The gas phase content and evolution of the circumgalactic medium

The baryon cycle is a key aspect of galaxy evolution that connects different objects and scales together, from individual stars within galaxies to gaseous structures in their surrounding halos. I will present recent work studying multiple aspects of the baryon cycle with different simulations. Using RAMSES zoom-in simulations, I studied the effects of cosmic ray feedback on the circumgalactic medium (CGM) of Milky Way progenitors. I found that the addition of this source of feedback resulted in cooler outflows and an increased covering fraction for certain ions (CIV and OVI) in the CGM, making the simulations more consistent with observations at z~1. This suggests that feedback from cosmic rays could be a crucial missing ingredient from larger galaxy formation codes. I also analyzed similar galaxy-halo systems from a subset of the IllustrisTNG simulation suite with a very high time resolution, allowing for detailed time-series analysis. I found that CGM gas experiences significant changes in many quantities like temperature and also mixes between different phases fairly often on ~200 Myr timescales, largely due to feedback from supernovae. Furthermore, over long enough (~1-2 Gyr) timescales, CGM gas evolves towards a similar state composed of a cold, dense, low-entropy phase at small radius and a hotter, more diffuse, high-entropy phase at large radius, indicating a relatively stable average population of CGM gas that emerges from various complicated evolutionary pathways.