EVOLUTION OF THE INTERSTELLAR-MEDIUM IN ELLIPTIC GALAXIES .2. X-RAY-PROPERTIES

We present the results of a variety of simulations concerning the evolution of the hot component of the interstellar medium in elliptical galaxies. Our models cover the range in galaxy luminosity from 10(9) to 10(11) L. and include a range of star formation histories, present Type I supernova rates, and the effects of massive dark halos. All our model galaxies evolve through an early Type II supernova-driven wind phase. Following this stage the model galaxies evolve through a series of evolutionary stages characterized by the flow profile of the interstellar medium (i.e., partial winds, total subsonic winds, and transonic winds). The exact evolutionary sequence exhibited by a given model galaxy depends primarily on the gravitational potential depth of the galaxy and the present Type I supernova rate. The present dynamic state of our model galaxies with massive dark halos and a present Type I supernova rate equal to the most recent estimate on early-type galaxies can be summarized as follows: (1) galaxies with M(B) less-than-or-similar-to -20 have cooling flows, (2) galaxies with -20 less-than-or-similar-to M(B) less-than-or-similar-to -19 have partial winds, (3) galaxies with -19 less-than-or-similar-to M(B) less-than-or-similar-to -18 have total subsonic winds, and (4) galaxies with M(B) less-than-or-similar-to -18 have have total transonic winds. Model galaxies fainter than M(B) almost-equal-to -20.5 without massive dark halos and the same present type I supernova rate per unit blue luminosity have transonic winds at the present time. A comparison of our models with Einstein X-ray observations shows that bright ellipticals must have massive dark halos in order to retain the large amounts of hot gas required to generate their observed X-ray luminosities. The dynamic state of the hot gas in ellipticals is directly reflected through observable X-ray properties (i.e., X-ray luminosity, surface brightness profile, emission-weighted temperature, and temperature profile). We show how observations of these X-ray diagnostics can determine the flow profile of the hot gas in ellipticals, the amount of dark matter and the present epoch Type I supernova rate.