Internal dark matter structure of the most massive galaxy clusters

TL;DR

This study uses cosmological simulations to show that the dark matter density profiles of the most massive galaxy clusters are remarkably similar from redshift 1 to today, indicating early formation and robustness to mergers.

Contribution

It provides the first detailed analysis of the evolution and stability of dark matter profiles in the most massive galaxy clusters across cosmic time.

Findings

Dark matter profiles are similar from z~1 to present.

Profiles follow a running power law shape like NFW.

Inner structure shows no signs of converging to an asymptotic slope.

Abstract

We investigate the evolution of the dark matter density profiles of the most massive galaxy clusters in the Universe. Using a `zoom-in' procedure on a large suite of cosmological simulations of total comoving volume of $3\,(h^{-1}\,\rm Gpc)^3$, we study the 25 most massive clusters in four redshift slices from $z\sim 1$ to the present. The minimum mass is $M_{500} > 5.5 \times 10^{14}$ M$_{\odot}$ at $z=1$. Each system has more than two million particles within $r_{500}$. Once scaled to the critical density at each redshift, the dark matter profiles within $r_{500}$ are strikingly similar from $z\sim1$ to the present day, exhibiting a low dispersion of 0.15 dex, and showing little evolution with redshift in the radial logarithmic slope and scatter. They have the running power law shape typical of the NFW-type profiles, and their inner structure, resolved to $3.8\,h^{-1}$ comoving kpc at $z=1$, shows no signs of converging to an asymptotic slope. Our results suggest that this type of profile is already in place at $z>1$ in the highest-mass haloes in the Universe, and that it remains exceptionally robust to merging activity.