AST/RO Observations of Photodissociations Regions in a Metal-Poor Environment

Details AST/RO Observations of Photodissociations Regions in a Metal-Poor Environment AST/RO Observations of Photodissociations Regions in a Metal-Poor Environment

May 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aas...192.5808b&link_type=abstract

American Astronomical Society, 192nd AAS Meeting, #58.08; Bulletin of the American Astronomical Society, Vol. 30, p.904

Astronomy and Astrophysics

Astrophysics

Scientific paper

We report observations of the (3) P_1->(3) P_0 fine structure transition of neutral carbon ([C I], lambda =609\ mu m) and the J=4->3 rotational transition of CO (lambda =652\ mu m) on the Large Magellanic Cloud. These measurements were performed using the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) during the 1995, 1996 and 1997 seasons. Neutral carbon originates in the warm interface regions of molecular clouds known as Photodissociation Regions (PDRs), where CO is split into its atomic components by UV radiation. [C I] emission is thus thought to trace this transition occurring at a visual extinction of a few (A_v ~ 1-3). Middle rotational transitions of CO trace relatively dense (n_H~10(5) cm(-3) ) and warm (T>20 K) molecular gas. PDR regions are enlarged in low metallicity environments, where the UV penetration is enhanced by the lower dust-to-gas ratios. We present a semianalytical model for the dependence of the [C II]/CO and [C I]/CO intensity ratios with metallicity and compare its predictions with the available observations of PDRs in metal-poor environments. The study of PDRs in the low metallicity ISM will allow us to better understand the observational diagnostics for the first cosmic epochs of star formation. 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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