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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=Phot,th/Pcool,th. We apply the model to the COS-Halos measurements and find that a nominal model withη= 3, gas distribution out tor≈ 0.6Rvir, andMcool= 3 × 109M⊙, corresponding to a volume filling fraction offV,cool≈ 1%, reproduces the Hiand low/intermediate metal ions (Cii, Ciii, Siii, Siiii, and Mgii) mean column densities. Variation of ±0.5 dex inηorMcoolencompasses ∼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 withMcool∼ 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 withfV,cool≈ 1%, we estimate an upper limit on the cloud sizes,Rcl≲ 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.
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A Comprehensive Investigation of Metals in the Circumgalactic Medium of Nearby Dwarf Galaxies
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 withM*= 106.5–9.5M⊙(M200m= 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 Hiand 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 withM200m= 1010.9M⊙(median of the sample), our model predicts a cool gas mass ofMCGM,cool∼ 108.4M⊙, 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 Hiand low ions may arise from a dense cool medium, while Civarises 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.
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- PAR ID:
- 10516757
- Publisher / Repository:
- The Astrophysical Journal
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 960
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 55
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.3847/1538-4357/acfe6b
