Other
Scientific paper
Dec 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aas...183.2607p&link_type=abstract
American Astronomical Society, 183rd AAS Meeting, #26.07; Bulletin of the American Astronomical Society, Vol. 25, p.1333
Other
Scientific paper
Since the (3) P_1 -> (3) P_0 (492 GHz) fine--structure transition of neutral carbon arises from a state only 23 K above ground, and has a critical density of ~ 10(3) cm(-3) , it should be readily observable over a large fraction of the dense interstellar medium. Observations of our Galaxy show that over large scales the 492 GHz line has a larger intensity than any individual (12) CO rotational line. The ratio of the 492 GHz [CI] line flux to the flux in the (12) CO J=2->1 line in the Milky Way (2.3+/-0.6), is also comparable to the inner regions of other galaxies (1.5+/-0.4 in IC 342; 1.3--1.6 in M82). This implies that the ground state fine--structure transitions of C(o) are important coolants of the dense neutral interstellar medium. Theories of photon dominated regions (PDRs) predict that [CI] emission should arise from a thin layer at the surfaces of UV illuminated molecular clouds. The large--scale [CI] observations show that the line emission must come from extended regions of molecular clouds, and cannot arise strictly from the immediate vicinities of massive star formation. The distribution of [CI] emission has been studied, on smaller scales, in a number of interstellar clouds. However, these observations are limited in area and are usually restricted to regions near ionization fronts. Therefore, we have little knowledge of the typical C(o) distribution and abundance over extended regions in molecular clouds. We will present results from the first large--scale (typically 30' times \ 30\arcmin ) mapping of the 492 GHz (3) P_1 -> (3) P_0 transition of neutral carbon toward CepA, M17, NGC 2024, S140, and W3. We will also present observations of the same regions in the (13) CO J=2->1 and C(18) O J=2->1 lines for comparison. The observations were made with the ``Texas Gaussian Focal Reducer" which reduces the effective aperture of the Caltech Submillimeter Observatory from 10.4m to ~ 60cm. The resulting beamsize at 492 GHz was 3' and allowed us to rapidly survey [CI] emission over large areas in 5 molecular clouds.
Jaffe David
Keene Jocelyn
Plume Rene
Tatematsu Ken'ichi
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