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We derive predictions from state-of-the-art cosmological galaxy simulations for the spatial distribution of the hot circumgalactic medium (CGM, [0.1–1] R 200c) through its emission lines in the X-ray soft band ([0.3–1.3] keV). In particular, we compare IllustrisTNG, EAGLE, and SIMBA and focus on galaxies with stellar mass |$10^{10-11.6}\, \rm {M}_{\odot }$| at z  = 0. The three simulation models return significantly different surface brightness radial profiles of prominent emission lines from ionized metals such as O  vii (f), O  viii , and Fe  xvii as a function of galaxy mass. Likewise, the three simulations predict varying azimuthal distributions of line emission with respect to the galactic stellar planes, with IllustrisTNG predicting the strongest angular modulation of CGM physical properties at radial range |${{\gtrsim}0.3{-}0.5\, R_{200c}}$|⁠. This anisotropic signal is more prominent for higher energy lines, where it can manifest as X-ray eROSITA-like bubbles. Despite different models of stellar and supermassive black hole (SMBH) feedback, the three simulations consistently predict a dichotomy between star-forming and quiescent galaxies at the Milky Way and Andromeda mass range, where the former are X-ray brighter than the latter. This is a signature of SMBH-driven outflows, which are responsible for quenching star formation. Finally, we explore the prospect of testing these predictions with a microcalorimeter-based X-ray mission concept with a large field of view. Such a mission would probe the extended hot CGM via soft X-ray line emission, determine the physical properties of the CGM, including temperature, from the measurement of line ratios, and provide critical constraints on the efficiency and impact of SMBH feedback on the CGM. [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 study the impact of resonantly scattered X-ray line emission on the observability of the hot circumgalactic medium (CGM) of galaxies. We apply a Monte Carlo radiative transfer post-processing analysis to the high-resolution TNG50 cosmological magnetohydrodynamical galaxy formation simulation. This allows us to model the resonant scattering of  O  vii (r) X-ray photons within the complex, multiphase, multiscale CGM. The resonant transition of the O  vii He-like triplet is one of the brightest, and most promising, X-ray emission lines for detecting the hot CGM and measuring its physical properties. We focus on galaxies with stellar masses |$10.0\lt \log {(M_\star /\rm {M_\odot })}\lt 11.0$| at z ≃ 0. After constructing a model for  O  vii (r) emission from the central galaxy, as well as from CGM gas, we forward model these intrinsic photons to derive observable surface brightness maps. We find that scattering significantly boosts the observable  O  vii (r) surface brightness of the extended and diffuse CGM. This enhancement can be large – an order of magnitude on average at a distance of 200 projected kpc for high-mass M ⋆ = 1010.7 M⊙ galaxies. The enhancement is larger for lower mass galaxies and can even reach a factor of 100, across the extended CGM. Galaxies with higher star formation rates, AGN luminosities, and central  O  vii (r) luminosities all have larger scattering enhancements, at fixed stellar mass. Our results suggest that next-generation X-ray spectroscopic missions, including XRISM, LEM, ATHENA, and HUBS – which aim to detect the hot CGM in emission – could specifically target haloes with significant enhancements due to resonant scattering. [ABSTRACT FROM AUTHOR]

We present a combined radio/X-ray study of six massive galaxy clusters, aimed at determining the potential for heating of the intra-cluster medium (ICM) by non-central radio galaxies. Since X-ray cavities associated with the radio lobes of non-central galaxies are generally not detectable, we use Giant Metrewave Radio Telescope 610 MHz observations to identify jet sources and estimate their size, and Chandra data to estimate the pressure of the surrounding ICM. In the radio, we detect 4.5 per cent of galaxies above the spectroscopic survey limit (M |$^{*}_{K}$|  + 2.0) of the Arizona cluster redshift survey (ACReS) that covers five of our six clusters. Approximately one-tenth of these are extended radio sources. Using star formation (SF) rates determined from mid-infrared data, we estimate the expected contribution to radio luminosity from the stellar population of each galaxy, and find that most of the unresolved or poorly resolved radio sources are likely SF dominated. The relatively low frequency and good spatial resolution of our radio data allows us to trace SF emission down to galaxies of stellar mass ∼10 9.5 M⊙. We estimate the enthalpy of the (AGN-dominated) jet/lobe and tailed sources, and place limits on the energy available from unresolved radio jets. We find jet powers in the range ∼1043 to 1046 erg s−1, comparable to those of brightest cluster galaxies. Our results suggest that while cluster-central sources are the dominant factor balancing ICM cooling over the long-term, non-central sources may have a significant impact, and that further investigation is possible and warranted. [ABSTRACT FROM AUTHOR]

We present Northern Extended Millimeter Array (NOEMA) CO(2–1) maps of the z  = 0.4418 cluster-central quasi-stellar object (QSO) IRAS 09104+4109, which trace ∼4.5 × 1010 M⊙ of molecular gas in and around the galaxy. As in many low-redshift cool-core clusters, the molecular gas is located in a series of clumps extending along the old radio jets and lobes. It has a relatively low velocity dispersion [336 |$^{+39}_{-35}$|  km s−1 full width at half-maximum (FWHM)] and shows no velocity gradients indicative of outflow or infall. Roughly half the gas is located in a central clump on the north-east side of the galaxy, overlapping a bright ionized gas filament and a spur of excess X-ray emission, suggesting that this is a location of rapid cooling. The molecular gas is unusually extended, out to ∼55 kpc radius, comparable to the scale of the filamentary nebula in the Perseus cluster, despite the much higher redshift of this system. The extent falls within the thermal instability radius of the intracluster medium (ICM), with t cool/ |$t_{\rm ff} \lt 25$| and t cool/ |$t_{\rm eddy} \sim 1$| within ∼70 kpc. Continuum measurements at 159.9 GHz from NOEMA and 850  |$\mu$| m from the James Clerk Maxwell Telescope (JCMT) Submillimeter Common-User Bolometer Array 2 (SCUBA-2) show excess far-infrared emission, which we interpret as free–free emission arising from the ongoing starburst. These observations suggest that ICM cooling is not strongly affected by the buried QSO, and that cooling from the ICM can build gas reservoirs sufficient to fuel quasar-mode activity and drive the reorientation of the central active galactic nuclei (AGN). [ABSTRACT FROM AUTHOR]

In the hierarchical scenario of structure formation, galaxy clusters are the ultimate virialized products in mass and time. Hot baryons in the intracluster medium (ICM) and cold baryons in galaxies inhabit a dark matter dominated halo. Internal processes, accretion, and mergers can perturb the equilibrium, which is established only at later times. However, the cosmic time when thermalization is effective is still to be assessed. Here, we show that massive clusters in the observed universe attained an advanced thermal equilibrium ∼1.8 Gyr ago, at redshift z  = 0.14 ± 0.06, when the universe was 11.7 ± 0.7 Gyr old. Hot gas is mostly thermalized after the time when cosmic densities of matter and dark energy match. We find in a statistically nearly complete and homogeneous sample of 120 clusters from the Planck Early Sunyaev-Zel'dovich (ESZ) sample that the kinetic energy traced by the galaxy velocity dispersion is a faithful probe of the gravitational energy since a look back time of at least ∼5.4 Gyr, whereas the efficiency of hot gas in converting kinetic to thermal energy, as measured through X-ray observations in the core-excised area within r 500, steadily increases with time. The evolution is detected at the ∼98 per cent probability level. Our results demonstrate that halo mass accretion history plays a larger role for cluster thermal equilibrium than radiative physics. The evolution of hot gas is strictly connected to the cosmic structure formation. [ABSTRACT FROM AUTHOR]

We present deep Chandra, XMM–Newton , Giant Metrewave Radio Telescope, and Hα observations of the group–group merger NGC 6338. X-ray imaging and spectral mapping show that as well as trailing tails of cool, enriched gas, the two cool cores are embedded in an extensive region of shock-heated gas with temperatures rising to ∼5 keV. The velocity distribution of the member galaxies show that the merger is occurring primarily along the line of sight, and we estimate that the collision has produced shocks of Mach number |$\mathcal {M}$|  = 2.3 or greater, making this one of the most violent mergers yet observed between galaxy groups. Both cool cores host potential AGN cavities and Hα nebulae, indicating rapid radiative cooling. In the southern cool core around NGC 6338, we find that the X-ray filaments associated with the Hα nebula have low entropies (<10 keV cm2) and short cooling times (∼200–300 Myr). In the northern core, we identify an Hα cloud associated with a bar of dense, cool X-ray gas offset from the dominant galaxy. We find no evidence of current jet activity in either core. We estimate the total mass of the system and find that the product of this group–group merger will likely be a galaxy cluster. [ABSTRACT FROM AUTHOR]

The mass of galaxy clusters can be inferred from the temperature of their X-ray-emitting gas, TX. Their masses may be underestimated if it is assumed that the gas is in hydrostatic equilibrium, by an amount bhyd ∼ (20 ± 10) per cent suggested by simulations. We have previously found consistency between a sample of observed Chandra X-ray masses and independent weak lensing measurements. Unfortunately, uncertainties in the instrumental calibration of Chandra and XMM–Newton observatories mean that they measure different temperatures for the same gas. In this paper, we translate that relative instrumental bias into mass bias, and infer that XMM–Newton masses of ∼1014 M⊙ ( ≳ 5 × 1014 M⊙) clusters are unbiased (∼35 per cent lower) compared to weak lensing masses. For massive clusters, Chandra's calibration may thus be more accurate. The opposite appears to be true at the low-mass end. We observe the mass bias to increase with cluster mass, but presence of Eddington bias precludes firm conclusions at this stage. Nevertheless, the systematic Chandra − XMM–Newton difference is important because Planck's detections of massive clusters via the Sunyaev–Zeldovich (SZ) effect are calibrated via XMM–Newton observations. The number of detected SZ clusters are inconsistent with Planck's cosmological measurements of the primary cosmic microwave background. Given the Planck cluster masses, if an (unlikely) uncorrected ∼20 per cent calibration bias existed, this tension would be eased, but not resolved. [ABSTRACT FROM PUBLISHER]