Hints on Galaxy Formation from the Metal Content of Galaxy Cluster and Other Fossil Evidence

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Clusters of galaxies allow a direct estimate of the metallicity and metal production yield on the largest scale so far. It is argued that cluster metallicity (1/3 solar) should be taken as representative of the low-z universe as a whole. There is now compelling evidence that the bulk of stars not only in cluster ellipticals but also in field ellipticals and bulges formed at high redshifts (z 3). Since such stars account for at least 30% of the baryons now locked into stars, it is argued that at least 30% of stars and metals formed before z≃ 3, and correspondingly the metallicity of the universe at z=3 is predicted to be 1/10 solar. This requires the cosmic star formation rate to run at least flat from z 1 to 5, which appears to agree with the most recent derect determinations of the star formation rate in Lyman-break galaxies.