Self-similarity of temperature profiles in distant galaxy clusters: the quest for a universal law

Abstract

We present the XMM-Newton temperature profiles of 12 bright clusters of galaxies at 0.4<z<0.9, with 5<kT<11 keV. The normalized temperature profiles (normalized by the mean temperature T500) are found to be generally self-similar. The sample was subdivided in 5 cool-core (CC) and 7 non cool-core (NCC) clusters, by introducing a pseudo-entropy ratio sigma=(T_IN/T_OUT)X(EM_IN/EM_OUT)^-1/3 and defining the objects with sigma<0.6 as CC clusters and those with sigma>=0.6 as NCC clusters. The profiles of CC and NCC clusters differ mainly in the central regions, with the latters exhibiting a marginally flatter central profile. A significant dependence of the temperature profiles on the pseudo-entropy ratio sigma is detected by fitting a function of both r and sigma, showing an indication that the outer part of the profiles becomes steeper for higher values of sigma (i.e. transitioning towards the NCC clusters). No significant evidence of redshift evolution could be found within the redshift range sampled by our clusters (0.4<z<0.9). A comparison of our high-z sample with intermediate clusters at 0.1<z<0.3, showed how both the CC and NCC clusters temperature profiles have experienced some sort of evolution. This can be due by the fact that higher z clusters are at less advanced stage of their formation and did not have enough time to create a relaxed structure, characterized by a central temperature dip in CC clusters and by flatter profiles in NCC clusters. This is the first time that a systematic study of the temperature profiles of galaxy clusters at z>0.4 has been attempted, as we were able to define the closest possible relation to a Universal law for the temperature profiles of galaxy clusters at 0.1<z<0.9, showing a dependence on both the state of relaxation of the clusters and the redshift.