Conserved actions, maximum entropy and dark matter halos

TL;DR

This paper derives a phase space distribution for virialized dark matter halos using maximum entropy principles, incorporating dynamical constraints to better match simulation data, especially in the central cusp region.

Contribution

It introduces a novel maximum entropy-based distribution function for dark matter halos that includes orbital action constraints, improving upon previous models.

Findings

Accurately predicts the distribution of particles in simulated halos

Reproduces the central cusp when dynamical timescales are considered

Matches high-resolution simulation data for various halo masses

Abstract

We use maximum entropy arguments to derive the phase space distribution of a virialized dark matter halo. Our distribution function gives an improved representation of the end product of violent relaxation. This is achieved by incorporating physically motivated dynamical constraints (specifically on orbital actions) which prevent arbitrary redistribution of energy. We compare the predictions with three high-resolution dark matter simulations of widely varying mass. The numerical distribution function is accurately predicted by our argument, producing an excellent match for the vast majority of particles. The remaining particles constitute the central cusp of the halo (<4% of the dark matter). They can be accounted for within the presented framework once the short dynamical timescales of the centre are taken into account.