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To understand the formation and growth of supermassive black holes (SMBHs) and their coevolution with host galaxies, it is essential to know the impact of environment on the activity of active galactic nuclei (AGNs). We present new Chandra X-ray observations of nuclear emission from member galaxies in the Antlia cluster, the nearest non-cool core and the nearest merging galaxy cluster, residing at D = 35.2 Mpc. Its inner region, centered on two dominant galaxies NGC 3268 and NGC 3258, has been mapped with three deep Chandra ACIS-I pointings. Nuclear X-ray sources are detected in 7/84 (8.3%) early-type galaxies (ETG) and 2/8 (25%) late-type galaxies with a median detection limit of 8 × 1038 erg s−1. All nuclear X-ray sources but one have a corresponding radio continuum source detected by MeerKAT at the L band. Nuclear X-ray sources detected in early-type galaxies are considered the genuine X-ray counterpart of low-luminosity AGN. When restricted to a detection limit of log (L X / erg s − 1) ≥ 38.9 and a stellar mass of 10 ≤ log (M ⋆ / M ⊙) < 11.6 , six of 11 ETGs are found to contain an X-ray AGN in Antlia, exceeding the AGN occupation fraction of 7/39 (18.0%) and 2/12 (16.7%) in the more relaxed, cool core clusters, Virgo and Fornax, respectively, and rivaling that of the AMUSE-Field ETG of 27/49 (55.1%). Furthermore, more than half of the X-ray AGN in Antlia is hosted by its younger subcluster, centered on NGC 3258. We believe that this is because SMBH activity is enhanced in a dynamically young cluster compared to relatively relaxed clusters. [ABSTRACT FROM AUTHOR]

When subhaloes infall into galaxy clusters, their gas content is ram pressure stripped by the intracluster medium (ICM) and may turn into cometary tails. We report the discovery of two spectacular X-ray double tails in a single galaxy cluster, Z8338, revealed by 70 ks Chandra observations. The brighter one, with an X-ray bolometric luminosity of 3.9 × 1042 erg s−1, is a detached tail stripped from the host halo and extended at least 250 kpc in projection. The head of the detached tail is a cool core with the front tip of the cold front ∼30 kpc away from the nucleus of its former host galaxy. The cooling time of the detached cool core is ∼0.3 Gyr. For the detached gas, the gravity of the once-associated dark matter halo further enhances the Rayleigh–Taylor instability. From its survival, we find that a magnetic field of a few μG is required to suppress the hydrodynamic instability. The X-ray temperature in the tail increases from 0.9 keV at the front tip to 1.6 keV in the wake region, which suggests the turbulent mixing with the hotter ICM. The fainter double X-ray tail, with a total X-ray luminosity of 2.7 × 1042 erg s−1, appears to stem from the cool core of a subcluster in Z8338, and likely was formed during the ongoing merger. This example suggests that X-ray cool cores can be displaced and eventually destroyed by mergers, while the displaced cool cores can survive for some extended period of time. [ABSTRACT FROM AUTHOR]

We present XSHOOTER observations with previous ALMA, MUSE, and HST observations to study the nature of radio jet triggered star formation and the interaction of radio jets with the interstellar medium in the brightest cluster galaxy (BCG) in the Abell 1795 cluster. Using HST UV data, we determined an ongoing star formation rate of 9.3 M⊙ yr−1. The star formation follows the global Kennicutt–Schmidt law; however, it has a low efficiency compared to circumnuclear starbursts in nearby galaxies with an average depletion time of ∼1 Gyr. The star formation and molecular gas are offset by ∼1 kpc indicating that stars have decoupled from the gas. We detected an arc of high linewidth in ionized gas where electron densities are elevated by a factor of ∼4 suggesting a shock front driven by radio jets or peculiar motion of the BCG. An analysis of nebular emission line flux ratios suggests that the gas is predominantly ionized by star formation with a small contribution from shocks. We also calculated the velocity structure function (VSF) of the ionized and molecular gases using velocity maps to characterize turbulent motion in the gas. The ionized gas VSF suggests that the radio jets are driving supersonic turbulence in the gas. Thus radio jets cannot only heat the atmosphere on large scales and may quench star formation on longer time-scales while triggering star formation in positive feedback on short time-scales of a few million years. [ABSTRACT FROM AUTHOR]

Molecular gas flows are analysed in 14 cluster galaxies (BCGs) centred in cooling hot atmospheres. The BCGs contain |$10^{9}\!-\!10^{11}~\rm M_\odot$| of molecular gas, much of which is being moved by radio jets and lobes. The molecular flows and radio jet powers are compared to molecular outflows in 45 active galaxies within z < 0.2. We seek to understand the relative efficacy of radio, quasar, and starburst feedback over a range of active galaxy types. Molecular flows powered by radio feedback in BCGs are ∼10–1000 times larger in extent compared to contemporary galaxies hosting quasar nuclei and starbursts. Radio feedback yields lower flow velocities but higher momenta compared to quasar nuclei, as the molecular gas flows in BCGs are usually ∼10–100 times more massive. The product of the molecular gas mass and lifting altitude divided by the AGN or starburst power – a parameter referred to as the lifting factor – exceeds starbursts and quasar nuclei by 2–3 orders of magnitude, respectively. When active, radio feedback is generally more effective at lifting gas in galaxies compared to quasars and starburst winds. The kinetic energy flux of molecular clouds generally lies below and often substantially below a few per cent of the driving power. We find tentatively that star formation is suppressed in BCGs relative to other active galaxies, perhaps because these systems rarely form molecular discs that are more impervious to feedback and are better able to promote star formation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We present results from a deep (174 ks) Chandra observation of the FR-II radio galaxy 3C 220.1, the central brightest cluster galaxy (BCG) of a kT ∼ 4 keV cluster at z  = 0.61. The temperature of the hot cluster medium drops from ∼5.9 to ∼3.9 keV at ∼35 kpc radius, while the temperature at smaller radii may be substantially lower. The central active galactic nucleus (AGN) outshines the whole cluster in X-rays, with a bolometric luminosity of 2.0 × 1046 erg s−1 (∼10 per cent of the Eddington rate). The system shows a pair of potential X-ray cavities ∼35 kpc east and west of the nucleus. The cavity power is estimated within the range of 1.0 × 1044 and 1.7 × 1045 erg s−1, from different methods. The X-ray enhancements in the radio lobes could be due to inverse Compton emission, with a total 2–10 keV luminosity of ∼8.0 × 1042 erg s−1. We compare 3C 220.1 with other cluster BCGs, including Cygnus A, as there are few BCGs in rich clusters hosting an FR-II galaxy. We also summarize the jet power of FR-II galaxies from different methods. The comparison suggests that the cavity power of FR-II galaxies likely underestimates the jet power. The properties of 3C 220.1 suggest that it is at the transition stage from quasar-mode feedback to radio-mode feedback. [ABSTRACT FROM AUTHOR]

We present a 250 ks Chandra observation of the cluster merger A2034 with the aim of understanding the nature of a sharp edge previously characterized as a cold front. The new data reveal that the edge is coherent over a larger opening angle and is significantly more bow-shock-shaped than previously thought. Within ∼27° about the axis of symmetry of the edge, the density, temperature, and pressure drop abruptly by factors of , , and , respectively. This is inconsistent with the pressure equilibrium expected of a cold front and we conclude that the edge is a shock front. We measure a Mach number and corresponding shock velocity vshock ≃ 2057 km s–1. Using spectra collected at the MMT with the Hectospec multi-object spectrograph, we identify 328 spectroscopically confirmed cluster members. Significantly, we find a local peak in the projected galaxy density associated with a bright cluster galaxy that is located just ahead of the nose of the shock. The data are consistent with a merger viewed within ∼23° of the plane of the sky. The merging subclusters are now moving apart along a north-south axis approximately 0.3 Gyr after a small impact parameter core passage. The gas core of the secondary subcluster, which was driving the shock, appears to have been disrupted by the merger. Without a driving “piston,” we speculate that the shock is dying. Finally, we propose that the diffuse radio emission near the shock is due to the revival of pre-existing radio plasma that has been overrun by the shock. [ABSTRACT FROM AUTHOR]

We present new Chandra observations of A2199 that show evidence of gas sloshing due to a minor merger, as well as impacts of the radio source, 3C 338, hosted by the central galaxy, NGC 6166, on the intracluster gas. The new data are consistent with previous evidence of a Mach ≃ 1.46 shock 100″ from the cluster center, although there is still no convincing evidence for the expected temperature jump. Other interpretations of this feature are possible, but none is fully satisfactory. Large scale asymmetries, including enhanced X-ray emission 200″ southwest of the cluster center and a plume of low entropy, enriched gas reaching 50″ to the north of the center, are signatures of gas sloshing induced by core passage of a merging subcluster about 400 Myr ago. An association between the unusual radio ridge and low entropy gas are consistent with this feature being the remnant of a former radio jet that was swept away from the active galactic nucleus by gas sloshing. A large discrepancy between the energy required to produce the 100″ shock and the enthalpy of the outer radio lobes of 3C 338 suggests that the lobes were formed by a more recent, less powerful radio outburst. The lack of evidence for shocks in the central 10″ indicates that the power of the jet now is some two orders of magnitude smaller than when the 100″ shock was formed. [ABSTRACT FROM AUTHOR]

Structure formation models predict that clusters of galaxies contain numerous massive subhalos. The gravity of a subhalo in a cluster compresses the surrounding intracluster gas and enhances its X-ray emission. We present a simple model, which treats subhalos as slow moving and gasless, for computing this effect. Recent weak lensing measurements by Okabe et al. have determined masses of ~1013M☉ for three mass concentrations projected within 300 kpc of the center of the Coma Cluster, two of which are centered on the giant elliptical galaxies NGC 4889 and NGC 4874. Adopting a smooth spheroidal β-model for the gas distribution in the unperturbed cluster, we model the effect of these subhalos on the X-ray morphology of the Coma Cluster, comparing our results to Chandra and XMM-Newton X-ray data. The agreement between the models and the X-ray morphology of the central Coma Cluster is striking. With subhalo parameters from the lensing measurements, the distances of the three subhalos from the Coma Cluster midplane along our line of sight are all tightly constrained. Using the model to fit the subhalo masses for NGC 4889 and NGC 4874 gives 9.1 × 1012M☉ and 7.6 × 1012M☉, respectively, in good agreement with the lensing masses. These results lend strong support to the argument that NGC 4889 and NGC 4874 are each associated with a subhalo that resides near the center of the Coma Cluster. In addition to constraining the masses and 3-d location of subhalos, the X-ray data show promise as a means of probing the structure of central subhalos. [ABSTRACT FROM AUTHOR]

We present evidence for the existence of substructure in the "relaxed appearing" cold front clusters Abell 2142 and RXJ 1720.1+2638. The detection of these substructures was made possible by comprehensive multi-object optical spectroscopy obtained with the Hectospec and DEep Imaging Multi-Object Spectrograph instruments on the 6.5 m MMT and 10 m Keck II telescope, respectively. These observations produced 956 and 400 spectroscopically confirmed cluster members within a projected radius of 3 Mpc from the centers of A2142 and RXJ 1720.1+2638, respectively. The substructure manifests itself as local peaks in the spatial distribution of member galaxies and also as regions of localized velocity substructure. For both Abell 2142 and RXJ 1720.1+2638, we identify group-scale substructures which, when considering the morphology of the cold fronts and the time since pericentric passage of a perturber estimated from the cold front radii, could plausibly have perturbed the cluster cores and generated the cold fronts observed in Chandra images. The results presented here are consistent with cold fronts being the result of merger activity and with cold fronts in relaxed appearing clusters being due to minor merger activity. [ABSTRACT FROM AUTHOR]

We use deep wide-field V-band imaging obtained with the Wide Field Camera at the prime focus of the Issac Newton Telescope to study the spatial and luminosity distribution of galaxies in three low redshift (0.04 < z < 0.2) clusters: Abell 119, Abell 2443 and Abell 2218. The absolute magnitude limits probed in these clusters are , respectively. The galaxy population, at all luminosities, along the line-of-sight to the clusters can be described by the linear combination of a King profile and a constant surface density of field galaxies. We find that, for these three clusters, the core radius is invariant with intrinsic luminosity of the cluster population to the above limits and thus there is no evidence for luminosity segregation in these clusters. The exception is the brightest galaxies in A2218 which exhibit a more compact spatial distribution. We find that the total projected luminosity distribution (within of the cluster centre) can be well represented by a single Schechter function with moderately flat faint-end slopes: (A119), (A2443) and (A2218). We perform a geometric deprojection of the cluster galaxy population and confirm that no ‘statistically significant’ evidence of a change in the shape of the luminosity distribution with cluster-centric radius exists. Again, the exception being A2218 which exhibits a core region with a flatter faint-end slope. [ABSTRACT FROM AUTHOR]

We present results from a deep photometric study of the rich galaxy cluster Abell 2218 (z = 0.18) based on archival Hubble Space Telescope WFPC2 F606W images. These have been used to derive the luminosity function to extremely faint limits (MF606W &assymp; ∼13.2 mag, μ0 &assymp; 24.7 mag arcsec-2) over a wide field of view (1.3 h-2 Mpc²). We find the faint-end slope of the luminosity function to vary with environment within the cluster, going from α = −1.23 ± 0.13 within the projected central core of the cluster (100 < r < 300 h-1 kpc) tocα = −1.49 ± 0.06 outside this radius (300 < r < 750 h-1 kpc). We infer that the core is ‘dwarf depleted’, and further quantify this by studying the ratio of ‘dwarf’ to ‘giant’ galaxies and its dependency as a function of clustercentric radius and local galaxy density. We find that this ratio varies strongly with both quantities, and that the dwarf galaxy population in A2218 has a more extended distribution than the giant galaxy population. [ABSTRACT FROM AUTHOR]

We present a study of the cavity system in the galaxy cluster RBS 797 based on Chandra and Very Large Array (VLA) data. RBS 797 (z = 0.35) is one of the most distant galaxy clusters in which two pronounced X-ray cavities have been discovered. The Chandra data confirm the presence of a cool core and indicate a higher metallicity along the cavity directions. This is likely due to the active galactic nucleus outburst, which lifts cool metal-rich gas from the center along the cavities, as seen in other systems. We find indications that the cavities are hotter than the surrounding gas. Moreover, the new Chandra images show bright rims contrasting with the deep, X-ray deficient cavities. The likely cause is that the expanding 1.4 GHz radio lobes have displaced the gas, compressing it into a shell that appears as bright cool arms. Finally, we show that the large-scale radio emission detected with our VLA observations may be classified as a radio mini-halo, powered by the cooling flow, as it nicely follows the trend Pradio versus PCF predicted by the reacceleration model. [ABSTRACT FROM AUTHOR]

We present an analysis of the structures and dynamics of the merging cluster Abell 1201, which has two sloshing cold fronts around a cooling core, and an offset gas core approximately 500 kpc northwest of the center. New Chandra and XMM-Newton data reveal a region of enhanced brightness east of the offset core, with breaks in surface brightness along its boundary to the north and east. This is interpreted as a tail of gas stripped from the offset core. Gas in the offset core and the tail is distinguished from other gas at the same distance from the cluster center chiefly by having higher density, hence lower entropy. In addition, the offset core shows marginally lower temperature and metallicity than the surrounding area. The metallicity in the cool core is high and there is an abrupt drop in metallicity across the southern cold front. We interpret the observed properties of the system, including the placement of the cold fronts, the offset core, and its tail in terms of a simple merger scenario. The offset core is the remnant of a merging subcluster, which first passed pericenter southeast of the center of the primary cluster and is now close to its second pericenter passage, moving at ≃ 1000 km s–1. Sloshing excited by the merger gave rise to the two cold fronts and the disposition of the cold fronts reveals that we view the merger from close to the plane of the orbit of the offset core. [ABSTRACT FROM AUTHOR]