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

The large spatial extent of hot, X-ray-emitting gaseous halos around massive elliptical galaxies indicates that most of this gas has not been generated by stellar mass loss. Instead, much of this gas results from an intergalactic gaseous inflow toward the overdensity from which giant ellipticals and their associated galaxy groups formed. Since these hot gaseous halos are old, they contain important information about the star formation history of elliptical galaxies. In this paper we show that the enrichment history of this hot gas is closely linked to its gasdynamical history; supernovae provide both energy and metal enrichment. We find that Type II supernovae based on a Salpeter initial mass function (IMF), plus a small number of additional Type Ia supernovae, can explain the density, temperature, and abundance profiles currently observed in gaseous halos around massive ellipticals. Within the central, optically bright region of luminous ellipticals, approximately half of the interstellar iron is produced by Type Ia supernovae and half by mass lost from evolving stars that were originally enriched in iron by Type IT supernovae. However, iron and silicon abundances in the intracluster gas within rich clusters suggest enrichment by a larger number of supernovae per unit optical light than we require for massive ellipticals. The additional 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 to be fundamentally different. Neither currently discussed resolution of this discrepancy-an increased number of Type TI supernovae (flat IMF) or strong Type Ia enrichment in clusters-is attractive. Although the global hot gas iron abundance is similar in all large galaxy clusters, silicon is enhanced in hotter, richer clusters. This Si/Fe variation implies that E and SO galaxies are not the only sources of cluster gas enrichment; perhaps spirals or low-mass galaxies are also important.