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Iron Abundance in the Intracluster Medium at High Redshift

We present the analysis of the X-ray spectra of 18 distant clusters of galaxies with redshift 0.3 < z < 1.3. Most of them were observed with the Chandra satellite in long exposures ranging from 36 to 180 ks. For two of the z > 1 clusters, we also use deep XMM-Newton observations. Overall, these clusters probe the temperature range 3 keV ≲ kT ≲ 8 keV. Our analysis is aimed at deriving the iron abundance in the intracluster medium (ICM) out to the highest redshifts probed to date. Using a combined spectral fit of cluster subsamples in different redshift bins, we investigate the evolution of the mean ICM metallicity with cosmic epoch. We find that the mean Fe abundance at = 0.8 is Z = 0.25 Z☉, consistent with the local canonical metallicity value, Z ≃ 0.3 Z☉, within the 1 σ confidence level (c.l.). Medium- and low-temperature clusters (kT < 5 keV) tend to have larger iron abundances than hot clusters. At redshift ~ 1.2 (four clusters at z > 1), we obtain a statistically significant detection of the Fe K line in only one cluster (Z > 0.10 Z☉ at the 90% c.l.). Combining all the current data sets from Chandra and XMM at z > 1, the average metallicity is measured to be = 0.21 Z☉ (1 σ error), thus suggesting no evolution of the mean iron abundance out to z ≃ 1.2.