chemical enrichment of the Universe and its evolution.

2020 - Dissecting the turbulent weather driven by mechanical AGN feedback [Articolo su rivista]
Wittor, D.; Gaspari, M
abstract

Turbulence in the intracluster, intragroup, and circumgalactic medium plays a crucial role in the self-regulated feeding and feedback loop of central supermassive black holes. We dissect the 3D turbulent 'weather' in a high-resolution Eulerian simulation of active galactic nucleus (AGN) feedback, shown to be consistent with multiple multiwavelength observables of massive galaxies. We carry out post-processing simulations of Lagrangian tracers to track the evolution of enstrophy, a proxy of turbulence, and its related sinks and sources. This allows us to isolate in depth the physical processes that determine the evolution of turbulence during the recurring strong and weak AGN feedback events, which repeat self-similarly over the Gyr evolution. We find that the evolution of enstrophy/turbulence in the gaseous halo is highly dynamic and variable over small temporal and spatial scales, similar to the chaotic weather processes on Earth. We observe major correlations between the enstrophy amplification and recurrent AGN activity, especially via its kinetic power. While advective and baroclinc motions are always subdominant, stretching motions are the key sources of the amplification of enstrophy, in particular along the jet/cocoon, while rarefactions decrease it throughout the bulk of the volume. This natural self-regulation is able to preserve, as ensemble, the typically observed subsonic turbulence during cosmic time, superposed by recurrent spikes via impulsive anisotropic AGN features (wide outflows, bubbles, cocoon shocks). This study facilitates the preparation and interpretation of the thermo-kinematical observations enabled by new revolutionary X-ray integral field unit telescopes, such as XRISM and Athena.

2020 - Hot gaseous atmospheres of rotating galaxies observed with XMM-Newton [Articolo su rivista]
Juráňová, A.; Werner, N.; Nulsen, P. E. J.; Gaspari, M.; Lakhchaura, K.; Canning, R. E. A.; Donahue, M.; Hroch, F.; Voit, G. M.
abstract

X-ray emitting atmospheres of non-rotating early-type galaxies and their connection to central active galactic nuclei have been thoroughly studied over the years. However, in systems with significant angular momentum, processes of heating and cooling are likely to proceed differently. We present an analysis of the hot atmospheres of six lenticulars and a spiral galaxy to study the effects of angular momentum on the hot gas properties. We find an alignment between the hot gas and the stellar distribution, with the ellipticity of the X-ray emission generally lower than that of the optical stellar emission, consistent with theoretical predictions for rotationally supported hot atmospheres. The entropy profiles of NGC 4382 and the massive spiral galaxy NGC 1961 are significantly shallower than the entropy distribution in other galaxies, suggesting the presence of strong heating (via outflows or compressional) in the central regions of these systems. Finally, we investigate the thermal (in)stability of the hot atmospheres via criteria such as the TI- and C-ratio, and discuss the possibility that the discs of cold gas present in these objects have condensed out of the hot atmospheres.

2020 - Linking macro-, meso- and microscales in multiphase AGN feeding and feedback [Articolo su rivista]
Gaspari, Massimo; Tombesi, Francesco; Cappi, Massimo
abstract

Black hole feeding and feedback are often studied disjointly in both observations and simulations. We encourage the adoption of three physically motivated scales, linking them in a tight multiphase self-regulated loop. We pinpoint the key open questions of this unification problem and advocate for a multiwavelength, multiscale and interdisciplinary community.

2020 - Pressure Profiles and Mass Estimates Using High-resolution Sunyaev-Zel'dovich Effect Observations of Zwicky 3146 with MUSTANG-2 [Articolo su rivista]
Romero, Charles E.; Sievers, Jonathan; Ghirardini, Vittorio; Dicker, Simon; Giacintucci, Simona; Mroczkowski, Tony; Mason, Brian S.; Sarazin, Craig; Devlin, Mark; Gaspari, Massimo; Battaglia, Nicholas; Hilton, Matthew; Bulbul, Esra; Lowe, Ian; Stanchfield, Sara
abstract

The galaxy cluster Zwicky 3146 is a sloshing cool core cluster at z=0.291 that in X-ray imaging does not appear to exhibit significant pressure substructure in the intracluster medium (ICM). The published M500 values range between 3.88+0.62−0.58 to 22.50±7.58×10^14 M⊙, where ICM-based estimates with reported errors <20% suggest that we should expect to find a mass between 6.53+0.44−0.44×10^14 M⊙ (from Planck, with an 8.4σ detection) and 8.52+1.77−1.47×10^14 M⊙ (from ACT, with a 14σ detection). This broad range of masses is suggestive that there is ample room for improvement for all methods. Here, we investigate the ability to estimate the mass of Zwicky 3146 via the Sunyaev-Zel'dovich (SZ) effect with data taken at 90 GHz by MUSTANG-2 to a noise level better than 15 μK at the center, and a cluster detection of 104σ. We derive a pressure profile from our SZ data which is in excellent agreement with that derived from X-ray data. From our SZ-derived pressure profiles, we infer M500 and M2500 via three methods -- Y-M scaling relations, the virial theorem, and hydrostatic equilibrium -- where we employ X-ray constraints from \emph{XMM-Newton} on the electron density profile when assuming hydrostatic equilibrium. Depending on the model and estimation method, our M500 estimates range from 6.23±0.59 to 10.6±0.95×10^14 M⊙, where our estimate from hydrostatic equilibrium, is 8.29+1.93−1.24 (±19.1\% stat) +0.74−0.68 (±8.6\% sys, calibration) ×10^14 M⊙. Our fiducial mass, derived from a Y-M relation is 8.16+0.44−0.54 (±5.5% stat) +0.46−0.43 (±5.5\% sys, Y-M) +0.59−0.55 (±7.0% sys, cal.) ×10^14 M⊙.

2019 - A joint XMM-NuSTAR observation of the galaxy cluster Abell 523: Constraints on inverse Compton emission [Articolo su rivista]
Cova, F.; Gastaldello, Fabio; Wik, D. R.; Boschin, W.; Botteon, A.; Brunetti, Gianfranco; Buote, D. A.; DE GRANDI, Sabrina; Eckert, D.; Ettori, Stefano; Feretti, L.; Gaspari, Massimo; Ghizzardi, Simona; Giovannini, Gabriele; Girardi, M.; Govoni, Federica; Molendi, Silvano; Murgia, Matteo; Rossetti, Mariachiara; Vacca, Valentina
abstract

Aims: We present the results of a joint XMM-Newton and NuSTAR observation (200 ks) of the galaxy cluster Abell 523 at z = 0.104. The peculiar morphology of the cluster radio halo and its outlier position in the radio power P(1.4 GHz) - X-ray luminosity plane make it an ideal candidate for the study of radio and X-ray correlations and for the search of inverse Compton (IC) emission. Methods: We constructed bi-dimensional maps for the main thermodynamic quantities (i.e., temperature, pressure and entropy) derived from the XMM observations to describe the physical and dynamical state of the cluster's intracluster medium (ICM) in detail. We performed a point-to-point comparison in terms of surface brightness between the X-ray and radio emissions to quantify their morphological discrepancies. Making use of NuSTAR's unprecedented hard X-ray focusing capability, we looked for IC emission both globally and locally after properly modeling the purely thermal component with a multi-temperature description. Results: The thermodynamic maps obtained from the XMM observation suggest the presence of a secondary merging process that could be responsible for the peculiar radio halo morphology. This hypothesis is supported by the comparison between the X-ray and radio surface brightnesses, which shows a broad intrinsic scatter and a series of outliers from the best-fit relation, corresponding to those regions that could be influenced by a secondary merger. The global NuSTAR spectrum can be explained by purely thermal gas emission, and there is no convincing evidence that an IC component is needed. The 3σ upper limit on the IC flux in the 20-80 keV band is in the [2.2-4.0] × 10-13erg s-1cm-2range, implying a lower limit on the magnetic field strength in the B &gt;[0.23 - 0.31] μG range. Locally, we looked for IC emission in the central region of the cluster radio halo finding a 3σ upper limit on the 20-80 keV nonthermal flux of 3.17 × 10-14erg s-1cm-2, corresponding to a lower limit on the magnetic field strength of B ≳ 0.81 μG.

2019 - AGN feedback in galaxy group 3C 88: cavities, shock, and jet reorientation [Articolo su rivista]
Liu, Wenhao; Sun, Ming; Nulsen, Paul; Clarke, Tracy; Sarazin, Craig; Forman, William; Gaspari, Massimo; Giacintucci, Simona; Lal, Dharam Vir; Edge, Tim
abstract

We present results from the deep Chandra observation (105 ksec), together with new Giant Metrewave Radio Telescope and Very Large Array data of the AGN outburst in the radio-loud galaxy group 3C 88. The system shows a prominent X-ray cavity on the eastern side with a diameter of ∼50 kpc at ∼28 kpc from the nucleus. The total enthalpy of the cavity is 3.8×10^58 erg and the average power required to inflate the X-ray bubble is ∼2.0×10^43 erg s^-1. From surface brightness profiles we detect a shock with a Mach number of M=1.4±0.2, consistent with the value obtained from temperature jump. The shock energy is estimated to be 1.9×10^59 erg. The size and total enthalpy of the cavity in 3C 88 are the largest known in galaxy groups, as well as the shock energy. The eastern X-ray cavity is not aligned with the radio jet axis. This factor, combined with the radio morphology, strongly suggests jet reorientation in the last tens of million years. The bright rim and arm features surrounding the cavity show metallicity enhancement, suggesting they originated as high metallicity gas from the group center, lifted by the rising X-ray bubbles. Our Chandra study of 3C 88 also reveals that galaxy groups with powerful radio AGN can have high cavity power, although deep X-ray observations are typically required to confirm the cavities in galaxy groups.

2019 - Anatomy of a Cooling Flow: The Feedback Response to Pure Cooling in the Core of the Phoenix Cluster [Articolo su rivista]
Mcdonald, M.; Mcnamara, B. R.; Voit, G. M.; Bayliss, M.; Benson, B. A.; Brodwin, M.; Canning, R. E. A.; Florian, M. K.; Garmire, G. P.; Gaspari, Massimo; Gladders, M. D.; Hlavacek-Larrondo, J.; Kara, E.; Reichardt, C. L.; Russell, H. R.; Saro, Alexandro; Sharon, K.; Somboonpanyakul, T.; Tremblay, G. R.; van Weeren, R. J.
abstract

We present new, deep observations of the Phoenix cluster from the Chandra X-ray Observatory, the Hubble Space Telescope, and the Karl Jansky Very Large Array. These data provide an order of magnitude improvement in depth and/or angular resolution at X-ray, optical, and radio wavelengths, yielding an unprecedented view of the core of the Phoenix cluster. We find that the one-dimensional temperature and entropy profiles are consistent with expectations for pure-cooling hydrodynamic simulations and analytic descriptions of homogeneous, steady-state cooling flow models. In the inner ~10 kpc, the cooling time is shorter by an order of magnitude than any other known cluster, while the ratio of the cooling time to freefall time approaches unity, signaling that the ICM is unable to resist multiphase condensation on kpc scales. When we consider the thermodynamic profiles in two dimensions, we find that the cooling is highly asymmetric. The bulk of the cooling in the inner ~20 kpc is confined to a low-entropy filament extending northward from the central galaxy. We detect a substantial reservoir of cool (10^4 K) gas (as traced by the [OII] doublet), which is coincident with the low-entropy filament. The bulk of this cool gas is draped around and behind a pair of X-ray cavities, presumably bubbles that have been inflated by radio jets, which are detected for the first time on kpc scales. These data support a picture in which AGN feedback is promoting the formation of a multiphase medium via a combination of ordered buoyant uplift and locally enhanced turbulence. These processes ought to counteract the tendency for buoyancy to suppress condensation, leading to rapid cooling along the jet axis. The recent mechanical outburst has sufficient energy to offset cooling, and appears to be coupling to the ICM via a cocoon shock, raising the entropy in the direction orthogonal to the radio jets.

2019 - Black hole mass of central galaxies and cluster mass correlation in cosmological hydro-dynamical simulations [Articolo su rivista]
Bassini, Luigi; Rasia, Elena; Borgani, Stefano; Ragone-Figueroa, Cinthia; Biffi, Veronica; Dolag, Klaus; Gaspari, Massimo; Granato, Gian Luigi; Murante, Giuseppe; Taffoni, Giuliano; Tornatore, Luca
abstract

Recently, relations connecting the SMBH mass of central galaxies and global properties of the hosting cluster, such as temperature and mass, were observed. We investigate the correlation between SMBH mass and cluster mass and temperature, their establishment and evolution. We compare their scatter to that of the classical MBH−MBCG relation. We study how gas accretion and BH-BH mergers contribute to SMBH growth across cosmic time. We employed 135 groups and clusters with a mass range 1.4×10^13 M⊙−2.5×10^15 M⊙ extracted from a set of 29 zoom-in cosmological hydro-dynamical simulations where the baryonic physics is treated with various sub-grid models, including feedback by AGN. In our simulations we find that MBH correlates well with M500 and T500, with the scatter around these relations compatible within 2σ with the scatter around MBH−MBCG at z=0. The MBH−M500 relation evolves with time, becoming shallower at lower redshift as a direct consequence of hierarchical structure formation. On average, in our simulations the contribution of gas accretion to the total SMBH mass dominates for the majority of the cosmic time (z&gt;0.4), while in the last 2 Gyr the BH-BH mergers become a larger contributor. During this last process, substructures hosting SMBHs are disrupted in the merger process with the BCG and the unbound stars enrich the diffuse stellar component rather than increase BCG mass. From the results obtained in our simulations with simple sub-grid models we conclude that the scatter around the MBH−T500 relation is comparable to the scatter around the MBH−MBCG relation and that, given the observational difficulties related to the estimation of the BCG mass, clusters temperature and mass can be a useful proxy for the SMBHs mass, especially at high redshift.

2019 - Circumgalactic Gas and the Precipitation Limit [Articolo su rivista]
Voit, ; Mark, ; Babul, ; Arif, ; Babyk, ; Iurii, ; Bryan, ; Greg, ; Chen, ; Hsiao-Wen, ; Donahue, ; Megan, ; Fielding, ; Drummond, ; Gaspari, M; Li, ; Yuan, ; Mcdonald, ; Michael, ; O'Shea, ; Brian, ; Prasad, ; Deovrat, ; Sharma, ; Prateek, ; Sun, ; Ming, ; Tremblay, ; Grant, ; Werk, ; Jessica, K.; Werner, ; Norbert, ; Zahedy, ; Fakhri,
abstract

Observations increasingly suggest that the ambient CGM pressure cannot exceed the limit at which cold clouds start to condense and fuel feedback that limits further condensation. Such a feedback loop tends to suspend the CGM at the threshold pressure for precipitation. The coming decade will offer many opportunities to test this principle.

2019 - Constraining cold accretion on to supermassive black holes: molecular gas in the cores of eight brightest cluster galaxies revealed by joint CO and CN absorption [Articolo su rivista]
Rose, Tom; Edge, A. C.; Combes, F.; Gaspari, Massimo; Hamer, S.; Nesvadba, N.; Peck, A. B.; Sarazin, C.; Tremblay, G. R.; Baum, S. A.; Bremer, M. N.; Mcnamara, B. R.; O'Dea, C.; Oonk, J. B. R.; Russell, H.; Salomé, P.; Donahue, M.; Fabian, A. C.; Ferland, G.; Mittal, R.; Vantyghem, A.
abstract

To advance our understanding of the fuelling and feedback processes which power the Universe's most massive black holes, we require a significant increase in our knowledge of the molecular gas which exists in their immediate surroundings. However, the behaviour of this gas is poorly understood due to the difficulties associated with observing it directly. We report on a survey of 18 brightest cluster galaxies lying in cool cores, from which we detect molecular gas in the core regions of eight via carbon monoxide (CO), cyanide (CN) and silicon monoxide (SiO) absorption lines. These absorption lines are produced by cold molecular gas clouds which lie along the line of sight to the bright continuum sources at the galaxy centres. As such, they can be used to determine many properties of the molecular gas which may go on to fuel supermassive black hole accretion and AGN feedback mechanisms. The absorption regions detected have velocities ranging from -45 to 283 km/s relative to the systemic velocity of the galaxy, and have a bias for motion towards the host supermassive black hole. We find that the CN N = 0 - 1 absorption lines are typically 10 times stronger than those of CO J = 0 - 1. This is due to the higher electric dipole moment of the CN molecule, which enhances its absorption strength. In terms of molecular number density CO remains the more prevalent molecule with a ratio of CO/CN ∼10, similar to that of nearby galaxies. Comparison of CO, CN, and H I observations for these systems shows many different combinations of these absorption lines being detected.

2019 - Constraining Gas Motions in the Intra-Cluster Medium [Articolo su rivista]
Simionescu, Aurora; Zuhone, John; Zhuravleva, Irina; Churazov, Eugene; Gaspari, Massimo; Nagai, Daisuke; Werner, Norbert; Roediger, Elke; Canning, Rebecca; Eckert, Dominique; Gu, Liyi; Paerels, Frits
abstract

The detailed velocity structure of the diffuse X-ray emitting intra-cluster medium (ICM) remains one of the last missing key ingredients in understanding the microphysical properties of these hot baryons and constraining our models of the growth and evolution of structure on the largest scales in the Universe. Direct measurements of the gas velocities from the widths and shifts of X-ray emission lines were recently provided for the central region of the Perseus Cluster of galaxies by Hitomi, and upcoming high-resolution X-ray microcalorimeters onboard XRISM and Athena are expected to extend these studies to many more systems. In the mean time, several other direct and indirect methods have been proposed for estimating the velocity structure in the ICM, ranging from resonant scattering to X-ray surface brightness fluctuation analysis, the kinematic Sunyaev-Zeldovich effect, or using optical line emitting nebulae in the brightest cluster galaxies as tracers of the motions of the ambient plasma. Here, we review and compare the existing estimates of the velocities of the hot baryons, as well as the various overlapping physical processes that drive motions in the ICM, and discuss the implications of these measurements for constraining the viscosity and identifying the source of turbulence in clusters of galaxies.

2019 - Cooling in the X-ray halo of the rotating, massive early-type galaxy NGC 7049 [Articolo su rivista]
Juráňová, A.; Werner, N.; Gaspari, Massimo; Lakhchaura, K.; Nulsen, P. E. J.; Sun, M.; Canning, R. E. A.; Allen, S. W.; Simionescu, A.; Oonk, J. B. R.; Connor, T.; Donahue, M.
abstract

The relative importance of the physical processes shaping the thermodynamics of the hot gas permeating rotating, massive early-type galaxies is expected to be different from that in non-rotating systems. Here, we report the results of the analysis of XMM-Newton data for the massive, lenticular galaxy NGC 7049. The galaxy harbours a dusty disc of cool gas and is surrounded by an extended hot X-ray emitting gaseous atmosphere with unusually high central entropy. The hot gas in the plane of rotation of the cool dusty disc has a multitemperature structure, consistent with ongoing cooling. We conclude that the rotational support of the hot gas is likely capable of altering the multiphase condensation regardless of the t_cool/t_ff ratio, which is here relatively high, ∼40. However, the measured ratio of cooling time and eddy turnover time around unity (C-ratio ≈ 1) implies significant condensation, and at the same time, the constrained ratio of rotational velocity and the velocity dispersion (turbulent Taylor number) Ta_t >1 indicates that the condensing gas should follow non-radial orbits forming a disc instead of filaments. This is in agreement with hydrodynamical simulations of massive rotating galaxies predicting a similarly extended multiphase disc.

2019 - Deep and narrow CO absorption revealing molecular clouds in the Hydra-A brightest cluster galaxy [Articolo su rivista]
Rose, Tom; Edge, A. C.; Combes, F.; Gaspari, Massimo; Hamer, S.; Nesvadba, N.; Russell, H.; Tremblay, G. R.; Baum, S. A.; O'Dea, C.; Peck, A. B.; Sarazin, C.; Vantyghem, A.; Bremer, M.; Donahue, M.; Fabian, A. C.; Ferland, G.; Mcnamara, B. R.; Mittal, R.; Oonk, J. B. R.; Salomé, P.; Swinbank, A. M.; Voit, M.
abstract

Active galactic nuclei play a crucial role in the accretion and ejection of gas in galaxies. Although their outflows are well studied, finding direct evidence of accretion has proved very difficult and has so far been done for very few sources. A promising way to study the significance of cold accretion is by observing the absorption of an active galactic nucleus's extremely bright radio emission by the cold gas lying along the line of sight. As such, we present ALMA CO(1-0) and CO(2-1) observations of the Hydra-A brightest cluster galaxy (z = 0.054) which reveal the existence of cold, molecular gas clouds along the line of sight to the galaxy's extremely bright and compact mm-continuum source. They have apparent motions relative to the central supermassive black hole of between -43 and -4 km/s and are most likely moving along stable, low ellipticity orbits. The identified clouds form part of a ∼10^9 M_☉, approximately edge-on disc of cold molecular gas. With peak CO(2-1) optical depths of τ = 0.88 ^{+0.06}_{-0.06}, they include the narrowest and by far the deepest absorption of this type which has been observed to date in a brightest cluster galaxy. By comparing the relative strengths of the lines for the most strongly absorbing region, we are able to estimate a gas temperature of 42^{+25}_{-11} K and line of sight column densities of N_{CO}=2^{+3}_{-1}× 10^{17} cm^-2 and N_H2 = 7^{+10}_{-4}× 10^{20} cm^-2.

2019 - Do Supermassive Black Hole Winds Impact Galaxy Evolution? [Articolo su rivista]
Tombesi, ; Francesco, ; Cappi, ; Carrera, ; Chartas, ; Fukumura, ; Guainazzi, ; Kazanas, ; Kriss, ; Proga, ; Turner, ; Ueda, ; Veilleux, ; Brusa, ; Gaspari, M
abstract

Powerful winds driven by SMBHs are likely the main mechanism through which SMBHs regulate their own growth and influence the host galaxy evolution. However, their origin and their capability to impact the large-scale environment are still highly debated. Fundamental results will come from high- energy and spatial resolution X-ray observatories.

2019 - Exploring the multiphase medium in MKW 08: from the central active galaxy up to cluster scales [Articolo su rivista]
Tümer, A.; Tombesi, F.; Bourdin, H.; Ercan, E. N.; Gaspari, Massimo; Serafinelli, R.
abstract

The study of the brightest cluster galaxy (BCG) coronae embedded in noncool core (NCC) galaxy clusters is crucial to understand the BCG's role in galaxy cluster evolution as well as the activation of the self-regulated cooling and heating mechanism in the central regions of galaxy clusters. We explore the X-ray properties of the intracluster medium (ICM) of the NCC galaxy cluster MKW 08 and the BCG corona, along with their interface region. With recent and deep archival Chandra observations, we study the BCG corona in detail, and with archival XMM-Newton observations, we investigate the implications of the central active galactic nuclei (AGN) on the BCG. We carry out imaging and spectral analyses of MKW 08 with archival XMM-Newton and Chandra X-ray observations. Our spectral analysis suggests the presence of a central AGN by a power-law with a photon index of Γ ~ 1.8 at the core of its BCG. Although the ICM does not exhibit a cluster scale cool core, the BCG manifests itself as a mini cool core characterized by a cooling time as short as 64 Myr at r = 3 kpc centered at the galaxy. The isothermality of the BCG corona seems to favor mechanical feedback from the central AGN as the major source of gas heating. The gas pressure profile of this mini cool core suggests that the BCG coronal gas reaches pressure equilibrium with the hotter and less dense ICM inside an interface of nearly constant pressure, delimited by radii 4 &lt; r &lt; 10 kpc at the galactic center. As revealed by the presence of a metal enriched tail (Z ~ 0.5 - 0.9 Solar) extending up to 40 kpc, the BCG corona seems to be experiencing ram-pressure stripping by the surrounding ICM and/or interacting with a nearby galaxy, IC 1042.

2019 - Growth and disruption in the Lyra complex [Articolo su rivista]
Clavico, Sara; DE GRANDI, Sabrina; Ghizzardi, Simona; Rossetti, Mariachiara; Molendi, Silvano; Gastaldello, Fabio; Girardi, M.; Boschin, W.; Botteon, A.; Cassano, Rossella; Brüggen, M.; Brunetti, Gianfranco; Dallacasa, Daniele; Eckert, D.; Ettori, Stefano; Gaspari, Massimo; Sereno, Mauro; Shimwell, T.; van Weeren, R. J.
abstract

Nearby clusters of galaxies, z&lt;0.1, are cosmic structures still under formation. Understanding the thermodynamic properties of merging clusters can provide crucial information on how they grow in the local universe. A detailed study of the intra-cluster medium (ICM) properties of un-relaxed systems is essential to understand the fate of in-falling structures and, more generally, the virialization process. We analyzed a mosaic of XMM-Newton observations (240 ks) of the Lyra system (z=0.067) that shows a complex dynamical state. We find the main cluster RXC J1825.3+3026 to be in a late merger phase, whereas its companion CIZA J1824.1+3029 is a relaxed cool-core cluster. We estimate a mass ratio of ~1:2 for the pair. No diffuse X-ray emission is found in the region between them, indicating that these clusters are in a pre-merger phase. We found evidence of a galaxy group infalling on RXC J1825.3+3026 in an advanced state of disruption. The Southern Galaxy, one of the brightest galaxies in the Lyra complex, was very likely at the center of the infalling group. This galaxy has a gaseous corona indicating that it was able to retain some of its gas after the ram-pressure stripping of the intra-group medium. In this scenario the diffuse emission excess observed southwest of RXC J1825.3+3026 could be due to gas once belonging to the group and/or to cluster ICM dislocated by the passage of the group. Finally, we identified three high-velocity galaxies aligned between RXC J1825.3+3026 and the SG, two of these showing evidence of gas stripped from them during infall. We estimate them to be currently falling onto the main cluster at an infall velocity of ~ 3000 km/s. Our study of the Lyra complex provides important clues about the processes presiding over the virialization of massive clusters in the local Universe.

2019 - Hydrostatic mass profiles in X-COP galaxy clusters [Articolo su rivista]
Ettori, Stefano; Ghirardini, V.; Eckert, D.; Pointecouteau, E.; Gastaldello, Fabio; Sereno, Mauro; Gaspari, Massimo; Ghizzardi, Simona; Roncarelli, M.; Rossetti, Mariachiara
abstract

Aims: We present the reconstruction of hydrostatic mass profiles in 13 X-ray luminous galaxy clusters that have been mapped in their X-ray and Sunyaev-Zeldovich (SZ) signals out to R200for the XMM-Newton Cluster Outskirts Project (X-COP). Methods: Using profiles of the gas temperature, density, and pressure that have been spatially resolved out to median values of 0.9R500, 1.8R500, and 2.3R500, respectively, we are able to recover the hydrostatic gravitating mass profile with several methods and using different mass models. Results: The hydrostatic masses are recovered with a relative (statistical) median error of 3% at R500and 6% at R200. By using several different methods to solve the equation of the hydrostatic equilibrium, we evaluate some of the systematic uncertainties to be of the order of 5% at both R500and R200. A Navarro-Frenk-White profile provides the best-fit in 9 cases out of 13; the remaining 4 cases do not show a statistically significant tension with it. The distribution of the mass concentration follows the correlations with the total mass predicted from numerical simulations with a scatter of 0.18 dex, with an intrinsic scatter on the hydrostatic masses of 0.15 dex. We compare them with the estimates of the total gravitational mass obtained through X-ray scaling relations applied to YX, gas fraction, and YSZ, and from weak lensing and galaxy dynamics techniques, and measure a substantial agreement with the results from scaling laws, from WL at both R500and R200(with differences below 15%), from cluster velocity dispersions. Instead, we find a significant tension with the caustic masses that tend to underestimate the hydrostatic masses by 40% at R200. We also compare these measurements with predictions from alternative models to the cold dark matter, like the emergent gravity and MOND scenarios, confirming that the latter underestimates hydrostatic masses by 40% at R1000, with a decreasing tension as the radius increases, and reaches ∼15% at R200, whereas the former reproduces M500within 10%, but overestimates M200by about 20%. Conclusions: The unprecedented accuracy of these hydrostatic mass profiles out to R200allows us to assess the level of systematic errors in the hydrostatic mass reconstruction method, to evaluate the intrinsic scatter in the NFW c - M relation, and to robustly quantify differences among different mass models, different mass proxies, and different gravity scenarios.

2019 - Jet-driven Galaxy-scale Gas Outflows in the Hyperluminous Quasar 3C 273 [Articolo su rivista]
Husemann, Bernd; Bennert, Vardha N.; Jahnke, Knud; Davis, Timothy A.; Woo, Jong-Hak; Scharwächter, Julia; Schulze, Andreas; Gaspari, Massimo; Zwaan, Martin A.
abstract

We present an unprecedented view on the morphology and kinematics of the extended narrow-line region (ENLR) and molecular gas around the prototypical hyper-luminous quasar 3C273 (L∼10^47 erg/s at z=0.158) based on VLT-MUSE optical 3D spectroscopy and ALMA observations. We find that: 1) The ENLR size of 12.1±0.2kpc implies a smooth continuation of the size-luminosity relation out to large radii or a much larger break radius as previously proposed. 2) The kinematically disturbed ionized gas with line splits reaching 1000km/s out to 6.1±1.5kpc is aligned along the jet axis. 3) The extreme line broadening on kpc scales is caused by spatial and spectral blending of many distinct gas clouds separated on sub-arcsecond scales with different line-of-sight velocities. The ENLR velocity field combined with the known jet orientation rule out a simple scenario of a radiatively-driven radial expansion of the outflow. Instead we propose that a pressurized expanding hot gas cocoon created by the radio jet is impacting on an inclined gas disk leading to transverse and/or backflow motion with respect to our line-of-sight. The molecular gas morphology may either be explained by a density wave at the front of the outflow expanding along the jet direction as predicted by positive feedback scenario or the cold gas may be trapped in a stellar over-density caused by a recent merger event. Using 3C273 as a template for observations of high-redshift hyper-luminous AGN reveals that large-scale ENLRs and kpc scale outflows may often be missed due to the brightness of the nuclei and the limited sensitivity of current near-IR instrumentation.

2019 - Mass-Metallicity Relation from Cosmological Hydrodynamical Simulations and X-ray Observations of Galaxy Groups and Clusters [Articolo su rivista]
Truong, Nhut; Rasia, Elena; Biffi, Veronica; Mernier, François; Werner, Norbert; Gaspari, Massimo; Borgani, Stefano; Planelles, Susana; Fabjan, Dunja; Murante, Giuseppe
abstract

Recent X-ray observations of galaxy clusters show that the distribution of intra-cluster medium (ICM) metallicity is remarkably uniform in space and time. In this paper, we analyse a large sample of simulated objects, from poor groups to rich clusters, to study the dependence of the metallicity and related quantities on the mass of the systems. The simulations are performed with an improved version of the smoothed-particle-hydrodynamic GADGET-3 code and consider various astrophysical processes including radiative cooling, metal enrichment and feedback from stars and active galactic nuclei (AGNs). The scaling between the metallicity and the temperature obtained in the simulations agrees well in trend and evolution with the observational results obtained from two data samples characterized by a wide range of masses and a large redshift coverage. We find that the iron abundance in the cluster core (r < 0.1 R500) does not correlate with the temperature nor presents a significant evolution. The scale invariance is confirmed when the metallicity is related directly to the total mass. The slope of the best-fitting relations is shallow (β ∼ -0.1) in the innermost regions (r < 0.5 R500) and consistent with zero outside. We investigate the impact of the AGN feedback and find that it plays a key role in producing a constant value of the outskirts metallicity from groups to clusters. This finding additionally supports the picture of early enrichment.

2019 - Multiphase quasar-driven outflows in PG 1114+445. I. Entrained ultra-fast outflows [Articolo su rivista]
Serafinelli, Roberto; Tombesi, Francesco; Vagnetti, Fausto; Piconcelli, Enrico; Gaspari, Massimo; Saturni, FRANCESCO GABRIELE
abstract

Substantial evidence in the last few decades suggests that outflows from supermassive black holes (SMBH) may play a significant role in the evolution of galaxies.Large-scale outflows known as warm absorbers (WA) and fast disk winds known as ultra-fast outflows (UFO) are commonly found in the spectra of many Seyfert galaxies and quasars, and a correlation has been suggested between them. Recent detections of low ionization and low column density outflows, but with a high velocity comparable to UFOs, challenge such initial possible correlations. Observations of UFOs in AGN indicate that their energetics may be enough to have an impact on the interstellar medium (ISM). However, observational evidence of the interaction between the inner high-ionization outflow and the ISM is still missing. We present here the spectral analysis of 12 XMM-Newton/EPIC archival observations of the quasar PG 1114+445, aimed at studying the complex outflowing nature of its absorbers. Our analysis revealed the presence of three absorbing structures. We find a WA with velocity v∼530 km s^−1, ionization logξ/erg cm s^−1∼0.35, and column density logNH/cm^−2∼22, and a UFO with vout∼0.145c, logξ/erg cm s^−1∼4, and logNH/cm^−2∼23. We also find an additional absorber in the soft X-rays (E&lt;2 keV) with velocity comparable to that of the UFO (vout∼0.120c), but ionization (logξ/erg cm s^−1∼0.5) and column density (logNH/cm^−2∼21.5) comparable with those of the WA. The ionization, velocity, and variability of the three absorbers indicate an origin in a multiphase and multiscale outflow, consistent with entrainment of the clumpy ISM by an inner UFO moving at ∼15% the speed of light, producing an entrained ultra-fast outflow (E-UFO).

2019 - Non-thermal pressure support in X-COP galaxy clusters [Articolo su rivista]
Eckert, D.; Ghirardini, V.; Ettori, Stefano; Rasia, Elena; Biffi, V.; Pointecouteau, E.; Rossetti, Mariachiara; Molendi, Silvano; Vazza, Franco; Gastaldello, Fabio; Gaspari, Massimo; DE GRANDI, Sabrina; Ghizzardi, Simona; Bourdin, H.; Tchernin, C.; Roncarelli, M.
abstract

Galaxy clusters are the endpoints of structure formation and are continuously growing through the merging and accretion of smaller structures. Numerical simulations predict that a fraction of their energy content is not yet thermalized, mainly in the form of kinetic motions (turbulence, bulk motions). Measuring the level of non-thermal pressure support is necessary to understand the processes leading to the virialization of the gas within the potential well of the main halo and to calibrate the biases in hydrostatic mass estimates. We present high-quality measurements of hydrostatic masses and intracluster gas fraction out to the virial radius for a sample of 13 nearby clusters with available XMM-Newton and Planck data. We compare our hydrostatic gas fractions with the expected universal gas fraction to constrain the level of non-thermal pressure support. We find that hydrostatic masses require little correction and infer a median non-thermal pressure fraction of ∼6% and ∼10% at R500and R200, respectively. Our values are lower than the expectations of hydrodynamical simulations, possibly implying a faster thermalization of the gas. If instead we use the mass calibration adopted by the Planck team, we find that the gas fraction of massive local systems implies a mass bias 1 - b = 0.85 ± 0.05 for Sunyaev-Zeldovich-derived masses, with some evidence for a mass-dependent bias. Conversely, the high bias required to match Planck cosmic microwave background and cluster count cosmology is excluded by the data at high significance, unless the most massive halos are missing a substantial fraction of their baryons.

2019 - NuSTAR Measurement of Coronal Temperature in Two Luminous, High-redshift Quasars [Articolo su rivista]
Lanzuisi, Giorgio; Gilli, Roberto; Cappi, Massimo; Dadina, Mauro; Bianchi, Simone; Brusa, M.; Chartas, G.; Civano, F.; Comastri, Andrea; Marinucci, A.; Middei, R.; Piconcelli, Enrico; Vignali, C.; Brandt, W. N.; Tombesi, Francesco; Gaspari, Massimo
abstract

X-ray emission from AGN is believed to be produced via Comptonization of optical/UV seed photons emitted by the accretion disk, up-scattered by hot electrons in a corona surrounding the black hole. A critical compactness vs. temperature threshold is predicted above which any increase in the source luminosity, for a fixed size, would then generate positron-electron pairs rather than continue heating the coronal plasma. Current observations seem to confirm that all AGN populate the region below this critical line. These models, however, have never been probed by observations in the high-luminosity regime, where the critical line is expected to reach low temperatures. To fill this observational gap, we selected two luminous (log(Lbol)&gt;47.5 erg/s) quasars, 2MASSJ1614346+470420 (z=1.86) and B1422+231 (z=3.62), and obtained XMM-Newton and NuSTAR deep observations for them. We performed detailed spectral analysis of their quasi-simultaneous soft and hard X-ray data, in order to constrain the parameters of their coronae. Using a phenomenological cut-off power-law model, with the inclusion of a reflection component, we derived rest-frame values of the high energy cut-off of Ecut=106+102−37 keV and Ecut=66+17−12 keV, respectively. Comptonization models consistently give as best-fit parameters electron temperatures of ∼45 keV and ∼28 keV, respectively, and optically thick coronae (τ&gt;1). These low coronal temperatures fall in the limited region allowed at these luminosities to avoid runaway pair production.

2019 - On the Assembly Bias of Cool Core Clusters Traced by Hα Nebulae [Articolo su rivista]
Medezinski, Elinor; Mcdonald, Michael; More, Surhud; Miyatake, Hironao; Battaglia, Nicholas; Gaspari, Massimo; Spergel, David; Cen, Renyue
abstract

Do cool-core (CC) and non-cool-core (NCC) clusters live in different environments? We make novel use of Hα emission lines in the central galaxies of redMaPPer clusters as proxies to construct large (1000's) samples of CC and NCC clusters and measure their relative assembly bias using both clustering and weak lensing. We increase the statistical significance of the bias measurements from clustering by cross-correlating the clusters with an external galaxy redshift catalog from the Sloan Digital Sky Survey III, the LOWZ sample. Our cross-correlations can constrain assembly bias up to a statistical uncertainty of 6%. Given our Hα criteria for CC and NCC, we find no significant differences in their clustering amplitude. Interpreting this difference as the absence of halo assembly bias, our results rule out the possibility of having different large-scale (tens of Mpc) environments as the source of diversity observed in cluster cores. Combined with recent observations of the overall mild evolution of CC and NCC properties, such as central density and CC fraction, this would suggest that either the cooling properties of the cluster core are determined early on solely by the local (&lt;200 kpc) gas properties at formation or that local merging leads to stochastic CC relaxation and disruption in a periodic way, preserving the average population properties over time. Studying the small-scale clustering in clusters at high redshift would help shed light on the exact scenario.

2019 - Probing Macro-Scale Gas Motions and Turbulence in Diffuse Cosmic Plasmas [Articolo su rivista]
Bulbul, ; Esra, ; Gaspari, M; Alvarez, ; Gabriella, ; Avestruz, ; Camille, ; Bautz, ; Mark, ; Benson, ; Brad, ; Biffi, ; Veronica, ; Burke, ; Douglas, ; Clerc, ; Nicolas, ; Cucchetti, ; Edoardo, ; Chadayammuri, ; Urmila, ; Eckert, ; Dominique, ; Ettori, ; Stefano, ; Forman, ; Bill, ; Gastaldello, ; Fabio, ; Ghirardini, ; Vittorio, ; Kraft, ; Ralph, ; Markevitch, ; Maxim, ; Mcdonald, ; Mike, ; Miller, ; Eric, Mroczkowski; Tony, ; Nagai, ; Daisuke, ; Nulsen, ; Paul, ; Pratt, ; Gabriel, W.; Randall, ; Scott, ; Reiprich, ; Thomas, ; Roncarelli, ; Mauro, ; Simionescu, ; Aurora, ; Smith, ; Randall, ; Tremblay, ; Grant, ; Walker, ; Stephen, ; Zuhone, ; John, ; Zhuravleva, ; Irina,
abstract

Cluster outskirts provide crucial information on the assembly and virialisation processes of massive dark matter haloes and cosmology. This paper provide future prospects for measurements thermodynamic and kinematic properties of the intracluster medium in faint regions of galaxy clusters with forthcoming planned X-ray and SZ observatories.

2019 - Spectral imaging of the thermal Sunyaev-Zel'dovich effect in X-COP galaxy clusters: method and validation [Articolo su rivista]
Baldi, A. S.; Bourdin, H.; Mazzotta, P.; Eckert, D.; Ettori, Stefano; Gaspari, Massimo; Roncarelli, M.
abstract

The imaging of galaxy clusters through the Sunyaev-Zel'dovich effect is a valuable tool to probe the thermal pressure of the intra-cluster gas, especially in the outermost regions where X-ray observations suffer from photon statistics. For the first time, we produce maps of the Comptonization parameter by applying a locally parametric algorithm for sparse component separation to the latest frequency maps released by Planck. The algorithm takes into account properties of real cluster data through the two-component modelling of the spectral energy density of thermal dust, and the masking of bright point sources. Its robustness has been improved in the low signal-to-noise regime, thanks to the implementation of a deconvolution of Planck beams in the chi-square minimisation of each wavelet coefficient. We applied this procedure to twelve low-redshift galaxy clusters detected by Planck with the highest signal-to-noise ratio, considered in the XMM Cluster Oustkirts Project (X-COP). Our images show the presence of anisotropic features, such as small-scale blobs and filamentary substructures that are located in the outskirts of a number of clusters in the sample. The significance of their detection is established via a bootstrap-based procedure we propose here for the first time. In particular, we present a qualitative comparison with X-ray data for two interesting systems, namely A2029 and RXCJ1825. Our results are in agreement with the features detected in the outskirts of the clusters in the two bands.

2019 - Supermassive Black Hole Feedback [Articolo su rivista]
Ruszkowski, ; Mateusz, ; Nagai, ; Daisuke, ; Zhuravleva, ; Irina, ; Brummel-Smith, ; Corey, ; Li, ; Yuan, ; Hodges-Kluck, ; Edmund, ; Yang, ; Hsiang-Yi, Karen; Basu, ; Kaustuv, ; Chluba, ; Jens, ; Churazov, ; Eugene, ; Donahue, ; Megan, ; Fabian, ; Andrew, ; Faucher-Giguère, ; Claude-André, ; Gaspari, M; Hlavacek-Larrondo, ; Julie, ; Mcdonald, ; Michael, ; Mcnamara, ; Brian, ; Nulsen, ; Paul, ; Mroczkowski, ; Tony, ; Mushotzky, ; Richard, Reynolds; Christopher, ; Vikhlinin, ; Alexey, ; Voit, ; Mark, ; Werner, ; Norbert, ; Zuhone, ; John, ; Zweibel, ; Ellen,
abstract

Galaxy evolution is critically shaped by the energy injection from supermassive black holes (SMBHs). A major challenge is unraveling how the energy released near the SMBHs is distributed throughout galaxies and their environments. This white paper discusses the prospect of tackling this problem using high-resolution X-ray/microwave observations.

2019 - The Close AGN Reference Survey (CARS). A massive multi-phase outflow impacting the edge-on galaxy HE 1353-1917 [Articolo su rivista]
Husemann, B.; Scharwächter, J.; Davis, T. A.; Pérez-Torres, M.; Smirnova-Pinchukova, I.; Tremblay, G. R.; Krumpe, M.; Combes, F.; Baum, S. A.; Busch, G.; Connor, T.; Croom, S. M.; Gaspari, Massimo; Kraft, R. P.; O'Dea, C. P.; Powell, M.; Singha, M.; Urrutia, T.
abstract

We combine extensive spatially-resolved multi-wavelength observations, taken as part of the Close AGN Reference Survey (CARS), for the edge-on disc galaxy HE1353-1917 to characterize the impact of the AGN on its host galaxy via outflows and radiation. Multi-color broad-band photometry is combined with spatially-resolved optical, NIR and sub-mm and radio observations taken with VLT/MUSE, Gemini-N/NIFS, ALMA and the VLA to map the physical properties and kinematics of the multi-phase inter-stellar medium (ISM). We detect a biconical extended narrow-line region (ENLR) ionized by the luminous AGN oriented nearly parallel to the galaxy disc, extending out to at least 25 kpc. The extra-planar gas originates from galactic fountains initiated by star formation processes in the disc, rather than an AGN outflow, as shown by the kinematics and the metallicity of the gas. Nevertheless, a fast multi-phase AGN-driven outflow with speeds up to 1000 km/s is detected close to the nucleus at 1kpc distance. A radio jet, in connection with the AGN radiation field, is likely responsible for driving the outflow as confirmed by the energetics and the spatial alignment of the jet and multi-phase outflow. Evidence for negative AGN feedback suppressing the star formation rate (SFR) is mild and restricted to the central kpc. But while any SFR suppression must have happened recently, the outflow has the potential to greatly impact the future evolution of the galaxy disc due to its geometrical orientation. Our observations reveal that low-power radio jets can play a major role in driving fast multi-phase galaxy-scale outflows even in radio-quiet AGN. Since the outflow energetics for HE1353-1917 are consistent with literature scaling relations of AGN-driven outflows the contribution of radio jets as the driving mechanisms still needs to be systematically explored.

2019 - The Close AGN Reference Survey (CARS): Comparative analysis of the structural properties of star-forming and non-star-forming galaxy bars [Articolo su rivista]
Justus, Neumann; Dimitri A., Gadotti; Lutz, Wisotzki; Bernd, Husemann; Gerold, Busch; Françoise, Combes; Scott M., Croom; Timothy A., Davis; Gaspari, Massimo; Mirko, Krumpe; Miguel A., Pérez-Torres; Julia, Scharwächter; Irina, Smirnova-Pinchukova; Grant R., Tremblay; Tanya, Urrutia
abstract

The absence of star formation in the bar region that has been reported for some galaxies can theoretically be explained by shear. However, it is not clear how star-forming (SF) bars fit into this picture and how the dynamical state of the bar is related to other properties of the host galaxy. We used integral-field spectroscopy from VLT/MUSE to investigate how star formation within bars is connected to structural properties of the bar and the host galaxy. We derived spatially resolved Hα fluxes from MUSE observations from the CARS survey to estimate star formation rates in the bars of 16 nearby (0.01&lt;0.06) disc galaxies with stellar masses between 10^10 M⊙ and 10^11 M⊙. We further performed a detailed multicomponent photometric decomposition on images derived from the data cubes. We find that bars clearly divide into SF and non-star-forming (non-SF) types, of which eight are SF and eight are non-SF. Whatever the responsible quenching mechanism is, it is a quick process compared to the lifetime of the bar. The star formation of the bar appears to be linked to the flatness of the surface brightness profile in the sense that only the flattest bars (nbar≤0.4) are actively SF (SFRb&gt;0.5 M⊙/yr). Both parameters are uncorrelated with Hubble type. We find that star formation is 1.75 times stronger on the leading than on the trailing edge and is radially decreasing. The conditions to host non-SF bars might be connected to the presence of inner rings. Additionally, from testing an AGN feeding scenario, we report that the star formation rate of the bar is uncorrelated with AGN bolometric luminosity. The results of this study may only apply to type-1 AGN hosts and need to be confirmed for the full population of barred galaxies.

2019 - The Close AGN Reference Survey (CARS): Discovery of a global [C II] 158 μm line excess in AGN HE 1353-1917 [Articolo su rivista]
Smirnova-Pinchukova, I.; Husemann, B.; Busch, G.; Appleton, P.; Bethermin, M.; Combes, F.; Croom, S.; Davis, T. A.; Fischer, C.; Gaspari, Massimo; Groves, B.; Klein, R.; O'Dea, C. P.; Pérez-Torres, M.; Scharwächter, J.; Singha, M.; Tremblay, G. R.; Urrutia, T.
abstract

The [C II]λ158 μm line is one of the strongest far-infrared (FIR) lines and an important coolant in the interstellar medium of galaxies that is accessible out to high redshifts. The excitation of [C II] is complex and can best be studied in detail at low redshifts. Here we report the discovery of the highest global [C II] excess with respect to the FIR luminosity in the nearby AGN host galaxy HE 1353-1917. This galaxy is exceptional among a sample of five targets because the AGN ionization cone and radio jet directly intercept the cold galactic disk. As a consequence, a massive multiphase gas outflow on kiloparsec scales is embedded in an extended narrow-line region. Because HE 1353-1917 is distinguished by these special properties from our four bright AGN, we propose that a global [C II] excess in AGN host galaxies could be a direct signature of a multiphase AGN-driven outflow with a high mass-loading factor.

2019 - The Impact of Radio AGN Bubble Composition on the Dynamics and Thermal Balance of the Intracluster Medium [Articolo su rivista]
Yang, H. -Y. Karen; Gaspari, Massimo; Marlow, Carl
abstract

Feeding and feedback of active galactic nuclei (AGNs) are critical for understanding the dynamics and thermodynamics of the intracluster medium (ICM) within the cores of galaxy clusters. Although radio bubbles inflated by AGN jets could be dynamically supported by cosmic rays (CRs), the impact of CR-dominated jets is not well understood. In this work, we perform three-dimensional simulations of CR-jet feedback in an isolated cluster atmosphere; we find that CR jets impact the multiphase gas differently than jets dominated by kinetic energy. In particular, CR bubbles can more efficiently uplift the cluster gas and cause an outward expansion of the hot ICM. Due to adiabatic cooling from the expansion and less efficient heating from CR bubbles by direct mixing, the ICM is more prone to local thermal instabilities, which will later enhance chaotic cold accretion onto the AGN. The amount of cold gas formed during the bubble formation and its late-time evolution sensitively depend on whether or not CR transport processes are included. We also find that low-level, subsonic driving of turbulence by AGN jets holds for both kinetic and CR jets; nevertheless, the kinematics is consistent with the Hitomi measurements. Finally, we carefully discuss the key observable signatures of each bubble model, focusing on gamma-ray emission (and related comparison with Fermi), as well as thermal Sunyaev-Zel’dovich constraints.

2019 - The physics and astrophysics of X-ray outflows from Active Galactic Nuclei [Articolo su rivista]
Laha, ; Sibasish, ; Smith, ; Randall, ; Tzanavaris, ; Panayiotis, ; Kallman, ; Tim, ; Veilleux, ; Sylvain, ; Tombesi, ; Francesco, ; Kriss, ; Gerard, ; Guainazzi, ; Matteo, ; Gaspari, M; Kaastra, ; Jelle, ; Markowitz, ; Alex, ; Crenshaw, ; Mike, ; Behar, ; Ehud, ; Fukumura, ; Keigo, ; Longinotti, ; Anna, Lia; Rozanska, ; Agata, ; Ebrero, ; Jacobo, ; Ferland, ; Gary, ; Ricci, ; Claudio, ; Done, ; Chris, Proga; Daniel, ; Revalski, ; Mitchell, ; Vayner, ; Andrey,
abstract

AGN outflows are integral for understanding how the central super massive black hole interacts with the host galaxy and co-evolves in cosmic time. This white paper sets the primary science goals for the next decade and suggests the key parameters on which the next generation X-ray telescopes should be built to revolutionize our understanding.

2019 - The X-Ray Halo Scaling Relations of Supermassive Black Holes [Articolo su rivista]
Gaspari, Massimo; Eckert, D.; Ettori, Stefano; Tozzi, Paolo; Bassini, L.; Rasia, Elena; Brighenti, F.; Sun, M.; Borgani, Stefano; Johnson, S. D.; Tremblay, G. R.; Stone, J. M.; Temi, P.; Yang, H. -Y. K.; Tombesi, Francesco; Cappi, Massimo
abstract

We carry out a comprehensive Bayesian correlation analysis between hot halos and direct masses of supermassive black holes (SMBHs), by retrieving the X-ray plasma properties (temperature, luminosity, density, pressure, and masses) over galactic to cluster scales for 85 diverse systems. We find new key scalings, with the tightest relation being M_bh - T_x, followed by M_bh - L_x. The tighter scatter (down to 0.2 dex) and stronger correlation coefficient of all the X-ray halo scalings compared with the optical counterparts (as the M_bh - σ_e) suggest that plasma halos play a more central role than stars in tracing and growing SMBHs (especially those that are ultramassive). Moreover, M_bh correlates better with the gas mass than dark matter mass. We show the important role of the environment, morphology, and relic galaxies/coronae, as well as the main departures from virialization/self-similarity via the optical/X-ray fundamental planes. We test the three major channels for SMBH growth: hot/Bondi-like models have inconsistent anticorrelation with X-ray halos and too low feeding; cosmological simulations find SMBH mergers as subdominant over most of cosmic time and too rare to induce a central-limit-theorem effect; the scalings are consistent with chaotic cold accretion, the rain of matter condensing out of the turbulent X-ray halos that sustains a long-term self-regulated feedback loop. The new correlations are major observational constraints for models of SMBH feeding/feedback in galaxies, groups, and clusters (e.g., to test cosmological hydrodynamical simulations), and enable the study of SMBHs not only through X-rays, but also via the Sunyaev-Zel’dovich effect (Compton parameter), lensing (total masses), and cosmology (gas fractions).

2019 - Universal thermodynamic properties of the intracluster medium over two decades in radius in the X-COP sample [Articolo su rivista]
Ghirardini, V.; Eckert, D.; Ettori, Stefano; Pointecouteau, E.; Molendi, Silvano; Gaspari, Massimo; Rossetti, Mariachiara; DE GRANDI, Sabrina; Roncarelli, M.; Bourdin, H.; Mazzotta, P.; Rasia, Elena; Vazza, Franco
abstract

Context. The hot plasma in a galaxy cluster is expected to be heated to high temperatures through shocks and adiabatic compression. The thermodynamical properties of the gas encode information on the processes leading to the thermalization of the gas in the cluster's potential well and on non-gravitational processes such as gas cooling, AGN feedback, shocks, turbulence, bulk motions, cosmic rays and magnetic field. Aims: In this work we present the radial profiles of the thermodynamic properties of the intracluster medium (ICM) out to the virial radius for a sample of 12 galaxy clusters selected from the Planck all-sky survey. We determine the universal profiles of gas density, temperature, pressure, and entropy over more than two decades in radius, from 0.01R500to 2R500. Methods: We exploited X-ray information from XMM-Newton and Sunyaev-Zel'dovich constraints from Planck to recover thermodynamic properties out to 2R500. We provide average functional forms for the radial dependence of the main quantities and quantify the slope and intrinsic scatter of the population as a function of radius. Results: We find that gas density and pressure profiles steepen steadily with radius, in excellent agreement with previous observational results. Entropy profiles beyond R500closely follow the predictions for the gravitational collapse of structures. The scatter in all thermodynamical quantities reaches a minimum in the range [0.2 - 0.8]R500and increases outward. Somewhat surprisingly, we find that pressure is substantially more scattered than temperature and density. Conclusions: Our results indicate that once accreting substructures are properly excised, the properties of the ICM beyond the cooling region (R &gt;0.3R500) follow remarkably well the predictions of simple gravitational collapse and require few non-gravitational corrections.

2019 - Unveiling the Galaxy Cluster - Cosmic Web Connection with X-ray observations in the Next Decade [Articolo su rivista]
Walker, Stephen; Nagai, Daisuke; Simionescu, A.; Markevitch, M.; Akamatsu, H.; Arnaud, M.; Avestruz, C.; Bautz, M.; Biffi, V.; Borgani, Stefano; Bulbul, E.; Churazov, E.; Dolag, K.; Eckert, D.; Ettori, Stefano; Fujita, Y.; Gaspari, Massimo; Ghirardini, V.; Kraft, R.; Lau, E. T.; Mantz, A.; Matsushita, K.; Mcdonald, M.; Miller, E.; Mroczkowski, T.; Nulsen, P.; Okabe, N.; Ota, N.; Pointecouteau, E.; Pratt, G.; Sato, K.; Shi, X.; Tremblay, G.; Tremmel, M.; Vazza, Franco; Zhuravleva, I.; Zinger, E.; Zuhone, J.
abstract

In recent years, the outskirts of galaxy clusters have emerged as one of the new frontiers and unique laboratories for studying the growth of large scale structure in the universe. A next-generation X-ray telescope is required in order to reveal the full story of the growth of galaxy clusters and the cosmic web and their applications for cosmology.

2018 - A Galaxy-scale Fountain of Cold Molecular Gas Pumped by a Black Hole [Articolo su rivista]
Tremblay, G. R.; Combes, F.; Oonk, J. B. R.; Russell, H. R.; Mcdonald, M. A.; Gaspari, Massimo; Husemann, B.; Nulsen, P. E. J.; Mcnamara, B. R.; Hamer, S. L.; O'Dea, C. P.; Baum, S. A.; Davis, T. A.; Donahue, M.; Voit, G. M.; Edge, A. C.; Blanton, E. L.; Bremer, M. N.; Bulbul, E.; Clarke, T. E.; David, L. P.; Edwards, L. O. V.; Eggerman, D.; Fabian, A. C.; Forman, W.; Jones, C.; Kerman, N.; Kraft, R. P.; Li, Y.; Powell, M.; Randall, S. W.; Salomé, P.; Simionescu, A.; Su, Y.; Sun, M.; Urry, C. M.; Vantyghem, A. N.; Wilkes, B. J.; Zuhone, J. A.
abstract

We present Atacama Large Millimeter/submillimeter Array and Multi-Unit Spectroscopic Explorer observations of the brightest cluster galaxy in Abell 2597, a nearby (z = 0.0821) cool core cluster of galaxies. The data map the kinematics of a three billion solar mass filamentary nebula that spans the innermost 30 kpc of the galaxy’s core. Its warm ionized and cold molecular components are both cospatial and comoving, consistent with the hypothesis that the optical nebula traces the warm envelopes of many cold molecular clouds that drift in the velocity field of the hot X-ray atmosphere. The clouds are not in dynamical equilibrium, and instead show evidence for inflow toward the central supermassive black hole, outflow along the jets it launches, and uplift by the buoyant hot bubbles those jets inflate. The entire scenario is therefore consistent with a galaxy-spanning “fountain,” wherein cold gas clouds drain into the black hole accretion reservoir, powering jets and bubbles that uplift a cooling plume of low-entropy multiphase gas, which may stimulate additional cooling and accretion as part of a self-regulating feedback loop. All velocities are below the escape speed from the galaxy, and so these clouds should rain back toward the galaxy center from which they came, keeping the fountain long lived. The data are consistent with major predictions of chaotic cold accretion, precipitation, and stimulated feedback models, and may trace processes fundamental to galaxy evolution at effectively all mass scales.

2018 - ALMA Observations of Molecular Clouds in Three Group-centered Elliptical Galaxies: NGC 5846, NGC 4636, and NGC 5044 [Articolo su rivista]
Temi, Pasquale; Amblard, Alexandre; Gitti, Myriam; Brighenti, Fabrizio; Gaspari, Massimo; Mathews, William G.; David, Laurence
abstract

We present new ALMA CO(2-1) observations of two well-studied group-centered elliptical galaxies: NGC 4636 and NGC 5846. In addition, we include a revised analysis of Cycle 0 ALMA observations of the central galaxy in the NGC 5044 group. We find evidence that molecular gas is a common presence in bright group-centered galaxies (BGG). CO line widths are broader than Galactic molecular clouds, and using the reference Milky Way X_CO, the total molecular mass ranges from 2.6×10^5 M_☉ in NGC 4636 to 6.1×10^7 M_☉ in NGC 5044. Complementary observations using the ALMA Compact Array do not exhibit any detection of a CO diffuse component at the sensitivity level achieved by current exposures. The origin of the detected molecular features is still uncertain, but these ALMA observations suggest that they are the end product of the hot gas cooling process and not the result of merger events. Some of the molecular clouds are associated with dust features as revealed by HST dust extinction maps, suggesting that these clouds formed from dust-enhanced cooling. The global nonlinear condensation may be triggered via the chaotic turbulent field or buoyant uplift. The large virial parameter of the molecular structures and correlation with the warm (10^3 - 10^5 K)/hot (≥10^6) phase velocity dispersion provide evidence that they are unbound giant molecular associations drifting in the turbulent field, consistent with numerical predictions of the chaotic cold accretion process. Alternatively, the observed large CO line widths may be generated by molecular gas flowing out from cloud surfaces due to heating by the local hot gas atmosphere.

2018 - Athena X-IFU synthetic observations of galaxy clusters to probe the chemical enrichment of the Universe [Articolo su rivista]
Cucchetti, E.; Pointecouteau, E.; Peille, P.; Clerc, N.; Rasia, Elena; Biffi, V.; Borgani, Stefano; Tornatore, Luca; Dolag, K.; Roncarelli, M.; Gaspari, Massimo; Ettori, Stefano; Bulbul, E.; Dauser, T.; Wilms, J.; Pajot, F.; Barret, D.
abstract

Answers to the metal production of the Universe can be found in galaxy clusters, notably within their intra-cluster medium (ICM). The X-ray Integral Field Unit (X-IFU) on board the next-generation European X-ray observatory Athena (2030s) will provide the necessary leap forward in spatially-resolved spectroscopy required to disentangle the intricate mechanisms responsible for this chemical enrichment. In this paper, we investigate the future capabilities of the X-IFU in probing the hot gas within galaxy clusters. From a test sample of four clusters extracted from cosmological hydrodynamical simulations, we present comprehensive synthetic observations of these clusters at different redshifts (up to z ≤ 2) and within the scaled radius R500 performed using the instrument simulator SIXTE. Through 100 ks exposures, we demonstrate that the X-IFU will provide spatially resolved mapping of the ICM physical properties with little to no biases (⪉5%) and well within statistical uncertainties. The detailed study of abundance profiles and abundance ratios within R500 also highlights the power of the X-IFU in providing constraints on the various enrichment models. From synthetic observations out to z = 2, we have also quantified its ability to track the chemical elements across cosmic time with excellent accuracy, and thereby to investigate the evolution of metal production mechanisms as well as the link to the stellar initial mass-function. Our study demonstrates the unprecedented capabilities of the X-IFU of unveiling the properties of the ICM but also stresses the data analysis challenges faced by future high-resolution X-ray missions such as Athena.

2018 - Cosmological hydrodynamical simulations of galaxy clusters: X-ray scaling relations and their evolution [Articolo su rivista]
Truong, N.; Rasia, Elena; Mazzotta, P.; Planelles, S.; Biffi, V.; Fabjan, D.; Beck, A. M.; Borgani, Stefano; Dolag, K.; Gaspari, Massimo; Granato, Gian Luigi; Murante, Giuseppe; Ragone-Figueroa, C.; Steinborn, L. K.
abstract

We analyse cosmological hydrodynamical simulations of galaxy clusters to study the X-ray scaling relations between total masses and observable quantities such as X-ray luminosity, gas mass, X-ray temperature, and YX. Three sets of simulations are performed with an improved version of the smoothed particle hydrodynamics GADGET-3 code. These consider the following: non-radiative gas, star formation and stellar feedback, and the addition of feedback by active galactic nuclei (AGN). We select clusters with M500 &gt;10^14 M☉E(z)-1, mimicking the typical selection of Sunyaev-Zeldovich samples. This permits to have a mass range large enough to enable robust fitting of the relations even at z ∼ 2. The results of the analysis show a general agreement with observations. The values of the slope of the mass-gas mass and mass-temperature relations at z = 2 are 10 per cent lower with respect to z = 0 due to the applied mass selection, in the former case, and to the effect of early merger in the latter. We investigate the impact of the slope variation on the study of the evolution of the normalization. We conclude that cosmological studies through scaling relations should be limited to the redshift range z = 0-1, where we find that the slope, the scatter, and the covariance matrix of the relations are stable. The scaling between mass and YX is confirmed to be the most robust relation, being almost independent of the gas physics. At higher redshifts, the scaling relations are sensitive to the inclusion of AGNs which influences low-mass systems. The detailed study of these objects will be crucial to evaluate the AGN effect on the ICM.

2018 - Digging for red nuggets: discovery of hot halos surrounding massive, compact, relic galaxies [Articolo su rivista]
Werner, N.; Lakhchaura, K.; Canning, R. E. A.; Gaspari, Massimo; Simionescu, A.
abstract

We present the results of Chandra X-ray observations of the isolated, massive, compact, relic galaxies MRK 1216 and PGC 032873. Compact massive galaxies observed at z &gt;2, also called red nuggets, formed in quick dissipative events and later grew by dry mergers into the local giant ellipticals. Due to the stochastic nature of mergers, a few of the primordial massive galaxies avoided the mergers and remained untouched over cosmic time. We find that the hot atmosphere surrounding MRK 1216 extends far beyond the stellar population and has a 0.5-7 keV X-ray luminosity of LX = (7.0 ± 0.2) × 10^41 erg s-1, which is similar to the nearby X-ray bright giant ellipticals. The hot gas has a short central cooling time of ∼50 Myr and the galaxy has an ∼13-Gyr-old stellar population. The presence of an X-ray atmosphere with a short nominal cooling time and the lack of young stars indicate the presence of a sustained heating source, which prevented star formation since the dissipative origin of the galaxy 13 Gyr ago. The central temperature peak and the presence of radio emission in the core of the galaxy indicate that the heating source is radio-mechanical active galactic nucleus (AGN) feedback. Given that both MRK 1216 and PGC 032873 appear to have evolved in isolation, the order of magnitude difference in their current X-ray luminosity could be traced back to a difference in the ferocity of the AGN outbursts in these systems. Finally, we discuss the potential connection between the presence of hot haloes around such massive galaxies and the growth of super-/overmassive black holes via chaotic cold accretion.

2018 - Erratum: “X-Ray Properties of AGN in Brightest Cluster Galaxies. I. A Systematic Study of the Chandra Archive in the 0.2 < z < 0.3 and 0.55 < z < 0.75 Redshift Range” (2018, ApJ, 859, 65) [Articolo su rivista]
Yang, Lilan; Tozzi, Paolo; Yu, Heng; Lusso, Elisabeta; Gaspari, Massimo; Gilli, Roberto; Nardini, Emanuele; Risaliti, Guido
abstract

2018 - Formation of a Malin 1 analogue in IllustrisTNG by stimulated accretion [Articolo su rivista]
Zhu, Qirong; Xu, Dandan; Gaspari, Massimo; Rodriguez-Gomez, Vicente; Nelson, Dylan; Vogelsberger, Mark; Torrey, Paul; Pillepich, Annalisa; Zjupa, Jolanta; Weinberger, Rainer; Marinacci, Federico; Pakmor, Rüdiger; Genel, Shy; Li, Yuexing; Springel, Volker; Hernquist, Lars
abstract

The galaxy Malin 1 contains the largest stellar disc known but the formation mechanism of this structure has been elusive. In this paper, we report a Malin 1 analogue in the 100 Mpc IllustrisTNG simulation and describe its formation history. At redshift zero, this massive galaxy, having a maximum circular velocity V_max of 430 km/s, contains a 100 kpc gas/stellar disc with morphology similar to Malin 1. The simulated galaxy reproduces well many observed features of Malin 1's vast disc, including its stellar ages, metallicities, and gas rotation curve. We trace the extended disc back in time and find that a large fraction of the cold gas at redshift zero originated from the cooling of hot halo gas, triggered by the merger of a pair of intruding galaxies. Our finding provides a novel way to form large galaxy discs as extreme as Malin 1 within the current galaxy formation framework.

2018 - GAMER-2: a GPU-accelerated adaptive mesh refinement code - accuracy, performance, and scalability [Articolo su rivista]
Schive, Hsi-Yu; Zuhone, John A.; Goldbaum, Nathan J.; Turk, Matthew J.; Gaspari, Massimo; Cheng, Chin-Yu
abstract

We present GAMER-2, a GPU-accelerated adaptive mesh refinement (AMR) code for astrophysics. It provides a rich set of features, including adaptive time-stepping, several hydrodynamic schemes, magnetohydrodynamics, self-gravity, particles, star formation, chemistry, and radiative processes with GRACKLE, data analysis with YT, and memory pool for efficient object allocation. GAMER-2 is fully bitwise reproducible. For the performance optimization, it adopts hybrid OpenMP/MPI/GPU parallelization and utilizes overlapping CPU computation, GPU computation, and CPU-GPU communication. Load balancing is achieved using a Hilbert space-filling curve on a level-by-level basis without the need to duplicate the entire AMR hierarchy on each MPI process. To provide convincing demonstrations of the accuracy and performance of GAMER-2, we directly compare with ENZO on isolated disc galaxy simulations and with FLASH on galaxy cluster merger simulations. We show that the physical results obtained by different codes are in very good agreement, and GAMER-2 outperforms ENZO and FLASH by nearly one and two orders of magnitude, respectively, on the Blue Waters supercomputers using 1-256 nodes. More importantly, GAMER-2 exhibits similar or even better parallel scalability compared to the other two codes. We also demonstrate good weak and strong scaling using up to 4096 GPUs and 65 536 CPU cores, and achieve a uniform resolution as high as 10240^3 cells. Furthermore, GAMER-2 can be adopted as an AMR + GPUs framework and has been extensively used for the wave dark matter simulations. GAMER-2 is open source (available at https://github.com/gamer-project/gamer) and new contributions are welcome.

2018 - Measuring turbulence and gas motions in galaxy clusters via synthetic Athena X-IFU observations [Articolo su rivista]
Roncarelli, M.; Gaspari, M.; Ettori, S.; Biffi, V.; Brighenti, F.; Bulbul, E.; Clerc, N.; Cucchetti, E.; Pointecouteau, E.; Rasia, E.
abstract

Context. The X-ray Integral Field Unit (X-IFU) that will be on board the Athena telescope will provide an unprecedented view of the intracluster medium (ICM) kinematics through the observation of gas velocity, nu, and velocity dispersion, w, via centroid-shift and broadening of emission lines, respectively.Aims. The improvement of data quality and quantity requires an assessment of the systematics associated with this new data analysis, namely biases, statistical and systematic errors, and possible correlations between the different measured quantities.Methods. We have developed an end-to-end X-IFU simulator that mimics a full X-ray spectral fitting analysis on a set of mock event lists, obtained using SIXTE. We have applied it to three hydrodynamical simulations of a Coma-like cluster that include the injection of turbulence. This allowed us to assess the ability of X-IFU to map five physical quantities in the cluster core: emission measure, temperature, metal abundance, velocity, and velocity dispersion. Finally, starting from our measurements maps, we computed the 2D structure function (SF) of emission measure fluctuations, nu and w, and compared them with those derived directly from the simulations.Results. All quantities match with the input projected values without bias; the systematic errors were below 5%, except for velocity dispersion whose error reaches about 15%. Moreover, all measurements prove to be statistically independent, indicating the robustness of the fitting method. Most importantly, we recover the slope of the SFs in the inertial regime with excellent accuracy, but we observe a systematic excess in the normalization of both SF nu and SFw ascribed to the simplistic assumption of uniform and (bi-) Gaussian measurement errors.Conclusions. Our work highlights the excellent capabilities of Athena X-IFU in probing the thermodynamic and kinematic properties of the ICM. This will allow us to access the physics of its turbulent motions with unprecedented precision.

2018 - Revisiting the Cooling Flow Problem in Galaxies, Groups, and Clusters of Galaxies [Articolo su rivista]
Mcdonald, M.; Gaspari, Massimo; Mcnamara, B. R.; Tremblay, G. R.
abstract

We present a study of 107 galaxies, groups, and clusters spanning ∼3 orders of magnitude in mass, ∼5 orders of magnitude in central galaxy star formation rate (SFR), ∼4 orders of magnitude in the classical cooling rate \dot M_cool \equiv M_gas(r< r_cool)/t_cool of the intracluster medium (ICM), and ∼5 orders of magnitude in the central black hole accretion rate. For each system in this sample, we measure the ICM cooling rate, \dot M_cool, using archival Chandra X-ray data and acquire the SFR and systematic uncertainty in the SFR by combining over 330 estimates from dozens of literature sources. With these data, we estimate the efficiency with which the ICM cools and forms stars, finding ∊_cool \equiv SFR/\dot M_cool = 1.4% +/- 0.4% for systems with \dot M_cool >30 M_☉/yr. For these systems, we measure a slope in the SFR - \dot M_cool relation greater than unity, suggesting that the systems with the strongest cool cores are also cooling more efficiently. We propose that this may be related to, on average, higher black hole accretion rates in the strongest cool cores, which could influence the total amount (saturating near the Eddington rate) and dominant mode (mechanical versus radiative) of feedback. For systems with \dot M_cool < 30 M_☉/yr, we find that the SFR and \dot M_cool are uncorrelated and show that this is consistent with star formation being fueled at a low (but dominant) level by recycled ISM gas in these systems. We find an intrinsic log-normal scatter in SFR at a fixed \dot M_cool of 0.52 ± 0.06 dex (1σ rms), suggesting that cooling is tightly self-regulated over very long timescales but can vary dramatically on short timescales. There is weak evidence that this scatter may be related to the feedback mechanism, with the scatter being minimized (∼0.4 dex) for systems for which the mechanical feedback power is within a factor of two of the cooling luminosity.

2018 - Shaken Snow Globes: Kinematic Tracers of the Multiphase Condensation Cascade in Massive Galaxies, Groups, and Clusters [Articolo su rivista]
Gaspari, Massimo; Mcdonald, M.; Hamer, S. L.; Brighenti, F.; Temi, P.; Gendron-Marsolais, M.; Hlavacek-Larrondo, J.; Edge, A. C.; Werner, N.; Tozzi, Paolo; Sun, M.; Stone, J. M.; Tremblay, G. R.; Hogan, M. T.; Eckert, D.; Ettori, Stefano; Yu, H.; Biffi, V.; Planelles, S.
abstract

We propose a novel method to constrain turbulence and bulk motions in massive galaxies, galaxy groups, and clusters, exploring both simulations and observations. As emerged in the recent picture of top-down multiphase condensation, hot gaseous halos are tightly linked to all other phases in terms of cospatiality and thermodynamics. While hot halos (∼107K) are perturbed by subsonic turbulence, warm (∼104K) ionized and neutral filaments condense out of the turbulent eddies. The peaks condense into cold molecular clouds (&lt;100 K) raining in the core via chaotic cold accretion (CCA). We show that all phases are tightly linked in terms of the ensemble (wide-aperture) velocity dispersion along the line of sight. The correlation arises in complementary long-term AGN feedback simulations and high-resolution CCA runs, and is corroborated by the combined Hitomi and new Integral Field Unit measurements in the Perseus cluster. The ensemble multiphase gas distributions (from the UV to the radio band) are characterized by substantial spectral line broadening (σ v,los≈ 100-200 {km} {{{s}}}-1) with a mild line shift. On the other hand, pencil-beam detections (as H I absorption against the AGN backlight) sample the small-scale clouds displaying smaller broadening and significant line shifts of up to several 100 {km} {{{s}}}-1(for those falling toward the AGN), with increased scatter due to the turbulence intermittency. We present new ensemble σ v,losof the warm Hα+[N II] gas in 72 observed cluster/group cores: the constraints are consistent with the simulations and can be used as robust proxies for the turbulent velocities, in particular for the challenging hot plasma (otherwise requiring extremely long X-ray exposures). Finally, we show that the physically motivated criterion C ≡ t cool/t eddy≈ 1 best traces the condensation extent region and the presence of multiphase gas in observed clusters and groups. The ensemble method can be applied to many available spectroscopic data sets and can substantially advance our understanding of multiphase halos in light of the next-generation multiwavelength missions.

2018 - The Close AGN Reference Survey (CARS): SOFIA Detects Spatially Resolved [C II] Emission in the Luminous AGN HE 0433-1028 [Articolo su rivista]
Busch, G.; Husemann, B.; Smirnova-Pinchukova, I.; Eckart, A.; Baum, S. A.; Combes, F.; Croom, S. M.; Davis, T. A.; Fazeli, N.; Fischer, C.; Gaspari, Massimo; Klein, R.; Krumpe, M.; Mcelroy, R.; O'Dea, C. P.; Perez-Torres, M. A.; Powell, M. C.; Sánchez-Monge, Á.; Scharwächter, J.; Tremblay, G. R.; Urrutia, T.
abstract

We report spatially resolved [C II] λ158 μm observations of HE 0433-1028, which is the first detection of a nearby luminous active galactic nucleus (AGN; redshift 0.0355) with the Field-Imaging Far-Infrared Line Spectrometer (FIFI-LS) on board the airborne Stratospheric Observatory For Infrared Astronomy (SOFIA). We compare the spatially resolved star formation tracers [C II], as provided by our SOFIA observations, and Hα from the Multi Unit Spectroscopic Explorer (MUSE) optical integral-field spectroscopy. We find that the [C II] emission is mainly matching the extended star formation as traced by the extinction-corrected Hα line emission but some additional flux is present. While a larger sample is needed to statistically confirm our findings and investigate possible dependencies on AGN luminosity and star formation rate, our study underlines the necessity of collecting a spatially resolved optical-far-infrared data set for nearby AGNs, and shows that it is technically feasible to collect such data sets with FIFI-LS on board SOFIA.

2018 - The origin of ICM enrichment in the outskirts of present-day galaxy clusters from cosmological hydrodynamical simulations [Articolo su rivista]
Biffi, V.; Planelles, S.; Borgani, Stefano; Rasia, Elena; Murante, Giuseppe; Fabjan, D.; Gaspari, Massimo
abstract

The uniformity of the intracluster medium (ICM) enrichment level in the outskirts of nearby galaxy clusters suggests that chemical elements were deposited and widely spread into the intergalactic medium before the cluster formation. This observational evidence is supported by numerical findings from cosmological hydrodynamical simulations, as presented in Biffi et al., including the effect of thermal feedback from active galactic nuclei. Here, we further investigate this picture, by tracing back in time the spatial origin and metallicity evolution of the gas residing at z = 0 in the outskirts of simulated galaxy clusters. In these regions, we find a large distribution of iron abundances, including a component of highly enriched gas, already present at z = 2. At z &gt;1, the gas in the present-day outskirts was distributed over tens of virial radii from the main cluster and had been already enriched within high-redshift haloes. At z = 2, about 40 {per cent} of the most Fe-rich gas at z = 0 was not residing in any halo more massive than 10^{11} h^{-1} M_{☉} in the region and yet its average iron abundance was already 0.4, w.r.t. the solar value by Anders &amp; Grevesse. This confirms that the in situ enrichment of the ICM in the outskirts of present-day clusters does not play a significant role, and its uniform metal abundance is rather the consequence of the accretion of both low-metallicity and pre-enriched (at z &gt;2) gas, from the diffuse component and through merging substructures. These findings do not depend on the mass of the cluster nor on its core properties.

2018 - Thermodynamic properties, multiphase gas, and AGN feedback in a large sample of giant ellipticals [Articolo su rivista]
Lakhchaura, K.; Werner, N.; Sun, M.; Canning, R. E. A.; Gaspari, Massimo; Allen, S. W.; Connor, T.; Donahue, M.; Sarazin, C.
abstract

We present a study of the thermal structure of the hot X-ray emitting atmospheres for a sample of 49 nearby X-ray and optically bright elliptical galaxies using Chandra X-ray data. We focus on the connection between the properties of the hot X-ray emitting gas and the cooler Hα+[N II] emitting phase, and the possible role of the latter in the Active Galactic Nuclei (AGN) feedback cycle. We do not find evident correlations between the Hα+[N II] emission and global properties such as X-ray luminosity, mass of hot gas, and gas mass fraction. We find that the presence of Hα+[N II] emission is more likely in systems with higher densities, lower entropies, shorter cooling times, shallower entropy profiles, lower values of min(t_cool/t_ff), and disturbed X-ray morphologies (linked to turbulent motions). However, we see no clear separations in the observables obtained for galaxies with and without optical emission line nebulae. The AGN jet powers of the galaxies with X-ray cavities show hint of a possible weak positive correlation with their Hα+[N II] luminosities. This correlation and the observed trends in the thermodynamic properties may result from chaotic cold accretion (CCA) powering AGN jets, as seen in some high-resolution hydrodynamic simulations.

2018 - X-Ray Properties of AGN in Brightest Cluster Galaxies. I. A Systematic Study of the Chandra Archive in the 0.2 < z < 0.3 and 0.55 < z < 0.75 Redshift Range [Articolo su rivista]
Yang, Lilan; Tozzi, Paolo; Yu, Heng; Lusso, Elisabeta; Gaspari, Massimo; Gilli, Roberto; Nardini, Emanuele; Risaliti, Guido
abstract

We present a search for nuclear X-ray emission in the brightest cluster galaxies (BCGs) of a sample of groups and clusters of galaxies extracted from the Chandra archive. The exquisite angular resolution of Chandra allows us to obtain robust photometry at the position of the BCG, and to firmly identify unresolved X-ray emission when present, thanks to an accurate characterization of the extended emission at the BCG position. We consider two redshift bins (0.2 < z < 0.3 and 0.55 < z < 0.75) and analyze all the clusters observed by Chandra with exposure time larger than 20 ks. Our samples have 81 BCGs in 73 clusters and 51 BCGs in 49 clusters in the low- and high-redshift bins, respectively. X-ray emission in the soft (0.5-2 keV) or hard (2-7 keV) band is detected only in 14 and 9 BCGs (∼18% of the total samples), respectively. The X-ray photometry shows that at least half of the BCGs have a high hardness ratio, compatible with significant intrinsic absorption. This is confirmed by the spectral analysis with a power-law model plus intrinsic absorption. We compute the fraction of X-ray bright BCGs above a given hard X-ray luminosity, considering only sources with positive photometry in the hard band (12/5 sources in the low/high-z sample).

2017 - Deep Chandra observations of the stripped galaxy group falling into Abell 2142 [Articolo su rivista]
Eckert, D.; Gaspari, Massimo; Owers, M. S.; Roediger, E.; Molendi, Silvano; Gastaldello, Fabio; Paltani, S.; Ettori, Stefano; Venturi, Tiziana; Rossetti, Mariachiara; Rudnick, L.
abstract

In the local Universe, the growth of massive galaxy clusters mainly operates through the continuous accretion of group-scale systems. The infalling group in Abell 2142 is the poster child of such an accreting group, and as such, it is an ideal target to study the astrophysical processes induced by structure formation. We present the results of a deep (200 ks) observation of this structure with Chandra that highlights the complexity of this system in exquisite detail. In the core of the group, the spatial resolution of Chandra reveals a leading edge and complex AGN-induced activity. The morphology of the stripped gas tail appears straight in the innermost 250 kpc, suggesting that magnetic draping efficiently shields the gas from its surroundings. However, beyond 300 kpc from the core, the tail flares and the morphology becomes strongly irregular, which could be explained by a breaking of the drape, for example, caused by turbulent motions. The power spectrum of surface-brightness fluctuations is relatively flat (P2D ∝ k^-2.3), which indicates that thermal conduction is strongly inhibited even beyond the region where magnetic draping is effective. The amplitude of density fluctuations in the tail is consistent with a mild level of turbulence with a Mach number M_3D = 0.1 - 0.25. Overall, our results show that the processes leading to the thermalization and mixing of the infalling gas are slow and relatively inefficient.

2017 - Kinetic and radiative power from optically thin accretion flows [Articolo su rivista]
Sadowski, A; Gaspari, M
abstract

We perform a set of general relativistic, radiative, magneto-hydrodynamical simulations (GR-RMHD) to study the transition from radiatively inefficient to efficient state of accretion on a non-rotating black hole. We study ion to electron temperature ratios ranging from T-i/T-e = 10 to 100, and simulate flows corresponding to accretion rates as low as 10(-6) (M) over dot(Edd), and as high as 10(-2). (M) over dot(Edd). We have found that the radiative output of accretion flows increases with accretion rate, and that the transition occurs earlier for hotter electrons (lower Ti/Te ratio). At the same time, the mechanical efficiency hardly changes and accounts to approximate to 3 per cent of the accreted rest mass energy flux, even at the highest simulated accretion rates. This is particularly important for the mechanical active galactic nuclei (AGN) feedback regulating massive galaxies, groups and clusters. Comparison with recent observations of radiative and mechanical AGN luminosities suggests that the ion to electron temperature ratio in the inner, collisionless accretion flow should fall within 10 < T-i/T-e < 30, i.e. the electron temperature should be several percent of the ion temperature.

2017 - On the Connection between Turbulent Motions and Particle Acceleration in Galaxy Clusters [Articolo su rivista]
Eckert, D.; Gaspari, Massimo; Vazza, Franco; Gastaldello, Fabio; Tramacere, A.; Zimmer, S.; Ettori, Stefano; Paltani, S.
abstract

Giant radio halos are megaparsec-scale diffuse radio sources associated with the central regions of galaxy clusters. The most promising scenario to explain the origin of these sources is that of turbulent re-acceleration, in which MeV electrons injected throughout the formation history of galaxy clusters are accelerated to higher energies by turbulent motions mostly induced by cluster mergers. In this Letter, we use the amplitude of density fluctuations in the intracluster medium as a proxy for the turbulent velocity and apply this technique to a sample of 51 clusters with available radio data. Our results indicate a segregation in the turbulent velocity of radio halo and radio quiet clusters, with the turbulent velocity of the former being on average higher by about a factor of two. The velocity dispersion recovered with this technique correlates with the measured radio power through the relation P_radio \propto σ_v^3.3+/- 0.7, which implies that the radio power is nearly proportional to the turbulent energy rate. In case turbulence cascades without being dissipated down to the particle acceleration scales, our results provide an observational confirmation of a key prediction of the turbulent re-acceleration model and possibly shed light on the origin of radio halos.

2017 - Physical Origins of Gas Motions in Galaxy Cluster Cores: Interpreting Hitomi Observations of the Perseus Cluster [Articolo su rivista]
Lau, Erwin T.; Gaspari, Massimo; Nagai, Daisuke; Coppi, Paolo
abstract

The Hitomi X-ray satellite has provided the first direct measurements of the plasma velocity dispersion in a galaxy cluster. It finds a relatively “quiescent” gas with a line-of-sight velocity dispersion σ_{v,los} ≃ 160 km/s, at 30-60 kpc from the cluster center. This is surprising given the presence of jets and X-ray cavities that indicates on-going activity and feedback from the active galactic nucleus (AGN) at the cluster center. Using a set of mock Hitomi observations generated from a suite of state-of-the-art cosmological cluster simulations, and an isolated but higher resolution simulation of gas physics in the cluster core, including the effects of cooling and AGN feedback, we examine the likelihood of Hitomi detecting a cluster with the observed velocities. As long as the Perseus has not experienced a major merger in the last few gigayears, and AGN feedback is operating in a “‘gentle” mode, we reproduce the level of gas motions observed by Hitomi. The frequent mechanical AGN feedback generates net line-of-sight velocity dispersions ∼100-200 km/s, bracketing the values measured in the Perseus core. The large-scale velocity shear observed across the core, on the other hand, is generated mainly by cosmic accretion such as mergers. We discuss the implications of these results for AGN feedback physics and cluster cosmology and progress that needs to be made in both simulations and observations, including a Hitomi re-flight and calorimeter-based instruments with higher spatial resolution.

2017 - Preferential Heating and Acceleration of Heavy Ions in Impulsive Solar Flares [Articolo su rivista]
Kumar, Rahul; Eichler, David; Gaspari, Massimo; Spitkovsky, Anatoly
abstract

We simulate decaying turbulence in a homogeneous pair plasma using a three-dimensional electromagnetic particle-in-cell method. A uniform background magnetic field permeates the plasma such that the magnetic pressure is three times larger than the thermal pressure and the turbulence is generated by counter-propagating shear Alfvén waves. The energy predominately cascades transverse to the background magnetic field, rendering the turbulence anisotropic at smaller scales. We simultaneously move several ion species of varying charge to mass ratios in our simulation and show that the particles of smaller charge to mass ratios are heated and accelerated to non-thermal energies at a faster rate. This is in accordance with the enhancement of heavy ions and a non-thermal tail in their energy spectrum observed in the impulsive solar flares. We further show that the heavy ions are energized mostly in the direction perpendicular to the background magnetic field, with a rate consistent with our analytical estimate of the rate of heating due to cyclotron resonance with the Alfvén waves, of which a large fraction is due to obliquely propagating waves.

2017 - Pressure of the hot gas in simulations of galaxy clusters [Articolo su rivista]
Planelles, S.; Fabjan, D.; Borgani, Stefano; Murante, Giuseppe; Rasia, Elena; Biffi, V.; Truong, N.; Ragone-Figueroa, C.; Granato, Gian Luigi; Dolag, K.; Pierpaoli, E.; Beck, A. M.; Steinborn, Lisa K.; Gaspari, Massimo
abstract

We analyse the radial pressure profiles, the intracluster medium (ICM) clumping factor and the Sunyaev-Zel'dovich (SZ) scaling relations of a sample of simulated galaxy clusters and groups identified in a set of hydrodynamical simulations based on an updated version of the treepm-SPH GADGET-3 code. Three different sets of simulations are performed: the first assumes non-radiative physics, the others include, among other processes, active galactic nucleus (AGN) and/or stellar feedback. Our results are analysed as a function of redshift, ICM physics, cluster mass and cluster cool-coreness or dynamical state. In general, the mean pressure profiles obtained for our sample of groups and clusters show a good agreement with X-ray and SZ observations. Simulated cool-core (CC) and non-cool-core (NCC) clusters also show a good match with real data. We obtain in all cases a small (if any) redshift evolution of the pressure profiles of massive clusters, at least back to z = 1. We find that the clumpiness of gas density and pressure increases with the distance from the cluster centre and with the dynamical activity. The inclusion of AGN feedback in our simulations generates values for the gas clumping (√{C}_{ρ }∼ 1.2 at R200) in good agreement with recent observational estimates. The simulated YSZ-M scaling relations are in good accordance with several observed samples, especially for massive clusters. As for the scatter of these relations, we obtain a clear dependence on the cluster dynamical state, whereas this distinction is not so evident when looking at the subsamples of CC and NCC clusters.

2017 - Raining on black holes and massive galaxies: the top-down multiphase condensation model [Articolo su rivista]
Gaspari, Massimo; Temi, P.; Brighenti, F.
abstract

The plasma haloes filling massive galaxies, groups and clusters are shaped by active galactic nucleus (AGN) heating and subsonic turbulence (σ_v ∼ 150 km s^-1), as probed by Hitomi. Novel 3D high-resolution simulations show the soft X-ray, keV hot plasma cools rapidly via radiative emission at the high-density interface of the turbulent eddies, stimulating a top-down condensation cascade of warm 10^4 K filaments. The kpc-scale ionized (optical/ultraviolet) filaments form a skin enveloping the neutral filaments (optical/infrared/21 cm). The peaks of the warm filaments further condense into cold molecular clouds (<50 K; radio) with total mass of several 107 M☉ and inheriting the turbulent kinematics. In the core, the clouds collide inelastically, mixing angular momentum and leading to Chaotic Cold Accretion (CCA). The black hole accretion rate (BHAR) can be modelled via quasi-spherical viscous accretion, dot{M}_bullet ∝ ν _c, with clump collisional viscosity ν_c ≡ λ_c σ_v and λ_c ∼ 100 pc. Beyond the core, pressure torques shape the angular momentum transport. In CCA, the BHAR is recurrently boosted up to 2 dex compared with the disc evolution, which arises as turbulence becomes subdominant. With negligible rotation too, compressional heating inhibits the molecular phase. The CCA BHAR distribution is lognormal with pink noise, f^-1 power spectrum characteristic of fractal phenomena. Such chaotic fluctuations can explain the rapid luminosity variability of AGN and high-mass X-ray binaries. An improved criterium to trace non-linear condensation is proposed: σ_v/v_cool ≲ 1. The three-phase CCA reproduces key observations of cospatial multiphase gas in massive galaxies, including Chandra X-ray images, SOAR Hα filaments and kinematics, Herschel [C+] emission and ALMA molecular associations. CCA plays important role in AGN feedback and unification, the evolution of BHs, galaxies and clusters.

2017 - Spectral Energy Distribution Mapping of Two Elliptical Galaxies on Sub-kpc Scales [Articolo su rivista]
Amblard, A.; Temi, P.; Gaspari, Massimo; Brighenti, F.
abstract

We use high-resolution Herschel-PACS data of two nearby elliptical galaxies, IC 1459 and NGC 2768, to characterize their dust and stellar content. IC 1459 and NGC 2768 have an unusually large amount of dust for elliptical galaxies ((1-3) × 10^5 M_☉ ); this dust is also not distributed along the stellar content. Using data from GALEX (ultra-violet) to PACS (far-infrared, FIR), we analyze the spectral energy distribution (SED) of these galaxies with CIGALEMC as a function of the projected position, binning images in 7.″2 pixels. From this analysis, we derive maps of SED parameters, such as the metallicity, the stellar mass, the fraction of young stars, and the dust mass. The larger amount of dust in FIR maps seems related in our model to a larger fraction of young stars which can reach up to 4% in the dustier area. The young stellar population is fitted as a recent (∼0.5 Gyr) short burst of star formation for both galaxies. The metallicities, which are fairly large at the center of both galaxies, decrease with the radial distance with a fairly steep gradient for elliptical galaxies.

2017 - Testing the Large-scale Environments of Cool-core and Non-cool-core Clusters with Clustering Bias [Articolo su rivista]
Medezinski, Elinor; Battaglia, Nicholas; Coupon, Jean; Cen, Renyue; Gaspari, Massimo; Strauss, Michael A.; Spergel, David N.
abstract

There are well-observed differences between cool-core (CC) and non-cool-core (NCC) clusters, but the origin of this distinction is still largely unknown. Competing theories can be divided into internal (inside-out), in which internal physical processes transform or maintain the NCC phase, and external (outside-in), in which the cluster type is determined by its initial conditions, which in turn leads to different formation histories (I.e., assembly bias). We propose a new method that uses the relative assembly bias of CC to NCC clusters, as determined via the two-point cluster-galaxy cross-correlation function (CCF), to test whether formation history plays a role in determining their nature. We apply our method to 48 ACCEPT clusters, which have well resolved central entropies, and cross-correlate with the SDSS-III/BOSS LOWZ galaxy catalog. We find that the relative bias of NCC over CC clusters is b = 1.42 ± 0.35 (1.6σ different from unity). Our measurement is limited by the small number of clusters with core entropy information within the BOSS footprint, 14 CC and 34 NCC clusters. Future compilations of X-ray cluster samples, combined with deep all-sky redshift surveys, will be able to better constrain the relative assembly bias of CC and NCC clusters and determine the origin of the bimodality.

2017 - The effect of AGN feedback on Sunyaev-Zeldovich properties of simulated galaxy clusters [Relazione in Atti di Convegno]
Fabjan, Dunja; Planelles, S.; Borgani, S.; Murante, G.; Rasia, Elena; Biffi, V.; Truong, N.; Ragone-Figueroa, C.; Granato, G. L.; Dolag, K.; Pierpaoli, E.; Beck, A. M.; Steinborn, Lisa K.; Gaspari, Massimo
abstract

We studied the imprints that feedback from Active Galactic Nuclei (AGN) leaves on the intracluster plasma during the assembly history of galaxy clusters. To this purpose we used state-of-the-art cosmological hydrodynamical simulations based on an updated version of the Tree-PM SPH GADGET-3 code, comparing three sets of simulations with different prescriptions for the physics of baryons (including AGN and/or stellar feedback). We explore the effect of these different physics, in particular AGN feedback, on IntraCluster medium (ICM) properties observed via Sunyaev-Zel'dovich (SZ) effect using an extended set of galaxy clusters (~100 clusters with M 500masses above 5 × 1013M ☉/h). Some of the main findings are that the scaling relation between the integrated SZ flux and the galaxy cluster total mass is in good accordance with several observed samples, especially for massive clusters, and does not show any clear redshift evolution, with the slope of the relation close to the theoretical one in the AGN feedback case. As for the scatter of this relation, we obtain a mild dependence on the cluster dynamical state.

2017 - The history of chemical enrichment in the intracluster medium from cosmological simulations [Articolo su rivista]
Biffi, V.; Planelles, S.; Borgani, Stefano; Fabjan, D.; Rasia, Elena; Murante, Giuseppe; Tornatore, Luca; Dolag, K.; Granato, Gian Luigi; Gaspari, Massimo; Beck, A. M.
abstract

The distribution of metals in the intracluster medium (ICM) of galaxy clusters provides valuable information on their formation and evolution, on the connection with the cosmic star formation and on the effects of different gas processes. By analysing a sample of simulated galaxy clusters, we study the chemical enrichment of the ICM, its evolution, and its relation with the physical processes included in the simulation and with the thermal properties of the core. These simulations, consisting of re-simulations of 29 Lagrangian regions performed with an upgraded version of the smoothed particle hydrodynamics (SPH) gadget-3 code, have been run including two different sets of baryonic physics: one accounts for radiative cooling, star formation, metal enrichment and supernova (SN) feedback, and the other one further includes the effects of feedback from active galactic nuclei (AGN). In agreement with observations, we find an anti-correlation between entropy and metallicity in cluster cores, and similar radial distributions of heavy-element abundances and abundance ratios out to large cluster-centric distances (∼R<SUB>180</SUB>). In the outskirts, namely outside of ∼0.2 R<SUB>180</SUB>, we find a remarkably homogeneous metallicity distribution, with almost flat profiles of the elements produced by either SNIa or SNII. We investigated the origin of this phenomenon and discovered that it is due to the widespread displacement of metal-rich gas by early (z >2-3) AGN powerful bursts, acting on small high-redshift haloes. Our results also indicate that the intrinsic metallicity of the hot gas for this sample is on average consistent with no evolution between z = 2 and z = 0, across the entire radial range.

2017 - The Remarkable Similarity of Massive Galaxy Clusters from z~0 to z~1.9 [Articolo su rivista]
Mcdonald, M.; Allen, S. W.; Bayliss, M.; Benson, B. A.; Bleem, L. E.; Brodwin, M.; Bulbul, E.; Carlstrom, J. E.; Forman, W. R.; Hlavacek-Larrondo, J.; Garmire, G. P.; Gaspari, Massimo; Gladders, M. D.; Mantz, A. B.; Murray, S. S.
abstract

We present the results of a Chandra X-ray survey of the eight most massive galaxy clusters at z &gt;1.2 in the South Pole Telescope 2500 deg^2 survey. We combine this sample with previously published Chandra observations of 49 massive X-ray-selected clusters at 0 &lt; z &lt; 0.1 and 90 Sunyaev-Zel’dovich-selected clusters at 0.25 &lt; z &lt; 1.2 to constrain the evolution of the intracluster medium (ICM) over the past ~10 Gyr. We find that the bulk of the ICM has evolved self-similarly over the full redshift range probed here, with the ICM density at r&gt;0.2 R_500 scaling like E(z)^2. In the centers of clusters (r≲ 0.01 R_500), we find significant deviations from self-similarity (n_e \propto E(z)^0.2+/-0.5), consistent with no redshift dependence. When we isolate clusters with overdense cores (I.e., cool cores), we find that the average overdensity profile has not evolved with redshift—that is, cool cores have not changed in size, density, or total mass over the past ~9-10 Gyr. We show that the evolving “cuspiness” of clusters in the X-ray, reported by several previous studies, can be understood in the context of a cool core with fixed properties embedded in a self-similarly evolving cluster. We find no measurable evolution in the X-ray morphology of massive clusters, seemingly in tension with the rapidly rising (with redshift) rate of major mergers predicted by cosmological simulations. We show that these two results can be brought into agreement if we assume that the relaxation time after a merger is proportional to the crossing time, since the latter is proportional to H(z)^-1.

2017 - Thermodynamic perturbations in the X-ray halo of 33 clusters of galaxies observed with Chandra ACIS (Corrigendum) [Articolo su rivista]
Hofmann, F; Sanders, Js; Nandra, K; Clerc, N; Gaspari, M
abstract

2017 - Unifying the Micro and Macro Properties of AGN Feeding and Feedback [Articolo su rivista]
Gaspari, Massimo; Sądowski, Aleksander
abstract

We unify the feeding and feedback of supermassive black holes with the global properties of galaxies, groups, and clusters by linking for the first time the physical mechanical efficiency at the horizon and megaparsec scale. The macro hot halo is tightly constrained by the absence of overheating and overcooling as probed by X-ray data and hydrodynamic simulations (\varepsilon_BH ≃ 10^-3 T_{x,7.4}). The micro flow is shaped by general-relativistic effects tracked by state-of-the-art GR-RMHD simulations (\varepsilon_\bullet ≃ 0.03). The supermassive black hole properties are tied to the X-ray halo temperature T_x, or related cosmic scaling relation (as L_x). The model is minimally based on first principles, such as conservation of energy and mass recycling. The inflow occurs via chaotic cold accretion (CCA), the rain of cold clouds condensing out of the quenched cooling flow and then recurrently funneled via inelastic collisions. Within 100s gravitational radii, the accretion energy is transformed into ultrafast 10^4 km s^-1 outflows (UFOs) ejecting most of the inflowing mass. At larger radii, the energy-driven outflow entrains progressively more mass: at roughly kiloparsec scale, the velocities of the hot/warm/cold outflows are a few 10^3, 1000, and 500 km s^-1, with median mass rates ∼ 10, 100, and several 100 M_☉ yr-1, respectively. The unified CCA model is consistent with the observations of nuclear UFOs and ionized, neutral, and molecular macro outflows. We provide step-by-step implementation for subgrid simulations, (semi)analytic works, or observational interpretations that require self-regulated AGN feedback at coarse scales, avoiding the a-posteriori fine-tuning of efficiencies.

2016 - A textbook example of ram-pressure stripping in the Hydra A/A780 cluster [Articolo su rivista]
DE GRANDI, Sabrina; Eckert, D.; Molendi, Silvano; Girardi, M.; Roediger, E.; Gaspari, Massimo; Gastaldello, Fabio; Ghizzardi, Simona; Nonino, Mario; Rossetti, Mariachiara
abstract

In the current epoch, one of the main mechanisms driving the growth of galaxy clusters is the continuous accretion of group-scale halos. In this process, the ram pressure applied by the hot intracluster medium on the gas content of the infalling group is responsible for stripping the gas from its dark-matter halo, which gradually leads to the virialisation of the infalling gas in the potential well of the main cluster. Using deep wide-field observations of the poor cluster Hydra A/A780 with XMM-Newton and Suzaku, we report on the discovery of an infalling galaxy group 1.1 Mpc south of the cluster core. The presence of a substructure is confirmed by a dynamical study of the galaxies in this region. A wake of stripped gas is trailing behind the group over a projected scale of 760 kpc. The temperature of the gas along the wake is constant at kT ~ 1.3 keV, which is about a factor of two less than the temperature of the surrounding plasma. We observe a cold front pointing westwards compared to the peak of the group, which indicates that the group is currently not moving in the direction of the main cluster, but is moving along an almost circular orbit. The overall morphology of the group bears remarkable similarities with high-resolution numerical simulations of such structures, which greatly strengthens our understanding of the ram-pressure stripping process.

2016 - Kinetic AGN feedback effects on cluster cool cores simulated using SPH [Articolo su rivista]
Barai, Paramita; Murante, Giuseppe; Borgani, Stefano; Gaspari, Massimo; Granato, Gian Luigi; Monaco, Pierluigi; Ragone-Figueroa, Cinthia
abstract

We implement novel numerical models of AGN feedback in the SPH code GADGET-3, where the energy from a supermassive black hole (BH) is coupled to the surrounding gas in the kinetic form. Gas particles lying inside a bi-conical volume around the BH are imparted a one-time velocity (10 000 km s<SUP>-1</SUP>) increment. We perform hydrodynamical simulations of isolated cluster (total mass 10<SUP>14</SUP>h<SUP>-1</SUP>M<SUB>☉</SUB>), which is initially evolved to form a dense cool core, having central T ≤ 10<SUP>6</SUP>K. A BH resides at the cluster centre, and ejects energy. The feedback-driven fast wind undergoes shock with the slower moving gas, which causes the imparted kinetic energy to be thermalized. Bipolar bubble-like outflows form propagating radially outward to a distance of a few 100 kpc. The radial profiles of median gas properties are influenced by BH feedback in the inner regions (r < 20-50 kpc). BH kinetic feedback, with a large value of the feedback efficiency, depletes the inner cool gas and reduces the hot gas content, such that the initial cool core of the cluster is heated up within a time 1.9 Gyr, whereby the core median temperature rises to above 10<SUP>7</SUP>K, and the central entropy flattens. Our implementation of BH thermal feedback (using the same efficiency as kinetic), within the star formation model, cannot do this heating, where the cool core remains. The inclusion of cold gas accretion in the simulations produces naturally a duty cycle of the AGN with a periodicity of 100 Myr.

2016 - On the Nature of Hydrostatic Equilibrium in Galaxy Clusters [Articolo su rivista]
Biffi, V.; Borgani, Stefano; Murante, Giuseppe; Rasia, Elena; Planelles, S.; Granato, Gian Luigi; Ragone-Figueroa, C.; Beck, A. M.; Gaspari, Massimo; Dolag, K.
abstract

In this paper, we investigate the level of hydrostatic equilibrium (HE) in the intracluster medium of simulated galaxy clusters, extracted from state-of-the-art cosmological hydrodynamical simulations performed with the Smoothed-Particle-Hydrodynamic code GADGET-3. These simulations include several physical processes, among which are stellar and active galactic nucleus feedback, and have been performed with an improved version of the code that allows for a better description of hydrodynamical instabilities and gas mixing processes. Evaluating the radial balance between the gravitational and hydrodynamical forces via the gas accelerations generated, we effectively examine the level of HE in every object of the sample and its dependence on the radial distance from the center and on the classification of the cluster in terms of either cool-coreness or dynamical state. We find an average deviation of 10%-20% out to the virial radius, with no evident distinction between cool-core and non-cool-core clusters. Instead, we observe a clear separation between regular and disturbed systems, with a more significant deviation from HE for the disturbed objects. The investigation of the bias between the hydrostatic estimate and the total gravitating mass indicates that, on average, this traces the deviation from HE very well, even though individual cases show a more complex picture. Typically, in the radial ranges where mass bias and deviation from HE are substantially different, the gas is characterized by a significant amount of random motions (≳ 30 % ), relative to thermal ones. As a general result, the HE-deviation and mass bias, at a given distance from the cluster center, are not very sensitive to the temperature inhomogeneities in the gas.

2016 - The self-regulated AGN feedback loop: the role of chaotic cold accretion [Relazione in Atti di Convegno]
Gaspari, Massimo
abstract

Supermassive black hole accretion and feedback play central role in the evolution of galaxies, groups, and clusters. I review how AGN feedback is tightly coupled with the formation of multiphase gas and the newly probed chaotic cold accretion (CCA). In a turbulent and heated atmosphere, cold clouds and kpc-scale filaments condense out of the plasma via thermal instability and rain toward the black hole. In the nucleus, the recurrent chaotic collisions between the cold clouds, filaments, and central torus promote angular momentum cancellation or mixing, boosting the accretion rate up to 100 times the Bondi rate. The rapid variability triggers powerful AGN outflows, which quench the cooling flow and star formation without destroying the cool core. The AGN heating stifles the formation of multiphase gas and accretion, the feedback subsides and the hot halo is allowed to cool again, restarting a new cycle. Ultimately, CCA creates a symbiotic link between the black hole and the whole host via a tight self-regulated feedback which preserves the gaseous halo in global thermal equilibrium throughout cosmic time.

2016 - Thermal SZ fluctuations in the ICM: probing turbulence and thermodynamics in Coma cluster with Planck [Articolo su rivista]
Khatri, Rishi; Gaspari, Massimo
abstract

We report the detection of thermal Sunyaev-Zeldovich (SZ) effect fluctuations in the intracluster medium (ICM) of Coma cluster observed with Planck. The SZ data links the maximum observable X-ray scale to the large Mpc scale, extending our knowledge of the power spectrum of ICM fluctuations. Deprojecting the 2D SZ perturbations into 3D pressure fluctuations, we find an amplitude spectrum which peaks at δP/P = 33 ± 12 and 74 ± 19 per cent in the 15 and 40 arcmin radius region, respectively. We perform tests to ensure fluctuations are intrinsic to the cluster and not due to noise contamination. By using high-resolution hydrodynamical models, we improve the ICM turbulence constraints in Coma, finding 3D Mach number Ma_3d = 0.8 ± 0.3 (15 arcmin region), increasing to supersonic values at larger radii (40 arcmin) and an injection scale L_inj ≈ 500 kpc. Such properties are consistent with driving due to mergers, in particular tied to internal galaxy groups. The large pressure fluctuations show that Coma is in adiabatic mode (mediated by sound waves), rather than isobaric mode (mediated by buoyancy waves). As predicted by turbulence models, the distribution of SZ fluctuations is lognormal with mild non-Gaussianities (heavy tails). The substantial non-thermal pressure support implies hydrostatic mass bias b_M = -15 to -45 per cent from the core to the outskirt region, respectively. While total SZ power probes the thermal energy content, the SZ fluctuations constrain the non-thermal deviations important for precision cosmology. The proposed, novel approach can be exploited by multifrequency observations using ground-based interferometers and future space cosmic microwave background missions.

2016 - Thermodynamic perturbations in the X-ray halo of 33 clusters of galaxies observed with Chandra ACIS [Articolo su rivista]
Hofmann, F; Sanders, J S; Nandra, K; Clerc, N; Gaspari, M
abstract

In high-resolution X-ray observations of the hot plasma in clusters of galaxies, significant structures caused by AGN feedback, mergers, and turbulence can be detected. Many clusters have been observed by Chandra in great depth and at high resolution. Aims: With the use of archival data taken with the Chandra ACIS instrument, the aim was to study thermodynamic perturbations of the X-ray emitting plasma and to apply this to better understand the thermodynamic and dynamic state of the intracluster medium (ICM). We analysed deep observations for a sample of 33 clusters with more than 100 ks of Chandra exposure each at distances between redshift 0.025 and 0.45. The combined exposure of the sample is 8 Ms. Fitting emission models to different regions of the extended X-ray emission, we searched for perturbations in density, temperature, pressure, and entropy of the hot plasma. For individual clusters, we mapped the thermodynamic properties of the ICM and measured their spread in circular concentric annuli. Comparing the spread of different gas quantities to high-resolution 3D hydrodynamic simulations, we constrained the average Mach number regime of the sample to Mach1D ≈ 0.16 ± 0.07. In addition we found a tight correlation between metallicity, temperature, and redshift with an average metallicity of Z ≈ 0.3 ± 0.1 Z☉. Conclusions: This study provides detailed perturbation measurements for a large sample of clusters that can be used to study turbulence and make predictions for future X-ray observatories like eROSITA, Astro-H, and Athena.

2016 - Where does the gas fueling star formation in brightest cluster galaxies originate? [Articolo su rivista]
Molendi, Silvano; Tozzi, Paolo; Gaspari, Massimo; DE GRANDI, Sabrina; Gastaldello, Fabio; Ghizzardi, Simona; Rossetti, Mariachiara
abstract

Aims: We investigate the relationship between X-ray cooling and star formation in brightest cluster galaxies (BCGs). <BR />Methods: We present an X-ray spectral analysis of the inner regions, 10-40 kpc, of six nearby cool core clusters (z < 0.35) observed with Chandra ACIS. This sample is selected on the basis of the high star formation rate (SFR) observed in the BCGs. We restrict our search for cooling gas to regions that are roughly cospatial with the starburst. We fit single- and multi-temperature mkcflow models to constrain the amount of isobarically cooling intracluster medium. Results: We find that in all clusters, below a threshold temperature ranging between 0.9 and 3 keV, only upper limits can be obtained. In four out of six objects, the upper limits are significantly below the SFR and in two, namely A1835 and A1068, they are less than a tenth of the SFR. Conclusions: Our results suggests that a number of mechanisms conspire to hide the cooling signature in our spectra. In a few systems the lack of a cooling signature may be attributed to a relatively long delay time between the X-ray cooling and the star burst. However, for A1835 and A1068, where the X-ray cooling time is shorter than the timescale of the starburst, a possible explanation is that the region where gas cools out of the X-ray phase extends to very large radii, likely beyond the core of these systems.

2016 - 7.1 keV sterile neutrino constraints from X-ray observations of 33 clusters of galaxies with Chandra ACIS [Articolo su rivista]
Hofmann, F.; Sanders, J. S.; Nandra, K.; Clerc, N.; Gaspari, Massimo
abstract

Context. Recently an unidentified emission line at 3.55 keV has been detected in X-ray spectra of clusters of galaxies. The line has been discussed as a possible decay signature of 7.1 keV sterile neutrinos, which have been proposed as a dark matter (DM) candidate.Aims: We aim to put constraints on the proposed line emission in a large sample of Chandra-observed clusters and obtain limits on the mixing angle in a 7.1 keV sterile neutrino DM scenario.Methods: For a sample of 33 high-mass clusters of galaxies, we merge all observations from the Chandra data archive. Each cluster has more than 100 ks of combined exposure. The resulting high signal-to-noise spectra are used to constrain the flux of an unidentified line emission at 3.55 keV in the individual spectra and a merged spectrum of all clusters.Results: We obtained very detailed spectra around the 3.55 keV range and limits on an unidentified emission line. Assuming all DM were made of 7.1 keV sterile neutrinos, the upper limits on the mixing angle are sin2(2Θ) < 10.1×10^-11 from ACIS-I and < 40.3×10^-11 from ACIS-S data at 99.7 per cent confidence level.Conclusions: We do not find evidence for an unidentified emission line at 3.55 keV. The sample extends the list of objects searched for an emission line at 3.55 keV and will help to identify the best targets for future studies of the potential DM decay line with upcoming X-ray observatories like Hitomi (Astro-H), eROSITA, and Athena.

2015 - Chaotic cold accretion on to black holes in rotating atmospheres [Articolo su rivista]
Gaspari, Massimo; Brighenti, F.; Temi, P.
abstract

The fueling of black holes is one key problem in the evolution of baryons in the universe. Chaotic cold accretion (CCA) profoundly differs from classic accretion models, as Bondi and thin disc theories. Using 3D high-resolution hydrodynamic simulations, we now probe the impact of rotation on the hot and cold accretion flow in a typical massive galaxy. In the hot mode, with or without turbulence, the pressure-dominated flow forms a geometrically thick rotational barrier, suppressing the black hole accretion rate to ~1/3 of the spherical case value. When radiative cooling is dominant, the gas loses pressure support and quickly circularizes in a cold thin disk; the accretion rate is decoupled from the cooling rate, although it is higher than that of the hot mode. In the more common state of a turbulent and heated atmosphere, CCA drives the dynamics if the gas velocity dispersion exceeds the rotational velocity, i.e., turbulent Taylor number Ta_t < 1. Extended multiphase filaments condense out of the hot phase via thermal instability (TI) and rain toward the black hole, boosting the accretion rate up to 100 times the Bondi rate (Ṁ_bh ~ Ṁcool). Initially, turbulence broadens the angular momentum distribution of the hot gas, allowing the cold phase to condense with prograde or retrograde motion. Subsequent chaotic collisions between the cold filaments, clouds, and a clumpy variable torus promote the cancellation of angular momentum, leading to high accretion rates. As turbulence weakens (Ta_t >1), the broadening of the distribution and the efficiency of collisions diminish, damping the accretion rate ∝ Ta_t^-1, until the cold disk drives the dynamics. This is exacerbated by the increased difficulty to grow TI in a rotating halo. The simulated sub-Eddington accretion rates cover the range inferred from AGN cavity observations. CCA predicts inner flat X-ray temperature and r^-1 density profiles, as recently discovered in M 87 and NGC 3115. The synthetic Hα images reproduce the main features of cold gas observations in massive ellipticals, as the line fluxes and the filaments versus disk morphology. Such dichotomy is key for the long-term AGN feedback cycle. As gas cools, filamentary CCA develops and boosts AGN heating; the cold mode is thus reduced and the rotating disk remains the sole cold structure. Its consumption leaves the atmosphere in hot mode with suppressed accretion and feedback, reloading the cycle.

2015 - Shaping the X-ray spectrum of galaxy clusters with AGN feedback and turbulence [Articolo su rivista]
Gaspari, M
abstract

The hot plasma filling galaxy clusters emits copious X-ray radiation. The classic unheated and unperturbed cooling flow model predicts dramatic cooling rates and an isobaric X-ray spectrum with constant differential luminosity distribution. The observed cores of clusters (and groups) show instead a strong deficit of soft X-ray emission: dL(X)/dT proportional to (T/T-hot)(alpha) (= 2 +/- 1). Using 3D hydrodynamic simulations, we show that such deficit arises from the tight self-regulation between thermal instability condensation and AGN outflow injection: condensing clouds boost the AGN outflows, which quench cooling as they thermalize through the core. The resultant average distribution slope is alpha similar or equal to 2, oscillating within the observed 1 < alpha < 3. In the absence of thermal instability, the X-ray spectrum remains isothermal (alpha greater than or similar to 8), while unopposed cooling drives a too shallow slope, alpha < 1. AGN outflows deposit their energy inside-out, releasing more heat in the inner cooler phase; radially distributed heating alone induces a declining spectrum, 1 < alpha < 2. Turbulence further steepens the spectrum and increases the scatter: the turbulent Mach number in the hot phase is subsonic, while it becomes transonic in the cooler phase, making perturbations to depart from the isobaric mode. Such increase in dln P/dln T leads to alpha approximate to 3. Self-regulated AGN outflow feedback can address the soft X-ray problem through the interplay of heating and turbulence.

2015 - Unifying X-ray Scaling Relations from Galaxies to Clusters [Articolo su rivista]
Anderson, Michael E.; Gaspari, Massimo; White, Simon D. M.; Wang, Wenting; Dai, Xinyu
abstract

We examine a sample of ∼250 000 `locally brightest galaxies' selected from the Sloan Digital Sky Survey to be central galaxies within their dark matter haloes. We stack the X-ray emission from these haloes, as a function of the stellar mass of the central galaxy, using data from the ROSAT All-Sky Survey. We detect emission across almost our entire sample, including emission which we attribute to hot gas around galaxies spanning a range of 1.2 dex in stellar mass (corresponding to nearly two orders of magnitude in halo mass) down to M_star = 10^10.8 M☉ (M500 ≈ 10^12.6 M☉). Over this range, the X-ray luminosity can be fit by a power law, either of stellar mass or of halo mass. From this, we infer a single unified scaling relation between mass and LX which applies for galaxies, groups, and clusters. This relation has a slope steeper than expected for self-similarity, showing the importance of non-gravitational heating. Assuming this non-gravitational heating is predominately due to AGN feedback, the lack of a break in the relation shows that AGN feedback is tightly self-regulated and fairly gentle, in agreement with the predictions of recent high-resolution simulations. Our relation is consistent with established measurements of the LX-LK relation for elliptical galaxies as well as the LX-M500 relation for optically selected galaxy clusters. However, our LX-M500 relation has a normalization more than a factor of 2 below most previous relations based on X-ray-selected cluster samples. We argue that optical selection offers a less biased view of the LX-M500 relation for mass-selected clusters.

2014 - Can AGN Feedback Break the Self-similarity of Galaxies, Groups, and Clusters? [Articolo su rivista]
Gaspari, M; Brighenti, F; Temi, P; Ettori, S
abstract

It is commonly thought that active galactic nucleus (AGN) feedback can break the self-similar scaling relations of galaxies, groups, and clusters. Using high-resolution three-dimensional hydrodynamic simulations, we isolate the impact of AGN feedback on the Lx-Tx relation, testing the two archetypal and common regimes, self-regulated mechanical feedback and a quasar thermal blast. We find that AGN feedback has severe difficulty in breaking the relation in a consistent way. The similarity breaking is directly linked to the gas evacuation within R500, while the central cooling times are inversely proportional to the core density. Breaking self-similarity thus implies breaking the cool core, morphing all systems to non-cool-core objects, which is in clear contradiction with the observed data populated by several cool-core systems. Self-regulated feedback, which quenches cooling flows and preserves cool cores, prevents dramatic evacuation and similarity breaking at any scale; the relation scatter is also limited. The impulsive thermal blast can break the core-included Lx-Tx at T500 &lt;~ 1 keV, but substantially empties and overheats the halo, generating a perennial non-cool-core group, as experienced by cosmological simulations. Even with partial evacuation, massive systems remain overheated. We show that the action of purely AGN feedback is to lower the luminosity and heat the gas, perpendicular to the fit.

2014 - Kinetic or thermal AGN feedback in simulations of isolated and merging disc galaxies calibrated by the M-sigma relation [Articolo su rivista]
Barai, P; Viel, M; Murante, G; Gaspari, M; Borgani, S
abstract

We investigate two modes of coupling the feedback energy from a central active galactic nucleus (AGN) to the neighbouring gas in galaxy simulations: kinetic - velocity boost and thermal - heating. We formulate kinetic feedback models for energy-driven wind (EDW) and momentum-driven wind (MDW), using two free parameters: feedback efficiency ∊f and AGN wind velocity vw. A novel numerical algorithm is implemented in the smoothed particle hydrodynamics code GADGET-3, to prevent the expansion of a hole in the gas distribution around the black hole (BH). We perform simulations of isolated evolution and merger of disc galaxies, of Milky Way mass as well as lower and higher masses. We find that in the isolated galaxy BH kinetic feedback generates intermittent bipolar jet-like gas outflows. We infer that current prescriptions for BH subgrid physics in galaxy simulations can grow the BH to observed values even in an isolated disc galaxy. The BH growth is enhanced in a galaxy merger, which consequently requires different model parameters to fit the observations than an isolated case. Comparing the [MBH-σ⋆] relation obtained in our simulations with observational data, we conclude that it is possible to find parameter sets for a fit in all the models (e.g. vw = 10 000 km s-1 and ∊f = 0.25 for BH kinetic EDW), except for the case with MDW feedback in a galaxy merger, in which the BH is always too massive. The BH thermal feedback implementation of Springel et al. within the multiphase star formation model is found to have negligible impact on gas properties, and the effect claimed in all previous studies is attributed to gas depletion around the BH by the creation of an artificial hole. The BH mass accretion rate in our simulations exhibit heavy fluctuations. The star formation rate is quenched with feedback by removal of gas. The circumgalactic medium gas at galactocentric distances (20-100) h-1 kpc is found to give the best metallicity observational diagnostic to distinguish between BH models.

2014 - The relation between gas density and velocity power spectra in galaxy clusters: High-resolution hydrodynamic simulations and the role of conduction [Articolo su rivista]
Gaspari, M; Churazov, E; Nagai, D; Lau, Et; Zhuravleva, I
abstract

Exploring the power spectrum of fluctuations and velocities in the intracluster medium (ICM) can help us to probe the gas physics of galaxy clusters. Using high-resolution 3D plasma simulations, we study the statistics of the velocity field and its intimate relation with the ICM thermodynamic perturbations. The normalization of the ICM spectrum (related to density, entropy, or pressure fluctuations) is linearly tied to the level of large-scale motions, which excite both gravity and sound waves due to stratification. For a low 3D Mach number M similar to 0.25, gravity waves mainly drive entropy perturbations, which are traced by preferentially tangential turbulence. For M > 0.5, sound waves start to significantly contribute and pass the leading role to compressive pressure fluctuations, which are associated with isotropic (or slightly radial) turbulence. Density and temperature fluctuations are then characterized by the dominant process: isobaric (low M), adiabatic (high M), or isothermal (strong conduction). Most clusters reside in the intermediate regime, showing a mixture of gravity and sound waves, hence drifting toward isotropic velocities. Remarkably, regardless of the regime, the variance of density perturbations is comparable to the 1D Mach number, M-1D similar to delta rho/rho. This linear relation allows us to easily convert between gas motions and ICM perturbations (delta rho/rho < 1), which can be exploited by the available Chandra, XMM data and by the forthcoming Astro-H mission. At intermediate and small scales (10-100 kpc), the turbulent velocities develop a tight Kolmogorov cascade. The thermodynamic perturbations (which can be generally described by log-normal distributions) act as effective tracers of the velocity field, in broad agreement with the Kolmogorov-Obukhov-Corrsin advection theory. The cluster radial gradients and compressive features induce a flattening in the cascade of the perturbations. Thermal conduction, on the other hand, acts to damp the thermodynamic fluctuations, washing out the filamentary structures and steepening the spectrum, while leaving the velocity cascade unaltered. The ratio of the velocity and density spectrum thus inverts the downtrend shown by the non-diffusive models, as it widens up to similar to 5. This new key diagnostic can robustly probe the presence of conductivity in the ICM. We produce X-ray images of the velocity field, showing how future missions (e. g. Astro-H, Athena) can detect velocity dispersions of a few 100 km s(-1) (M > 0.1 in massive clusters), allowing us to calibrate the linear relation and to constrain relative perturbations down to just a few percent.

2014 - The Relation between Gas Density and Velocity Power Spectra in Galaxy Clusters: Qualitative Treatment and Cosmological Simulations [Articolo su rivista]
Zhuravleva, I; Churazov, Em; Schekochihin, Aa; Lau, Et; Nagai, D; Gaspari, M; Allen, Sw; Nelson, K; Parrish, Ij
abstract

We address the problem of evaluating the power spectrum of the velocity field of the intracluster medium using only information on the plasma density fluctuations, which can be measured today by Chandra and XMM-Newton observatories. We argue that for relaxed clusters there is a linear relation between the rms density and velocity fluctuations across a range of scales, from the largest ones, where motions are dominated by buoyancy, down to small, turbulent scales: (\delta \rho _k/\rho)^2 = \eta _1^2 (V_{1,k}/c_s)^2, where δρ k /ρ is the spectral amplitude of the density perturbations at wavenumber k, V_{1,k}^2=V_k^2/3 is the mean square component of the velocity field, cs is the sound speed, and η1 is a dimensionless constant of the order of unity. Using cosmological simulations of relaxed galaxy clusters, we calibrate this relation and find η1 ≈ 1 ± 0.3. We argue that this value is set at large scales by buoyancy physics, while at small scales the density and velocity power spectra are proportional because the former are a passive scalar advected by the latter. This opens an interesting possibility to use gas density power spectra as a proxy for the velocity power spectra in relaxed clusters across a wide range of scales.

2014 - The stripping of a galaxy group diving into the massive cluster A2142 [Articolo su rivista]
Eckert, D; Molendi, S; Owers, M; Gaspari, M; Venturi, T; Rudnick, L; Ettori, S; Paltani, S; Gastaldello, F; Rossetti, M
abstract

Structure formation in the current Universe operates through the accretion of group-scale systems onto massive clusters. The detection and study of such accreting systems is crucial to understand the build-up of the most massive virialized structures we see today. We report the discovery with XMM-Newton of an irregular X-ray substructure in the outskirts of the massive galaxy cluster Abell 2142. The tip of the X-ray emission coincides with a concentration of galaxies. The bulk of the X-ray emission of this substructure appears to be lagging behind the galaxies and extends over a projected scale of at least 800 kpc. The temperature of the gas in this region is 1.4 keV, which is a factor of ~4 lower than the surrounding medium and is typical of the virialized plasma of a galaxy group with a mass of a few 10^13 M☉. For this reason, we interpret this structure as a galaxy group in the process of being accreted onto the main dark-matter halo. The X-ray structure trailing behind the group is due to gas stripped from its original dark-matter halo as it moves through the intracluster medium (ICM). This is the longest X-ray trail reported to date. For an infall velocity of ~1200 km s-1 we estimate that the stripped gas has been surviving in the presence of the hot ICM for at least 600 Myr, which exceeds the Spitzer conduction timescale in the medium by a factor of ≳400. Such a strong suppression of conductivity is likely related to a tangled magnetic field with small coherence length and to plasma microinstabilities. The long survival time of the low-entropy intragroup medium suggests that the infalling material can eventually settle within the core of the main cluster.

2013 - Chaotic cold accretion on to black holes [Articolo su rivista]
Gaspari, M; Ruszkowski, M; Oh, Sp
abstract

Bondi theory is often assumed to adequately describe the mode of accretion in astrophysical environments. However, the Bondi flow must be adiabatic, spherically symmetric, steady, unperturbed, with constant boundary conditions. Using 3D adaptive mesh refinement simulations, linking the 50 kpc to the sub-parsec (sub-pc) scales over the course of 40 Myr, we systematically relax the classic assumptions in a typical galaxy hosting a supermassive black hole. In the more realistic scenario, where the hot gas is cooling, while heated and stirred on large scales, the accretion rate is boosted up to two orders of magnitude compared with the Bondi prediction. The cause is the non-linear growth of thermal instabilities, leading to the condensation of cold clouds and filaments when t_cool/t_ff ≲ 10. The clouds decouple from the hot gas, `raining' on to the centre. Subsonic turbulence of just over 100 km s^-1 (M &gt; 0.2) induces the formation of thermal instabilities, even in the absence of heating, while in the transonic regime turbulent dissipation inhibits their growth (t_turb/t_cool ≲ 1). When heating restores global thermodynamic balance, the formation of the multiphase medium is violent, and the mode of accretion is fully cold and chaotic. The recurrent collisions and tidal forces between clouds, filaments and the central clumpy torus promote angular momentum cancellation, hence boosting accretion. On sub-pc scales the clouds are channelled to the very centre via a funnel. In this study, we do not inject a fixed initial angular momentum, though vorticity is later seeded by turbulence. A good approximation to the accretion rate is the cooling rate, which can be used as subgrid model, physically reproducing the boost factor of 100 required by cosmological simulations, while accounting for the frequent fluctuations. Since our modelling is fairly general (turbulence/heating due to AGN feedback, galaxy motions, mergers, stellar evolution), chaotic cold accretion may be common in many systems, such as hot galactic haloes, groups and clusters. In this mode, the black hole can quickly react to the state of the entire host galaxy, leading to efficient self-regulated AGN feedback and the symbiotic Magorrian relation. Chaotic accretion can generate high-velocity clouds, likely leading to strong variations in the AGN luminosity, and the deflection or mass-loading of jets. During phases of overheating, the hot mode becomes the single channel of accretion, though strongly suppressed by turbulence. High-resolution data could determine the current mode of accretion: assuming quiescent feedback, the cold mode results in a quasi-flat-temperature core as opposed to the cuspy profile of the hot mode.

2013 - Cold fronts and metal anisotropies in the X-ray cool core of the galaxy cluster Zw 1742+3306 [Articolo su rivista]
Ettori, S; Gastaldello, F; Gitti, M; O'Sullivan, E; Gaspari, M; Brighenti, F; David, L; Edge, Ac
abstract

In recent years, our understanding of the cool cores of galaxy clusters has changed. Once thought to be relatively simple places where gas cools and flows towards the centre, now they are believed to be very dynamic places where heating from the central active galactic nucleus (AGN) and cooling, as inferred from active star formation, molecular gas, and Hα nebulosity, find an uneasy energetic balance. Aims: We want to characterize the X-ray properties of the nearby cool-core cluster Zw 1742+3306, selected because it is bright at X-ray (with a flux greater than 10^-11 erg s^-1 cm^-2 in the 0.1-2.4 keV band) and Hα wavelengths (Hα luminosity >10^40 erg s^-1). We used Chandra data to analyse the spatial and spectral properties of the cool core of Zw 1742+3306, a galaxy cluster at z = 0.0757 that emits in Hα and presents the brightest central galaxy located in a diffuse X-ray emission with multiple peaks in surface brightness. We show that the X-ray cool core of the galaxy cluster Zw 1742+3306 is thermodynamically very active with evidence of cold fronts and a weak shock in the surface brightness map and of an apparently coherent, elongated structure with metallicity greater than the value measured in the surrounding ambient gas by about 50%. This anisotropic structure is 280 × 90 kpc^2 and is aligned with the cold fronts and with the X-ray emission on larger scales. We suggest that all these peculiarities in the X-ray emission of Zw 1742+3306 are either a very fine-tuned output of a sloshing gas in the cluster core or the product of a metal-rich outflow from the central AGN.

2013 - Constraining turbulence and conduction in the hot ICM through density perturbations [Articolo su rivista]
Gaspari, M; Churazov, E
abstract

Turbulence and conduction can dramatically affect the evolution of baryons in the universe; current constraints are however rare and uncertain. Using 3D high-resolution hydrodynamic simulations, tracking both electrons and ions, we study the effects of turbulence and conduction in the hot intracluster medium. We show how the power spectrum of the gas density perturbations (δ = δρ/ρ) can accurately constrain both processes. The characteristic amplitude of density perturbations is linearly related to the strength of turbulence, i.e. the 3D Mach number, as A(k)δ,max = c M, where c ≃ 0.25 for injection scale of 500 kpc. The slope of Aδ(k) in turn reflects the level of diffusion, dominated by conduction. In a non-conductive medium, subsonic stirring motions advect density with a similar nearly Kolmogorov cascade, Eδ(k) ∝ k^- 5/3. Increasing conduction (parametrized via the magnetic suppression f = 10-3 → 1) progressively steepens the spectrum towards the Burgers-like regime, Eδ(k) ∝ k^-2. The slope is only weakly dependent on M. The turbulent Prandtl number defines the dynamic similarity of the flow; at scales where Pt ≡ t_cond/t_turb < 100, the power spectrum develops a significant decay, i.e. conduction stifles turbulent regeneration. The transition is gentle for highly suppressed conduction, f ≤ 10^-3, while sharp in the opposite regime. For strong conductivity (f ≥ 0.1), Pt ~ 100 occurs on spatial scales larger than the injection scale, globally damping density perturbations by a factor of 2-4, from large to small scales. The velocity spectrum is instead not much affected by conduction. The f ≥ 0.1 regime should also affect the appearance of X-ray images, in which Kelvin-Helmholtz and Rayleigh-Taylor rolls and filaments are washed out. In a stratified system, perturbations are characterized by a mixture of modes: weak/strong turbulence induces higher isobaric/adiabatic fluctuations, while conduction forces both modes towards the intermediate isothermal regime. We provide a general analytic fit which is applied to new deep Chandra observations of Coma cluster. The observed spectrum is best consistent with strongly suppressed effective isotropic conduction, f ≃ 10^-3, and mild subsonic turbulence, M ≃ 0.45 (assuming injection scale at ~250 kpc). The latter implies Eturb ≃ 0.11 Eth, in agreement with cosmological simulations and line-broadening observations. The low conductivity corroborates the survival of sharp features in the ICM (cold fronts, filaments, bubbles), and indicates that cooling flows may not be balanced by conduction.

2013 - Solving the cooling flow problem through mechanical AGN feedback [Articolo su rivista]
Gaspari, M; Brighenti, F; Ruszkowski, M
abstract

Unopposed radiative cooling of plasma would lead to the cooling catastrophe, a massive inflow of condensing gas, manifest in the core of galaxies, groups and clusters. The last generation X-ray telescopes, Chandra and XMM, have radically changed our view on baryons, indicating AGN heating as the balancing counterpart of cooling. This work reviews our extensive investigation on self-regulated heating. We argue that the mechanical feedback, based on massive subrelativistic outflows, is the key to solving the cooling flow problem, i.e. dramatically quenching the cooling rates for several Gyr without destroying the cool-core structure. Using a modified version of the 3D hydrocode FLASH, we show that bipolar AGN outflows can further reproduce fundamental observed features, such as buoyant bubbles, weak shocks, metals dredge-up, and turbulence. The latter is an essential ingredient to drive nonlinear thermal instabilities, which cause the formation of extended cold gas, a residual of the quenched cooling flow and, later, fuel for the feedback engine. Compared to clusters, groups and galaxies require a gentler mechanical feedback, in order to avoid catastrophic overheating. We highlight the essential characteristics for a realistic AGN feedback, with emphasis on observational consistency.

2013 - The Hot and Energetic Universe: A White Paper presenting the science theme motivating the Athena+ mission [Altro]
Nandra, ; Kirpal, ; Barret, ; Didier, ; Barcons, ; Xavier, ; Fabian, ; Andy, ; Den, Herder; Jan-Willem, ; Piro, ; Luigi, ; Watson, ; Mike, ; Adami, ; Christophe, ; Aird, ; James, ; Afonso, ; Jose, Manuel; Alexander, ; Dave, ; Argiroffi, ; Costanza, ; Amati, ; Lorenzo, ; Arnaud, ; Monique, ; Atteia, ; Jean-Luc, ; Audard, ; Marc, ; Badenes, ; Carles, ; Ballet, ; Jean, ; Ballo, ; Lucia, ; Bamba, ; Aya, Bhardwaj; Anil, ; Stefano, Battistelli; Elia, ; Becker, ; Werner, ; De, Becker; Michaël, ; Behar, ; Ehud, ; Bianchi, ; Stefano, ; Biffi, ; Veronica, ; Bîrzan, ; Laura, ; Bocchino, ; Fabrizio, ; Bogdanov, ; Slavko, ; Boirin, ; Laurence, ; Boller, ; Thomas, ; Borgani, ; Stefano, ; Borm, ; Katharina, ; Bouché, ; Nicolas, ; Bourdin, ; Hervé, ; Bower, ; Richard, ; Braito, ; Valentina, ; Branchini, ; Enzo, ; Branduardi-Raymont, ; Graziella, ; Bregman, ; Joel, ; Brenneman, ; Laura, ; Brightman, ; Murray, ; Brüggen, ; Marcus, ; Buchner, ; Johannes, ; Bulbul, ; Esra, ; Brusa, ; Marcella, ; Bursa, ; Michal, ; Caccianiga, ; Alessandro, ; Cackett, ; Ed, ; Campana, ; Sergio, ; Cappelluti, ; Nico, ; Cappi, ; Massimo, ; Carrera, ; Francisco, ; Ceballos, ; Maite, ; Christensen, ; Finn, ; Chu, ; You-Hua, ; Churazov, ; Eugene, ; Clerc, ; Nicolas, ; Corbel, ; Stephane, ; Corral, ; Amalia, ; Comastri, ; Andrea, ; Costantini, ; Elisa, ; Croston, ; Judith, ; Dadina, ; Mauro, ; D'Ai, ; Antonino, ; Decourchelle, ; Anne, ; Della, Ceca; Roberto, ; Dennerl, ; Konrad, ; Dolag, ; Klaus, ; Done, ; Chris, ; Dovciak, ; Michal, ; Drake, ; Jeremy, ; Eckert, ; Dominique, ; Edge, ; Alastair, ; Ettori, ; Stefano, ; Ezoe, ; Yuichiro, ; Feigelson, ; Eric, ; Fender, ; Rob, ; Feruglio, ; Chiara, ; Finoguenov, ; Alexis, ; Fiore, ; Fabrizio, ; Galeazzi, ; Massimiliano, ; Gallagher, ; Sarah, ; Gandhi, ; Poshak, ; Gaspari, M; Gastaldello, ; Fabio, ; Georgakakis, ; Antonis, ; Georgantopoulos, ; Ioannis, ; Gilfanov, ; Marat, ; Gitti, ; Myriam, ; Gladstone, ; Randy, ; Goosmann, ; Rene, ; Gosset, ; Eric, ; Grosso, ; Nicolas, ; Guedel, ; Manuel, ; Guerrero, ; Martin, ; Haberl, ; Frank, ; Hardcastle, ; Martin, ; Heinz, ; Sebastian, ; Alonso, Herrero; Almudena, ; Hervé, ; Anthony, ; Holmstrom, ; Mats, ; Iwasawa, ; Kazushi, ; Jonker, ; Peter, ; Kaastra, ; Jelle, ; Kara, ; Erin, ; Karas, ; Vladimir, ; Kastner, ; Joel, ; King, ; Andrew, ; Kosenko, ; Daria, ; Koutroumpa, ; Dimita, ; Kraft, ; Ralph, ; Kreykenbohm, ; Ingo, ; Lallement, ; Rosine, ; Lanzuisi, ; Giorgio, ; Lee, ; Lemoine-Goumard, ; Marianne, ; Lobban, ; Andrew, ; Lodato, ; Giuseppe, ; Lovisari, ; Lorenzo, ; Lotti, ; Simone, ; Mccharthy, ; Ian, ; Mcnamara, ; Brian, ; Maggio, ; Antonio, ; Maiolino, ; Roberto, ; De, Marco; Barbara, ; De, Martino; Domitilla, ; Mateos, ; Silvia, ; Matt, ; Giorgio, ; Maughan, ; Ben, ; Mazzotta, ; Pasquale, ; Mendez, ; Mariano, ; Merloni, ; Andrea, ; Micela, ; Giuseppina, ; Miceli, ; Marco, ; Mignani, ; Robert, ; Miller, ; Jon, ; Miniutti, ; Giovanni, ; Molendi, ; Silvano, ; Montez, ; Rodolfo, ; Moretti, ; Alberto, ; Motch, ; Christian, ; Nazé, ; Yaël, ; Nevalainen, ; Jukka, ; Nicastro, ; Fabrizio, ; Nulsen, ; Paul, ; Ohashi, ; Takaya, ; O'Brien, ; Paul, ; Osborne, ; Julian, ; Oskinova, ; Lida, ; Pacaud, ; Florian, ; Paerels, ; Frederik, ; Page, ; Mat, ; Papadakis, ; Iossif, ; Pareschi, ; Giovanni, ; Petre, ; Robert, ; Petrucci, ; Pierre-Olivier, ; Piconcelli, ; Enrico, ; Pillitteri, ; Ignazio, ; Pinto, ; De, Plaa; Jelle, ; Pointecouteau, ; Etienne, ; Ponman, ; Trevor, ; Ponti, ; Gabriele, ; Porquet, ; Delphine, ; Pounds, ; Ken, ; Pratt, ; Gabriel, ; Predehl, ; Peter, ; Proga, ; Daniel, ; Psaltis, ; Dimitrios, ; Rafferty, ; David, ; Ramos-Ceja, ; Miriam, ; Ranalli, ; Piero, ; Rasia, ; Elena, ; Rau, ; Arne, ; Rauw, ; Gregor, ; Rea, ; Nanda, ; Read, ; Andy, ; Reeves, ; James, ; Reiprich, ; Thomas, ; Renaud, ; Matthieu, ; Reynolds, ; Chris, ; Risaliti, ; Guido, ; Rodriguez, ; Jerome, ; Rodriguez, Hidalgo; Paola, ; Roncarelli, ; Mauro, ; Rosario, ; Davi
abstract

This White Paper, submitted to the recent ESA call for science themes to define its future large missions, advocates the need for a transformational leap in our understanding of two key questions in astrophysics: 1) How does ordinary matter assemble into the large scale structures that we see today? 2) How do black holes grow and shape the Universe? Hot gas in clusters, groups and the intergalactic medium dominates the baryonic content of the local Universe. To understand the astrophysical processes responsible for the formation and assembly of these large structures, it is necessary to measure their physical properties and evolution. This requires spatially resolved X-ray spectroscopy with a factor 10 increase in both telescope throughput and spatial resolving power compared to currently planned facilities. Feedback from supermassive black holes is an essential ingredient in this process and in most galaxy evolution models, but it is not well understood. X-ray observations can uniquely reveal the mechanisms launching winds close to black holes and determine the coupling of the energy and matter flows on larger scales. Due to the effects of feedback, a complete understanding of galaxy evolution requires knowledge of the obscured growth of supermassive black holes through cosmic time, out to the redshifts where the first galaxies form. X-ray emission is the most reliable way to reveal accreting black holes, but deep survey speed must improve by a factor ~100 over current facilities to perform a full census into the early Universe. The Advanced Telescope for High Energy Astrophysics (Athena+) mission provides the necessary performance (e.g. angular resolution, spectral resolution, survey grasp) to address these questions and revolutionize our understanding of the Hot and Energetic Universe. These capabilities will also provide a powerful observatory to be used in all areas of astrophysics.

2013 - The Hot and Energetic Universe: AGN feedback in galaxy clusters and groups [Altro]
Croston, ; J., H.; Sanders, ; J., S.; Heinz, ; Hardcastle, ; M., J.; Zhuravleva, ; Bîrzan, ; Bower, ; R., G.; Brüggen, ; Churazov, ; Edge, ; A., C.; Ettori, ; Fabian, ; A., C.; Finoguenov, ; Kaastra, ; Gaspari, M; Gitti, ; Nulsen, ; P. E., J.; Mcnamara, ; B., R.; Pointecouteau, ; Ponman, ; T. J., Pratt; G., W.; Rafferty, ; D., A.; Reiprich, ; T., H.; Sijacki, ; Worrall, ; D., M.; Kraft, ; R., P.; Mccarthy, ; Wise,
abstract

Mechanical feedback via Active Galactic Nuclei (AGN) jets in the centres of galaxy groups and clusters is a crucial ingredient in current models of galaxy formation and cluster evolution. Jet feedback is believed to regulate gas cooling and thus star formation in the most massive galaxies, but a robust physical understanding of this feedback mode is currently lacking. The large collecting area, excellent spectral resolution and high spatial resolution of Athena+ will provide the breakthrough diagnostic ability necessary to develop this understanding, via: (1) the first kinematic measurements on relevant spatial scales of the hot gas in galaxy, group and cluster haloes as it absorbs the impact of AGN jets, and (2) vastly improved ability to map thermodynamic conditions on scales well-matched to the jets, lobes and gas disturbances produced by them. Athena+ will therefore determine for the first time how jet energy is dissipated and distributed in group and cluster gas, and how a feedback loop operates in group/cluster cores to regulate gas cooling and AGN fuelling. Athena+ will also establish firmly the cumulative impact of powerful radio galaxies on the evolution of baryons from the epoch of group/cluster formation to the present day.

2013 - The Hot and Energetic Universe: The astrophysics of galaxy groups and clusters [Altro]
Ettori, ; Pratt, ; G., W.; De, Plaa; Eckert, ; Nevalainen, ; Battistelli, ; E., S.; Borgani, ; Croston, ; J., H.; Finoguenov, ; Kaastra, ; Gaspari, M; Gastaldello, ; Gitti, ; Molendi, ; Pointecouteau, ; Ponman, ; T., J.; Reiprich, ; T., H.; Roncarelli, ; Rossetti, ; Sanders, ; J. S., Sun; Trinchieri, ; Vazza, ; Arnaud, ; Böringher, ; Brighenti, ; Dahle, ; De, Grandi; Mohr, ; J., J.; Moretti, ; Schindler,
abstract

As the nodes of the cosmic web, clusters of galaxies trace the large-scale distribution of matter in the Universe. They are thus privileged sites in which to investigate the complex physics of structure formation. However, the complete story of how these structures grow, and how they dissipate the gravitational and non-thermal components of their energy budget over cosmic time, is still beyond our grasp. Fundamental questions such as How do hot diffuse baryons accrete and dynamically evolve in dark matter potentials? How and when was the energy that we observe in the ICM generated and distributed? Where and when are heavy elements produced and how are they circulated? are still unanswered. Most of the cluster baryons exists in the form of a diffuse, hot, metal-enriched plasma that radiates primarily in the X-ray band (the intracluster medium, ICM), allowing the X-ray observations of the evolving cluster population to provide a unique opportunity to address these topics. Athena+ with its large collecting area and unprecedented combination of high spectral and angular resolution offers the only way to make major advances in answering these questions. Athena+ will show how the baryonic gas evolves in the dark matter potential wells by studying the motions and turbulence in the ICM. Athena+ will be able to resolve the accreting region both spatially and spectroscopically, probing the true nature and physical state of the X-ray emitting plasma. Athena+ has the capabilities to permit a definitive understanding of the formation and evolution of large-scale cosmic structure through the study of the cluster population.

2013 - Unification of X-ray winds in Seyfert galaxies: from ultra-fast outflows to warm absorbers [Articolo su rivista]
Tombesi, F; Cappi, M; Reeves, Jn; Nemmen, Rs; Braito, V; Gaspari, M; Reynolds, Cs
abstract

The existence of ionized X-ray absorbing layers of gas along the line of sight to the nuclei of Seyfert galaxies is a well established observational fact. This material is systematically outflowing and shows a large range in parameters. However, its actual nature and dynamics are still not clear. In order to gain insights into these important issues we performed a literature search for papers reporting the parameters of the soft X-ray warm absorbers (WAs) in 35 type 1 Seyferts and compared their properties to those of the ultra-fast outflows (UFOs) detected in the same sample. The fraction of sources with WAs is >60 per cent, consistent with previous studies. The fraction of sources with UFOs is >34 per cent, >67 per cent of which also show WAs. The large dynamic range obtained when considering all the absorbers together, spanning several orders of magnitude in ionization, column, velocity and distance allows us, for the first time, to investigate general relations among them. In particular, we find significant correlations indicating that the closer the absorber is to the central black hole, the higher the ionization, column, outflow velocity and consequently the mechanical power. In all the cases, the absorbers continuously populate the whole parameter space, with the WAs and the UFOs lying always at the two ends of the distribution. These evidence strongly suggest that these absorbers, often considered of different types, could actually represent parts of a single large-scale stratified outflow observed at different locations from the black hole. The UFOs are likely launched from the inner accretion disc and the WAs at larger distances, such as the outer disc and/or torus. We argue that the observed parameters and correlations are, to date, consistent with both radiation pressure through Compton scattering and magnetohydrodynamic processes contributing to the outflow acceleration, the latter playing a major role. Most of the absorbers, especially the UFOs, show a sufficiently high mechanical power (at least ∼0.5 per cent of the bolometric luminosity) to provide a significant contribution to active galactic nuclei (AGN) feedback and thus to the evolution of the host galaxy. In this regard, we find possible evidence for the interaction of the AGN wind with the surrounding environment on large scales.

2012 - Cause and Effect of Feedback: Multiphase Gas in Cluster Cores Heated by AGN Jets [Articolo su rivista]
Gaspari, M; Ruszkowski, M; Sharma, P
abstract

Multiwavelength data indicate that the X-ray-emitting plasma in the cores of galaxy clusters is not cooling catastrophically. To a large extent, cooling is offset by heating due to active galactic nuclei (AGNs) via jets. The cool-core clusters, with cooler/denser plasmas, show multiphase gas and signs of some cooling in their cores. These observations suggest that the cool core is locally thermally unstable while maintaining global thermal equilibrium. Using high-resolution, three-dimensional simulations we study the formation of multiphase gas in cluster cores heated by collimated bipolar AGN jets. Our key conclusion is that spatially extended multiphase filaments form only when the instantaneous ratio of the thermal instability and free-fall timescales (t_TI/t_ff) falls below a critical threshold of ≈10. When this happens, dense cold gas decouples from the hot intracluster medium (ICM) phase and generates inhomogeneous and spatially extended Hα filaments. These cold gas clumps and filaments "rain" down onto the central regions of the core, forming a cold rotating torus and in part feeding the supermassive black hole. Consequently, the self-regulated feedback enhances AGN heating and the core returns to a higher entropy level with t_TI/t_ff &gt; 10. Eventually, the core reaches quasi-stable global thermal equilibrium, and cold filaments condense out of the hot ICM whenever t_TI/t_ff &lt;~ 10. This occurs despite the fact that the energy from AGN jets is supplied to the core in a highly anisotropic fashion. The effective spatial redistribution of heat is enabled in part by the turbulent motions in the wake of freely falling cold filaments. Increased AGN activity can locally reverse the cold gas flow, launching cold filamentary gas away from the cluster center. Our criterion for the condensation of spatially extended cold gas is in agreement with observations and previous idealized simulations.

2012 - Mechanical AGN feedback: controlling the thermodynamical evolution of elliptical galaxies [Articolo su rivista]
Gaspari, M; Brighenti, F; Temi, P
abstract

A fundamental gap in the current understanding of galaxies concerns the thermodynamical evolution of ordinary, baryonic matter. On the one hand, radiative emission drastically decreases the thermal energy content of the interstellar plasma (ISM), inducing a slow cooling flow towards the centre. On the other hand, the active galactic nucleus (AGN) struggles to prevent the runaway cooling catastrophe, injecting huge amount of energy into the ISM. The present study intends to investigate thoroughly the role of mechanical AGN feedback in (isolated or massive) elliptical galaxies, extending and completing the mass range of tested cosmic environments. Our previously successful feedback models in galaxy clusters and groups demonstrated that AGN outflows, self-regulated by cold gas accretion, are able to quench the cooling flow properly without destroying the cool core. Via three-dimensional hydrodynamic simulations (FLASH 3.3), also including stellar evolution, we show that massive mechanical AGN outflows can indeed solve the cooling-flow problem for the entire life of the galaxy, at the same time reproducing typical observational features and constraints such as buoyant underdense bubbles, elliptical shock cocoons, sonic ripples, dredge-up of metals, subsonic turbulence and extended filamentary or nuclear cold gas. In order to avoid overheating and totally emptying the isolated galaxy, the frequent mechanical AGN feedback should be less powerful and efficient (∊∼10^-4) compared with the heating required for more massive and bound ellipticals surrounded by the intragroup medium (∊∼10^-3).

2011 - AGN feedback in galaxy groups: the delicate touch of self-regulated outflows [Articolo su rivista]
Gaspari, Massimo; Brighenti, Fabrizio; D'Ercole, A.; Melioli, Claudio
abstract

Active galactic nucleus (AGN) heating, through massive subrelativistic outflows, might be the key to solve the long-lasting ‘cooling flow problem’ in cosmological systems. In a previous paper, we showed that cold accretion feedback and, to a lesser degree, Bondi self-regulated models are in fact able to quench cooling rates for several Gyr, at the same time preserving the main cool-core features, like observed density and temperature profiles. Is it true also for lighter systems, such as galaxy groups? The answer is globally yes, although with remarkable differences. Adopting a modified version of the adaptive mesh refinement code FLASH 3.2, we found that successful 3D simulations with cold and Bondi models are almost convergent in the galaxy group environment, with mechanical efficiencies in the range 5.e-4 - 1.e-3 and 5.e-2 - 1.e-1, respectively. The evolutionary storyline of galaxy groups is dominated by a quasi-continuous gentle injection with sub-Eddington outflows (with the mechanical power around 1.e44 erg/s, v circa 1.e4 km/s). The cold and hybrid accretion models present, in addition, very short quiescence periods, followed by moderate outbursts (10 times the previous phase), which generate a series of 10 - 20 kpc size cavities with high density contrast, temperatures similar to the ambient medium and cold rims. After shock heating, a phase of turbulence promotes gas mixing and diffusion of metals, which peak along the jet-axis (up to 40 kpc) during active phases. At this stage, the tunnel, produced by the enduring outflow (hard to detect in the mock X-ray surface brightness maps), is easily fragmented, producing tiny buoyant bubbles, typically a few kpc in size. In contrast to galaxy clusters, the AGN self-regulated feedback has to be persistent, with a ‘delicate touch’, rather than rare and explosive strokes. This evolutionary difference dictates that galaxy groups are not scaled-down versions of clusters: AGN heating might operate in different regimes, contributing to the self-similarity breaking observed.

2011 - The dance of heating and cooling in galaxy clusters: three-dimensional simulations of self-regulated active galactic nuclei outflows [Articolo su rivista]
Gaspari, Massimo; Melioli, C.; Brighenti, Fabrizio; D'Ercole, A.
abstract

It is now widely accepted that heating processes play a fundamental role in galaxy clusters, struggling in an intricate but fascinating ‘dance' with its antagonist, radiative cooling. Last-generation observations, especially X-ray, are giving us tiny hints about the notes of this endless ballet. Cavities, shocks, turbulence and wide absorption lines indicate that the central active nucleus is injecting a huge amount of energy in the intracluster medium. However, which is the real dominant engine of self-regulated heating? One of the models we propose is massive subrelativistic outflows, probably generated by a wind disc or just the result of the entrainment on kpc scale by the fast radio jet. Using a modified version of the adaptive mesh refinement code FLASH 3.2, we have explored several feedback mechanisms that self-regulate the mechanical power. Two are the best schemes that answer our primary question, that is, quenching cooling flow and at the same time preserving a cool core appearance for a long-term evolution (7 Gyr): one is more explosive (with efficiencies ˜ 5 × 10-3-10-2), triggered by central cooled gas, and the other is gentler, ignited by hot gas Bondi accretion (with ɛ= 0.1). These three-dimensional simulations show that the total energy injected is not the key aspect, but the results strongly depend on how energy is given to the intracluster medium. We follow the dynamics of the best models (temperature, density, surface brightness maps and profiles) and produce many observable predictions: buoyant bubbles, ripples, turbulence, iron abundance maps and hydrostatic equilibrium deviation. We present an in-depth discussion of the merits and flaws of all our models, with a critical eye towards observational concordance.

2009 - 3D Numerical Simulations of AGN Outflows in Clusters and Groups [Relazione in Atti di Convegno]
Gaspari, Massimo; Melioli, C.; Brighenti, Fabrizio; D'Ercole, A.
abstract

We compute 3D hydrodynamic models of jet outflows from the central AGN that carry mass as well as energy to the hot gas in galaxy clusters and groups. These flows have many attractive attributes for solving the cooling flow problem: why the hot gas temperature and density profiles resemble cooling flows but show no spectral evidence of cooling to low temperatures. Subrelativistic jets, described by a few parameters, are assumed to be activated when gas flows toward or cools near a central SMBH. As the jets proceed out from the center, they entrain more and more ambient gas. Using approximate models for a rich cluster (A1795), a poor cluster (2A 0336+096) and a group (NGC 5044), we show that mass-carrying jets with intermediate mechanical efficiencies (~10−3) can reduce for many Gyr the global cooling rate to or below the low values implied by X-ray spectra, while maintaining T and profiles similar to those observed, at least in clusters. Groups are much more sensitive to AGN heating and present extreme time variability in both profiles. Finally, the intermittency of the feedback generates multiple generations of X-ray cavities similar to those observed in Perseus cluster and elsewhere. Thus, we also study the formation of buoyant bubbles and weak shocks in the ICM, along with the injection of metals by SNIa and stellar winds.