Neutral Atomic Phases of the ISM in the Galaxy
نویسندگان
چکیده
Much of the interstellar medium in disk galaxies is in the form of neutral atomic hydrogen, H I. This gas can be in thermal equilibrium at relatively low temperatures, T < ∼ 300 K (the cold neutral medium, or CNM) or at temperatures somewhat less than 10 K (the warm neutral medium, or WNM). These two phases can coexist over a narrow range of pressures, Pmin ≤ P ≤ Pmax. We determine Pmin and Pmax in the plane of the Galaxy as a function of Galactocentric radius R using recent determinations of the gas heating rate and the gas phase abundances of interstellar gas. We provide an analytic approximation for Pmin as a function of metallicity, far-ultraviolet radiation field, and the ionization rate
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