2023/02/01 by Yakov Faerman, Jessica K. Werk, Faerman, Yakov +1 · 1 citation
Chemistry · Physics and Astronomy · #Astrophysics and Star Formation Studies #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena #Spectroscopy and Laser Applications
paper · pdf · doi:10.48550/arxiv.2302.00692
openalex publication_date 2023/02/01 · openalex created_date 2023/02/04 · openalex updated_date 2026/07/28
We present an analytic model for the cool, T ≈ 104 K, circumgalactic medium (CGM), describing the gas distribution, thermal and ionization state. Our model assumes (total) pressure equilibrium with the ambient warm/hot CGM, photoionization by the metagalactic radiation field, and allows for non-thermal pressure support, parametrized by the ratio of thermal pressures, η= P\rm hot,th/P\rm cool,th. We apply the model to the COS-Halos data set and find that a nominal model with η= 3, gas distribution out to r ≈ 0.6 R\rm vir, and M\rm cool = 3 × 109~\rm M\odot, corresponding to a volume filling fraction of f\rm V,cool ≈ 1%, reproduces the mean measured column densities of HI and low/intermediate metal ions (CII, CIII, SiII, SiIII, MgII). Variation of ± 0.5 dex in the non-thermal pressure or gas mass encompasses ∼ 2/3 of the scatter between objects. Our nominal model underproduces the measured CIV and SiIV columns, and we show these can be reproduced with (i) a cool phase with M\rm cool ≈ 1010~\rm M\odot and η≈ 5, or (ii) an additional component at intermediate temperatures, of cooling or mixing gas, with M ≈ 1.5 × 1010~\rm M\odot and occupying ∼ 1/2 of the total CGM volume. For cool gas with f\rm V,cool ≈ 1% we provide an upper limit on the cloud sizes, R\rm cl \lesssim 0.5 kpc. Our results suggest that for the average galaxy CGM, the mass and non-thermal support in the cool phase are lower than estimated in previous works, and extreme scenarios for galactic feedback and non-thermal support may not be necessary. We estimate the rates of cool gas depletion and replenishment, and find accretion onto the galaxy can be entirely offset by condensation, outflows, and IGM accretion, allowing M\rm cool∼0 over long timescales.