The effect of cosmic rays on the observational properties of the CGM
Résumé
The circumgalactic medium (CGM) contains information on the cumulative effect of galactic outflows over time, generally thought to be caused by feedback from star formation and active galactic nuclei. Observations of such outflows via absorption in CGM gas of quasar sightlines show a significant amount of cold (|${\lesssim}10^4\,{\rm K}$|) gas, which cosmological simulations struggle to reproduce. Here, we use the adaptive mesh refinement hydrodynamical code Ramses to investigate the effect of cosmic rays (CR) on the cold gas content of the CGM using three zoom realizations of a z = 1 star-forming galaxy with supernova mechanical feedback: one with no CR feedback (referred to as no-CR), one with a medium CR diffusion coefficient |$\kappa = 10^{28} \, \rm {cm^{2}\, s^{-1}}$| (CR−κ_med), and one with a high rate of diffusion of |$\kappa = 3\times 10^{29} \, \rm {cm^{2}\,\, s^{-1}}$| (CR−κ_high). We find that, for CR−κ_med, the effects of CRs are largely confined to the galaxy itself as CRs do not extend far into the CGM. However, for CR−κ_high, the CGM temperature is lowered and the amount of outflowing gas is boosted. Our CR simulations fall short of the observed Mg ii covering fraction, a tracer of gas at temperatures |${\lesssim}10^4\,{\rm K}$|, but the CR−κ_high simulation is more in agreement with covering fractions of C iv and O vi, which trace higher temperature gas.
Domaines
Astrophysique [astro-ph]
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