The phase-space distribution of infalling dark matter subhalos

We use high-resolution numerical simulations to study the physical properties of subhalos when they merge into their host halos. An improved algorithm is used to identify the subhalos. We then examine their spatial and velocity distributions in spherical and triaxial halo models. We find that the accretion of satellites preferentially occurs along the major axis and perpendicular to the spin axis of the host halo. Furthermore, the massive subhalos show a stronger preference to be accreted along the major axis of the host halo than the low-mass ones. Approximate fitting formulae are provided for the physical properties of subhalos. Combined with analytical and semi-analytic techniques, these empirical formulae provide a useful basis for studying the subsequent evolution of subhalos and satellite galaxies in their hosts. Future studies should however account for satellites that may not be undergoing the first infall in their evolution.