Physical and Chemical Processes in the Diffuse and Dense Neutral ISM

Publisher: Edp Sciences

E-ISSN: 1638-1963|34|issue|151-161

ISSN: 1633-4760

Source: EAS Publications Series, Vol.34, Iss.issue, 2008-12, pp. : 151-161

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Abstract

Most of the mass of the interstellar medium is in neutral phases that are heated by far-ultravioletradiation from star forming regions. The gas, in turn, emits line radiation in the infrared and submillimeter that potentially has great diagnostic value. In this paper, we will review the physical processes (including heating, cooling, gas phase and grain surface chemistry) that give rise to this line emission and present diagnostic diagrams. We will also discuss several examples where models of neutral gas emission have been used to interpret line emission, including observations of H2O and O2 in molecular clouds and an example which points out the caution that must be used when applying the diagnostics to kiloparsec-sized regions in other galaxies.