The redshift dependence of the structure of massive LCDM halos

TL;DR

This study uses large cosmological simulations to analyze how the density profiles and concentrations of relaxed LCDM dark matter halos depend on redshift and mass, revealing systematic deviations from the NFW profile and weak mass dependence.

Contribution

It provides new insights into the redshift and mass dependence of halo density profiles and concentrations, using empirical fits and large simulations.

Findings

Profiles deviate from NFW, better fit by Einasto profile

Shape parameter alpha increases with halo mass

Halo concentration weakly depends on mass and redshift

Abstract

(Abridged) We use two very large cosmological simulations to study how the density profiles of relaxed LCDM dark halos depend on redshift and on halo mass. We confirm that these profiles deviate slightly but systematically from the NFW form and are better approximated by the empirical formula, $d\log \rho/d\log r \propto r^{\alpha}$, first used by Einasto to fit star counts in the Milky Way. The best-fit value of the additional shape parameter, $\alpha$, increases gradually with mass, from alpha ~ 0.16 for present-day galaxy halos to alpha~ 0.3 for the rarest and most massive clusters. Halo concentrations depend only weakly on mass at z=0, and this dependence weakens further at earlier times. At z ~3 the average concentration of relaxed halos does not vary appreciably over the mass range accessible to our simulations (M >=3e11Msun). Furthermore, in our biggest simulation, the average concentration of the most massive}, relaxed halos is constant at c200 ~3.5 to 4 for 0<=z<= 3. These results have important implications for currently planned surveys of distant clusters.