Cosmological and environmental influences on hot gas observed in elliptical galaxies

The X-ray emission from hot gas in bright elliptical galaxies often extends far beyond the radius of the stellar system. This "circumgalactic" gas acc ounts for most or all of the large spread in X-ray luminosity L-X among ell iptical galaxies having similar optical luminosities L-B. We have developed gasdynamical models describing the evolution of gas within and around elli ptical galaxies beginning with an overdensity perturbation in a simple flat cosmology. At some early time, we form the stellar galaxy and release supe rnova energy, conserving dark and baryonic matter. We follow the subsequent evolution of intergalactic and interstellar gas to the present time. These models confirm that hot gas density and temperature distributions currentl y observed in massive, group-dominant elliptical galaxies can be understood as a combination of intergalactic gas that has flowed into the galaxy grou p over time and gas lost from galactic stars. Furthermore, if the hot gas a nd dark matter halos are subject to differential tidal truncations or mass exchanges between group members, then the observed correlation between L-X/ L-B and the relative sizes of galactic X-ray images can be understood. The distribution and physical properties of hot interstellar gas observed in ma ssive elliptical salaries today are sensitive to the cosmic baryon fraction , the time of maximum star formation, and the amount of "feedback" energy d elivered to the gas by Type II supernovae at the epoch of galaxy formation.