WWhat Heavy Elements in Clusters of Galaxies Tell About Clusters and   Galaxies
  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 which ICM is hotter than $\sim 2$ keV, and the elemental proportions (i.e. the [$\alpha$/Fe] ratio) appear to be solar. The simplest interpretation of these evidences is that both the IMF as well the relative contributions of SN types are universal. Currently available abundances in cooler clusters and groups are much more uncertain, possibly due to insufficiently accurate atomic physics data for multi-electron ions, or to the ICM being multi-phase, or to a combination thereof. This uncertainty automatically extends to the reality of radial abundance gradients so far reported in cool clusters. It is emphasized that most metals reside in the ICM rather than in galaxies, which demonstrates that energetic winds operated early in the evolution of massive galaxies, the likely producers of most metals now in the ICM. The ICM metallicity is also used to set a semiempirical constraint of $\sim 0.1$ keV per particle to the ICM {\it preheating} due to supernova driven galactic winds. A lower limit of the universe global metallicity at $z=3$ is also mentioned. 
Alvio Renzini (European Southern Observatory)