Search

We present the analysis of the baryonic content of 65 X-ray luminous galaxy clusters observed with Chandra in the redshift range 0.143–1.273. Our study aims at resolving the gas mass fraction in these objects to put constraints on the cosmological parameters Ωm, ΩΛ and the ratio between the pressure and density of the “dark” energy, w. By assuming that the galaxy clusters are representative of the cosmic baryon budget, the distribution of the cluster baryon fraction in the hottest (Tgas > 5 keV) systems as function of redshift is used to constrain the cosmological parameters. We discuss how our constraints are affected from several systematics, namely the assumed baryon fraction in stars, the depletion parameter, the sample selection.

We present a Chandra analysis of the X-ray spectra of 56 clusters of galaxies at z > 0.3, which cover a temperature range of 3 > kT > 15 keV. Our analysis is aimed at measuring the iron abundance in the ICM out to the highest redshift probed to date. We find that the emission-weighted iron abundance measured within (0.15-0.3) Rvir in clusters below 5 keV is, on average, a factor of ∼2 higher than in hotter clusters, following Z(T) ≃0.88 T−0.47 Z⊙, which confirms the trend seen in local samples. We made use of combined spectral analysis performed over five redshift bins at 0.3 > z > 1.3 to estimate the average emission weighted iron abundance. We find a constant average iron abundance ZFe ≃0.25 Z⊙ as a function of redshift, but only for clusters at z > 0.5. The emission-weighted iron abundance is significantly higher (ZFe ≃0.4 Z⊙) in the redshift range z ≃0.3 - 0.5, approaching the value measured locally in the inner 0.15 Rvir radii for a mix of cool-core and non cool-core clusters in the redshift range 0.1 ≪ z ≪ 0.3. The decrease in ZFe with z can be parametrized by a power law of the form ∼(1+z)−1.25. The observed evolution implies that the average iron content of the ICM at the present epoch is a factor of ∼2 larger than at z ≃1.2. We confirm that the ICM is already significantly enriched (ZFe ≃0.25 Z⊙) at a look-back time of 9 Gyr. Our data provide significant constraints on the time scales and physical processes that drive the chemical enrichment of the ICM.