The mass-concentration relation in massive galaxy clusters at redshift ~1
Abstract
Mass and concentration of clusters of galaxies are related and evolving with redshift. We study the properties of a sample of 31 massive galaxy clusters at high redshift, 0.8 < z < 1.5, using weak and strong lensing observations. Concentration is a steep function of mass, c200 ~M200-0.83 +-0.39, with higher-redshift clusters being less concentrated. Mass and concentration from the stacked analysis, M200=(4.1+-0.4)x1014MSun/h and c200=2.3+-0.2, are in line with theoretical results extrapolated from the local universe. Clusters with signs of dynamical activity preferentially feature high concentrations. We discuss the possibility that the whole sample is a mix of two different kinds of haloes. Over-concentrated clusters might be accreting haloes out of equilibrium in a transient phase of compression, whereas less concentrated ones might be more relaxed.