The contribution of population III to the enrichment and preheating of theintracluster medium

Intracluster medium (ICM) abundances are higher than expected assuming enri chment by supernovae with progenitors belonging to the simple stellar popul ation (SSP) observed in cluster galaxies if stars formed with a standard in itial mass function (IMF). Moreover, new results on ICM oxygen abundances i mply that nucleosynthesis occurred with nonstandard yields. The hypothesis that hypernovae in general, and hypernovae associated with Population III ( Pop III) stars in particular, may significantly contribute to ICM enrichmen t is presented and evaluated. The observed abundance anomalies can be expla ined by a hypernova-producing subpopulation of the SSP, but only if the sub population accounts for half of all supernova explosions and if Type Ia sup ernova rates are very low. Also, the implied energy release may be excessiv e. However, an independent Pop III contribution-in the form of metal-free, very massive stars that evolve into hypernovae-can also account for all of the observed abundances while avoiding these drawbacks and accommodating a normal IMF in subsequent stellar generations. The required number of Pop II I stars provides sufficient energy injection (at high redshift) to explain the ICM "entropy floor." Pop III hypernovae preenrich the intergalactic med ium and can produce a significant fraction of the metals observed in the Ly alpha forest. Several testable predictions for ICM and intergalactic mediu m observations are made.