PHOTODISSOCIATION REGIONS AND H II REGIONS IN NGC 6334

摘要

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 a. (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 mu M emission), and of ionized gas (traced by radio continuum emission), is precisely that expected for a photodissociated 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 in 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 NG