Investigations of the Inner Dark Matter Density Profiles of Dwarf Galaxies using Rotation Curves and Multiple Stellar Populations


UCR Astronomy/High Energy Seminar

Abstract: The Λ cold dark matter (DM) model successfully explains the distribution of large scale structure and the cosmic microwave background but, there are several problems concerning the distribution of DM on sub-galactic scales. I present an analysis of rotation curves testing the (stellar) mass dependent halo profile of Di Cintio et al. (2014). The (stellar) mass dependent halo profile links together the local and global properties of the halo (e.g. inner slope and Mhalo) which allows for measurements of Mhalo without virial tracers. I find that this halo profile can explain rotation curve observations over a wide range of Mstar. However, the expected correlation between halo concentration and Mhalo is not found and a large portion of galaxies below Mstar∼10^9 M⊙ are hosted by smaller halos than expected. This suggests either a mischaracterization of the halo response due to baryonic processes or additional non-standard dark matter physics.

I present a second complementary analysis searching for multiple stellar populations in the Milky Way satellites galaxy, Ursa Minor. If a dispersion supported galaxy contains multiple stellar populations they act as independent tracers and can break modeling degeneracies. This includes new Keck/DEIMOS spectroscopic observations of Ursa Minor and a new technique for separating global stellar populations utilizing metallicty, line-of-sight velocity, and spatial information. I identify two chemodynamical stellar population at high significance with distinct kinematic, metallicity, and spatial distributions. By utilizing the dynamics of multiple stellar populations we find the DM slope is more consistent with a ‘cored’ halo than a ‘cuspy’ halo but several systematics prevent a robust measurement.