Speaker
Description
Despite the many successes of cosmological galaxy formation and evolution simulations, they commonly implement baryonic feedback in a phenomenological manner by calibrating “boosting” parameters, which somewhat diminishes their predictive power and restricts their usefulness in interpreting observational data. An alternative approach is to improve the modelling of feedback processes from first principles, by self-consistently including components which have by-and-large been overlooked. One of these alternatives has been to model cosmic rays (CRs) injected by supernova shocks, which has been seen to have a drastic effect on the evolution of Milky Way-like galaxies and the thermal state of their interstellar medium (ISM). Given their slow-cooling properties, they can efficiently transport stellar-injected energy from the ISM to the large scales of the circum-galactic medium (CGM). Using a suite of high-resolution cosmological zoom simulations of a Milky Way analogue including magnetic fields and CR injection via supernovae, we have explored the role of CR feedback in the thermo-dynamical state of the CGM. While simulations without CRs present the classical, cold filamentary accretion at high redshift, strong feedback in the CR simulation disrupts these inflows well beyond the virial region, resulting in lower-density material approaching the inner halo. This deceleration of streaming inflows creates a reservoir of low-velocity gas at a distance between 0.3 and 0.5 times the virial radius. We have determined that this
reservoir of low-velocity gas is predominantly warm ionised gas supported by CR pressure gradients, continuously heated by the UV background. We term this newly characterised region of the CGM the meta-stable CR corona. Based on this new understanding of the dynamical properties of inflows and the CGM in the presence of CRs, we present criteria for the stability of cosmological accretion shocks taking into account CR heating and transport, as well as a CR+thermal gas mixture. We present how these results can be used to extend current models of galaxy formation to take into account the multi-scale impact of CRs across cosmic time.
