Generating Equilibrium Dark Matter Halos: Inadequacies of the Local Maxwellian Approximation
Abstract
We describe an algorithm for constructing N-body realizations of equilibrium spherical systems. A general form for the mass density rho(r) is used, making it possible to represent most of the popular density profiles found in the literature, including the cuspy density profiles found in high-resolution cosmological simulations. We demonstrate explicitly that our models are in equilibrium. In contrast, many existing N-body realizations of isolated systems have been constructed under the assumption that the local velocity distribution is Maxwellian. We show that a Maxwellian halo with an initial r^{-1} central density cusp immediately develops a constant density core. Moreover, after just one crossing time the orbital anisotropy has changed over the entire system and the initially isotropic model becomes radially anisotropic. These effects have important implications for many studies, including the survival of substructure in cold dark matter (CDM) models. Comparing the evolution and mass loss of Maxwellian and self-consistent satellites orbiting inside a static host CDM potential, we find that the former are unrealistically susceptible to tidal disruption. Thus recent studies of the mass loss and disruption time-scales of substructure in CDM halos may be compromized by using Maxwellian models.Keywords
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