Yakov Faerman

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 ⊙ ) < 9.5 ) at z = 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 within R _{200 c} reside in the CGM, with ∼70% of CGM mass existing in a warm gas phase, 10 ^4.5 < T < 10 ^5.5 K, that dominates beyond r / R _{200 c} ∼ 0.5. The warm and cool (10 ^4.0 < T < 10 ^4.5 K) 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 of z ∼ 0 low ion detections beyond b / R _{200 c} ∼ 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.

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 ≤ 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 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.

For half a century now, the galaxy formation and evolution community has recognized the critical role of gas accretion to sustain star formation (e.g., Refs. 1, 2). Gas is thought to transition into galaxies through accretion processes and, in turn, get expelled from galaxies through feedback processes, an interplay that regulates galactic gas content. What is now broadly called “feedback” includes the ejection of both matter and energy from stellar winds, radiation, and supernovae as well as active galactic nuclei (AGN), and both theory and observation have implicated feedback as central to regulating, perhaps even halting (or quenching), star formation. The discovery of a ubiquitous circumgalactic medium (CGM; Fig. 1) from quasar absorption line studies supports this paradigm: (1) the dark matter halos in which galaxies reside contain a substantial baryonic component well beyond any stellar extent of a galaxy (a potential source of fuel for star formation)⁴; (2) the gaseous halos permeating their dark matter counterparts are correlated with their host galaxy star formation properties (connecting the CGM to central galaxy activity)^5,6; (3) galaxy environment impacts the gas reservoirs of galaxies living in overdense environments such as groups and clusters (where quenched galaxies reside in great numbers)⁷; and (4) more than half of the metals in the universe reside outside galaxies, which implicates ejection from sites of star formation (galaxies) into the CGM.⁸

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 _* = 10^6.5−9.5 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, M _cCGM, as a function of halo mass. For volume-filling (f _V = 1) models, we find M _cCGM = 5 × 10⁸–2 × 10⁹ M _⊙, constituting ≲10% of the halo baryon budget. For clumpy gas, with f _V = 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 M _cCGM, 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.

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 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 / 3 Y 500 / M vir , 12 5 / 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.