A comparison of metal enrichment histories in rich clusters and individualluminous elliptical galaxies

The large spatial extent of hot, X-ray-emitting gaseous halos around massiv e elliptical galaxies indicates that most of this gas has not been generate d by stellar mass loss. Instead, much of this gas results from an intergala ctic gaseous inflow toward the overdensity from which giant ellipticals and their associated galaxy groups formed. Since these hot gaseous halos are o ld, they contain important information about the star formation history of elliptical galaxies. In this paper we show that the enrichment history of t his hot gas is closely linked to its gasdynamical history; supernovae provi de both energy and metal enrichment. We find that Type II supernovae based on a Salpeter initial mass function (IMF), plus a small number of additiona l Type Ia supernovae, can explain the density, temperature, and abundance p rofiles currently observed in gaseous halos around massive ellipticals. Wit hin the central, optically bright region of luminous ellipticals, approxima tely half of the interstellar iron is produced by Type Ia supernovae and ha lf by mass lost from evolving stars that were originally enriched in iron b y Type IT supernovae. However, iron and silicon abundances in the intraclus ter gas within rich clusters suggest enrichment by a larger number of super novae per unit optical light than we require for massive ellipticals. The a dditional supernovae implied by cluster data cannot be reconciled with our models for individual massive ellipticals. Evidently, rich clusters cannot be constructed by simply combining ellipticals and their associated groups, since the enrichment history of clusters and massive ellipticals appears t o be fundamentally different. Neither currently discussed resolution of thi s discrepancy-an increased number of Type TI supernovae (flat IMF) or stron g Type Ia enrichment in clusters-is attractive. Although the global hot gas iron abundance is similar in all large galaxy clusters, silicon is enhance d in hotter, richer clusters. This Si/Fe variation implies that E and SO ga laxies are not the only sources of cluster gas enrichment; perhaps spirals or low-mass galaxies are also important.