Distribution Function in Center of Dark Matter Halo

Abstract

N-body simulations of dark matter halos show that the density profiles of halos behave as $ρ(r)\propto r^{-α(r)}$, where the density logarithmic slope $α\simeq 1\sim1.5$ in the center and $α\simeq 3\sim 4$ in the outer parts of halos. However, some observations are not in agreement with simulations in the very central region of halos. The simulations also show that velocity dispersion anisotropy parameter $β\approx 0$ in the inner part of the halo and the so called "pseudo phase-space density" $ρ/σ^3$ behaves as a power-law in radius $r$. With these results in mind, we study the distribution function and the pseudo phase-space density $ρ/σ^3$ of the center of dark matter halos and find that they are closely-related.