Evolution of the Multiphase Hot Interstellar Medium in Elliptical Galaxies

We present the results of a variety of simulations concerning the evolutionof multiphase (inhomogeneous) hot interstellar medium (ISM) in ellipticalgalaxies. We assume the gases ejected from stars do not mix globally with thecircumferential gas. The ejected gas components evolve separately according totheir birth time, position, and origin. We consider cases where supernovaremnants (SNRs) mix with local ISM. The components with high metal abundanceand/or high density cool and drop out of the hot ISM gas faster than the othercomponents because of their high metal abundance and/or density. This makes theaverage metal abundance of the hot ISM low. Furthermore, since the metalabundance of mass-loss gas decreases with radius, gas inflow from outer regionmakes the average metal abundance of the hot ISM smaller than that of mass-lossgas in the inner region. As gas ejection rate of stellar system decreases, massfraction of mass-loss gas ejected at outer region increases in a galaxy. If themixing of SNRs is ineffective, our model predicts that observed [Si/Fe] and[Mg/Fe] should decrease towards the galactic center because of strong ironemission by SNRs. In the outer region, where the cooling of time of the ISM islong, the selective cooling is ineffective and most of gas components remainhot. Thus, the metal abundance of the ISM in this region directly reflects thatof the gas ejected from stars. Our model shows that supernovae are noteffective heating sources in the inner region of elliptical galaxies, becausemost of the energy released by them radiates. Therefore, cooling flow isestablished even if the supernova rate is high. Mixing of SNRs with ambient ISMmakes the energy transfer between supernova explosion and ambient ISM moreeffective.Comment: 21 pages (AASTeX), 14 figures, accepted for publication in The Astrophysical Journa