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The interaction between supermassive black hole (SMBH) feedback and the circumgalactic medium (CGM) continues to be an open question in galaxy evolution. In our study, we use smoothed particle hydrodynamics simulations to explore the impact of SMBH feedback on galactic metal retention and the motion of metals and gas into and through the CGM of L* galaxies. We examine 140 galaxies from the 25 Mpc cosmological volume Romulus25, with stellar masses between log(M */ M ⊙) = 9.5–11.5. We measure the fraction of metals remaining in the interstellar medium (ISM) and CGM of each galaxy and calculate the expected mass of each SMBH based on the M BH– σ relation (Kormendy & Ho 2013). The deviation of each SMBH from its expected mass, Δ M BH, is compared to the potential of its host via σ. We find that SMBHs with accreted mass above M BH– σ are more effective at removing metals from the ISM than undermassive SMBHs in star-forming galaxies. Overall, overmassive SMBHs suppress the total star formation of their host galaxies and more effectively move metals from the ISM into the CGM. However, we see little to no evacuation of gas from the CGM out of their halos, in contrast with other simulations. Finally, we predict that C iv column densities in the CGM of L* galaxies are unlikely to depend on host galaxy SMBH mass. Our results show that the scatter in the low-mass end of the M BH– σ relation may indicate how effective an SMBH is in the local redistribution of mass in its host galaxy. [ABSTRACT FROM AUTHOR]

We present an analytic model for the cool, T ∼ 104 K, circumgalactic medium (CGM), describing the gas distribution, and thermal and ionization states. Our model assumes (total) pressure equilibrium with the ambient warm/hot CGM, photoionization by the metagalactic radiation, and allows for nonthermal pressure support, parameterized by the ratio of thermal pressures, η = P hot,th/ P cool,th. We apply the model to the COS-Halos measurements and find that a nominal model with η = 3, gas distribution out to r ≈ 0.6 R vir, and M cool = 3 × 109 M ⊙, corresponding to a volume filling fraction of f V,cool ≈ 1%, reproduces the H i and low/intermediate metal ions (C ii, C iii, Si ii, Si iii, and Mg ii) mean column densities. Variation of ±0.5 dex in η or M cool encompasses ∼2/3 of the scatter between objects. Our nominal model underproduces the measured C iv and Si iv columns, and these can be reproduced with (i) a cool phase with M cool ∼ 1010 M ⊙ and η ≈ 5, or (ii) cooling or mixing gas at intermediate temperatures, with M ∼ 1.5 × 1010 M ⊙ and occupying ∼1/2 of the total CGM volume. For cool gas with f V,cool ≈ 1%, we estimate an upper limit on the cloud sizes, R cl ≲ 0.5 kpc. Our results suggest that for the average galaxy CGM, the mass and nonthermal support in the cool phase are lower than previously estimated, and extreme scenarios are not necessary. We estimate the rates of cool gas depletion and replenishment, and find accretion onto the galaxy can be offset, allowing M ̇ cool ≈ 0 over long timescales. [ABSTRACT FROM AUTHOR]

This study addresses how the incidence rate of strong O vi absorbers in a galaxy's circumgalactic medium (CGM) depends on galaxy mass and, independently, on the amount of star formation in the galaxy. We use Hubble Space Telescope/Cosmic Origins Spectrograph absorption spectroscopy of quasars to measure O vi absorption within 400 projected kpc and 300 km s−1 of 52 galaxies with M * ∼ 3 × 1010 M ⊙. The galaxies have redshifts 0.12 < z < 0.6, stellar masses 1010.1 M ⊙ < M * < 1010.9 M ⊙, and spectroscopic classifications as star-forming or passive. We compare the incidence rates of high column density O vi absorption (N O VI ≥ 1014.3 cm−2) near star-forming and passive galaxies in two narrow ranges of stellar mass and, separately, in a matched range of halo mass. In all three mass ranges, the O vi covering fraction within 150 kpc is higher around star-forming galaxies than around passive galaxies with greater than 3 σ -equivalent statistical significance. On average, the CGM of star-forming galaxies with M * ∼ 3 × 1010 M ⊙ contains more O vi than the CGM of passive galaxies with the same mass. This difference is evidence for a CGM transformation that happens together with galaxy quenching and is not driven primarily by halo mass. [ABSTRACT FROM AUTHOR]

We use hydrodynamical simulations of two Milky Wayâ€"mass galaxies to demonstrate the impact of cosmic-ray pressure on the kinematics of cool and warm circumgalactic gas. Consistent with previous studies, we find that cosmic-ray pressure can dominate over thermal pressure in the inner 50 kpc of the circumgalactic medium (CGM), creating an overall cooler CGM than that of similar galaxy simulations run without cosmic rays. We generate synthetic sight lines of the simulated galaxies’ CGM and use Voigt profile-fitting methods to extract ion column densities, Doppler- b parameters, and velocity centroids of individual absorbers. We directly compare these synthetic spectral line fits with HST/COS CGM absorption-line data analyses, which tend to show that metallic species with a wide range of ionization potential energies are often kinematically aligned. Compared to the Milky Way simulation run without cosmic rays, the presence of cosmic-ray pressure in the inner CGM creates narrower O vi absorption features and broader Si iii absorption features, a quality that is more consistent with observational data. Additionally, because the cool gas is buoyant due to nonthermal cosmic-ray pressure support, the velocity centroids of both cool and warm gas tend to align in the simulated Milky Way with feedback from cosmic rays. Our study demonstrates that detailed, direct comparisons between simulations and observations, focused on gas kinematics, have the potential to reveal the dominant physical mechanisms that shape the CGM. [ABSTRACT FROM AUTHOR]

We combine 126 new galaxy-O vi absorber pairs from the CGM2 survey with 123 pairs drawn from the literature to examine the simultaneous dependence of the column density of O vi absorbers (N O VI) on galaxy stellar mass, star-formation rate, and impact parameter. The combined sample consists of 249 galaxy-O vi absorber pairs covering z = 0â€"0.6, with host galaxy stellar masses M * = 107.8â€"1011.2 M ⊙ and galaxy-absorber impact parameters R ⊥ = 0â€"400 proper kiloparsecs. In this work, we focus on the variation of N O VI with galaxy mass and impact parameter among the star-forming galaxies in the sample. We find that the average N O VI within one virial radius of a star-forming galaxy is greatest for star-forming galaxies with M * = 109.2â€"1010 M ⊙. Star-forming galaxies with M * between 108 and 1011.2 M ⊙ can explain most O vi systems with column densities greater than 1013.5 cmâˆ'2. Sixty percent of the O vi mass associated with a star-forming galaxy is found within one virial radius, and 35% is found between one and two virial radii. In general, we find that some departure from hydrostatic equilibrium in the CGM is necessary to reproduce the observed O vi amount, galaxy mass dependence, and extent. Our measurements serve as a test set for CGM models over a broad range of host galaxy masses. [ABSTRACT FROM AUTHOR]

We present initial results from the Cosmic Origins Spectrograph (COS) and Gemini Mapping the Circumgalactic Medium (CGMCGM ≡ CGM2) survey. The CGM2 survey consists of 1689 galaxies, all with high-quality Gemini-GMOS spectra, within 1 Mpc of 22 z ≲ 1 quasars, all with a signal-to-noise ratio of ∼10 Hubble Space Telescope/COS G130M+G160M spectra. For 572 of these galaxies with stellar masses 107 M⊙ < M⋆ < 1011 M⊙ and z ≲ 0.5, we show that the H i covering fraction above a threshold of NHI > 1014cm−2 is ≳0.5 within 1.5 virial radii (Rvir ∼ R200m). We examine the H i kinematics and find that the majority of absorption lies within ±250 km s−1 of the galaxy systemic velocity. We examine H i covering fractions over a range of impact parameters to infer a characteristic size of the CGM, , as a function of galaxy mass. is the impact parameter at which the probability of observing an absorber with NHI >1014 cm−2 is >50%. In this framework, the radial extent of the CGM of M⋆ > 109.9 M⊙ galaxies is kpc or. Intermediate-mass galaxies with 109.2 < M⋆/M⊙ < 109.9 have an extent of kpc or. Low-mass galaxies, M⋆ < 109.2 M⊙, show a smaller physical scale of kpc and extend to. Our analysis suggests that using Rvir as a proxy for the characteristic radius of the CGM likely underestimates its extent. [ABSTRACT FROM AUTHOR]

From our position embedded within the Milky Way's interstellar medium, we have limited ability to detect gas at low relative velocities in the extended Galactic halo because those spectral lines are blended with much stronger signals from dense foreground gas. As a result, the content of the Milky Way's circumgalactic medium (CGM) is poorly constrained at ∣vLSR∣ ≲150 km s−1. To overcome this complication, the QuaStar survey applies a spectral differencing technique using paired quasar−star sight lines to measure the obscured content of the Milky Way's CGM for the first time. We present measurements of the C iv doublet (λλ1548, 1550), a rest-frame UV metal line transition, detected in Hubble Space Telescope/Cosmic Origins Spectrograph spectra of 30 halo-star/quasar pairs evenly distributed across the sky at Galactic latitudes ∣b∣ > 30°. The 30 halo stars have well-constrained distances (d ≈ 5–14 kpc) and are paired with quasars separated by <2.°8. We argue that the difference in absorption between the quasar and stellar sight lines originates primarily in the Milky Way's extended CGM beyond ∼10 kpc. For the Milky Way's extended, low-velocity CGM (∣v∣ <150 km s−1), we place an upper limit on the mean C iv column density of < 13.39 and find a covering fraction of 20% [6/30], a value significantly lower than the covering fraction for star-forming galaxies at low redshift. Our results suggest either that the bulk of Milky Way's C iv -traced CGM lies at low Galactic latitudes or that the Milky Way's CGM is lacking in warm, ionized material compared to low-redshift (z < 0.1) star-forming galaxy halos. [ABSTRACT FROM AUTHOR]

We analyse the low-redshift (z≈0.2) circumgalactic medium (CGM) by comparing absorption-line data from the COS-Halos survey to absorption around a matched galaxy sample from two cosmological hydrodynamic simulations. The models include different prescriptions for galactic outflows, namely hybrid energy/momentum driven wind (ezw), and constant winds (cw). We compare equivalent widths, covering factors, ion ratios, and kinematics. Both wind models show generally ≲1σ agreement with these observations for H I and certain low-ionization metal lines, but poorer agreement with higher ionization metal lines including Si III and O VI that are well observed by COS-Halos. This suggests that both models predict too much cool, metal-enriched gas and not enough hot gas, and / or that metals are not sufficiently mixed. This may reflect our model assumption of ejecting outflows as cool and unmixing gas. Our ezw simulation includes a heuristic prescription to quench massive galaxies by superheating interstellar medium gas. This produces low-ionization absorption broadly consistent with observations, but substantial O VI absorption inconsistent with data, suggesting that gas around quenched galaxies in the real Universe does not cool. At impact parameters of ≲50 kpc, recycling winds dominate the absorption of low ions and even H I, while O VI generally arises from metals ejected ≳1 Gyr ago. The similarity between the wind models is surprising, since they differ substantially in the amount and phase distribution of halo gas.We show that this similarity owes mainly to our comparison at fixed stellar (not halo) mass, suggesting that CGM properties are more closely tied to galaxy's stellar (versus halo) mass. [ABSTRACT FROM AUTHOR]

We present a budget and accounting of metals in and around star-forming galaxies at z ∼ 0. We combine empirically derived star formation histories with updated supernova and asymptotic giant branch yields and rates to estimate the total mass of metals produced by galaxies with present-day stellar mass of 109.3-1011.6 M☼. On the accounting side of the ledger, we show that a surprisingly constant 20%-25% mass fraction of produced metals remain in galaxies' stars, interstellar gas and interstellar dust, with little dependence of this fraction on the galaxy stellar mass (omitting those metals immediately locked up in remnants). Thus, the bulk of metals are outside of galaxies, produced in the progenitors of today's L* galaxies. The COS-Halos survey is uniquely able to measure the mass of metals in the circumgalactic medium (CGM, to impact parameters of <150 kpc) of low-redshift ∼L* galaxies. Using these data, we map the distribution of CGM metals as traced by both the highly ionized O VI ion and a suite of low-ionization species; combined with constraints on circumgalactic dust and hotter X-ray emitting gas out to similar impact parameters, we show that ∼40% of metals produced by M⋆ ∼ 1010 M☼ galaxies can be easily accounted for out to 150 kpc. With the current data, we cannot rule out a constant mass of metals within this fixed physical radius. This census provides a crucial boundary condition for the eventual fate of metals in galaxy evolution models. [ABSTRACT FROM AUTHOR]

We combine data sets from the CGM2 and CASBaH surveys to model a transition point, R cross, between circumgalactic and intergalactic media (CGM and IGM, respectively). In total, our data consist of 7244 galaxies at z < 0.5 with precisely measured spectroscopic redshifts, all having impact parameters of 0.01–20 comoving Mpc from 28 QSO sightlines with high-resolution UV spectra that cover H i Ly α. Our best-fitting model is a two-component model that combines a 3D absorber–galaxy cross-correlation function with a simple Gaussian profile at inner radii to represent the CGM. By design, this model gives rise to a determination of R cross as a function of galaxy stellar mass, which can be interpreted as the boundary between the CGM and IGM. For galaxies with 108 ≤ M ⋆/ M ⊙ ≤ 1010.5, we find that R cross(M ⋆) ≈ 2.0 ± 0.6 R vir. Additionally, we find excellent agreement between R cross(M ⋆) and the theoretically determined splashback radius for galaxies in this mass range. Overall, our results favor models of galaxy evolution at z < 0.5 that distribute T ≈ 104K gas to distances beyond the virial radius. [ABSTRACT FROM AUTHOR]

Using the N-body+Smoothed particle hydrodynamics code, ChaNGa, we identify two merger-driven processes—disk disruption and supermassive black hole (SMBH) feedback—which work together to quench L* galaxies for over 7 Gyr. Specifically, we examine the cessation of star formation in a simulated Milky Way (MW) analog, driven by an interaction with two minor satellites. Both interactions occur within ∼100 Myr of each other, and the satellites both have masses 5–20 times smaller than that of their MW-like host galaxy. Using the genetic modification process of Roth et al., we generate a set of four zoom-in, MW-mass galaxies all of which exhibit unique star formation histories due to small changes to their assembly histories. In two of these four cases, the galaxy is quenched by z = 1. Because these are controlled modifications, we are able to isolate the effects of two closely spaced minor merger events, the relative timing of which determines whether the MW-mass main galaxy quenches. This one–two punch works to: (1) fuel the SMBH at its peak accretion rate and (2) disrupt the cold, gaseous disk of the host galaxy. The end result is that feedback from the SMBH thoroughly and abruptly ends the star formation of the galaxy by z ≈ 1. We search for and find a similar quenching event in R omulus 25, a hydrodynamical (25 Mpc)3 volume simulation, demonstrating that the mechanism is common enough to occur even in a small sample of MW-mass quenched galaxies at z = 0. [ABSTRACT FROM AUTHOR]

We analyze the physical conditions of the cool, photoionized (T ∼104 K) circumgalactic medium (CGM) using the COS-Halos suite of gas column density measurements for 44 gaseous halos within 160 kpc of L ∼ L* galaxies at z ∼ 0.2. These data are well described by simple photoionization models, with the gas highly ionized (nH II /nH ≳ 99%) by the extragalactic ultraviolet background. Scaling by estimates for the virial radius, Rvir, we show that the ionization state (tracked by the dimensionless ionization parameter, U) increases with distance from the host galaxy. The ionization parameters imply a decreasing volume density profile nH = (10–4.2 ± 0.25)(R/Rvir)–0.8 ± 0.3. Our derived gas volume densities are several orders of magnitude lower than predictions from standard two-phase models with a cool medium in pressure equilibrium with a hot, coronal medium expected in virialized halos at this mass scale. Applying the ionization corrections to the H I column densities, we estimate a lower limit to the cool gas mass M☼ for the volume within R < Rvir. Allowing for an additional warm-hot, O VI-traced phase, the CGM accounts for at least half of the baryons purported to be missing from dark matter halos at the 1012M☼ scale. [ABSTRACT FROM AUTHOR]

The gas surrounding galaxies outside their disks or interstellar medium and inside their virial radii is known as the circumgalactic medium (CGM). In recent years this component of galaxies has assumed an important role in our understanding of galaxy evolution owing to rapid advances in observational access to this diffuse, nearly invisible material. Observations and simulations of this component of galaxies suggest that it is a multiphase medium characterized by rich dynamics and complex ionization states. The CGM is a source for a galaxy's star-forming fuel, the venue for galactic feedback and recycling, and perhaps the key regulator of the galactic gas supply. We review our evolving knowledge of the CGM with emphasis on its mass, dynamical state, and coevolution with galaxies. Observations from all redshifts and from across the electromagnetic spectrum indicate that CGM gas has a key role in galaxy evolution. We summarize the state of this field and pose unanswered questions for future research. [ABSTRACT FROM AUTHOR]

We use medium-resolution Keck/Echellette Spectrograph and Imager spectroscopy of bright quasars to study cool gas traced by Ca ii λλ 3934, 3969 and Na i λλ 5891, 5897 absorption in the interstellar/circumgalactic media of 21 foreground star-forming galaxies at redshifts 0.03 < z < 0.20 with stellar masses 7.4 ≤ log M */ M ⊙ ≤ 10.6. The quasarâ€"galaxy pairs were drawn from a unique sample of Sloan Digital Sky Survey quasar spectra with intervening nebular emission, and thus have exceptionally close impact parameters (R ⊥ < 13 kpc). The strength of this line emission implies that the galaxies’ star formation rates (SFRs) span a broad range, with several lying well above the star-forming sequence. We use Voigt profile modeling to derive column densities and component velocities for each absorber, finding that column densities N (Ca ii) > 1012.5 cmâˆ'2 (N (Na i) > 1012.0 cmâˆ'2) occur with an incidence f C(Ca ii) = 0.63+0.10âˆ'0.11 (f C(Na i) = 0.57+0.10âˆ'0.11). We find no evidence for a dependence of f C or the rest-frame equivalent widths W r (Ca ii K) or W r (Na i 5891) on R ⊥ or M *. Instead, W r (Ca ii K) is correlated with local SFR at >3 σ significance, suggesting that Ca ii traces star formation-driven outflows. While most of the absorbers have velocities within ±50 km sâˆ'1 of the host redshift, their velocity widths (characterized by Î" v 90) are universally 30â€"177 km sâˆ'1 larger than that implied by tilted-ring modeling of the velocities of interstellar material. These kinematics must trace galactic fountain flows and demonstrate that they persist at R ⊥ > 5 kpc. Finally, we assess the relationship between dust reddening and W r (Ca ii K) (W r (Na i 5891)), finding that 33% (24%) of the absorbers are inconsistent with the best-fit Milky Way E (B âˆ'V)- W r relations at >3 σ significance. [ABSTRACT FROM AUTHOR]

We present the design and methods of the COS-Halos survey, a systematic investigation of the gaseous halos of 44 z = 0.15-0.35 galaxies using background QSOs observed with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope. This survey has yielded 39 spectra of zem ≃ 0.5 QSOs with S/N ∼10-15 per resolution element. The QSO sightlines pass within 150 physical kpc of the galaxies, which span early and late types over stellar mass log M*/M☼ = 9.5-11.5. We find that the circumgalactic medium exhibits strong H I, averaging ≃ 1 Å in Lyα equivalent width out to 150 kpc, with 100% covering fraction for star-forming galaxies and 75% covering for passive galaxies. We find good agreement in column densities between this survey and previous studies over similar range of impact parameter. There is weak evidence for a difference between early- and late-type galaxies in the strength and distribution of H I. Kinematics indicate that the detected material is bound to the host galaxy, such that ≳ 90% of the detected column density is confined within ±200 km s–1 of the galaxies. This material generally exists well below the halo virial temperatures at T ≲ 105 K. We evaluate a number of possible origin scenarios for the detected material, and in the end favor a simple model in which the bulk of the detected H I arises in a bound, cool, low-density photoionized diffuse medium that is generic to all L* galaxies and may harbor a total gaseous mass comparable to galactic stellar masses. [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]

Using 10 sight lines observed with the Hubble Space Telescope/Cosmic Origins Spectrograph, we study the circumgalactic medium (CGM) and outflows of IC 1613, which is a low-mass (M* ∼ 108M⊙), dwarf irregular galaxy on the outskirts of the Local Group. Among the sight lines, four are pointed toward UV-bright stars in IC 1613, and the other six sight lines are background QSOs at impact parameters from 6 kpc (<0.1R200) to 61 kpc (0.6R200). We detect a number of Si ii , Si iii , Si iv , C ii , and C iv absorbers, most of which have velocities less than the escape velocity of IC 1613 and thus are gravitationally bound. The line strengths of these ion absorbers are consistent with the CGM absorbers detected in dwarf galaxies at low redshifts. Assuming that Si ii , Si iii , and Si iv comprise nearly 100% of the total silicon, we find 3% (∼8 × 103M⊙), 2% (∼7 × 103M⊙), and 32%–42% [∼(1.0–1.3) × 105M⊙] of the silicon mass in the stars, interstellar medium, and within 0.6R200 of the CGM of IC 1613. We also estimate the metal outflow rate to be and the instantaneous metal mass loading factor to be ηZ ≥ 0.004, which are in broad agreement with available observation and simulation values. This work is the first time a dwarf galaxy of such low mass is probed by a number of both QSO and stellar sight lines, and it shows that the CGM of low-mass, gas-rich galaxies can be a large reservoir enriched with metals from past and ongoing outflows. [ABSTRACT FROM AUTHOR]

Large reservoirs of cold (∼104 K) gas exist out to and beyond the virial radius in the circumgalactic medium (CGM) of all types of galaxies. Photoionization modeling suggests that cold CGM gas has significantly lower densities than expected by theoretical predictions based on thermal pressure equilibrium with hot CGM gas. In this work, we investigate the impact of cosmic-ray physics on the formation of cold gas via thermal instability. We use idealized three-dimensional magnetohydrodynamic simulations to follow the evolution of thermally unstable gas in a gravitationally stratified medium. We find that cosmic-ray pressure lowers the density and increases the size of cold gas clouds formed through thermal instability. We develop a simple model for how the cold cloud sizes and the relative densities of cold and hot gas depend on cosmic-ray pressure. Cosmic-ray pressure can help counteract gravity to keep cold gas in the CGM for longer, thereby increasing the predicted cold mass fraction and decreasing the predicted cold gas inflow rates. Efficient cosmic-ray transport, by streaming or diffusion, redistributes cosmic-ray pressure from the cold gas to the background medium, resulting in cold gas properties that are in between those predicted by simulations with inefficient transport and simulations without cosmic rays. We show that cosmic rays can significantly reduce galactic accretion rates and resolve the tension between theoretical models and observational constraints on the properties of cold CGM gas. [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]

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 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 explore the circumgalactic metal content traced by commonly observed low ion absorbers, including |${\rm{C\,{\small II}}}$|⁠, |${\rm{Si\,{\small II}}}$|⁠, |${\rm{Si\,{\small III}}}$|⁠, |$\rm{Si\,{\small IV}}$|⁠, and |${\rm{Mg\,{\small II}}}$|⁠. We use a set of cosmological hydrodynamical zoom simulations run with the EAGLE model and including a non-equilibrium ionization and cooling module that follows 136 ions. The simulations of |$z$| ≈ 0.2 L * (M 200 = 1011.7 − 1012.3M⊙) haloes hosting star-forming galaxies and group-sized (M 200 = 1012.7 − 1013.3M⊙) haloes hosting mainly passive galaxies reproduce key trends observed by the COS–Halos survey – low ion column densities show 1) little dependence on galaxy-specific star formation rate, 2) a patchy covering fraction indicative of 104 K clumps with a small volume filling factor, and 3) a declining covering fraction as impact parameter increases from 20−160kpc. Simulated |${\rm{Si\,{\small II}}}$|⁠, |${\rm{Si\,{\small III}}}$|⁠, |$\rm{Si\,{\small IV}}$|⁠, |${\rm{C\,{\small II}}}$|⁠, and |${\rm{C\,{\small III}}}$| column densities show good (mostly within 0.3 dex) agreement with observations, while |${\rm{Mg\,{\small II}}}$| is under-predicted. Low ions trace a significant metal reservoir, ≈108M⊙, residing primarily at 10−100kpc from star-forming and passive central galaxies. These clumps preferentially flow inwards and most will accrete onto the central galaxy within the next several Gyr, while a small fraction are entrained in strong outflows. A multiphase structure describes the inner CGM (<0.5 R 200) with low-ion metal clumps surrounded by a hot, ambient medium. The dense, cool phase is separate from the |$\rm{O\,{\small VI}}$| observed by COS–Halos, which arises from the outer CGM (>0.5 R 200) tracing virial temperature gas around L * galaxies. Our simulations support previous ionization models indicating that cloud covering factors decline while densities and pressures show little decline with increasing impact parameter (typically <0.3 dex from 40 to 160 kpc). We find the cool clumps have lower pressures than the ambient medium they are embedded in, and discuss that numerical effects within the hydrodynamic solver likely play a role. [ABSTRACT FROM AUTHOR]

We analyse the mass, temperature, metal enrichment, and OVI abundance of the circumgalactic medium (CGM) around z ~ 0.2 galaxies of mass 109M☉ < M* < 1011.5M☉ in the Illustris simulation. Among star-forming galaxies, the mass, temperature, and metallicity of the CGM increase with stellar mass, driving an increase in the OVI column-density profile of ~0.5 dex with each 0.5 dex increase in stellar mass. Observed OVI column-density profiles exhibit a weaker mass dependence than predicted; the simulated OVI abundance profiles are consistent with those observed for star-forming galaxies of mass M* = 1010.5-11.5M☉, but underpredict the observed OVI abundances by ≳0.8 dex for lower mass galaxies. We suggest that this discrepancy may be alleviated with additional heating of the abundant cool gas in low-mass haloes, or with increased numerical resolution capturing turbulent/conductive mixing layers between CGM phases. Quenched galaxies of mass M* = 1010.5-11.5M☉ are found to have 0.3-0.8 dex lower OVI column-density profiles than star-forming galaxies of the same mass, in qualitative agreement with the observed OVI abundance bimodality. This offset is driven by AGN feedback, which quenches galaxies by heating theCGMand ejecting significant amounts of gas from the halo. Finally, we find that the inclusion of the central-galaxy's radiation field may enhance the photoionization of the CGM within ~50 kpc, further increasing the predicted OVI abundance around star-forming galaxies. [ABSTRACT FROM AUTHOR]

Modern analyses of structure formation predict a universe tangled in a 'cosmic web' of dark matter and diffuse baryons. These theories further predict that at low z, a significant fraction of the baryons will be shock-heated to T ~ 105-105 K yielding a warm-hot intergalactic medium (WHIM), but whose actual existence has eluded a firm observational confirmation.We present a novel experiment to detect theWHIM, by targeting the putative filaments connecting galaxy clusters. We use HST/COS to observe a remarkable quasi-stellar object (QSO) sightline that passes within Δd = 3 Mpc from the seven intercluster axes connecting seven independent cluster pairs at redshifts 0.1 ≤ z ≤ 0.5.We find tentative excesses of total HI, narrow HI (NLA; Doppler parameters b < 50 km s-1), broad HI (BLA; b ≥ 50 km s-1) and OVI absorption lines within rest-frame velocities of Δv Δ 1000 km s-1 from the cluster-pairs redshifts, corresponding to ~2, ~1.7, ~6 and ~4 times their field expectations, respectively. Although the excess of OVI likely comes from gas close to individual galaxies, we conclude that most of the excesses of NLAs and BLAs are truly intergalactic. We find the covering fractions, fc, of BLAs close to cluster pairs are ~4-7 times higher than the random expectation (at the ~2σ c.l.), whereas the fc of NLAs and OVI are not significantly enhanced. We argue that a larger relative excess of BLAs compared to those of NLAs close to cluster pairs may be a signature of the WHIM in intercluster filaments. By extending this analysis to tens of sightlines, our experiment offers a promising route to detect the WHIM. [ABSTRACT FROM AUTHOR]

We study the high-ion content and kinematics of the circumgalactic medium around low-redshift galaxies using a sample of 23 Lyman limit systems (LLSs) at 0.08 < z < 0.93 observed with the Cosmic Origins Spectrograph on board the Hubble Space Telescope. In Lehner et al., we recently showed that low-z LLSs have a bimodal metallicity distribution. Here we extend that analysis to search for differences between the high-ion and kinematic properties of the metal-poor and metal-rich branches. We find that metal-rich LLSs tend to show higher O VI columns and broader O VI profiles than metal-poor LLSs. The total H I line width (Δv90 statistic) in LLSs is not correlated with metallicity, indicating that the H I kinematics alone cannot be used to distinguish inflow from outflow and gas recycling. Among the 17 LLSs with O VI detections, all but two show evidence of kinematic sub-structure, in the form of O VI-H I centroid offsets, multiple components, or both. Using various scenarios for how the metallicities in the high-ion and low-ion phases of each LLS compare, we constrain the ionized hydrogen column in the O VI phase to lie in the range log N(H II) ∼ 17.6-20. The O VI phase of LLSs is a substantial baryon reservoir, with M(high-ion) ∼ 108.5-10.9 (r/150 kpc)2M☼, similar to the mass in the low-ion phase. Accounting for the O VI phase approximately doubles the contribution of low-z LLSs to the cosmic baryon budget. [ABSTRACT FROM AUTHOR]

We present UV and optical observations from the Cosmic Origins Spectrograph on the Hubble Space Telescope and Keck of a z = 0.27395 Lyman limit system (LLS) seen in absorption against the QSO PG1630+377. We detect H I absorption with log N(H I) = 17.06 ± 0.05 as well as Mg II, C III, Si III, and O VI in this system. The column densities are readily explained if this is a multi-phase system, with the intermediate and low ions arising in a very low metallicity ([Mg/H] = -1.71 ± 0.06) photoionized gas. We identify via Keck spectroscopy and Large Binocular Telescope imaging a 0.3 L* star-forming galaxy projected 37 kpc from the QSO at nearly identical redshift (z = 0.27406 and Δv = -26 km s-1) with near solar metallicity ([O/H] = -0.20 ± 0.15). The presence of very low metallicity gas in the proximity of a near-solar metallicity, sub-L* galaxy strongly suggests that the LLS probes gas infalling onto the galaxy. A search of the literature reveals that such low-metallicity LLSs are not uncommon. We found that 50% (4/8) of the well-studied z ≲ 1 LLSs have metallicities similar to the present system and show sub-L* galaxies with ρ < 100 kpc in those fields where redshifts have been surveyed. We argue that the properties of these primitive LLSs and their host galaxies are consistent with those of cold mode accretion streams seen in galaxy simulations. [ABSTRACT FROM AUTHOR]

Outflowing winds of multiphase plasma have been proposed to regulate the buildup of galaxies, but key aspects of these outflows have not been probed with observations. By using ultraviolet absorption spectroscopy, we show that "warm-hot" plasma at 105.5 kelvin contains 10 to 150 times more mass than the cold gas in a post-starburst galaxy wind. This wind extends to distances > 68 kilopersecs, and at least some portion of it wit[ escape. Moreover, the kinematical correlation of the cold and warm-hot phases indicates that the warm-hot plasma is related to the interaction of the cold matter with a hotter (unseen) phase at >>106 kelvin. Such multiphase winds can remove substantial masses and alter the evolution of post-starburst galaxies. [ABSTRACT FROM AUTHOR]