The origins of the circumgalactic medium in the FIRE simulations

Zachary Hafen*, Claude André Faucher-Giguère, Daniel Anglés-Alcázar, Jonathan Stern, Dušan Kereš, Cameron Hummels, Clarke Esmerian, Shea Garrison-Kimmel, Kareem El-Badry, Andrew Wetzel, T. K. Chan, Philip F. Hopkins, Norman Murray

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

142 Scopus citations


We use a particle tracking analysis to study the origins of the circumgalactic medium (CGM), separating it into (1) accretion from the intergalactic medium (IGM), (2) wind from the central galaxy, and (3) gas ejected from other galaxies. Our sample consists of 21 FIRE-2 simulations, spanning the halo mass range Mh ∼ 1010–1012 M, and we focus on z = 0.25 and z = 2. Owing to strong stellar feedback, only ∼L haloes retain a baryon mass 50 per cent of their cosmic budget. Metals are more efficiently retained by haloes, with a retention fraction 50 per cent. Across all masses and redshifts analysed 60 per cent of the CGM mass originates as IGM accretion (some of which is associated with infalling haloes). Overall, the second most important contribution is wind from the central galaxy, though gas ejected or stripped from satellites can contribute a comparable mass in ∼L haloes. Gas can persist in the CGM for billions of years, resulting in well mixed-halo gas. Sightlines through the CGM are therefore likely to intersect gas of multiple origins. For low-redshift ∼L haloes, cool gas (T < 104.7 K) is distributed on average preferentially along the galaxy plane, however with strong halo-to-halo variability. The metallicity of IGM accretion is systematically lower than the metallicity of winds (typically by 1 dex), although CGM and IGM metallicities depend significantly on the treatment of subgrid metal diffusion. Our results highlight the multiple physical mechanisms that contribute to the CGM and will inform observational efforts to develop a cohesive picture.

Original languageEnglish
Pages (from-to)1248-1272
Number of pages25
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
StatePublished - 1 Sep 2019
Externally publishedYes


FundersFunder number
Center for Interdisciplinary Exploration and Research in Astrophysics
Flatiron Institute
National Science FoundationAST-1715216, DGE-0948017, 1715847, AST-1652522, AST-1412836, 1455342, AST-1517491
National Aeronautics and Space Administration17-ATP17-0067, NNX15AB22G
Alfred P. Sloan Foundation17-ATP17-0214, JPL 1589742, HST-GO-14734, 80NSSC18K1097, HST-AR-15057, NNX15AT06G
Simons Foundation
Research Corporation for Science Advancement
Northwestern UniversityAST-1714658, HST-AR-13917, AST-1715101
Space Telescope Science InstituteHST-GO-14268.022A, HST-GO-14681.011, HST-AR-14293.001-A
Natural Sciences and Engineering Research Council of Canada
Canada Research ChairsTG-AST130039, TG-AST120025


    • Cosmology: theory
    • Galaxies: evolution
    • Galaxies: formation
    • Galaxies: haloes
    • Galaxies: interactions
    • Intergalactic medium


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