Chemical Evolution on the Scale of Clusters of Galaxies, and Beyond

Clusters of galaxies allow a direct estimate of the metallicity and metal production yield on the largest scale so far. The ratio of the total iron mass in the ICM to the total optical luminosity of the cluster (the iron mass-to-light-ratio) is the same for all clusters whose ICM is hotter than ~2 keV, and the elemental proportions (i.e. the [a/Fe] ratio) appear to be solar. From this evidence it is argued that both the IMF as well the relative contributions of SN types are likely to be universal. Constraints on the past SN activity in galaxy clusters are then derived, and support is given to the notion that the average SNIa rate was much higher in the past, i.e. at least 10 times more than currently observed in local ellipticals.