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25 April 2024 |
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Article overview
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Properties of the Circumgalactic Medium in Cosmic Ray-Dominated Galaxy Halos | | Suoqing Ji
; T. K. Chan
; Cameron B. Hummels
; Philip F. Hopkins
; Jonathan Stern
; Dušan Kereš
; Eliot Quataert
; Claude-André Faucher-Giguère
; Norman Murray
; | | Date: |
30 Aug 2019 | | Abstract: | We investigate the impact of cosmic rays (CRs) on the circumgalactic medium
(CGM) in FIRE-2 simulations, for ultra-faint dwarf through Milky Way (MW)-mass
halos hosting star-forming (SF) galaxies. Our CR treatment includes injection
by supernovae, anisotropic streaming and diffusion along magnetic field lines,
collisional and streaming losses, with constant parallel diffusivity
$kappasim3 imes10^{29},mathrm{cm^2 s^{-1}}$ chosen to match $gamma$-ray
observations. With this, CRs become more important at larger halo masses and
lower redshifts, and dominate the pressure in the CGM in MW-mass halos at
$zlesssim 1-2$. The gas in these ’’CR-dominated’’ halos differs significantly
from runs without CRs: the gas is primarily cool (a few $sim10^{4},$K), and
the cool phase is volume-filling and has a thermal pressure below that needed
for virial or local thermal pressure balance. Ionization of the ’’low’’ and
’’mid’’ ions in this diffuse cool gas is dominated by photo-ionization, with O
VI columns $gtrsim 10^{14.5},mathrm{cm^{-2}}$ at distances $gtrsim
150,mathrm{kpc}$. CR and thermal gas pressure are locally anti-correlated,
maintaining total pressure balance, and the CGM gas density profile is
determined by the balance of CR pressure gradients and gravity. Neglecting CRs,
the same halos are primarily warm/hot ($Tgtrsim 10^{5},$K) with thermal
pressure balancing gravity, collisional ionization dominates, O VI columns are
lower and Ne VIII higher, and the cool phase is confined to dense filaments in
local thermal pressure equilibrium with the hot phase. | | Source: | arXiv, 1909.0003 | | Services: | Forum | Review | PDF | Favorites | |
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