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H1821+643 is the nearest quasar hosted by a galaxy cluster. The energy output by the quasar, in the form of intense radiation and radio jets, is captured by the surrounding hot atmosphere. Here, we present a new deep Chandra observation of H1821+643 and extract the hot gas properties into the region where Compton cooling by the quasar radiation is expected to dominate. Using detailed simulations to subtract the quasar light, we show that the soft-band surface brightness of the hot atmosphere increases rapidly by a factor of ∼30 within the central |$\sim\!{10}\ \rm kpc$|⁠. The gas temperature drops precipitously to |$\lt 0.4\rm \,\, keV$| and the density increases by over an order of magnitude. The remarkably low metallicity here is likely due to photoionization by the quasar emission. The variations in temperature and density are consistent with hydrostatic compression of the hot atmosphere. The extended soft-band peak cannot be explained by an undersubtraction of the quasar or scattered quasar light and is instead due to thermal interstellar medium. The radiative cooling time of the gas falls to only |$12\pm 1\rm \,\, Myr$|⁠ , below the free fall time, and we resolve the sonic radius. H1821+643 is therefore embedded in a cooling flow with a mass deposition rate of up to |$3000\ {\rm M}_{\odot}\,{\rm yr}^{-1}$|⁠. Multiwavelength observations probing the star-formation rate and cold gas mass are consistent with a cooling flow. We show that the cooling flow extends to much larger radii than can be explained by Compton cooling. Instead, the active galactic nucleus appears to be underheating the core of this cluster. [ABSTRACT FROM AUTHOR]

We present the deepest Chandra observation to date of the galaxy M84 in the Virgo Cluster, with over 840 ks of data provided by legacy observations and a recent 730 ks campaign. The increased signal-to-noise ratio allows us to study the origins of the accretion flow feeding the supermassive black hole in the centre of M84 from the kiloparsec scales of the X-ray halo to the Bondi radius, R B. Temperature, metallicity, and deprojected density profiles are obtained in four sectors about M84's active galactic nucleus (AGN), extending into the Bondi radius. Rather than being dictated by the potential of the black hole, the accretion flow is strongly influenced by the AGN's bipolar radio jets. Along the jet axis, the density profile is consistent with n e ∝  r −1; however, the profiles flatten perpendicular to the jet. Radio jets produce a significant asymmetry in the flow, violating a key assumption of Bondi accretion. Temperature in the inner kiloparsec is approximately constant, with only a slight increase from 0.6 to 0.7 keV approaching R B, and there is no evidence for a temperature rise imposed by the black hole. The Bondi accretion rate |$\dot{M}_{\rm B}$| exceeds the rate inferred from AGN luminosity and jet power by over four orders of magnitude. In sectors perpendicular to the jet, |$\dot{M}_{\rm B}$| measurements agree; however, the accretion rate is >4σ lower in the North sector along the jet, likely due to cavities in the X-ray gas. Our measurements provide unique insight into the fuelling of AGN responsible for radio mode feedback in galaxy clusters. [ABSTRACT FROM AUTHOR]

We present a new |$2\rm \, Ms$| Chandra observation of the cluster merger Abell 2146, which hosts two huge M ∼ 2 shock fronts each |${\sim }500\rm \, kpc$| across. For the first time, we resolve and measure the width of cluster merger shocks. The best-fitting width for the bow shock is |$17\pm 1\rm \, kpc$| and for the upstream shock is |$10.7\pm 0.3\rm \, kpc$|⁠. A narrow collisionless shock will appear broader in projection if its smooth shape is warped by local gas motions. We show that both shock widths are consistent with collisionless shocks blurred by local gas motions of |$290\pm 30{\rm \, km\rm \, s^{-1}}$|⁠. The upstream shock forms later on in the merger than the bow shock and is therefore expected to be significantly narrower. From the electron temperature profile behind the bow shock, we measure the time-scale for the electrons and ions to come back into thermal equilibrium. We rule out rapid thermal equilibration of the electrons with the shock-heated ions at the 6σ level. The observed temperature profile instead favours collisional equilibration. For these cluster merger shocks, which have low sonic Mach numbers and propagate through a high β plasma, we find no evidence for electron heating over that produced by adiabatic compression. Our findings are expected to be valid for collisionless shocks with similar parameters in other environments and support the existing picture from the solar wind and supernova remnants. The upstream shock is consistent with this result but has a more complex structure, including a |${\sim}2\rm \, keV$| increase in temperature |${\sim }50\rm \, kpc$| ahead of the shock. [ABSTRACT FROM AUTHOR]

We present a new $300\rm \, ks$ Chandra observation of M87 that limits pileup to only a few per cent of photon events and maps the hot gas properties closer to the nucleus than has previously been possible. Within the supermassive black hole's gravitational sphere of influence, the hot gas is multiphase and spans temperatures from 0.2 to $1\rm \, keV$. The radiative cooling time of the lowest temperature gas drops to only $0.1\hbox{--}0.5\rm \, Myr$ , which is comparable to its free fall time. Whilst the temperature structure is remarkably symmetric about the nucleus, the density gradient is steep in sectors to the N and S, with ρ ∝ r−1.5 ± 0.1, and significantly shallower along the jet axis to the E, where ρ ∝ r−0.93 ± 0.07. The density structure within the Bondi radius is therefore consistent with steady inflows perpendicular to the jet axis and an outflow directed E along the jet axis. By putting limits on the radial flow speed, we rule out Bondi accretion on the scale resolved at the Bondi radius. We show that deprojected spectra extracted within the Bondi radius can be equivalently fitted with only a single cooling flow model, where gas cools from $1.5\rm \, keV$ down below $0.1\rm \, keV$ at a rate of $0.03\rm \, M_{{\odot }}\rm \, yr^{-1}\,$. For the alternative multitemperature spectral fits, the emission measures for each temperature component are also consistent with a cooling flow model. The lowest temperature and most rapidly cooling gas in M87 is therefore located at the smallest radii at $\sim 100\rm \, pc$ and may form a mini cooling flow. If this cooling gas has some angular momentum, it will feed into the cold gas disc around the nucleus, which has a radius of $\sim 80\rm \, pc$ and therefore lies just inside the observed transition in the hot gas structure. [ABSTRACT FROM AUTHOR]

Chandra X-ray observations of the nearby brightest cluster galaxy M87 resolve the hot gas structure across the Bondi accretion radius of the central supermassive black hole (SMBH), a measurement possible in only a handful of systems but complicated by the bright nucleus and jet emission. By stacking only short frame-time observations to limit pileup, and after subtracting the nuclear point spread function, we analysed the X-ray gas properties within the Bondi radius at 0.12-0.22 kpc (1.5-2.8 arcsec), depending on the black hole mass. Within 2 kpc radius, we detect two significant temperature components, which are consistent with constant values of 2 and 0.9 keV down to 0.15 kpc radius. No evidence was found for the expected temperature increase within ~0.25 kpc due to the influence of the SMBH. Within the Bondi radius, the density profile is consistent with ρ ∝ r-1. The lack of a temperature increase inside the Bondi radius suggests that the hot gas structure is not dictated by the SMBH's potential and, together with the shallow density profile, shows that the classical Bondi rate may not reflect the accretion rate on to the SMBH. If this density profile extends in towards the SMBH, the mass accretion rate on to the SMBH could be at least two orders of magnitude less than the Bondi rate, which agrees with Faraday rotation measurements for M87. We discuss the evidence for outflow from the hot gas and the cold gas disc and for cold feedback, where gas cooling rapidly from the hot atmosphere could feed the cirumnuclear disc and fuel the SMBH. At 0.2 kpc radius, the cooler X-ray temperature component represents ~20 per cent of the total X-ray gas mass and, by losing angular momentum to the hot gas component, could provide a fuel source of cold clouds within the Bondi radius. [ABSTRACT FROM AUTHOR]

We present a new Chandra X-ray observation of the off-axis galaxy group merger RX J0751.3+5012. The hot atmospheres of the two colliding groups appear highly distorted by the merger. The images reveal arc-like cold fronts around each group core, produced by the motion through the ambient medium, and the first detection of a group merger shock front. We detect a clear density and temperature jump associated with a bow shock of Mach number M = 1.9 ± 0.4 ahead of the northern group. Using galaxy redshifts and the shock velocity of 1100 ± 300 km s−1, we estimate that the merger axis is only ∼10° from the plane of the sky. From the projected group separation of ∼90 kpc, this corresponds to a time since closest approach of ∼0.1 Gyr. The northern group hosts a dense, cool core with a ram pressure stripped tail of gas extending ∼100 kpc. The sheared sides of this tail appear distorted and broadened by Kelvin–Helmholtz instabilities. We use the presence of this substructure to place an upper limit on the magnetic field strength and, for Spitzer-like viscosity, show that the development of these structures is consistent with the critical perturbation length above which instabilities can grow in the intragroup medium. The northern group core also hosts a galaxy pair, UGC 4052, with a surrounding IR and near-UV ring ∼40 kpc in diameter. The ring may have been produced by tidal stripping of a smaller galaxy by UGC 4052 or it may be a collisional ring generated by a close encounter between the two large galaxies. [ABSTRACT FROM PUBLISHER]

We present a detailed study of the thermodynamic properties of the intracluster medium (ICM) of the only low-redshift galaxy cluster to contain a highly luminous quasar, H1821+643. The cluster is a highly massive, strong cool core cluster. We find that the ICM entropy around the quasar is significantly lower than that of other similarly massive, strong cool core clusters within the central 80 kpc, and that the entropy lies significantly below the extrapolated baseline entropy profile from hierarchical structure formation. By comparing the scaled temperature profile with those of other strong cool core clusters of similar total mass, we see that the entropy deficiency is due to the central temperature being significantly lower. This suggests that the presence of the quasar in the core of H1821+643 has had a dramatic cooling effect on the ICM around it. We find that, if the quasar was brighter in the past, Compton cooling by radiation from the quasar may have caused the low entropy and temperature levels in the ICM around the quasar. Curiously, the gradients of the steep central temperature and entropy decline are in reasonable agreement with the profiles expected for a constant pressure cooling flow. It is possible that the system has been locked into a Compton-cooled feedback cycle which prevents energy release from the black hole heating the gas sufficiently to switch it off, leading to the formation of a huge (∼3 × 1010 M⊙) supermassive black hole. [ABSTRACT FROM AUTHOR]

ABSTRACT We present a 100 ks Chandra observation studying the extended X-ray emission around the powerful z= 1.04 quasar PKS 1229−021. The diffuse cluster X-ray emission can be traced out to ∼15 arcsec (∼120 kpc) radius and there is a drop in the calculated hardness ratio inside the central 5 arcsec consistent with the presence of a cool core. Radio observations of the quasar show a strong core and a bright, one-sided jet leading to the south-west hotspot and a second hotspot visible on the counter-jet side. Although the wings of the quasar point spread function (PSF) provided a significant contribution to the total X-ray flux at all radii where the extended cluster emission was detected, we were able to accurately subtract the PSF emission using Chandra Ray Tracer and marx simulations. The resulting steep cluster surface brightness profile for PKS 1229−021 appears similar to the profile for the FR II (Fanaroff-Riley class II) radio galaxy 3C 444, which has a similarly rapid surface brightness drop caused by a powerful shock surrounding the radio lobes. Using a model surface brightness profile based on 3C 444, we estimated the total cluster luminosity for PKS 1229−021 to be . We discuss the difficulty of detecting cool-core clusters, which host bright X-ray sources, in high redshift surveys. [ABSTRACT FROM AUTHOR]

We present a new Chandra observation of the galaxy cluster Abell 2146 which has revealed a complex merging system with a gas structure that is remarkably similar to the Bullet cluster. The X-ray image and temperature map show a cool subcluster with a ram pressure stripped tail of gas just exiting the disrupted primary cluster. From the sharp jump in the temperature and density of the gas, we determine that the subcluster is preceded by a bow shock with a Mach number , corresponding to a velocity relative to the main cluster. We estimate that the subcluster passed through the primary core only ago. In addition, we observe a slower upstream shock propagating through the outer region of the primary cluster and calculate a Mach number . Based on the measured shock Mach numbers and the strength of the upstream shock, we argue that the mass ratio between the two merging clusters is between 3 and 4 to one. By comparing the Chandra observation with an archival Hubble Space Telescope observation, we find that a group of galaxies is located in front of the X-ray subcluster core but the brightest cluster galaxy is located immediately behind the X-ray peak. [ABSTRACT FROM AUTHOR]

We present a Chandra observation of the only low redshift, , galaxy cluster to contain a highly luminous radio-quiet quasar, H1821+643. By simulating the quasar point spread function, we subtract the quasar contribution from the cluster core and determine the physical properties of the cluster gas down to ) from the point source. The temperature of the cluster gas decreases from down to in the centre, with a short central radiative cooling time of , typical of a strong cool-core cluster. The X-ray morphology in the central shows extended spurs of emission from the core, a small radio cavity and a weak shock or cold front forming a semicircular edge at radius. The quasar bolometric luminosity was estimated to be , requiring a mass accretion rate of , which corresponds to half the Eddington accretion rate. We explore possible accretion mechanisms for this object and determine that Bondi accretion, when boosted by Compton cooling of the accretion material, could provide a significant source of the fuel for this outburst. We consider H1821+643 in the context of a unified active galactic nucleus (AGN) accretion model and, by comparing H1821+643 with a sample of galaxy clusters, we show that the quasar has not significantly affected the large-scale cluster gas properties. [ABSTRACT FROM AUTHOR]

We examine deep XMM–Newton Reflection Grating Spectrometer (RGS) spectra from the cores of three X-ray bright cool-core galaxy clusters, Abell 262, Abell 3581 and HCG 62. Each of the RGS spectra shows Fe xvii emission lines indicating the presence of gas around 0.5 keV. There is no evidence for O vii emission which would imply gas at still cooler temperatures. The range in detected gas temperature in these objects is a factor of 3.7, 5.6 and 2 for Abell 262, Abell 3581 and HCG 62, respectively. The coolest detected gas only has a volume filling fraction of 6 and 3 per cent for Abell 262 and Abell 3581, but is likely to be volume filling in HCG 62. Chandra spatially resolved spectroscopy confirms the low volume filling fractions of the cool gas in Abell 262 and Abell 3581, indicating this cool gas exists as cold blobs. Any volume heating mechanism aiming to prevent cooling would overheat the surroundings of the cool gas by a factor of 4. If the gas is radiatively cooling below 0.5 keV, it is cooling at a rate at least an order of magnitude below that at higher temperatures in Abell 262 and Abell 3581 and two orders of magnitude lower in HCG 62. The gas may be cooling non-radiatively through mixing in these cool blobs, where the energy released by cooling is emitted in the infrared. We find very good agreement between smooth particle inference modelling of the cluster and conventional spectral fitting. Comparing the temperature distribution from this analysis with that expected in a cooling flow, there appears to be an even larger break below 0.5 keV as compared with previous empirical descriptions of the deviations of cooling flow models. [ABSTRACT FROM AUTHOR]

Temperature, density and abundance profiles of the hot intracluster medium (ICM) are important diagnostics of the complex interactions of gravitational and feedback processes in the cores of galaxy clusters. Deprojection of X-ray data by methods such asprojct, which are model dependent, can produce large and unphysical oscillating temperature profiles. Here, we validate a deprojection routine, Direct Spectral Deprojection (dsdeproj), showing that it solves some of the issues inherent to model-dependent deprojection routines.dsdeproj is a model-independent approach, assuming only spherical symmetry, which subtracts projected spectra from each successive annulus to produce a set of deprojected spectra. [ABSTRACT FROM AUTHOR]