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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 ≈ 0.6R 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 Ṁcool≈0 over long timescales.

We analyze measurements of the thermal Sunyaev–Zeldovich (tSZ) effect arising in the circumgalactic medium (CGM) of L* galaxies, reported by J. N. Bregman et al. (B+22) and S. Das et al. (D+23). In our analysis, we use the Y. Faerman et al. CGM models, a new power-law model (PLM), and the TNG100 simulation. For a given M vir, our PLM has four parameters: the fraction, f hCGM, of the halo baryon mass in hot CGM gas, the ratio, ϕ T , of the actual gas temperature at the virial radius to the virial temperature, and the power-law indices, a P,th and a n for the thermal electron pressure and the hydrogen nucleon density. The B+22 Compton-y profile implies steep electron pressure slopes (a P,th ≃ 2). For isothermal conditions, the temperature is at least 1.1 × 106 K, with a hot CGM gas mass of up to 3.5 × 1011 M ⊙ for a virial mass of 2.75 × 1012 M ⊙. However, if isothermal, the gas must be expanding out of the halos. An isentropic equation of state is favored for which hydrostatic equilibrium is possible. The B+22 and D+23 results are consistent with each other and with recent (0.5–2 keV) CGM X-ray observations of Milky Way mass systems. For M vir ≃ 3 × 1012 M ⊙, the scaled Compton pressure integrals, E(z)−2/3Y500/Mvir,125/3 , lie in the narrow range, 2.5 × 10−4–5.0 × 10−4 kpc2, for all three sets of observations. TNG100 underpredicts the tSZ parameters by factors ∼0.5 dex for the L* galaxies, suggesting that the feedback strengths and CGM gas losses are overestimated in the simulated halos at these mass scales.

We investigate the prospects for detecting and constraining density and temperature inhomogeneities in the circumgalactic medium using absorption measurements of metal ions. Distributions in the gas thermal properties could arise from turbulence, gas cooling from the hot phase, and mixing between the cool and hot phases. Focusing on these physically motivated models, we parameterize each with a single parameter for simplicity and provide empirical and theoretical estimates for reasonable parameter values. We then construct the probability distribution functions for each of these scenarios, calculate the effective ion fractions, and fit our models to the COS-Halos absorption measurements to infer the gas densities and metallicities. We find that the models we consider (i) produce similarly good fits to the observations with or without distributions in the gas thermal properties, and (ii) result in detectable changes in the column densities only at the boundaries of reasonable parameter values. We show that He ii self-shielding can have a larger effect on the ion fractions than density and temperature fluctuations. As a result, uncertainties in cloud geometry and their spatial distribution, affecting the details of radiation transfer, may obscure the effect of inhomogeneities.

We use H i absorption measurements to constrain the amount of cool (≈104 K), photoionized gas in the circumgalactic medium (CGM) of dwarf galaxies with M* = 106.5−9.5 M⊙ in the nearby Universe (z < 0.3). We show analytically that volume-filling gas gives an upper limit on the gas mass needed to reproduce a given H i column density profile. We introduce a power-law density profile for the gas distribution and fit our model to archival H i observations to infer the cool CGM gas mass, McCGM, as a function of halo mass. For volume-filling (fV = 1) models, we find McCGM = 5 × 108–2 × 109 M⊙, constituting ≲10% of the halo baryon budget. For clumpy gas, with fV = 0.01, the masses are a factor of ≈​​​​​​11 lower, in agreement with our analytic approximation. Our assumption that the measured H i forms entirely in the cool CGM provides a conservative upper limit on McCGM, and possible contributions from the intergalactic medium or warm/hot CGM will further strengthen our result. We estimate the mass uncertainties due to the range of redshifts in our sample and the unknown gas metallicity to be ≈15% and ≈10%, respectively. Our results show that dwarf galaxies have only ≲15% of their baryon budget in stars and the cool CGM, with the rest residing in the warm/hot CGM or ejected from the dark matter halos.

Dwarf galaxies are found to have lost most of their metals via feedback processes; however, there still lacks consistent assessment on the retention rate of metals in their circumgalactic medium (CGM). Here we investigate the metal content in the CGM of 45 isolated dwarf galaxies with M * = 106.5–9.5 M ⊙ (M 200m = 1010.0–11.5 M ⊙) using the Hubble Space Telescope/Cosmic Origins Spectrograph. While H i (Lyα) is ubiquitously detected (89%) within the CGM, we find low detection rates (≈5%–22%) in C ii, C iv, Si ii, Si iii, and Si iv, largely consistent with literature values. Assuming these ions form in the cool (T ≈ 104 K) CGM with photoionization equilibrium, the observed H i and metal column density profiles can be best explained by an empirical model with low gas density and high volume filling factor. For a typical galaxy with M 200m = 1010.9 M ⊙ (median of the sample), our model predicts a cool gas mass of M CGM,cool ∼ 108.4 M ⊙, corresponding to ∼2% of the galaxy’s baryonic budget. Assuming a metallicity of 0.3 Z ⊙, we estimate that the dwarf galaxy’s cool CGM likely harbors ∼10% of the metals ever produced, with the rest either in more ionized states in the CGM or transported to the intergalactic medium. We further examine the EAGLE simulation and show that H i and low ions may arise from a dense cool medium, while C iv arises from a diffuse warmer medium. Our work provides the community with a uniform data set on dwarf galaxies’ CGM that combines our recent observations, additional archival data and literature compilation, which can be used to test various theoretical models of dwarf galaxies.

Dwarf galaxies are uniquely sensitive to feedback processes and known to experience substantial mass and metal loss from their disks. Here, we investigate the circumgalactic medium (CGM) of 64 isolated dwarf galaxies ( 6.040% toward lower masses. Our findings highlight the CGM (particularly its warm phase) as a key reservoir of mass and metals for dwarf galaxies across stellar masses, underscoring its importance in understanding the baryon cycle in the low-mass regime. Finally, we provide individual simulated galaxy properties and quantify the fraction of UV-observable mass to support future observational programs aimed at performing a metal budget around dwarf galaxies.

This paper investigates the physical conditions of the circumgalactic medium of L⋆ galaxies through explorations of observed ion tracer gas kinematics and comparisons of observations to different ionization models. For this analysis, we utilize C iv observations from the CIViL⋆ survey (∼0.14 ≤ zgal ≤ 0.25) and directly compare them to observations of matched lines of sight from the Cosmic Origins Spectrograph-Halos survey. We find that the kinematic parameters for C iv and O vi are likely (>95%) drawn from the same parent distribution, suggesting that these two ions are kinematically coincident and potentially originate under the same physical conditions. We find that the measured C iv/O vi and N v/O vi ratios are inconsistent with single-phase equilibrium models. For 70% of the objects in our sample, regions allowed by the column density ratios in the density-temperature space do not overlap, creating a “zone of avoidance.” We also investigate the origins of C iv, N v, and O vi by exploring a cooling flow model under collisional ionization. We find that both N v and O vi are consistent with the predictions of the model, but the column densities of C iv are ∼2.5 times higher than the predictions. As C iv has a lower ionization energy than N v and O vi, it is possible that C iv has contributions from both the warm/hot and cool photoionized phase.

The Large Magellanic Cloud (LMC) is home to many H ii regions, which may lead to significant outflows. We examine the LMC’s multiphase gas (T∼104-5 K) in H i, S ii, Si iv, and C iv using 110 stellar sight lines from the Hubble Space Telescope’s Ultraviolet Legacy Library of Young Stars as Essential Standards program. We develop a continuum fitting algorithm based on the concept of Gaussian process regression and identify reliable LMC interstellar absorption over v helio = 175–375 km s−1. Our analyses show disk-wide ionized outflows in Si iv and C iv across the LMC with bulk velocities of ∣v out, bulk∣ ∼ 20–60 km s−1, which indicates that most of the outflowing mass is gravitationally bound. The outflows’ column densities correlate with the LMC’s star formation rate surface densities (ΣSFR), and the outflows with higher ΣSFR tend to be more ionized. Considering outflows from both sides of the LMC as traced by C iv, we conservatively estimate a total outflow rate of Ṁout≳0.03M⊙ yr−1 and a mass-loading factor of η ≳ 0.15. We compare the LMC’s outflows with those detected in starburst galaxies and simulation predictions, and find a universal scaling relation of ∣vout,bulk∣∝ΣSFR0.23 over a wide range of star-forming conditions (ΣSFR ∼ 10−4.5–102 M ⊙ yr−1 kpc−2). Lastly, we find that the outflows are corotating with the LMC’s young stellar disk and the velocity field does not seem to be significantly impacted by external forces; we thus speculate on the existence of a bow shock leading the LMC, which may have shielded the outflows from ram pressure as the LMC orbits the Milky Way.

This paper investigates C iv absorption in the circumgalactic medium (CGM) of L⋆ galaxies and its relationship with galaxy star formation rates. We present new observations from the C iv in L⋆ galaxies survey (PID#17076) using the Hubble Space Telescope/Cosmic Origins Spectrograph. By combining these measurements with archival C iv data (46 observations total), we estimate detection fractions for star-forming (sSFR > 10−11 yr−1) and passive galaxies (sSFR ≤ 10−11 yr−1 ) to be 72 −18+14 % [21/29] and 23 −15+27 % [3/13], respectively. This indicates a significant dichotomy in C iv presence between L⋆ star-forming and passive galaxies, with over 99% confidence. This finding aligns with J. Tumlinson et al., which noted a similar dichotomy in O vi absorption. Our results imply a substantial carbon reservoir in the CGM of L⋆ galaxies, suggesting a minimum carbon mass of ≳3.03 × 106 M⊙ out to 120 kpc. Together, these findings highlight a strong connection between star formation in galaxies and the state of their CGM, providing insight into the mechanisms governing galaxy evolution.

We present an analysis of Hubble Space Telescope COS/G160M observations of C IV in the inner circumgalactic medium (CGM) of a novel sample of eight z ∼ 0, L ≈ L ⋆ galaxies, paired with UV-bright QSOs at impact parameters (R proj) between 25 and 130 kpc. The galaxies in this stellar-mass-controlled sample (log10 M ⋆/M ⊙ ∼ 10.2–10.9 M ⊙) host supermassive black holes (SMBHs) with dynamically measured masses spanning log10 M BH/M ⊙ ∼ 6.8–8.4; this allows us to compare our results with models of galaxy formation where the integrated feedback history from the SMBH alters the CGM over long timescales. We find that the C IV column density measurements (N C IV; average log10 N C IV,CH = 13.94 ± 0.09 cm−2) are largely consistent with existing measurements from other surveys of N C IV in the CGM (average log10 N C IV,Lit = 13.90 ± 0.08 cm−2), but do not show obvious variation as a function of the SMBH mass. By contrast, specific star formation rate (sSFR) is highly correlated with the ionized content of the CGM. We find a large spread in sSFR for galaxies with log10 M BH/M ⊙ > 7.0, where the CGM C IV content shows a clear dependence on galaxy sSFR but not M BH. Our results do not indicate an obvious causal link between CGM C IV and the mass of the galaxy’s SMBH; however, through comparisons to the EAGLE, Romulus25, and IllustrisTNG simulations, we find that our sample is likely too small to constrain such causality.