Entropy profiles in X - ray luminous galaxy clusters at z > 0 . 1

The entropy distribution of the intracluster gas reflects both accretion history of the gas and processes of feedback which provide a further non-gravitational energy besides the potential one. In this work, we study the profiles and the scaling properties of the gas entropy in 24 hot (kTgas > 6 keV) galaxy clusters observed with Chandra in the redshift range 0.14–0.82 and showing different states of relaxation. We recover the gas density, temperature and entropy profiles in a non-parametric way, just relying on the assumption of a spherically symmetric emission in the deprojection of the best-fit results of the spatially resolved X-ray spectral analysis. Adding the hydrostatic equilibrium hypothesis, radial profiles are also obtained from the deprojection of the surface brightness, allowing to verify whether the hydrostatic equilibrium is a tenable hypothesis by comparison with the spectral measurements. We confirm that this is the case on scales larger than 100 kpc and discuss the deviations observed in few non-cooling core clusters in the inner regions. We show that the entropy profiles are remarkably similar outside the core and can be described by simple power-laws with slope of 1.0− 1.2. We measure an entropy level at 0.1R200 of 100− 500 keVcm and a central plateau which spans a wide range of value (∼ a few−200 keVcm) depending on the state of relaxation of the source. The entropy values resolved at given fraction of the virial radius are proportional to the gas temperature in these hot systems and appear larger at higher redshift once they are compared to the local estimates. To characterize the energetic of the central regions, we compare the radial behaviour of the temperature of the gas with the temperature of the dark matter (TDM, defined as σ DMμmp), by estimating the excess of energy ∆E = 3/2 k(Tgas − TDM). We point out that ∆E ranges from ≈ 0 in typical cooling-core clusters to few keV within 100 kpc in noncooling core systems. We also measure a significant correlation between the total iron mass and the entropy outside the cooling region,whereas in the inner regions they anti-correlate strongly. We find that none of the current models in literature on the extra-gravitational energy is able to justify alone the evidences we obtained on the entropy, metallicity and gas+dark matter temperature profiles.