Scaling laws in X-ray galaxy clusters at redshift between 0.4 and 1.3

Abstract

We present a study of the integrated physical properties of a sample of 28 X-ray galaxy clusters observed with Chandra at a redshift between 0.4 and 1.3. In particular, we have twelve objects in the redshift range 0.4-0.6, five between 0.6 and 0.8, seven between 0.8 and 1 and four at z > 1.0, compounding the largest sample available for such a study. We focus particularly on the properties and evolution of the X-ray scaling laws. We fit both a single and a double β-model with the former which provides a good representation of the observed surface brightness profiles, indicating that these clusters do not show any significant excess in their central brightness. By using the best-fit parameters of the β-model together with the measured emission-weighted temperature (in the range 3-11 keV), we recover gas luminosity, gas mass and total gravitating mass out to R500. We observe scaling relations steeper than expected from the self-similar model by a significant (>3σ) amount in the L - T and Mgas - T relations and by a marginal value in the Mtot - T and L - Mtot relations. The degree of evolution of the Mtot - T relation is found to be consistent with the expectation based on the hydrostatic equilibrium for gas within virialized dark matter halos. We detect hints of negative evolution in the L - T, Mgas - T and L - Mtot relations, thus suggesting that systems at higher redshift have lower X-ray luminosity and gas mass for fixed temperature. In particular, when the 16 clusters at z > 0.6 are considered, the evolution becomes more evident and its power-law modelization is a statistically good description of the data, In this subsample, we also find significant evidence for positive evolution, such as (1 + z) 0.3, in the Ez4/3 S - T relation, where the entropy S is defined as T/ngas2/3 and is measured at 0.1R200. Such results point toward a scenario in which a relatively lower gas density is present in high-redshift objects, thus implying a suppressed X-ray emission, a smaller amount of gas mass and a higher entropy level. This represents a non-trivial constraint for models aiming at explaining the thermal history of the intra-cluster medium out to the highest redshift reached so far.