Density Profiles of Collisionless Equilibria. II. Anisotropic Spherical Systems

Abstract

It has long been realized that dark matter halos formed in cosmological N-body simulations are characterized by density profiles rho(r) that, when suitably scaled, have similar shapes. Additionally, combining the density and velocity dispersion profiles sigma(r), each of which have decidedly nonpower-law shapes, leads to quantity rho/(sigma^3) that is a power-law in radius over 3 orders of magnitude in radius. Halos' velocity anisotropy profiles beta(r) vary from isotropic near the centers of halos to quite radially anisotropic near the virial radius. Finally, there appears to be a nearly linear correlation between beta and the logarithmic density slope gamma for a wide variety of halos. This work is part of a continuing investigation of the above interrelationships and their origins using analytical and semi-analytical techniques. Our finding suggest that the nearly linear beta--gamma relationship is not just another expression of scale-free rho/(sigma^3) behavior. We also note that simultaneously reproducing density and anisotropy profiles like those found in simulations requires beta(r) and gamma(r) to have similar shapes, leading to nearly linear beta--gamma correlations. This work suggests that the beta--gamma and power-law rho/(sigma^3) relations have distinct physical origins.