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

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.

19 pages, 16 figures. Comments are welcome. Version consistent with those accepted from PASJ