Dwarf Galaxies as Probes of the Nature and Distribution of Dark Matter

Abstract

is presently the most successful, and simplest, model of our Universe. The model consists of two main ingredients. The first is dark energy, , causing our Universe to expand. The second is cold dark matter (CDM), an unknown substance that makes up most of the matter content of our Universe. Despite the numerous successes of on large scales, problems persist on small scales -- the scales of dwarf galaxies. predicts that galaxies should reside in ``haloes'' of dark matter, in which the central density distribution should follow a steep power-law ``cusp''. This is contrary to observations, which instead suggest a constant density ``core''. This discrepancy became known as the ``core-cusp problem''. In this thesis, I focus on the possible solutions to this problem. I first examine a particular kind of dwarf galaxies, which contain two spatially and chemo-dynamically distinct stellar populations. These can provide independent constraints on the dark matter density distribution. I show that various formation mechanisms of the two populations sometimes result in them exhibiting varying degrees of asphericity and spatial misalignment. These phenomena complicate dynamical analyses, resulting in a false inference of a core. I then move on to test various Jeans equation-based approaches on a sample of fully cosmological simulated dwarf galaxies in Cold and Self-interacting dark matter models. I show that the line-of-sight data alone is, at present, insufficient to distinguish between cores and cusps, even when constraints from higher-order moments of the velocity distribution are available. Finally, I look at the evidence for a core in the Fornax dwarf galaxy, suggested by its low inferred central dark matter density. I show that, within the framework, Fornax is consistent with having a cuspy halo the density of which has been reduced by Galactic tides.