Bimodal star formation in elliptical galaxies and the enrichment of the intra-cluster medium

Abstract

A detailed model of galactic evolution is proposed to explain both the iron content of the Intra-Cluster Medium (ICM) and of the ellipticals pertaining to the cluster. SNII are responsible for the production of Fe in the galaxies and of its partial ejection in the surrounding medium. A high formation rate of massive stars only ($m>3~{\rm M_{\sun}}$) at the very early stage of evolution of ellipticals, reminiscent of starburst galaxies, is advocated. The high rate of SNII explosions induces a powerful galactic wind, followed by a more quiescent evolution where stars are formed, with a normal Initial Mass Function (IMF), from the enriched gas remaining after the wind phase and from the gas restored by the longest living stars produced during the early phase. Most of the iron is produced by the high-mass stars created in the early burst phase.