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Observationally, constraining the baryonic cycle within massive galaxies has proven to be quite difficult. In particular, the role of black hole feedback in regulating star formation, a key process in our theoretical understanding of galaxy formation, remains highly debated. We present here observational evidence showing that, at fixed stellar velocity dispersion, the temperature of the hot gas is higher for those galaxies hosting more massive black holes in their centres. Analysed in the context of well-established scaling relations, particularly the mass–size plane, the relation between the mass of the black hole and the temperature of the hot gas around massive galaxies provides further observational support to the idea that baryonic processes within massive galaxies are regulated by the combined effects of the galaxy halo virial temperature and black hole feedback, in agreement with the expectations from the EAGLE cosmological numerical simulation. [ABSTRACT FROM AUTHOR]

Quasar absorption-line studies in the ultraviolet (UV) can uniquely probe the nature of the multiphase cool–warm (104 < T < 106 K) gas in and around galaxy clusters, promising to provide unprecedented insights into (1) interactions between the circumgalactic medium (CGM) associated with infalling galaxies and the hot (T > 106 K) X-ray emitting intracluster medium (ICM), (2) the stripping of metal-rich gas from the CGM, and (3) a multiphase structure of the ICM with a wide range of temperatures and metallicities. In this work, we present results from a high-resolution simulation of an |$\sim 10^{14} \, \mathrm{M}_{\odot }$| galaxy cluster to study the physical properties and observable signatures of this cool–warm gas in galaxy clusters. We show that the ICM becomes increasingly multiphased at large radii, with the cool–warm gas becoming dominant in cluster outskirts. The diffuse cool–warm gas also exhibits a wider range of metallicity than the hot X-ray emitting gas. We make predictions for the covering fractions of key absorption-line tracers, both in the ICM and in the CGM of cluster galaxies, typically observed with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope (HST). We further extract synthetic spectra to demonstrate the feasibility of detecting and characterizing the thermal, kinematic, and chemical composition of the cool–warm gas using H  i , O  vi , and C  iv lines, and we predict an enhanced population of broad Ly α absorbers tracing the warm gas. Lastly, we discuss future prospects of probing the multiphase structure of the ICM beyond HST. [ABSTRACT FROM AUTHOR]

We analyse the intracluster medium (ICM) and circumgalactic medium (CGM) in seven X-ray-detected galaxy clusters using spectra of background quasi-stellar objects (QSOs) (HSTCOS/ STIS), optical spectroscopy of the cluster galaxies (MMT/Hectospec and SDSS), and X-ray imaging/spectroscopy (XMM-Newton and Chandra). First, we report a very low covering fraction of HI absorption in the CGM of these cluster galaxies, fc = 25+25 -15 per cent, to stringent detection limits (N(H I) <1013 cm-2). As field galaxies have an HI covering fraction of ~100 per cent at similar radii, the dearth of CGM HI in our data indicates that the cluster environment has effectively stripped or overionized the gaseous haloes of these cluster galaxies. Secondly, we assess the contribution of warm-hot (105-106 K) gas to the ICM as traced by OVI and broad Ly α (BLA) absorption. Despite the high signal-to-noise ratio of our data, we do not detect OVI in any cluster, and we only detect BLA features in the QSO spectrum probing one cluster. We estimate that the total column density of warm-hot gas along this line of sight totals to ~3 per cent of that contained in the hot T > 107 K X-ray emitting phase. Residing at high relative velocities, these features may trace pre-shocked material outside the cluster. Comparing gaseous galaxy haloes from the low-density 'field' to galaxy groups and high-density clusters, we find that the CGM is progressively depleted of HI with increasing environmental density, and the CGM is most severely transformed in galaxy clusters. This CGM transformation may play a key role in environmental galaxy quenching. [ABSTRACT FROM AUTHOR]

We have initiated a programme to study the physical/dynamical state of gas in galaxy clusters and the impact of the cluster environment on gaseous haloes of individual galaxies using X-ray imaging and UV absorption line spectroscopy of background QSOs. Here, we report results from the analysis Chandra and XMM–Newton archival data of five galaxy clusters with such QSOs, one of which has an archival UV spectrum. We characterize the gravitational masses and dynamical states, as well as the hot intracluster medium (ICM) properties of these clusters. Most clusters are dynamically disturbed clusters based on the X-ray morphology parameters, the X-ray temperature profiles, the large offset between X-ray peak, and brightest cluster galaxy (BCG). The baryon contents in the hot ICM and stars of these clusters within r 500are lower than the values expected from the gravitational masses, according to the standard cosmology. We also estimate column densities of the hot ICM along the sightlines towards the background QSOs as well as place upper limits on the warm-hot phase for the one sightline with existing UV observations. These column densities, compared with those of the warm and warm-hot ICM to be measured with UV absorption line spectroscopy, will enable us to probe the relationship among various gaseous phases and their connection to the heating/cooling and dynamical processes of the clusters. Furthermore, our analysis of the archival QSO spectrum probing one cluster underscores the need for high-quality, targeted UV observations to robustly constrain the 105–6K gas phase. [ABSTRACT FROM AUTHOR]

We present a study of metal-enriched halo gas traced by Mg  ii and C  iv absorption at z < 2 in the MUSE Analysis of Gas around Galaxies survey and the Quasar Sightline and Galaxy Evolution survey. Using these large and complete galaxy surveys in quasar fields, we study the dependence of the metal distribution on galaxy properties and overdensities, out to physical projected separations of 750 kpc. We find that the cool, low-ionization gas is significantly affected by the environment across the full redshift range probed, with ≈2–3 times more prevalent and stronger Mg  ii absorption in higher overdensity group environments and in regions with greater overall stellar mass and star formation rates. Complementary to these results, we have further investigated the more highly ionized gas as traced by C  iv absorption, and found that it is likely to be more extended than the Mg  ii gas, with ≈2 times higher covering fraction at a given distance. We find that the strength and covering fraction of C  iv absorption show less significant dependence on galaxy properties and environment than the Mg  ii absorption, but more massive and star-forming galaxies nevertheless also show ≈2 times higher incidence of C  iv absorption. The incidence of Mg  ii and C  iv absorption within the virial radius shows a tentative increase with redshift, being higher by a factor of ≈1.5 and ≈4, respectively, at z > 1. It is clear from our results that environmental processes have a significant impact on the distribution of metals around galaxies and need to be fully accounted for when analysing correlations between gaseous haloes and galaxy properties. [ABSTRACT FROM AUTHOR]

We outline theoretical predictions for extended emission from Mg  ii , tracing cool ∼104 K gas in the circumgalactic medium (CGM) of star-forming galaxies in the high-resolution TNG50 cosmological magnetohydrodynamical simulation. We synthesize surface brightness maps of this strong rest-frame ultraviolet metal emission doublet (λλ2796, 2803), adopting the assumption that the resonant scattering of Mg  ii can be neglected and connecting to recent and upcoming observations with the Keck/KCWI, VLT/MUSE, and BlueMUSE optical integral field unit spectrographs. Studying galaxies with stellar masses 7.5 < log (M ⋆/ M ⊙) < 11 at redshifts z = 0.3, 0.7, 1, and 2 we find that extended Mg  ii haloes in emission, similar to their Ly α counterparts, are ubiquitous across the galaxy population. Median surface brightness profiles exceed 10−19 erg s−1 cm−2 arcsec−2 in the central |$\sim \,$| 10 s of kpc, and total halo Mg  ii luminosity increases with mass for star-forming galaxies, reaching 1040 erg s−1 for M ⋆ ∼ 109.5 M⊙. Mg  ii halo sizes increase from a few kpc to ≳ 20 kpc at the highest masses, and sizes are larger for haloes in denser environments. Mg  ii haloes are highly structured, clumpy, and asymmetric, with isophotal axial ratio increasing with galaxy mass. Similarly, the amount and distribution of Mg  ii emission depends on the star formation activity of the central galaxy. Kinematically, inflowing versus outflowing gas dominates the Mg  ii luminosity at high and low galaxy masses, respectively, although the majority of Mg  ii halo emission at z ∼ 0.7 traces near-equilibrium fountain flows and gas with non-negligible rotational support, rather than rapidly outflowing galactic winds. [ABSTRACT FROM AUTHOR]

Quasar absorption systems encode a wealth of information about the abundances, ionization structure, and physical conditions in intergalactic and circumgalactic media. Simple (often single-phase) photoionization models are frequently used to decode such data. Using five discrete absorbers from the COS Absorption Survey of Baryon Harbors (CASBaH) that exhibit a wide range of detected ions (e.g. Mg  ii , S  ii – S  vi , O  ii – O  vi , Ne  viii), we show several examples where single-phase ionization models cannot reproduce the full set of measured column densities. To explore models that can self-consistently explain the measurements and kinematic alignment of disparate ions, we develop a Bayesian multiphase ionization modelling framework that characterizes discrete phases by their unique physical conditions and also investigates variations in the shape of the UV flux field, metallicity, and relative abundances. Our models require at least two (but favour three) distinct ionization phases ranging from T ≈ 104 K photoionized gas to warm-hot phases at T ≲ 105.8 K. For some ions, an apparently single absorption 'component' includes contributions from more than one phase, and up to 30 per cent of the H  i is not from the lowest ionization phase. If we assume that all of the phases are photoionized, we cannot find solutions in thermal pressure equilibrium. By introducing hotter, collisionally ionized phases, however, we can achieve balanced pressures. The best models indicate moderate metallicities, often with subsolar N/ α , and, in two cases, ionizing flux fields that are softer and brighter than the fiducial Haardt & Madau UV background model. [ABSTRACT FROM AUTHOR]

Davies et al. established that for L * galaxies the fraction of baryons in the circumgalactic medium (CGM) is inversely correlated with the mass of their central supermassive black holes (BHs) in the EAGLE hydrodynamic simulation. The interpretation is that, over time, a more massive BH has provided more energy to transport baryons beyond the virial radius, which additionally reduces gas accretion and star formation. We continue this research by focusing on the relationship between the (1) BH masses (M BH), (2) physical and observational properties of the CGM, and (3) galaxy colours for Milky Way-mass systems. The ratio of the cumulative BH feedback energy over the gaseous halo binding energy is a strong predictor of the CGM gas content, with BHs injecting significantly higher than the binding energy resulting in gas-poor haloes. Observable tracers of the CGM, including |$\rm {C\, \small{IV}}$|⁠ , |$\rm {O\, \small{VI}}$|⁠ , and |${\rm {H\, \small{I}}}$| absorption line measurements, are found to be effective tracers of the total z ∼ 0 CGM halo mass. We use high-cadence simulation outputs to demonstrate that BH feedback pushes baryons beyond the virial radius within 100 Myr time-scales, but that CGM metal tracers take longer (0.5–2.5 Gyr) to respond. Secular evolution of galaxies results in blue, star-forming or red, passive populations depending on the cumulative feedback from BHs. The reddest quartile of galaxies with M * = 1010.2−10.7 M⊙ (median u − r  = 2.28) has a CGM mass that is 2.5 times lower than the bluest quartile (u − r  = 1.59). We propose observing strategies to indirectly ascertain f CGM via metal lines around galaxies with measured M BH. We predict statistically detectable declines in |$\rm {C\, \small{IV}}$| and |$\rm {O\, \small{VI}}$| covering fractions with increasing M BH for central galaxies with M * = 1010.2−10.7M⊙. [ABSTRACT FROM AUTHOR]

We report a tentative detection of the circumgalactic medium (CGM) of Wolf–Lundmark–Melotte (WLM), an isolated, low-mass (log M */M⊙ ≈ 7.6), dwarf irregular galaxy in the Local Group (LG). We analyse an HST /COS archival spectrum of a quasar sightline (PHL2525), which is 45 kpc (0.5 virial radius) from WLM and close to the Magellanic Stream (MS). Along this sightline, two ion absorbers are detected in Si  ii , Si  iii , Si  iv , C  ii , and C  iv at velocities of ∼−220 km s−1 (Component v-220) and ∼−150 km s−1 (Component v-150). To identify their origins, we study the position–velocity alignment of the components with WLM and the nearby MS. Near the magellanic longitude of PHL2525, the MS-related neutral and ionized gas moves at ≲−190 km s−1, suggesting an MS origin for Component v-220, but not for Component v-150. Because PHL2525 passes near WLM and Component v-150 is close to WLM's systemic velocity (∼−132 km s−1), it is likely that Component v-150 arises from the galaxy's CGM. This results in a total Si mass in WLM's CGM of |$M_{\rm Si}^{\rm CGM}\sim (0.2-1.0)\times 10^5~\mathrm{M}_\odot$| using assumption from other COS dwarf studies. Comparing |$M_{\rm Si}^{\rm CGM}$| to the total Si mass synthesized in WLM over its lifetime (∼1.3 × 105 M⊙), we find ∼3 per cent is locked in stars, ∼6 per cent in the ISM, ∼15–77 per cent in the CGM, and the rest (∼14–76 per cent) is likely lost beyond the virial radius. Our finding resonates with other COS dwarf galaxy studies and theoretical predictions that low-mass galaxies can easily lose metals into their CGM due to stellar feedback and shallow gravitational potential. [ABSTRACT FROM AUTHOR]

We present new measurements of the flux power-spectrum P (k) of the z < 0.5 H   i Lyman-α Forest spanning scales |$k \sim 0.001\!-\!0.1\, \mathrm{s \, km}^{-1}$|⁠. These results were derived from 65 far-ultraviolet quasar spectra (resolution |$R \sim 18\, 000$|⁠) observed with the Cosmic Origin Spectrograph (COS) on board the Hubble Space Telescope. The analysis required careful masking of all contaminating, coincident absorption from H   i and metal–line transitions of the Galactic interstellar medium and intervening absorbers as well as proper treatment of the complex COS line-spread function. From the P (k) measurements, we estimate the H   i photoionization rate (⁠|$\Gamma _{\rm H\,{\small I}}$|⁠) in the z < 0.5 intergalactic medium. Our results confirm most of the previous |$\Gamma _{\rm H\,{\small I}}$| estimates. We conclude that previous concerns of a photon underproduction crisis are now resolved by demonstrating that the measured |$\Gamma _{\rm H\,{\small I}}$| can be accounted for by ultraviolet emission from quasars alone. In a companion paper, we will present constraints on the thermal state of the z < 0.5 intergalactic medium from the P (k) measurements presented here. [ABSTRACT FROM AUTHOR]