Outflows of heavy elements with and without Cosmic Rays


This compares a Milky Way mass galaxy at present day (our “m12i” galaxy), evolving over cosmic time, in mean projected metallicity (abundance of heavy elements synthesized in supernova explosions), 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, leading to bursty “venting” events, and a highly-variable and irregular outflow morphology. With CRs, because the dominant pressure is in CRs, outflows can be more “gently” accelerated out through the CGM, and lower pressures resist outflows, leading to gentler, more steady outflow activity which retains a more biconical morphology. Movie made by Cameron Hummels.

© Philip Hopkins 2015