First Submillimeter Neutral Carbon Observations of the Large Magellanic Cloud: Photodissociation Regions in a Metal Poor Environment

Details First Submillimeter Neutral Carbon Observations of the Large Magellanic Cloud: Photodissociation Regions in a Metal Poor Environment First Submillimeter Neutral Carbon Observations of the Large Magellanic Cloud: Photodissociation Regions in a Metal Poor Environment

May 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996aas...188.5107b&link_type=abstract

American Astronomical Society, 188th AAS Meeting, #51.07; Bulletin of the American Astronomical Society, Vol. 28, p.901

Astronomy and Astrophysics

Astrophysics

Scientific paper

Using the Antarctic Submillimeter Telescope/Remote Observatory (AST/RO), in operation since January 1995, we have observed the (3) P_1->(3) P_0 492 GHz transition of neutral atomic carbon [CI] towards two positions in the Large Magellanic Cloud: the compact HII region N159 and the massive star formation region 30 Doradus. Neutral carbon, a product of the photodissociation of CO, traces the transition zone of the interstellar medium occurring at visual extinctions of a few (A_v ~ 1-3) where the presence of H_2 is not traced by CO. The extent of these so called photodissociation regions (PDRs) is enhanced in metal-poor systems, where low C and O abundances are coupled with low dust-to-gas ratios. Lower CO abundances result in diminished CO self-shielding, and lower dust-to-gas ratios decrease dust shielding. Consequently, the beam filling factor of the PDR is augmented, which leads to enhanced I_{[CI]}/ICO intensity ratios. Our observation of N159 yields a ratio of I_{[CI]}/I_{(12) CO (1-0)} ~ 0.2 when data is compared in the same beam. In the Galaxy this ratio is roughly 0.1. Towards 30 Doradus AST/RO has detected the faintest [CI] line ever seen, with a peak brightness of 28 mK. The ratio I_{[CI]}/I_{(12) CO (1-0)} ~ 0.05 found for this region possibly reflects the extremely intense UV field to which the gas is exposed. This research was supported in part by the National Science Foundation under a cooperative agreement with the Center for Astrophysical Research in Antarctica (CARA), grant number NSF OPP 89-20223. CARA is a National Science Foundation Science and Technology Center.

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