Hints on the nature of dark matter from the properties of Milky Way satellites

Abstract

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