Redshift Evolution in the Iron Abundance of the Intracluster Medium

Clusters of galaxies provide a closed box within which one can determine the chemical evolution of the gaseous baryons with cosmic time. We studied this metallicity evolution in the hot X-ray emitting baryons through an analysis of XMM-Newton observations of 29 galaxy clusters in the redshift range, 0.3 < z < 1.3. Taken alone, this data set does not show evidence for significant evolution. However, when we also include a comparable sample of 115 clusters observed with Chandra and a lower redshift sample of 70 clusters observed with XMM at z < 0.3, there is definitive evidence for a decrease in the metallicity. This decrease is approximately a factor of two from z = 0 to z ≈ 1, over which we find a least-squares best-fit line Z(z)/Z _sun = (0.46 ± 0.05) - (0.38 ± 0.03)z. The greatest uncertainty in the evolution comes from poorly constrained metallicities in the highest redshift bin.