Tidal Debris as a Dark Matter Probe

Abstract

Tidal debris streams from galaxy satellites can provide insight into the dark matter distribution in halos. This is because we have more information about stars in a debris structure than about a purely random population of stars: we know that in the past they were all bound to the same dwarf galaxy; and we know that they form a dynamically cold population moving on similar orbits. They also probe a different region of the matter distribution in a galaxy than many other methods of mass determination, as their orbits take them far beyond the typical extent of those for the bulk of stars. Although conclusive results from this information have yet to be obtained, significant progress has been made in developing the methodologies for determining both the global mass distribution of the Milky Way's dark matter halo and the amount of dark matter substructure within it. Methods for measuring the halo shape are divided into "predictive methods," which predict the tidal debris properties from the progenitor satellite's mass and orbit, given an assumed parent galaxy mass distribution; and "fundamental methods," which exploit properties fundamental to the nature of tidal debris as global potential constraints. Methods for quantifying the prevalence of dark matter subhalos within halos through the analysis of the gaps left in tidal streams after these substructures pass through them are reviewed.