From the analysis of the high spatial resolution mid infrared images of the cometary HII region NGC 6334 F we can make the following conclusions:
1) Three mid-IR sources and an extended diffuse emission, are present in the 11.2µm image.
2) The source MIR 2 (IRS-I 1) coincident with the HII region, is resolved with a size of approximately 3-6 1016 cm. The flux distribution of this source (Fig. 4) indicates that the 11.2µm emission is due to a circumstellar dust at Td 105-130 K. Its morphology and size are similar to the diffuse emission observed at 2.2µm and in the radio continuum. This suggests that the dust and gas are well mixed inside the HII region or just at the edge of the ionization front.
3) The source MIR 3 located east of the HII region is identified with the source IRS-I 3 of Harvey & Gatley (1983) and shows a spectral index n = - 2.2, typical of very young stellar objects. Lack of radio continuum emission places this source in an earlier evolutionary stage with respect to MIR 2 (IRS-I 1).
4) A very diffuse 11.2µm emission is observed in the densest part of the molecular cloud (Figs. 2 and 5) west of the HII region, where the CO bipolar molecular outflow is also located. A plausible explanation for the emission comes from PAHs in the molecular cloud.
5) Because of this diffuse emission we cannot confirm the presence of the very cold (presumably unresolved) object IRS-I 2 that has been suggested as the driving source of the bipolar outflow. We can only exclude that the 7 mm clump is heated by an internal early type star unless the extinction is so high (AV 110-140) to inhibit detection at 11.2µm of the hot dust envelope surrounding the early type star. High resolution images at longer wavelengths (20µm or submillimeter) as well as a better definition of the bipolar outflow center are needed to establish which is the energy source of the bipolar outflow.
© European Southern Observatory (ESO) 1998
Online publication: July 27, 1998