An official website of the United States government
Abstract We investigate the 1D plane-parallel front connecting the warm (104K) and hot (106K) phases of the circumgalactic medium (CGM), focusing on the influence of cosmic rays (CRs) in shaping these transition layers. We find that cosmic rays dictate the thermal balance while other fluxes (thermal conduction, radiative cooling, and gas flow) adjust to compensate. We compute column densities and ratios for the transition-temperature ions Siiv, Civ, Ovi, and Nv, and compare them with observational data. While most models struggle to simultaneously reproduce the observed Siiv/Civand Civ/Oviratios, a subset with intermediate magnetic field strength (e.g.,B= 20μG) shows overlap with the data, although we make no claims for their uniqueness. These discrepancies suggest that the models perform better at reproducing higher-temperature ions but underestimate the contribution from cooler, photoionized regions. Compared to models without CRs, CR-mediated fronts in sufficiently strong magnetic fields produce broader transition layers and higher ion ratios, indicating that CRs can significantly alter the thermal and ionization structure of the CGM. Our results suggest that CR heating may help explain some observed ion columns under specific conditions, though additional physics may be needed for full agreement with observations.
more »
« less
This content will become publicly available on October 23, 2026
Highly Ionized Gas in the Zone of Avoidance: Using the CIViL ⋆ Survey to Pinpoint Physical Conditions of Gaseous Halos
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 ≤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 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.
more »
« less
- Award ID(s):
- 2044303
- PAR ID:
- 10688926
- Publisher / Repository:
- Astrophysical Journal
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 993
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 44
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract In dwarf galaxy models, outflows expel metal-enriched interstellar medium (ISM) into the circumgalactic medium (CGM) to reproduce their observed low metallicities, but measurements of dwarf CGM properties are scarce. We present a study of the CGM of an isolated dwarf atz= 0.5723 with a stellar mass of ≈5 × 107M⊙and star formation rate (≈0.05M⊙yr−1) and ISM metallicity ([O/H] ≈ −0.9) consistent with the star-forming main sequence and mass–metallicity relation. A background quasar sight line with archival UV spectra probes the dwarf’s CGM at a projected distance of 28 kpc, corresponding to approximately half of the estimated virial radius. The dwarf’s CGM is detected in Hi;intermediate metal ions of Ciii, Oiii, Oiv, and Sv; and kinematically broader, highly ionized Ovibut is undetected in Nivand Neviii. Photoionization modeling of the intermediate ions indicates a modest volume filling factor (∼6% along the sight line or ∼2% globally) and a mass of ∼2 × 108M⊙, ∼4× higher than the dwarf’s stellar mass but ∼10× less than the highly ionized CGM. The Ovikinematics are comparable to the dwarf’s estimated virial velocity, suggesting that it is likely associated with cool, photoionized, and volume-filling CGM, with bulk motion or turbulence dominating over thermal pressure. The metallicity inferred for the intermediate ions is [O/H] = −0.6, but with low relative abundances of [C/O] = −0.6 and [N/O] < −1.0. The [N/O] is below levels expected of the dwarf’s ISM but consistent with core-collapse supernova ejecta, suggesting that supernova-enriched gas escaped the dwarf without mixing significantly with ISM enriched in nitrogen from evolved, low-mass stars.more » « less
-
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 (Rproj) 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 log10MBH/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 (NC IV; average log10NC IV,CH= 13.94 ± 0.09 cm−2) are largely consistent with existing measurements from other surveys ofNC IVin the CGM (average log10NC 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 log10MBH/M⊙> 7.0, where the CGM CIVcontent shows a clear dependence on galaxy sSFR but notMBH. 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.more » « less
-
Abstract We measure line-of-sight velocities of metal absorption and HIemission along 132 QSO sight lines in order to study gas accretion and outflow at the disk–halo interface of the Milky Way. While previous studies have focused on high- and intermediate-velocity clouds and complexes, we examine material at predominantly low velocities relative to the local standard of rest (i.e., all absorbers at ∣vLSR∣ < 90 km s−1, and absorbers at 90 < ∣vLSR∣ < 150 km s−1not associated with any well-defined cloud complexes). We find that gas accretion velocities in the northern Galactic hemisphere are correlated with the ionization potential energy of the multiphase metal ions we include in our analysis; more highly ionized material traced by Civ, Siiv, and Nvis moving toward the disk 10−15 km s−1faster than low ionization state material traced by Sii, Cii* , and Niii. We interpret this dependence as potential evidence of warm accreting gas cooling as it reaches the disk–halo interface, causing a pileup of slower-moving cool gas. We find that with the number of available sight lines, kinematic modeling cannot rule out exponential density distributions or layers of gas that sandwich the Galactic disk. Our results paint a picture of a complex, dynamic disk–halo interface in which low-velocity material likely plays an important role in fueling star formation in the Milky Way.more » « less
-
Abstract We analyze the cool gas in and around 14 nearby galaxies (at z < 0.1) mapped with the Sloan Digital Sky Survey IV MaNGA survey by measuring absorption lines produced by gas in spectra of background quasars/active galactic nuclei at impact parameters of 0–25 effective radii from the galactic centers. Using Hubble Space Telescope/Cosmic Origins Spectrograph, we detect absorption at the galactic redshift and measure or constrain column densities of neutral (H i , N i , O i , and Ar i ), low-ionization (Si ii , S ii , C ii , N ii , and Fe ii ), and high-ionization (Si iii , Fe iii , N v , and O vi ) species for 11 galaxies. We derive the ionization parameter and ionization-corrected metallicity using cloudy photoionization models. The H i column density ranges from ∼10 13 to ∼10 20 cm −2 and decreases with impact parameter for r ≳ R e . Galaxies with higher stellar mass have weaker H i absorption. Comparing absorption velocities with MaNGA radial velocity maps of ionized gas line emissions in galactic disks, we find that the neutral gas seen in absorption corotates with the disk out to ∼10 R e . Sight lines with lower elevation angles show lower metallicities, consistent with the metallicity gradient in the disk derived from MaNGA maps. Higher-elevation angle sight lines show higher ionization, lower H i column density, supersolar metallicity, and velocities consistent with the direction of galactic outflow. Our data offer the first detailed comparisons of circumgalactic medium (CGM) properties (kinematics and metallicity) with extrapolations of detailed galaxy maps from integral field spectroscopy; similar studies for larger samples are needed to more fully understand how galaxies interact with their CGM.more » « less
