Using Hydrodynamic Simulations To Understand The Structure And Composition Of The Circumgalactic Medium Of Milky Way Sized Galaxies

We explore the structure and evolution of baryons within Milky Way-sized halos (M ~ 1012 Msun) via hydrodynamic simulations. First, we employ a two-fluid model to study the dynamics of a relativistic, diffusive cosmic ray proton (CR) fluid interacting with the thermal interstellar medium (ISM). This model was implemented into the eulerian hydrodynamics code enzo, used throughout this dissertation. After testing this model on analytically tractable scenarios in one dimension, it is unleashed upon an idealized disk simulation in a rapidly-star forming setting, where we find evidence for robust, mass-loaded winds driven by the diffusive CR fluid. These winds reduce the galaxy’s star formation rate (SFR) and circulate on order as much mass into winds as into forming stars. We then extend this model to a cosmological setting where the diffuse CR fluid proves capable of redistributing star formation within the forming disk, reducing the overly-peaked rotation curves in non-CR runs and producing thin, extended disks with visible spiral structure.