Dark matter debris flows in the Milky Way

We show that subhalos falling into the Milky Way create a flow of tidally-stripped debris particles near the Galactic center with characteristic speed behavior, but no spatial features. Using the Via Lactea-II N-body simulation, we study the unvirialized component arising from particles that were bound in subhalos around the time of reionization but have since been tidally stripped. These debris particles constitute a few percent of the local density today and have speeds peaked at 340 km/s in the solar neighborhood. This spatially-homogeneous velocity substructure has important implications for surveys of low-metallicity stars, as well as direct detection experiments sensitive to dark matter with large scattering thresholds.