The thermalisation of massive galaxy clusters

Abstract

In the hierarchical scenario of structure formation, galaxy clusters are the ultimate virialised products in mass and time. Hot baryons in the intracluster medium (ICM) and cold baryons in galaxies inhabit a dark matter dominated halo. Internal processes, accretion, and mergers can perturb the equilibrium, which is established only at later times. However, the cosmic time when thermalisation is effective is still to be assessed. Here we show that massive clusters in the observed universe attained an advanced thermal equilibrium $\sim 1.8\text{Gyr}$ ago, at redshift $z=0.14\pm 0.06$, when the universe was $11.7\pm 0.7\text{Gyr}$ old. Hot gas is mostly thermalised after the time when cosmic densities of matter and dark energy match. We find in a statistically nearly complete and homogeneous sample of 120 clusters from the {\it Planck} Early Sunyaev-Zel'dovich (ESZ) sample that the kinetic energy traced by the galaxy velocity dispersion is a faithful probe of the gravitational energy since a look back time of at least $\sim 5.4\text{Gyr}$, whereas the efficiency of hot gas in converting kinetic to thermal energy, as measured through X-ray observations in the core-excised area within $r_{500}$, steadily increases with time. The evolution is detected at the $\sim 98$ per cent probability level. Our results demonstrate that halo mass accretion history plays a larger role for cluster thermal equilibrium than radiative physics. The evolution of hot gas is strictly connected to the cosmic structure formation.

10 pages, 3 figures, in press on MNRAS

References in corpus (16)

• Galaxy Clusters Discovered via the Sunyaev-Zel'dovich Effect in the 2500-square-degree SPT-SZ survey
• The Quiescent Intracluster Medium in the Core of the Perseus Cluster
• Virial Scaling of Massive Dark Matter Halos: Why Clusters Prefer a High Normalization Cosmology
• Weighing the Giants IV: Cosmology and Neutrino Mass
• Scaling Properties of a Complete X-ray Selected Galaxy Group Sample
• The relation between velocity dispersion and mass in simulated clusters of galaxies: dependence on the tracer and the baryonic physics
• XMM-Newton and Chandra Cross Calibration Using HIFLUGCS Galaxy Clusters: Systematic Temperature Differences and Cosmological Impact
• The MUSIC of CLASH: predictions on the concentration-mass relation
• X-Ray morphological analysis of the Planck ESZ clusters
• CoMaLit III. Literature Catalogs of weak Lensing Clusters of galaxies (LC^2)
• Universality of dark matter haloes shape over six decades in mass: Insights from the Millennium XXL and SBARBINE simulations
• HICOSMO - Cosmology with a complete sample of galaxy clusters: I. Data analysis, sample selection and luminosity-mass scaling-relation
• Detection of anti-correlation of hot and cold baryons in galaxy clusters
• XXL Survey groups and clusters in the Hyper Suprime-Cam Survey. Scaling relations between X-ray properties and weak lensing mass
• CLUMP-3D. Three dimensional lensing and multi-probe analysis of MACS J1206.2-0847, a remarkably regular cluster
• Internal dark matter structure of the most massive galaxy clusters

Cited by in corpus (2)

• A study of the hydrostatic mass bias dependence and evolution within The Three Hundred clusters
• The Three Hundred Project: the evolution of physical baryon profiles