Probing the nature of dark matter with Milky Way subhaloes

The nature of dark matter is one of the most pressing questions in modern physics. Efforts to answer this question have centred on observations that determine its impact on the properties of galaxies plus attempts to detect rare events in which the dark matter indirectly generates photons. In this talk I presented work on using the properties of Milky Way satellite galaxies to constrain models of self-interacting dark matter (SIDM) and warm dark matter (WDM). First I used N-body simulations of an SIDM model with a very large self-interaction at low relative velocities (sigma > 100 cm(2)gr(-1)) to demonstrate that subhaloes in such models undergo gravothermal collapse and increase the diversity of satellite matter distributions in line with inferences from observations. Second, I considered the radial distribution of subhaloes in WDM simulations from the point-of-view of stellar stream gap constraints. I showed that the subhalo population within 50 kpc of the host halo centre is comprised of massive satellites that have sunk under dynamical friction. Given that the abundance and structure of massive satellites in WDM is very similar to the fiducial cold dark matter (CDM) model, the differences between the subhalo populations in the two models in the inner halo are much smaller than for the halo as a whole, and therefore the stellar stream gaps statistics, which are only available out to 30 kpc, are not as powerful at discriminating between the models as previously anticipated. I ended with a brief presentation of estimates for the production rate of X-ray photons in dark matter decay, and predicted that the velocity dispersion of X-ray decay lines to be probed in nearby galaxy clusters will have values in the range [500,800] kms(-1).