Iron Abundance in the Intracluster Medium at High Redshift

Abstract

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 3keV<~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^+0.04_-0.06Z_solar, consistent with the local canonical metallicity value, Z~=0.3Z_solar, 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>0.10Z_solar 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^+0.10_-0.05Z_solar (1 σ error), thus suggesting no evolution of the mean iron abundance out to z~=1.2.