The Cool Circumgalactic Medium of Low-redshift Star-forming Galaxies. I. Empirical Model and Mean Properties
We present an analytic model for the cool, T ∼ 10 ^4 K, 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 nonther...
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| Format: | Article |
| Language: | English |
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IOP Publishing
2023-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/acf217 |
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| author | Yakov Faerman Jessica K. Werk |
| author_facet | Yakov Faerman Jessica K. Werk |
| author_sort | Yakov Faerman |
| collection | DOAJ |
| description | We present an analytic model for the cool, T ∼ 10 ^4 K, 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 with η = 3, gas distribution out to r ≈ 0.6 R _vir , and M _cool = 3 × 10 ^9 M _⊙ , corresponding to a volume filling fraction of f _V,cool ≈ 1%, reproduces the H i and low/intermediate metal ions (C ii , C iii , Si ii , Si iii , and Mg ii ) mean column densities. Variation of ±0.5 dex in η or M _cool encompasses ∼2/3 of the scatter between objects. Our nominal model underproduces the measured C iv and Si iv columns, and these can be reproduced with (i) a cool phase with M _cool ∼ 10 ^10 M _⊙ and η ≈ 5, or (ii) cooling or mixing gas at intermediate temperatures, with M ∼ 1.5 × 10 ^10 M _⊙ and occupying ∼1/2 of the total CGM volume. For cool gas with f _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. |
| first_indexed | 2024-03-11T18:52:41Z |
| format | Article |
| id | doaj.art-7491ab5a8cfb4e848cc7d2da82b29022 |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-11T18:52:41Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-7491ab5a8cfb4e848cc7d2da82b290222023-10-11T09:00:40ZengIOP PublishingThe Astrophysical Journal1538-43572023-01-0195629210.3847/1538-4357/acf217The Cool Circumgalactic Medium of Low-redshift Star-forming Galaxies. I. Empirical Model and Mean PropertiesYakov Faerman0https://orcid.org/0000-0003-3520-6503Jessica K. Werk1https://orcid.org/0000-0002-0355-0134Astronomy Department, University of Washington , Seattle, WA 98195, USA ; yakov.faerman@gmail.comAstronomy Department, University of Washington , Seattle, WA 98195, USA ; yakov.faerman@gmail.comWe present an analytic model for the cool, T ∼ 10 ^4 K, 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 with η = 3, gas distribution out to r ≈ 0.6 R _vir , and M _cool = 3 × 10 ^9 M _⊙ , corresponding to a volume filling fraction of f _V,cool ≈ 1%, reproduces the H i and low/intermediate metal ions (C ii , C iii , Si ii , Si iii , and Mg ii ) mean column densities. Variation of ±0.5 dex in η or M _cool encompasses ∼2/3 of the scatter between objects. Our nominal model underproduces the measured C iv and Si iv columns, and these can be reproduced with (i) a cool phase with M _cool ∼ 10 ^10 M _⊙ and η ≈ 5, or (ii) cooling or mixing gas at intermediate temperatures, with M ∼ 1.5 × 10 ^10 M _⊙ and occupying ∼1/2 of the total CGM volume. For cool gas with f _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.https://doi.org/10.3847/1538-4357/acf217Circumgalactic mediumGalaxy structureGalaxy evolutionQuasar absorption line spectroscopyIntergalactic mediumGalaxy formation |
| spellingShingle | Yakov Faerman Jessica K. Werk The Cool Circumgalactic Medium of Low-redshift Star-forming Galaxies. I. Empirical Model and Mean Properties The Astrophysical Journal Circumgalactic medium Galaxy structure Galaxy evolution Quasar absorption line spectroscopy Intergalactic medium Galaxy formation |
| title | The Cool Circumgalactic Medium of Low-redshift Star-forming Galaxies. I. Empirical Model and Mean Properties |
| title_full | The Cool Circumgalactic Medium of Low-redshift Star-forming Galaxies. I. Empirical Model and Mean Properties |
| title_fullStr | The Cool Circumgalactic Medium of Low-redshift Star-forming Galaxies. I. Empirical Model and Mean Properties |
| title_full_unstemmed | The Cool Circumgalactic Medium of Low-redshift Star-forming Galaxies. I. Empirical Model and Mean Properties |
| title_short | The Cool Circumgalactic Medium of Low-redshift Star-forming Galaxies. I. Empirical Model and Mean Properties |
| title_sort | cool circumgalactic medium of low redshift star forming galaxies i empirical model and mean properties |
| topic | Circumgalactic medium Galaxy structure Galaxy evolution Quasar absorption line spectroscopy Intergalactic medium Galaxy formation |
| url | https://doi.org/10.3847/1538-4357/acf217 |
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