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

Cosmology and Nongalactic Astrophysics