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Astron. Astrophys. 323, L13-L16 (1997)

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Letter to the Editor

CI fine-structure emission from non-equilibrium PDRs

H. Störzer 1, 2, J. Stutzki 1 and A. Sternberg 3

1 I. Physikalisches Institut der Universität zu Köln, Zülpicher Straße 77, D-50937 Köln, Germany
2 MS 245-3, NASA Ames Research Center, Moffett Field, CA 94035, USA
3 School of Physics and Astronomy, Tel Aviv University, Ramat Aviv, Israel

Received 26 November 1996 / Accepted 13 March 1997


We present computations of [CI] 609 µm and 370 µm fine-structure line emission from non-equilibrium clouds which are suddenly shielded from initially intense far-ultraviolet radiation fields. After the incident UV fluxes are diminished the initially abundant C [FORMULA] ions rapidly recombine, and the neutral atomic carbon is then slowly incorporated into CO molecules. The cloud cooling times are longer than the CI formation times, and intense [CI] emission persists as the clouds cool. The [CI] emission is thus much brighter from cooling clouds than in equilibrium photon dominated regions. We argue that if UV-scattering is inefficient the extended [CI] emission observed in star-forming regions may be better explained by non-equilibrium models than by steady state models.

Key words: Line: formation - ISM: clouds - ISM: molecules - Radio lines: interstellar

Send offprint requests to: H. Störzer

© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998