Inner structure of cold and warm dark matter halos from particle dynamics

TL;DR

This study characterizes the phase-space structure of cold and warm dark matter halos using particle dynamics, revealing consistent double power-law density profiles with model-dependent outer slopes.

Contribution

It introduces a novel analysis of halo structures based on apocenter passages and radial action, extending previous work and highlighting model-dependent outer profile behaviors.

Findings

Inner density profile follows a $ ho \,\propto \, r^{-1}$ power law.

Outer profiles differ: steeper for $p$-classified particles, flatter for $J_r$-classified particles.

Profile amplitude varies with dark matter model due to halo concentration differences.

Abstract

Using the number of apocenter passages $p$ and the radial action $J_r$ of each particle, we characterize the phase-space structure within the multi-stream regions of cold and warm dark matter halos in cosmological $N$-body simulations. Building on previous work by Enomoto et al. (2024), we analyze the radial density profiles of particles classified by $p$ and $J_r$. We find that the profiles consistently follow a double power-law structure, independent of the dark matter model or halo mass. The inner profile exhibits a $\rho \propto r^{-1}$ behavior, which is consistent with previous studies. Notably, this characteristics persist across both classification schemes. In contrast, the outer power-law profiles display distinct behaviors depending on the classification. While particles classified by $p$ exhibit a steeper slope, ranging from $-6$ to $-8$, those classified by $J_r$ follow a common slope of approximately $-3.5$. Overall, the amplitude of the double power-law profiles varies between simulations for different dark matter models, but this variation can be attributed to statistical differences in the concentration of halos across the models.