Substructure in CDM Halos and the Heating of Stellar Disks

Abstract

Numerical simulations have revealed the presence of long-lived substructure in Cold Dark Matter (CDM) halos. These surviving cores of past merger and accretion events vastly outnumber the known satellites of the Milky Way. This finding has prompted suggestions that substructure in cold dark matter (CDM) halos may be incompatible with observation and in conflict with the presence of thin, dynamically fragile stellar disks. N-body simulations of a disk/bulge/halo model of the Milky Way that includes several hundred dark matter satellites with masses, densities and orbits derived from high-resolution cosmological CDM simulations indicate that substructure plays only a minor dynamical role in the heating of the disk. This is because the orbits of satellites seldom take them near the disk, where their tidal effects are greatest. We conclude that substructure might not preclude virialized CDM halos from being acceptable hosts of thin stellar disks like that of the Milky Way.