EVOLUTION OF THE MULTIPHASE HOT INTERSTELLAR-MEDIUM IN ELLIPTIC GALAXIES

We present the results of a variety of simulations concerning the evol ution of the multiphase (inhomogeneous) hot interstellar medium (ISM) in elliptical galaxies. We assume the gases ejected from stars do not mix globally with the circumferential gas. The ejected gas components evolve separately according to their birth time, position, and origin. We consider cases where supernova remnants (SNRs) mix with the local ISM. The high metal abundance and/or high density of some gas componen ts causes them to cool and drop out of the hot ISM gas faster than oth er components. This makes the average metal abundance of the hot ISM l ow. Furthermore, since the metal abundance of mass-loss gas decreases with radius, gas inflow from the outer region makes the average metal abundance of the hot ISM less than that of mass-loss gas in the inner region. As the gas ejection rate of the stellar system decreases, the mass fraction of mass-loss gas ejected at the outer region increases i n the galaxy. If the mixing of SNRs is ineffective, our model predicts that observed [Si/Fe] and [Mg/Fe] should decrease toward the galactic center because of strong iron emission by SNRs. In the outer region, where the cooling time of the ISM is long, the selective cooling is in effective, and most of the gas components remain hot. Thus, the metal abundance of the ISM in this region directly reflects that of the gas ejected from stars. Our model shows that supernovae are not effective heating sources in the inner region of elliptical galaxies, because mo st of the energy released by them radiates. Therefore, a cooling how i s established even if the supernova rate is high. Mixing of SNRs with the ambient ISM makes the energy transfer between supernova explosion and the ambient ISM more effective.