Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...503..785k&link_type=abstract
Astrophysical Journal v.503, p.785
Astronomy and Astrophysics
Astronomy
23
Infrared: Ism: Continuum, Ism: H Ii Regions, Ism: Individual Ngc Number: Ngc 6334, Stars: Formation
Scientific paper
The [O I] 63 mu m transition has been imaged around five far-infrared (FIR) and radio continuum sources in the southern massive star formation region NGC 6334. The [O I] 63 mu m line is found in absorption toward the FIR continuum source NGC 6334V. This is only the second case in which the [O I] 63 mu m line has been seen in absorption against a continuum source. From the depth of the absorption line, the minimum column density of oxygen is calculated to be N(O0) >~ 5 x 1018 cm-2. This amount of oxygen is consistent with [O I] 63 mu m absorption due to atomic gas in the foreground molecular cloud. The [O I] 63 mu m line is found in emission toward the other four sources observed: NGC 6334, sources A, C, D, and E. Single-component photodissociation region (PDR) models suggest densities of n ~ 104 cm-3 for these sources, based on previously observed [O I] 145 mu m and [C II] 158 mu m intensities. However, unphysically large far-ultraviolet (FUV) fields are implied for three of the sources, particularly for NGC 6334A. Neither one- nor two-component photodissociation region models can explain the anomalously low [O I] 63 mu m intensity toward NGC 6334A nor the absorption toward NGC 6334V. We suggest that self-absorption of the [O I] 63 mu m line, such as has been suggested toward DR 21, is suppressing the observed [O I] 63 mu m intensity. This underestimate leads to an overestimate of the derived FUV field strengths throughout NGC 6334. The discovery of several more star-forming sites in which the [O I] 63 mu m is in absorption or is self-absorbed implies that this line is not always a reliable PDR diagnostic because the PDR models do not treat the radiative transfer through the molecular cloud.
Jackson James M.
Kraemer Kathleen E.
Lane Adair P.
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