Submillimeter Wave Astronomy Satellite and Arecibo Observations of H2O and OH in a Diffuse Cloud along the Line of Sight to W51
Abstract
Observations of W51 with the Submillimeter Wave Astronomy Satellite have yielded the first detection of water vapor in a diffuse molecular cloud. The water vapor lies in a foreground cloud that gives rise to an absorption feature at an LSR velocity of 6 km s-1. The inferred water column density is 2.5×1013 cm-2. Observations with the Arecibo radio telescope of hydroxyl molecules at 10 positions in W51 imply an OH column density of 8×1013 cm- 2 in the same diffuse cloud. The observed H2O/OH ratio of ~0.3 is significantly larger than an upper limit derived previously from ultraviolet observations of the similar diffuse molecular cloud lying in front of HD 154368. The observed variation in H2O/OH likely points to the presence in one or both of these clouds of a warm (T>~400K) gas component in which neutral-neutral reactions are important sources of OH and/or H2O.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 2002
- DOI:
- 10.1086/343077
- arXiv:
- arXiv:astro-ph/0207344
- Bibcode:
- 2002ApJ...580..278N
- Keywords:
-
- ISM: Abundances;
- ISM: Clouds;
- ISM: Molecules;
- Molecular Processes;
- Radio Lines: ISM;
- Submillimeter;
- Astrophysics
- E-Print:
- 15 pages (AASTeX) including 4 (eps) figures. To appear in the Astrophysical Journal