Multiphase Chemical Evolution in Elliptical Galaxies

Abstract

Recent ASCA results show that the iron abundance of the X-ray-emitting hot gas of elliptical galaxies is less than the solar abundance. The observed low iron abundance is inconsistent with the predictions of previous chemical evolution models. In order to solve this problem, we present a simple model of chemical evolution for elliptical galaxies after the galactic-wind period, assuming that the gases ejected from stars do not mix with the circumferential gas. The ejected gas components evolve separately according to their birth time and origin. We have investigated their evolution qualitatively. The gas Components originated from supernova remnant shells cool and drop out of the hot gas faster than the other components because of their high density and metal abundance. As a result, supernovae cannot heat all the gas of an elliptical galaxy effectively, contrary to previous results. If the metal abundance of mass-loss gas is not uniform, the mass-loss gas with higher abundance also easily drops out, and the average abundance of the hot gas can decrease. We believe that this is a hint toward solving the low- abundance problem.