The thermalization of massive galaxy clusters

ABSTRACT In the hierarchical scenario of structure formation, galaxy clusters are ultimate virialized products in mass and time. Hot baryons intracluster medium (ICM) cold galaxies inhabit a dark matter dominated halo. Internal processes, accretion, mergers can perturb equilibrium, which is established only at later times. However, cosmic time when thermalization effective still to be assessed. Here, we show that massive observed universe attained an advanced thermal equilibrium ∼1.8 Gyr ago, redshift z = 0.14 ± 0.06, was 11.7 0.7 old. gas mostly thermalized after densities energy match. We find statistically nearly complete homogeneous sample 120 from Planck Early Sunyaev-Zel’dovich (ESZ) kinetic traced by velocity dispersion faithful probe gravitational since look back least ∼5.4 Gyr, whereas efficiency hot converting energy, as measured through X-ray observations core-excised area within r500, steadily increases with The evolution detected ∼98 per cent probability level. Our results demonstrate halo accretion history plays larger role for cluster than radiative physics. strictly connected formation.