Cold Dark Matter Substructure and the Dynamical Evolution of Galaxy Disks

We use numerical simulations to study the dynamical effect of substructure in Cold Dark Matter (CDM) halos on stellar galactic disks. Substructure halos with masses, densities and orbits derived from high-resolution cosmological CDM simulations play only a minor dynamical role in the heating of the disk over several Gyrs. This is because the orbits of dark satellites in CDM halos seldom take them near the disk, where their tidal effects are greatest. The most noticeable effects of substructure in our simulation may be traced to the most massive sub-halo and include: (i) the forcing of short-lived stellar warps in the disk as a result of tidal shocks that arise during each pericentric passage, and (ii) the tilting of the disk caused by the orbital decay of the satellite. These results imply that substructure might not preclude virialized CDM halos from being acceptable hosts of thin stellar disks like that of the Milky Way, and that the ubiquity of minor stellar warps may be associated with the recurrent tidal influence on the disk of the most massive substructure halos