The haloes of bright satellite galaxies in a warm dark matter universe

Abstract

High resolution N-body simulations of galactic cold dark matter haloes\nindicate that we should expect to find a few satellite galaxies around the\nMilky Way whose haloes have a maximum circular velocity in excess of 40 kms.\nYet, with the exception of the Magellanic Clouds and the Sagittarius dwarf,\nwhich likely reside in subhaloes with significantly larger velocities than\nthis, the bright satellites of the Milky Way all appear to reside in subhaloes\nwith maximum circular velocities below 40 kms. As recently highlighted by\nBoylan-Kolchin et al., this discrepancy implies that the majority of the most\nmassive subhaloes within a cold dark matter galactic halo are much too\nconcentrated to be consistent with the kinematic data for the bright Milky Way\nsatellites. Here we show that no such discrepancy exists if haloes are made of\nwarm, rather than cold dark matter because these haloes are less concentrated\non account of their typically later formation epochs. Warm dark matter is one\nof several possible explanations for the observed kinematics of the satellites.\n