PRODUCTION AND CIRCULATION OF IRON IN ELLIPTIC GALAXIES AND CLUSTERS OF GALAXIES

We introduce the concept of cluster iron mass-to-light ratio (IMLR) an d estimate its value for both the intracluster medium and the stars, f inding the amount of iron to be nearly the same in the two cluster com ponents. We discuss under which conditions the past supernova activity can account for the observed IMLR and provide evidence that either th e past average rate of Type Ia supernovae was at least a factor of app roximately 10 higher than the present rate in ellipticals, or massive stars in clusters formed with a very flat initial mass function (IMF). A solution in which approximately 1/4 of the observed iron in cluster s of galaxies was contributed by Type II supernovae, and approximately 3/4 by Type Ia supernovae, presents several advantages, as it would a llow to preserve the current scenario for the establishment of element abundance ratios in the Galactic halo, bulge, and disk and would leav e open the possibility of a universal IMF. We consider the iron abunda nce in the gas flow of individual elliptical galaxies, emphasize a mac roscopic discrepancy that has recently emerged between the predicted i ron abundance in the flow and that derived from X-ray observations, an d discuss possible solutions of the discrepancy. We argue that the iro n in the intracluster medium (ICM) of rich clusters was ejected from i ndividual galaxies by internal forces generated by supernovae or activ e galactic nuclei (AGNs), rather than stripped by external forces such as ram pressure. We go further in considering the supernova heating a nd the presupernova light production which are implied by the observed IMLR and discuss their implications for elliptical galaxy formation. We suggest a possible test for the proposed scenarios, based on the pr edicted difference in elemental ratios between the ICM and cluster ell iptical galaxies, with alpha-elements to iron ratio being below solar in the ICM and above solar in the stellar component of galaxies.