Dark Matter Substructure within Galactic Halos

Abstract

We use numerical simulations to examine the substructure within galactic and\ncluster mass halos that form within a hierarchical universe. Clusters are\neasily reproduced with a steep mass spectrum of thousands of substructure\nclumps that closely matches observations. However, the survival of dark matter\nsubstructure also occurs on galactic scales, leading to the remarkable result\nthat galaxy halos appear as scaled versions of galaxy clusters. The model\npredicts that the virialised extent of the Milky Way's halo should contain\nabout 500 satellites with circular velocities larger than Draco and Ursa-Minor\ni.e. bound masses > 10^8Mo and tidally limited sizes > kpc. The substructure\nclumps are on orbits that take a large fraction of them through the stellar\ndisk leading to significant resonant and impulsive heating. Their abundance and\nsingular density profiles has important implications for the existence of old\nthin disks, cold stellar streams, gravitational lensing and indirect/direct\ndetection experiments.\n