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
Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher.
Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?
Some links on this page may take you to non-federal websites. Their policies may differ from this site.
-
Abstract 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 theM BH–σ relation (Kormendy & Ho 2013). The deviation of each SMBH from its expected mass, ΔM BH, is compared to the potential of its host viaσ . We find that SMBHs with accreted mass aboveM 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 Civ 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 theM BH–σ relation may indicate how effective an SMBH is in the local redistribution of mass in its host galaxy.Free, publicly-accessible full text available May 22, 2025 -
Abstract In this study, we investigate interstellar absorption lines along the line of sight toward the galactic low-mass X-ray binary Cygnus X-2. We combine absorption line data obtained from high-resolution X-ray spectra collected with the Chandra and XMM-Newton satellites, along with far-UV absorption lines observed by the Hubble Space Telescope’s (HST) Cosmic Origins Spectrograph (COS) instrument. Our primary objective is to understand the abundance and depletion of oxygen, iron, sulfur, and carbon. To achieve this, we have developed an analysis pipeline that simultaneously fits both the UV and X-ray data sets. This novel approach takes into account the line-spread function of HST/COS, enhancing the precision of our results. We examine the absorption lines of Fe
ii , Sii , Cii , and Ci present in the far-UV spectrum of Cygnus X-2, revealing the presence of at least two distinct absorbers characterized by different velocities. Additionally, we employCloudy simulations to compare our findings concerning the ionic ratios for the studied elements. We find that gaseous iron and sulfur exist in their singly ionized forms, Feii and Sii , respectively, while the abundances of Cii and Ci do not agree with the Cloudy simulations of the neutral ISM. Finally, we explore discrepancies in the X-ray atomic data of iron and discuss their impact on the overall abundance and depletion of iron.Free, publicly-accessible full text available April 15, 2025 -
Abstract The cycling of metals between interstellar gas and dust is a critical aspect of the baryon cycle of galaxies, yet our understanding of this process is limited. This study focuses on understanding dust depletion effects in the low-metallicity regime (<20%
Z ⊙) typical of cosmic noon. Using medium-resolution UV spectroscopy from the Cosmic Origins Spectrograph on board the Hubble Space Telescope, gas-phase abundances and depletions of iron and sulfur were derived toward 18 sight lines in local dwarf galaxies IC 1613 and Sextans A. The results show that the depletion of Fe and S is consistent with that found in the Milky Way (MW), LMC, and SMC. The depletion level of Fe increases with gas column density, indicating dust growth in the interstellar medium. The level of Fe depletion decreases with decreasing metallicity, resulting in the fraction of iron in gas ranging from 3% in the MW to 9% in IC 1613 and ∼19% in Sextans A. The dust-to-gas and dust-to-metal ratios (D /G ,D /M ) for these dwarf galaxies were estimated based on the MW relations between the depletion of Fe and other elements. The study finds thatD /G decreases only slightly sublinearly with metallicity, withD /M decreasing from 0.41 ± 0.05 in the MW to 0.11 ± 0.11 at 0.10Z ⊙(at logN (H) = 21 cm−2). The trend ofD /G versus metallicity using depletion in local systems is similar to that inferred in Damped Lyα systems from abundance ratios but lies higher than the trend inferred from far-IR measurements in nearby galaxies.Free, publicly-accessible full text available April 26, 2025 -
ABSTRACT The relevance of some galactic feedback mechanisms, in particular cosmic-ray (CR) feedback and the hydrogen ionizing radiation field, has been challenging to definitively describe in a galactic context, especially far outside the galaxy in the circumgalactic medium (CGM). Theoretical and observational uncertainties prevent conclusive interpretations of multiphase CGM properties derived from ultraviolet (UV) diagnostics. We conduct three-dimensional magnetohydrodynamic simulations of a section of a galactic disc with star formation and feedback, including radiative heating from stars, a UV background, and CR feedback. We utilize the temperature phases present in our simulations to generate Cloudy models to derive spatially and temporally varying synthetic UV diagnostics. We find that radiative effects without additional heating mechanisms are not able to produce synthetic diagnostics in the observed ranges. For low CR diffusivity $\kappa _{\rm {cr}}=10^{28} \rm {cm}^2 \rm {s}^{-1}$, CR streaming heating in the outflow helps our synthetic line ratios roughly match observed ranges by producing transitional temperature gas (T ∼ 105–106 K). High CR diffusivity $\kappa _{\rm {cr}}=10^{29} \rm {cm}^2 \rm {s}^{-1}$, with or without CR streaming heating, produced transitional temperature gas. The key parameter controlling the production of this gas phase remains unclear, as the different star formation history and outflow evolution itself influences these diagnostics. Our work demonstrates the use of UV plasma diagnostics to differentiate between galactic/circumgalactic feedback models.
Free, publicly-accessible full text available February 15, 2025 -
Abstract 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 *= 106.5–9.5M ⊙(M 200m= 1010.0–11.5M ⊙) using the Hubble Space Telescope/Cosmic Origins Spectrograph. While Hi (Lyα ) is ubiquitously detected (89%) within the CGM, we find low detection rates (≈5%–22%) in Cii , Civ , Siii , Siiii , and Siiv , largely consistent with literature values. Assuming these ions form in the cool (T ≈ 104K) CGM with photoionization equilibrium, the observed Hi 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 withM 200m= 1010.9M ⊙(median of the sample), our model predicts a cool gas mass ofM CGM,cool∼ 108.4M ⊙, corresponding to ∼2% of the galaxy’s baryonic budget. Assuming a metallicity of 0.3Z ⊙, 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 Hi and low ions may arise from a dense cool medium, while Civ 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. -
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 Hi and low/intermediate metal ions (Cii , Ciii , Siii , Siiii , and Mgii ) mean column densities. Variation of ±0.5 dex inη orM coolencompasses ∼2/3 of the scatter between objects. Our nominal model underproduces the measured Civ and Siiv columns, 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 over long timescales. -
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 Ovi absorption within 400 projected kpc and 300 km s−1of 52 galaxies withM *∼ 3 × 1010M ⊙. The galaxies have redshifts 0.12 <z < 0.6, stellar masses 1010.1M ⊙<M *< 1010.9M ⊙, and spectroscopic classifications as star-forming or passive. We compare the incidence rates of high column density Ovi absorption (N OVI ≥ 1014.3cm−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 Ovi covering fraction within 150 kpc is higher around star-forming galaxies than around passive galaxies with greater than 3σ -equivalent statistical significance. On average, the CGM of star-forming galaxies withM *∼ 3 × 1010M ⊙contains more Ovi 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 CGM2and 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 atz < 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 Hi Lyα . 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 ofR crossas 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 thatR cross(M ⋆) ≈ 2.0 ± 0.6R vir. Additionally, we find excellent agreement betweenR cross(M ⋆) and the theoretically determined splashback radius for galaxies in this mass range. Overall, our results favor models of galaxy evolution atz < 0.5 that distributeT ≈ 104K gas to distances beyond the virial radius. -
Abstract The circumgalactic medium (CGM) is often assumed to exist in or near hydrostatic equilibrium, with the regulation of accretion and the effects of feedback treated as perturbations to a stable balance between gravity and thermal pressure. We investigate global hydrostatic equilibrium in the CGM using four highly resolved
L *galaxies from the Figuring Out Gas & Galaxies in Enzo (FOGGIE) project. The FOGGIE simulations were specifically targeted at fine spatial and mass resolution in the CGM (Δx ≲ 1 kpch −1andM ≃ 200M ⊙). We develop a new analysis framework that calculates the forces provided by thermal pressure gradients, turbulent pressure gradients, ram pressure gradients of large-scale radial bulk flows, centrifugal rotation, and gravity acting on the gas in the CGM. Thermal and turbulent pressure gradients vary strongly on scales of ≲5 kpc throughout the CGM. Thermal pressure gradients provide the main supporting force only beyond ∼0.25R 200, or ∼50 kpc atz = 0. Within ∼0.25R 200, turbulent pressure gradients and rotational support provide stronger forces than thermal pressure. More generally, we find that global equilibrium models are neither appropriate nor predictive for the small scales probed by absorption line observations of the CGM. Local conditions generally cannot be derived by assuming a global equilibrium, but an emergent global equilibrium balancing radially inward and outward forces is obtained when averaging over the nonequilibrium local conditions on large scales in space and time. Approximate hydrostatic equilibrium holds only at large distances from galaxies, even when averaging out small-scale variations. -
Abstract We use hydrodynamical simulations of two Milky Way–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 Ovi absorption features and broader Siiii 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.