Dark Matter Substructure within Galactic Halos

We use numerical simulations to examine the substructure within galactic andcluster mass halos that form within a hierarchical universe. Clusters areeasily reproduced with a steep mass spectrum of thousands of substructureclumps that closely matches observations. However, the survival of dark mattersubstructure also occurs on galactic scales, leading to the remarkable resultthat galaxy halos appear as scaled versions of galaxy clusters. The modelpredicts that the virialised extent of the Milky Way's halo should containabout 500 satellites with circular velocities larger than Draco and Ursa-Minori.e. bound masses > 10^8Mo and tidally limited sizes > kpc. The substructureclumps are on orbits that take a large fraction of them through the stellardisk leading to significant resonant and impulsive heating. Their abundance andsingular density profiles has important implications for the existence of oldthin disks, cold stellar streams, gravitational lensing and indirect/directdetection experiments.