ABSTRACT We investigate the impact of cosmic rays (CRs) on the circumgalactic medium (CGM) in FIRE2 simulations, for ultrafaint dwarf through Milky Way (MW)mass haloes hosting starforming (SF) galaxies. Our CR treatment includes injection by supernovae, anisotropic streaming and diffusion along magnetic field lines, and collisional and streaming losses, with constant parallel diffusivity $\kappa \sim 3\times 10^{29}\, \mathrm{cm^2\ s^{1}}$ chosen to match γray observations. With this, CRs become more important at larger halo masses and lower redshifts, and dominate the pressure in the CGM in MWmass haloes at z ≲ 1–2. The gas in these ‘CRdominated’ haloes differs significantly from runs without CRs: the gas is primarily cool (a few ${\sim}10^{4}\,$ K), and the cool phase is volumefilling 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 photoionization, with O vi columns ${\gtrsim}10^{14.5}\, \mathrm{cm^{2}}$ at distances ${\gtrsim}150\, \mathrm{kpc}$. CR and thermal gas pressure are locally anticorrelated, 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 haloes are primarily warm/hot ($T\gtrsim 10^{5}\,$K) with thermal pressure balancing gravity,more »
This content will become publicly available on January 1, 2023
Regimes of cosmicray diffusion in Galactic turbulence
Abstract Cosmicray transport in astrophysical environments is often dominated by the diffusion of particles in a magnetic field composed of both a turbulent and a mean component. This process, which is twofold turbulent mixing in that the particle motion is stochastic with respect to the field lines, needs to be understood in order to properly model cosmicray signatures. One of the most important aspects in the modeling of cosmicray diffusion is that fully resonant scattering, the most effective such process, is only possible if the wave spectrum covers the entire range of propagation angles. By taking the wave spectrum boundaries into account, we quantify cosmicray diffusion parallel and perpendicular to the guide field direction at turbulence levels above 5% of the total magnetic field. We apply our results of the parallel and perpendicular diffusion coefficient to the Milky Way. We show that simple purely diffusive transport is in conflict with observations of the inner Galaxy, but that just by taking a Galactic wind into account, data can be matched in the central 5 kpc zone. Further comparison shows that the outer Galaxy at $$>5$$ > 5 kpc, on the other hand, should be dominated by perpendicular diffusion, likely changing to more »
 Award ID(s):
 2007323
 Publication Date:
 NSFPAR ID:
 10348583
 Journal Name:
 SN Applied Sciences
 Volume:
 4
 Issue:
 1
 ISSN:
 25233963
 Sponsoring Org:
 National Science Foundation
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