Statistical mechanics of collisionless orbits. II. Structure of halos

TL;DR

This paper demonstrates that the DARKexp energy distribution accurately predicts the density and velocity profiles of collisionless halos, supporting the application of statistical mechanics to their structure.

Contribution

It introduces the DARKexp distribution for isotropic systems and validates it against ESIM simulations, showing its effectiveness in describing relaxed self-gravitating halos.

Findings

DARKexp fits ESIM halo energy distributions well

Statistical mechanics can explain the structure of collisionless halos

Inner halo properties are accurately modeled by DARKexp

Abstract

In this paper, we present the density, \rho, velocity dispersion, \sigma, and \rho/\sigma^3 profiles of isotropic systems which have the energy distribution, N(E)\propto[\exp(\phi_0-E)-1], derived in Paper I. This distribution, dubbed DARKexp, is the most probable final state of a collisionless self-gravitating system, which is relaxed in terms of particle energies, but not necessarily in terms of angular momentum. We compare the DARKexp predictions with the results obtained using the extended secondary infall model (ESIM). The ESIM numerical scheme is optimally suited for the purpose because (1) it relaxes only through energy redistribution, leaving shell/particle angular momenta unaltered, and (2) being a shell code with radially increasing shell thickness it has very good mass resolution in the inner halo, where the various theoretical treatments give different predictions. The ESIM halo properties, and especially their energy distributions, are very well fit by DARKexp, implying that the techniques of statistical mechanics can be used to explain the structure of relaxed self-gravitating systems.