Physics – Atomic Physics
Scientific paper
Jan 1985
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985apj...288...58l&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 288, Jan. 1, 1985, p. 58-64.
Physics
Atomic Physics
54
Cosmic Gases, Equations Of State, Interstellar Gas, Quasars, Thermodynamic Properties, Astronomical Models, Atomic Physics, Gas Heating, Gas Ionization, Thermal Stability, X Ray Spectroscopy
Scientific paper
Interstellar gas may be in a variety of thermal phases, depending on how it is heated and ionized; here a unified picture of the equation of state of interstellar and quasar gas is presented for a variety of such mechanisms over a broad range of temperatures, densities, and column densities of absorbing matter. It is found that for select ranges of gas pressure, photoionizing flux, and heating, three thermally stable phases are allowed: coronal gas (T above 100,000 K); warm gas (T about 10,000 K); and cold gas (T less than 100 K). With attenuation of ultraviolet and X-ray radiation, the cold phase may undergo a transition to molecules. In quasar broad-line clouds, this transition occurs at column density N(H) = about 10 to the 23rd/sq cm and could result in warm molecular cores and observable emission from H2 and OH. The underlying atomic physics behind each of these phase transitions and their relevance to interstellar matter and quasars are discussed.
Kallman Tim
Lepp Stephen
McCray Richard
Shull Michael J.
Woods Tod D.
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