Interactions between Dark Matter Substructure and Galaxies

Abstract

In this thesis we study how subhaloes evolve and interact in the central regions of galactic dark matter haloes in a ΛCDM universe. We examine the effect that subhalo impacts have on disc galaxies and what visible signatures they leave behind. We use the Aquarius simulations, a set of high resolution simulations of Milky Way mass haloes, as the basis of the work in this thesis. We summarise the main properties of these haloes and show that they are typical haloes for most characteristics.

We develop a method to approximate the potential of host haloes that helps us understand how subhaloes evolve in the tidal field of their host. Using a basis function expansion method, we show that it is possible to create a time-evolving density/potential approximation of the late growth of simulated N-body dark matter haloes, and that particle and subhalo orbits can be integrated in this realistic, time-varying halo potential approximation at much lower computational cost than the original simulations.

Using samples of subhaloes extracted from the Aquarius haloes, we estimate the disc heating caused by substructure bombardment using the Benson et al. (2004) semi-analytical model. A critical evaluation of the model, however, finds that there are problems with the original implementation, including a numerical factor, that call into question its validity. We then approach the same problem using high resolution N-body simulations of subhalo interactions with discs. We find that only the most massive of subhaloes appreciably affect stellar discs, heating and thickening them, and that the majority of any heating occurs at early times and happens quickly. However, the substructure bombardment since redshift one is negligible in most of the haloes, and in the haloes that do show significant heating it is caused by a single massive subhalo.