Mass profiles and concentration-dark matter relation in X-ray luminous galaxy clusters

Context. Galaxy clusters represent valuable cosmological probes us ing tests that mainly rely on measurements of cluster masses and baryon fractions. X-ray observations represent one of the m ain tools for uncovering these quantities. Aims. We aim to constrain the cosmological parameters Ωm andσ8 using the observed distribution of the both values of the con centrations and dark mass within R200 and of the gas mass fraction within R500. Methods. We applied two different techniques to recover the profiles t he gas and dark mass, described according to the Navarro, Frenk & White (1997, ApJ, 490, 493) functional form, of a samp le of 44 X-ray luminous galaxy clusters observed with XMM-Newton in the redshift range0.1− 0.3. We made use of the spatially resolved spectroscopic data an d of the PSF–deconvolved surface brightness and assumed that hydrostatic equilibrium holds betwee n the intracluster medium and the gravitational potential. We evaluated several systematic uncertainties that affect our reconstr uction of the X-ray masses. Results. We measured the concentration c200, the dark massM200 and the gas mass fraction in all the objects of our sample, pro viding the largest dataset of mass parameters for galaxy clu sters in the redshift range 0.1 − 0.3. We confirm that a tight correlation betweenc200 andM200 is present and in good agreement with the predictions from nu erical simulations and previous observations. When we consider a subsample of relaxed clusters that host a l w entropy core, we measure a flatter c − M relation with a total scatter that is lower by 40 per cent. We conclude, however, th at the slope of thec−M relation cannot be reliably determined from the fitting over a narrow mass range as the one considered in the pr es nt work. From the distribution of the estimates of c200 andM200, with associated statistical (15–25%) and systematic (5–15 %) errors, we used the predicted values from semi-analytic p rescriptions calibrated through N-body numerical runs and obtain σ8 Ω m = 0.45 ± 0.01 (at 2σ level, statistical only) for the subsample of the clusters where the mass reconstruction has been obtai ned more robustly and σ8 Ω m = 0.39 ± 0.02 for the subsample of the 11 more relaxed LEC objects. With the further constrai n from the gas mass fraction distribution in our sample, we b reak the degeneracy in the σ8 − Ωm plane and obtain the best-fit values σ8 ≈ 1.0± 0.2 (0.83± 0.1 when the subsample of the more relaxed objects is considered) and Ωm = 0.26 ± 0.02. Conclusions. We demonstrate that the analysis of the distribution of the c200 −M200 − fgas values represents a mature and competitive technique in the present era of precision cosmology, e ven though it needs more detailed analysis of the output of la rger sets of cosmological numerical simulations to provide definitive a nd robust results.