Abstract
The variation of temperature and density in the hot, X-ray emitting gas around massive, group dominant elliptical galaxies can be understood as a combination of gas ejected from evolving galactic stars and gas that accumulates in the outer halo by secondary cosmic infall. Beginning with an overdensity perturbation in a simple flat cosmology, we can duplicate observed properties of the hot gas. At some early time we form the stellar galaxy and release supernova energy, conserving dark and baryonic matter. Using a potential appropriate to the large elliptical NGC 4472, we follow the evolution of intergalactic and interstellar gas to the present time when the computed gas density and temperature agree with X-ray observations of NGC 4472. If the hot gas and dark matter halos are subject to differential tidal truncations or mass exchanges between group members, then the correlation between $L_x/L_B$ and the relative sizes of galactic X-ray images can be generated. The physical properties of hot interstellar gas observed in bright ellipticals today are sensitive to the cosmic baryon fraction, the time of maximum star formation and the amount of ``feedback'' energy delivered to the gas by Type II supernovae at the epoch of galaxy formation.
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