Generating Equilibrium Dark Matter Halos: Inadequacies of the Local Maxwellian Approximation

We describe an algorithm for constructing N-body realizations of equilibriumspherical systems. A general form for the mass density rho(r) is used, makingit possible to represent most of the popular density profiles found in theliterature, including the cuspy density profiles found in high-resolutioncosmological simulations. We demonstrate explicitly that our models are inequilibrium. In contrast, many existing N-body realizations of isolated systemshave been constructed under the assumption that the local velocity distributionis Maxwellian. We show that a Maxwellian halo with an initial r^{-1} centraldensity cusp immediately develops a constant-density core. Moreover, after justone crossing time the orbital anisotropy has changed over the entire system,and the initially isotropic model becomes radially anisotropic. These effectshave important implications for many studies, including the survival ofsubstructure in cold dark matter (CDM) models. Comparing the evolution andmass-loss rate of isotropic Maxwellian and self-consistent Navarro, Frenk, &White (NFW) satellites orbiting inside a static host CDM potential, we findthat the former are unrealistically susceptible to tidal disruption. Thus,recent studies of the mass-loss rate and disruption timescales of substructurein CDM models may be compromized by using the Maxwellian approximation. We alsodemonstrate that a radially anisotropic, self-consistent NFW satellite losesmass at a rate several times higher than that of its isotropic counterpart onthe same external tidal field and orbit.Comment: Accepted for publication in ApJ, 10 pages, 6 figures, LaTeX (uses emulateapj5.sty