Water in Molecular Clouds

Details Water in Molecular Clouds Water in Molecular Clouds

Dec 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aas...195.6302s&link_type=abstract

American Astronomical Society, 195th AAS Meeting, #63.02; Bulletin of the American Astronomical Society, Vol. 31, p.1465

Astronomy and Astrophysics

Astronomy

Scientific paper

We have used SWAS to observe the 110}->1{01 rotational transition of ortho-H2O in a large sample of molecular clouds within the Galaxy. This transition arises from only 27 K above the ortho-H2O ground state, and thus is a unique probe of water in cooler molecular gas. Water emission was detected in nearly all giant molecular cloud cores observed. Maps of the emission were obtained for Orion and M17 and the spatial extent, line widths, and line center velocity of the emission are consistent with the emission arising in the cold, dense, quiescent gas of these cloud cores. In dark cloud cores, ortho-H2O was not detected in emission from the quiescent gas. However, in some dark clouds narrow water absorption features were detected at the velocity of the quiescent gas against broad water emission arising from outflows. Our estimates of the abundance of ortho-water relative to molecular hydrogen in giant molecular cloud cores range from 1*E-9 to 1*E-7, considerably smaller than the abundance of water found in the hot, shocked gas. Observations of ortho-H218O were also obtained in selected giant molecular cloud cores. Upper limits on the emission in this line yield abundance limits consistent with those derived from the main isotopic line. This work was supported by NASA's SWAS contract NAS5-30702 and NSF grant AST97-25951 to the Five College Radio Astronomy Observatory.

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