UC San Diego

In Chapter 2, we study the inner dark matter profiles of galaxies with halo masses between 1e9-1e12Msun and stellar masses between 1e4-1e11Msun in the ``Feedback In Realistic Environment'' (FIRE) cosmological simulations. We find repeated episodes of feedback-driven outflows can transfer energy to DM and flatten the inner DM profiles. kpc-size DM cores form in galaxies with halo masses similar 1e11Msun, since feedback energy is sufficient to reduce inner DM density. At halo mass similar to 1e12 Msun, baryonic infall into halo center can contract DM halos, which effectively cancel the effect from feedback, producing DM profiles close to the Navarro-Frenk-White (NFW) profile.

In Chapter 3, we study the formation mechanism of the ultra diffuse galaxies (UDGs) with galaxies with the z=0 stellar masses between 1e4-1e11Msun in the cosmological FIRE simulations. We show dwarf galaxies with stellar mass similar to 1e8 Msun, expanded by stellar feedback, quenched, and then passively evolving in galaxy clusters, can reproduce the properties of ``red'' UDGs. We find if those dwarf galaxies are not quenched, they produce blue diffuse galaxies, which could be prevalent in the field environment.

In Chapter 4, we present the first implementation of the cosmic ray (CR) feedback in the FIRE simulation. We study non cosmological simulations of dwarf, dwarf starburst, and Lstar galaxies with CR feedback, including advection, isotropic/anisotropic diffusion, and/or streaming. We constrain CR propagation models by comparing the simulated star formation rate and GeV gamma-ray emission with the observed nearby and starburst galaxies. We find the ``effective'' isotropic diffusion coefficients to be around 3e29cm^2/s to match the observations.