Scaling laws in X - ray Galaxy Clusters at redshift between 0 . 4 and 1 . 3

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), in the E z S − T relation, where the entropy S is defined as T/n 2/3 gas 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.