ABSTRACT We analyse the different fates of the circumgalactic medium (CGM) in FIRE-2 cosmological simulations, focusing on the redshifts z = 0.25 and 2 representative of recent surveys. Our analysis includes 21 zoom-in simulations covering the halo mass range $M_{\rm h}(z=0) \sim 10^{10} \!-\! 10^{12} \rm {\,M}_\odot$. We analyse both where the gas ends up after first leaving the CGM (its ‘proximate’ fate) and its location at z = 0 (its ‘ultimate’ fate). Of the CGM at z = 2, about half is found in the ISM or stars of the central galaxy by z = 0 in Mh(z = 2) ∼ 5 × 1011 M⊙ haloes, but most of the CGM in lower mass haloes ends up in the intergalactic medium (IGM). This is so even though most of the CGM in Mh(z = 2) ∼ 5 × 1010 M⊙ haloes first accretes on to the central galaxy before being ejected into the IGM. On the other hand, most of the CGM mass at z = 0.25 remains in the CGM by z = 0 at all halo masses analysed. Of the CGM gas that subsequently accretes on to the central galaxy in the progenitors of Mh(z = 0) ∼ 1012 M⊙ haloes, most of it is cool (T ∼ 104 K) at z = 2 but hot (∼Tvir) at z ∼ 0.25, consistent with the expected transition from cold mode to hot mode accretion. Despite the transition in accretion mode, at both z = 0.25 and $2 \, {\gtrsim} 80{{\ \rm per\ cent}}$ of the cool gas in $M_{\rm h} \gtrsim 10^{11} \rm {M}_\odot$ haloes will accrete on to a galaxy. We find that the metallicity of CGM gas is typically a poor predictor of both its proximate and ultimate fates. This is because there is in general little correlation between the origin of CGM gas and its fate owing to substantial mixing while in the CGM.
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The origins of the circumgalactic medium in the FIRE simulations
ABSTRACT 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 $\gtrsim\! 50\hbox{ per cent}$ of their cosmic budget. Metals are more efficiently retained by haloes, with a retention fraction $\gtrsim\! 50\hbox{ per cent}$. Across all masses and redshifts analysed $\gtrsim \!60\hbox{ per cent}$ 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.
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- NSF-PAR ID:
- 10105536
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 488
- Issue:
- 1
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- 1248 to 1272
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/mnras/stz1773
