The satellite population of the Milky Way in a ΛCDM universe

We compare the structure and kinematics of the 11 known satellites of the Milky Way with high-resolution simulations of the formation of its dark halo in a LambdaCDM universe. In contrast to earlier work, we find excellent agreement. The observed kinematics are exactly those predicted for stellar populations with the observed spatial structure orbiting within the most massive 'satellite' substructures in our simulations. Less massive substructures have weaker potential wells than those hosting the observed satellites. If there is a halo substructure 'problem', it consists of understanding why halo substructures have been so inefficient in making stars. Suggested modifications of dark matter properties (for example, self-interacting or warm dark matter) may well spoil the good agreement found for standard cold dark matter.