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ABSTRACT Simulations suggest that turbulence is ubiquitous in the circumgalactic medium (CGM), though the source and properties of CGM turbulence is uncertain. Using analytic considerations and hydrodynamic simulations, we study how CGM turbulence is driven by gas accretion, thus providing a baseline for additional turbulence driving processes such as galaxy feedback. We demonstrate that in haloes with mass $$\sim 10^{10}-10^{12}\, {\rm M}_\odot$$ at $$0\,\lt\, z\,\lt\,2$$, accretion amplifies mild turbulent velocities near the virial radius of $$\sigma _{\rm t}(R_{\rm vir})\sim 10\, {\rm km}\, {\rm s}^{-1}$$ to virial velocities at inner CGM radii, $$\sigma _{\rm t}(0.1R_{\rm vir})\approx v_{\rm vir}\sim 100\, {\rm km}\, {\rm s}^{-1}$$. Rapid cooling at these inner radii further implies that thermal pressure support is small, and the gas is dominated by the cool and warm ($$\sim 10^4-10^5\, {\rm K}$$) phases. Inner CGM energetics in these haloes is thus dominated by turbulence, with gas density distributions and velocity structure functions similar to those seen in simulations of isothermal supersonic turbulence, rather than those seen in subsonically turbulent stratified media such as the intracluster medium. The accretion rate in these systems is regulated by the turbulence dissipation rate, in contrast with being regulated by the cooling rate as in more massive haloes. We argue that galaxy feedback is unlikely to qualitatively change our conclusions unless it significantly depletes the CGM or continuously injects high specific energy material ($$\gg v^2_{\rm vir}$$). Such ‘turbulence-dominated’ CGM can be identified in observations via the predicted wide lognormal ionization distributions and large velocity dispersions in ultraviolet absorption spectra. 

ABSTRACT We present a fast and robust analytic framework for predicting surface brightness (SB) of emission lines in galactic winds as a function of radius up to $$\sim 100$$ kpc out in the circum-galactic medium. We model multiphase structure in galactic winds by capturing emission from both the volume-filling hot phase (T $$\sim 10^{6-7}$$ K) and turbulent radiative mixing layers that host intermediate temperature gas at the boundaries of cold clouds (T $$\sim 10^4$$ K). Our multiphase framework makes significantly different predictions of emission signatures compared to traditional single-phase models and explains the paucity of O vi SB measurements in the literature. After accounting for ram pressure equilibrium between the cold clouds and hot wind in supersonic outflows, non-equilibrium ionization effects, and energy budgets other than mechanical energy from core-collapse supernovae, our O vi SB predictions qualitatively match observational results. Our framework provides constraints on the optimal galactic wind properties that facilitate O vi emission observations, including star formation rate surface density, hot phase mass loading factor, and thermalization efficiency factor. These constraints are consistent with existing observations and can help inform future target selections. 

Abstract 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 Heiiself-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. 

Abstract This paper investigates the physical conditions of the circumgalactic medium ofL^⋆galaxies through explorations of observed ion tracer gas kinematics and comparisons of observations to different ionization models. For this analysis, we utilize Civobservations from the CIViL^⋆survey (∼0.14 ≤z_gal≤ 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 Civand Oviare likely (>95%) drawn from the same parent distribution, suggesting that these two ions are kinematically coincident andpotentiallyoriginate under the same physical conditions. We find that the measured Civ/Oviand Nv/Oviratios 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 Civ, Nv, and Oviby exploring a cooling flow model under collisional ionization. We find that both Nvand Oviare consistent with the predictions of the model, but the column densities of Civare ∼2.5 times higher than the predictions. As Civhas a lower ionization energy than Nvand Ovi, it is possible that Civhas contributions from both the warm/hot and cool photoionized phase. 

Abstract 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 ( $6.0<\log (M_{*}/M_{\odot })<9.5$ ) atz= 0 from the Marvel-ous Dwarfs and Marvelous Massive Dwarfs simulations. Our galaxies produce column densities broadly consistent with current observations. We investigate these column densities in the context of mass and metal retention rates, and CGM physical properties. We find 48% ± 11% of all baryons withinR_200creside in the CGM, with ∼70% of CGM mass existing in a warm gas phase, 10^4.5 < T < 10^5.5K, that dominates beyondr/R_200c ∼ 0.5. The warm and cool (10^4.0 < T < 10^4.5K) gas phases each retain 5%–10% of metals formed by the dwarf galaxy. The significant fraction of mass and metals residing in the warm CGM phase provides an interpretation for the lack ofz ∼ 0 low ion detections beyondb/R_200c ∼ 0.5, as the majority of mass in this region exists in higher ions. We find a weak correlation between galaxy mass and total CGM metal retention despite the fraction of metals lost from the halo increasing from ∼10% to >40% 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. 

Abstract We present an analytic model for the cool,T∼ 10⁴K, 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 withη= 3, gas distribution out tor≈ 0.6R_vir, andM_cool= 3 × 10⁹M_⊙, corresponding to a volume filling fraction off_V,cool≈ 1%, reproduces the Hiand low/intermediate metal ions (Cii, Ciii, Siii, Siiii, and Mgii) mean column densities. Variation of ±0.5 dex inηorM_coolencompasses ∼2/3 of the scatter between objects. Our nominal model underproduces the measured Civand Siivcolumns, and these can be reproduced with (i) a cool phase withM_cool∼ 10¹⁰M_⊙andη≈ 5, or (ii) cooling or mixing gas at intermediate temperatures, withM∼ 1.5 × 10¹⁰M_⊙and occupying ∼1/2 of the total CGM volume. For cool gas withf_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 ${\dot{M}}_{\mathrm{cool}}\approx 0$ over long timescales. 

ABSTRACT We develop and present the Descriptive Parametric Model (DPM), a tool for generating profiles of gaseous haloes (pressure, electron density, and metallicity) as functions of radius, halo mass, and redshift. The model assumes single-phase, spherically symmetric, volume-filling warm/hot gas. The DPM framework enables mock observations of the circumgalactic medium (CGM), group haloes, and clusters across a number of wavebands including X-ray, sub-millimetre/millimetre, radio, and ultraviolet (UV). We introduce three model families calibrated to reproduce cluster profiles while having different extrapolations to the CGM – (i) self-similar haloes, (ii) a reduced gas model for lower halo masses, and (iii) a model with shallower radial slopes at lower masses. We demonstrate how our $$z=0.0{\!-\!}0.6$$ models perform when applied to stacked and individual X-ray emission profiles, measurements of the thermal and kinetic Sunyaev–Zel’dovich effect, electron dispersion measures from fast radio bursts, $$\rm{O\,{\small VI}}$$ absorption, and UV-derived pressures. Our investigation supports models that remove baryons from haloes more effectively and have shallower profiles at lower halo mass. We discuss biases and systematics when modelling observables using consistent hot gaseous halo models for all wavebands explored. We release the dpmhalo code to encourage the use of our framework and new formulations in future investigations. Included with the dpmhalo distribution is a set of recent observations that allow the reproduction of most plots in this paper. 

Abstract The Large Magellanic Cloud (LMC) is home to many Hiiregions, which may lead to significant outflows. We examine the LMC’s multiphase gas (T∼10^4-5K) in Hi, Sii, Siiv, and Civusing 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 overv_helio= 175–375 km s⁻¹. Our analyses show disk-wide ionized outflows in Siivand Civacross 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 (Σ_SFR), and the outflows with higher Σ_SFRtend to be more ionized. Considering outflows from both sides of the LMC as traced by Civ, we conservatively estimate a total outflow rate of ${\dot{M}}_{\mathrm{out}}\gtrsim 0.03M_{\odot }{\mathrm{yr}}^{-1}$ and a mass-loading factor ofη≳ 0.15. We compare the LMC’s outflows with those detected in starburst galaxies and simulation predictions, and find a universal scaling relation of $\mid v_{\mathrm{out},\mathrm{bulk}}\mid \propto {\mathrm{\Sigma }}_{\mathrm{SFR}}^{0.23}$ over a wide range of star-forming conditions (Σ_SFR∼ 10^−4.5–10²M_⊙yr⁻¹kpc⁻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. 

Abstract We present an analysis of Hubble Space Telescope COS/G160M observations of CIVin the inner circumgalactic medium (CGM) of a novel sample of eightz∼ 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 (log₁₀M_⋆/M_⊙∼ 10.2–10.9M_⊙) host supermassive black holes (SMBHs) with dynamically measured masses spanning log₁₀M_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 CIVcolumn density measurements (N_{C IV}; average log₁₀N_{C IV,CH}= 13.94 ± 0.09 cm⁻²) are largely consistent with existing measurements from other surveys ofN_{C IV}in the CGM (average log₁₀N_{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 log₁₀M_BH/M_⊙> 7.0, where the CGM CIVcontent shows a clear dependence on galaxy sSFR but notM_BH. Our results do not indicate an obvious causal link between CGM CIVand 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. 

ABSTRACT Motivated by integral field units (IFUs) on large ground telescopes and proposals for ultraviolet-sensitive space telescopes to probe circumgalactic medium (CGM) emission, we survey the most promising emission lines and how such observations can inform our understanding of the CGM and its relation to galaxy formation. We tie our emission estimates to both HST/COS absorption measurements of ions around z ≈ 0.2 Milky Way mass haloes and models for the density and temperature of gas. We also provide formulas that simplify extending our estimates to other samples and physical scenarios. We find that O iii 5007 Å and N ii 6583 Å, which at fixed ionic column density are primarily sensitive to the thermal pressure of the gas they inhabit, may be detectable with KCWI and especially IFUs on 30 m telescopes out to half a virial radius. O v 630 Å and O vi 1032,1038 Å are perhaps the most promising ultraviolet lines, with models predicting intensities >100 γ cm−2 s−1 sr−1 in the inner 100 kpc of Milky Way-like systems. A detection of O vi would confirm the collisionally ionized picture and constrain the density profile of the CGM. Other ultraviolet metal lines constrain the amount of gas that is actively cooling and mixing. We find that C iii 978 Å and C iv 1548 Å may be detectable if an appreciable fraction of the observed O vi column is associated with mixing or cooling gas. H α emission within $$100\,$$ kpc of Milky Way-like galaxies is within reach of current IFUs even for the minimum signal from ionizing background fluorescence, while hydrogen n > 2 Ly-series lines are too weak to be detectable.