Internal dark matter structure of the most massive galaxy clusters

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 Gpc)^3, we study the 25 most massive clusters in four redshift slices from z ∼ 1 to the present. The minimum mass is M_500 > 5.5 × 10^14 M_⊙ 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 ∼ 1 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 Navarro–Frenk–White 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.