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Abstract 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 × 10 10 M ⊙ . The galaxies have redshifts 0.12 < z < 0.6, stellar masses 10 10.1 M ⊙ < M * < 10 10.9 M ⊙ , and spectroscopic classifications as star-forming or passive. We compare the incidence rates of high column density O vi absorption ( N O VI ≥ 10 14.3 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 × 10 10 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 We combine data sets from the CGM 2 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 10 8 ≤ M ⋆ / M ⊙ ≤ 10 10.5 , 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 ≈ 10 4 K gas to distances beyond the virial radius. 

Abstract The Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) are the closest massive satellite galaxies of the Milky Way. They are probably on their first passage on an infalling orbit towards our Galaxy 1 and trace the continuing dynamics of the Local Group 2 . Recent measurements of a high mass for the LMC ( M halo  ≈ 10 11.1–11.4   M ⊙ ) 3–6 imply that the LMC should host a Magellanic Corona: a collisionally ionized, warm-hot gaseous halo at the virial temperature (10 5.3–5.5  K) initially extending out to the virial radius (100–130 kiloparsecs (kpc)). Such a corona would have shaped the formation of the Magellanic Stream 7 , a tidal gas structure extending over 200° across the sky 2,8,9 that is bringing in metal-poor gas to the Milky Way 10 . Here we show evidence for this Magellanic Corona with a potential direct detection in highly ionized oxygen (O +5 ) and indirectly by means of triply ionized carbon and silicon, seen in ultraviolet (UV) absorption towards background quasars. We find that the Magellanic Corona is part of a pervasive multiphase Magellanic circumgalactic medium (CGM) seen in many ionization states with a declining projected radial profile out to at least 35 kpc from the LMC and a total ionized CGM mass of log 10 ( M H II,CGM / M ⊙ ) ≈ 9.1 ± 0.2. The evidence for the Magellanic Corona is a crucial step forward in characterizing the Magellanic group and its nested evolution with the Local Group. 

Abstract We present the KODIAQ-Z survey aimed to characterize the cool, photoionized gas at 2.2 ≲z≲ 3.6 in 202 Hi-selected absorbers with 14.6 ≤ $\log N_{\mathrm{H}\mathrm{I}}$< 20 that probe the interface between galaxies and the intergalactic medium (IGM). We find that gas with $14.6\le \log N_{\mathrm{H}\mathrm{I}}<20$at 2.2 ≲z≲ 3.6 can be metal-rich (−1.6 ≲ [X/H] ≲ − 0.2) as seen in damped Lyαabsorbers (DLAs); it can also be very metal-poor ([X/H] < − 2.4) or even pristine ([X/H] < − 3.8), which is not observed in DLAs but is common in the IGM. For $16<\log N_{\mathrm{H}\mathrm{I}}<20$absorbers, the frequency of pristine absorbers is about 1%–10%, while for $14.6\le \log N_{\mathrm{H}\mathrm{I}}\le 16$absorbers it is 10%–20%, similar to the diffuse IGM. Supersolar gas is extremely rare (<1%) at these redshifts. The factor of several thousand spread from the lowest to highest metallicities and large metallicity variations (a factor of a few to >100) between absorbers separated by less than Δv< 500 km s⁻¹imply that the metals are poorly mixed in $14.6\le \log N_{\mathrm{H}\mathrm{I}}<20$gas. We show that these photoionized absorbers contribute to about 14% of the cosmic baryons and 45% of the cosmic metals at 2.2 ≲z≲ 3.6. We find that the mean metallicity increases withN_Hi, consistent with what is found inz< 1 gas. The metallicity of gas in this column density regime has increased by a factor ∼8 from 2.2 ≲z≲ 3.6 toz< 1, but the contribution of the $14.6\le \log N_{\mathrm{H}\mathrm{I}}<19$absorbers to the total metal budget of the universe atz< 1 is a quarter of that at 2.2 ≲z≲ 3.6. We show that FOGGIE cosmological zoom-in simulations have a similar evolution of [X/H] withN_Hi, which is not observed in lower-resolution simulations. In these simulations, very metal-poor absorbers with [X/H] < − 2.4 atz∼ 2–3 are tracers of inflows, while higher-metallicity absorbers are a mixture of inflows and outflows. 

Abstract We combine 126 new galaxy-O vi absorber pairs from the CGM 2 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 = 0–0.6, with host galaxy stellar masses M * = 10 7.8 –10 11.2 M ⊙ and galaxy-absorber impact parameters R ⊥ = 0–400 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 * = 10 9.2 –10 10 M ⊙ . Star-forming galaxies with M * between 10 8 and 10 11.2 M ⊙ can explain most O vi systems with column densities greater than 10 13.5 cm −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 The bimodal absorption system imaging campaign (BASIC) aims to characterize the galaxy environments of a sample of 36 H i -selected partial Lyman limit systems (pLLSs) and Lyman limit systems (LLSs) in 23 QSO fields at z ≲ 1. These pLLSs/LLSs provide a unique sample of absorbers with unbiased and well-constrained metallicities, allowing us to explore the origins of metal-rich and low-metallicity circumgalactic medium (CGM) at z < 1. Here we present Keck/KCWI and Very Large Telescope/MUSE observations of 11 of these QSO fields (19 pLLSs) that we combine with Hubble Space Telescope/Advanced Camera for Surveys imaging to identify and characterize the absorber-associated galaxies at 0.16 ≲ z ≲ 0.84. We find 23 unique absorber-associated galaxies, with an average of one associated galaxy per absorber. For seven absorbers, all with <10% solar metallicities, we find no associated galaxies with log M ⋆ ≳ 9.0 within ρ / R vir and ∣Δ v ∣/ v esc ≤ 1.5 with respect to the absorber. We do not find any strong correlations between the metallicities or H i column densities of the gas and most of the galaxy properties, except for the stellar mass of the galaxies: the low-metallicity ([X/H] ≤ −1.4) systems have a probability of 0.39 − 0.15 + 0.16 for having a host galaxy with log M ⋆ ≥ 9.0 within ρ / R vir ≤ 1.5, while the higher metallicity absorbers have a probability of 0.78 − 0.13 + 0.10 . This implies metal-enriched pLLSs/LLSs at z < 1 are typically associated with the CGM of galaxies with log M ⋆ > 9.0 , whereas low-metallicity pLLSs/LLSs are found in more diverse locations, with one population arising in the CGM of galaxies and another more broadly distributed in overdense regions of the universe. Using absorbers not associated with galaxies, we estimate the unweighted geometric mean metallicity of the intergalactic medium to be [X/H] ≲ −2.1 at z < 1, which is lower than previously estimated.