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Title:
Photodissociation Regions and H II Regions in NGC 6334
Authors:
Jackson, James M.; Kraemer, Kathleen E.
Publication:
The Astrophysical Journal, Volume 512, Issue 1, pp. 260-270. (ApJ Homepage)
Publication Date:
02/1999
Origin:
APJ
ApJ Keywords:
ISM: H II REGIONS, ISM: INDIVIDUAL: NGC NUMBER: NGC 6334, ISM: MOLECULES, RADIO LINES: ISM, STARS: FORMATION
DOI:
10.1086/306760
Bibliographic Code:
1999ApJ...512..260J

Abstract

Using the VLA at 8.485 GHz, we have imaged the southern portion of the star-forming ridge of molecular gas in NGC 6334. The diffuse radio source G351.20+0.70, discovered by Moran et al. (1990), is now resolved into a roughly spherical shell of radius ~1' (0.5 pc). The distribution of molecular gas (traced by CO emission), of photodissociated gas (traced by [C II] 158 μm emission), and of ionized gas (traced by radio continuum emission), is precisely that expected for a photodissociation region-the ionized gas lies on the interior of the shell, the photodissociated gas just outside the ionized gas, and the molecular gas just outside the photodissociated gas. We also detected faint radio counterparts to the strong infrared sources NGC 6334 IV IRS 20 and NGC 6334 V. If these objects are zero-age main-sequence stars, they produce far less radio free-free emission than would be expected for the observed infrared flux. Some possible explanations for this discrepancy are the following: (1) the radio free-free emission is optically thick, (2) the stellar ionizing radiation is obscured by dust, (3) the objects are not single OB stars but very compact clusters of later type stars, or (4) the objects are protostars. For both NGC 6334 V and NGC 6334 IV IRS 20, the radio spectrum for the unresolved sources is inconsistent with optically thick free-free emission or dust obscuration from a homogeneous H II region. The radio spectral index for NGC 6334 IV IRS 20 is consistent with the value of 0.6 expected for an optically thick H II region for a star undergoing mass loss, but that of NGC 6334 V is not. Because the IR sources in NGC 6334 V are very compact (<~0.02 pc), the stellar volume densities for a cluster of later-type stars would be unreasonably large. The objects in NGC 6334 V are probably protostars.
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