Evolution of the interstellar medium in elliptical galaxies. II - 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_sun_ 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_ <~ -20 have cooling flows, (2) galaxies with -20 <~ M_B_ <~ -19 have partial winds, (3) galaxies with -19 <~ M_B_ <~ -18 have total subsonic winds, and (4) galaxies with M_B_ >~ -18 have total transonic winds. Model galaxies fainter than M_B_ ~ -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 proNe). 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.