Circum-galactic Phases with and without Cosmic Rays

This compares a Milky Way mass galaxy at present day (our “m12i” galaxy), evolving over cosmic time, in column density of gas (left) and mass-weighted mean gas temperature (right), comparing a model with detailed physics of cooling, star formation, stellar feedback, supernovae, magnetic fields, conduction, viscosity, and more (top), and a model including all of that but also cosmic rays (CRs)  accelerated in supernovae, followed fully-explicitly with anisotropic diffusion and streaming, hadronic collisions, resonant Alfven wave interactions, and more (bottom). The extended halo of cosmic rays (shown in the previous movie) provides dominant pressure support at late times. This has a dramatic impact on the phase structure of the CGM. Without CRs, the cold gas is primarily in small, relatively dense and thermally-unstable “clouds” which come and go (and fragment down to our resolution limit), and outflows are very ‘hot’ and explosive. With CRs, because the dominant pressure is in CRs, diffuse cool/warm gas can be supported against gravity and gas at a wide range of temperatures can co-exist at similar densities, generating a broad/diffuse, volume-filling, low-density “warm" phase. Movie made by Cameron Hummels.

© Philip Hopkins 2015