Hints on the Nature of Dark Matter from the Properties of Milky Way
  Satellites
  The nature of dark matter is still unknown and one of the most fundamental
scientific mysteries. Although successfully describing large scales, the
standard cold dark matter model (CDM) exhibits possible shortcomings on
galactic and sub-galactic scales. It is exactly at these highly non-linear
scales where strong astrophysical constraints can be set on the nature of the
dark matter particle. While observations of the Lyman-$\alpha$ forest probe the
matter power spectrum in the mildly non-linear regime, satellite galaxies of
the Milky Way provide an excellent laboratory as a test of the underlying
cosmology on much smaller scales. Here we present results from a set of high
resolution simulations of a Milky Way sized dark matter halo in eight distinct
cosmologies: CDM, warm dark matter (WDM) with a particle mass of 2 keV and six
different cold plus warm dark matter (C+WDM) models, varying the fraction,
$f_{\rm wdm}$, and the mass, $m_{\rm wdm}$, of the warm component. We used
three different observational tests based on Milky Way satellite observations:
the total satellite abundance, their radial distribution and their mass
profile. We show that the requirement of simultaneously satisfying all three
constraints sets very strong limits on the nature of dark matter. This shows
the power of a multi-dimensional small scale approach in ruling out models
which would be still allowed by large scale observations.
