1.0-mm Continuum, 12CO, 13CO and C18O Mapping of the NGC 6334 Complex and Comparison with IRAS Observations

Abstract

We present high spatial resolution well sampled observations of the NGC 6334 cloud complex in the 12CO, 13CO and C18O isotopic species, and 1.0-mm continuum emission from cool dust, covering the far infrared emission Peaks I-V, a new Peak IV, and the cold (T=20K) sub-mm Peak I(North) cloud (Cheung et al. 1978, Gezari 1982). The 12CO and 13CO emission was mapped previously by Scoville and Wannier (1976) with 2 – 4 arcmin sampling. These 1.0-mm continuum maps were obtained at the CTIO 4-m telescope with 65 arcsec FWHM resolution in June 1981, and the CO line observations were made at the NRAO 36-foot telescope with 1 arcmin FWHM resolution in April 1982. Several new observational results are presented here, including the large-scale detailed structure of the 1.0-mm continuum and 13CO line emission a ~0.7 pc scale (Figure la-c), and half beam width (0.5 arcmin) sampled 12CO, 13CO and C18O maps of the dense Peak I(North) region (Figure 2). A comparison of the I.0-mm continuum (Figure la) and CO isotopes (Figure 2) shows that the highest TA *(12CO) = 16K occurs at the position of sub-mm Peak I and compact HII region “E” (Rodriguez, Canto and Moran 1982), consistent with the distribution expected of optically thick gas heated by warm dust associated with the compact HII region. In contrast, the map of integrated TA *(13CO) shows two distinct peaks similar to the 400 µm continuum structure mapped by Gezari (1982). The highest TA *(13CO) = 20K at Peak I(North), and the 13CO/12CO ratio is greater there than at Peak I indicating that the cold Peak I(North) source can not be optically thin in 13CO and is massive, in spite of relativly weak 12CO emission. The optically thin C18O source (Figure 3) is very compact and also brightest at Peak I(North), the position of the highest 1.0-mm dust column density (NH2 = 1 × 1024 cm−2). The C18O distribution confirms that Peak I(North) apparently has among the highest derived visual extinction (mv > 100 mag). The 13CO lines at I(North) are narrow (6 km s−1 FWHM) and may arise from the envelope of a protostellar cloud still in the collapse phase. The four color IRAS obvservations (Figure 3), while considerably lower in spatial resolution, show that the warmest (12 – 25 µm) dust emission is concentrated about 5 arcmin SW of the strongest 1.0-mm and CO emission, and is associated with the prominent, extended visible HII region NGC 6334. This work was partially supported by NSF grant ASF-86-18763, and by NASA RTOP 188-41-55. Open image in new window Figure 1 a) 1.0-mm continuum map of the NGC 6334 complex with 65 arcsec (FWHM) beam. The region was sampled on a 30 aresec grid near the strong peaks, and 1 arcmin elswhere. The contour interval in 1.0-mm brightness is 15 Janskys/beam (peak = 135); since the dust is optically thin this is equivalent to an interval of 1 × 1023 cm−2 in derived molecular hydrogen column density. (Note: Peaks labled I-IV by Cheung et al. (1978) are actually I/North, I, II and III in current nomenclature). b) Peak TA *(13CO), contour interval is 2K (peak = 20K), full beam width sampled (1 arcmin) over the region and half beam sampled near Peak I. c) Integrated TA *(13CO) line intensity, contour interval is 6 Jy km s−1arcmin−2 (peak = 131), same sampling as in Figure lb. Open image in new window Figure 2 12CO, 13CO and C18O peak TA * and integrated TA * intensity maps near far infrared NGC 6334 peak I, half beam width sampled (30 arcsec). The cross (+) marks the cold sum-mm peak I(North) object, an asterisk (*) marks compact HII region “E”. Peak TA * (12CO) = 16K,peak integrated TA * (12CO) line intensity = 166 K km s−larcmin−2; peak TA * (13CO) = 20K, peak integrated TA * (13CO) = 131 K km s−larcmin−2; peak TA *(C18O) = 4.5K, peak integrated TA *(C18O) line = 20 K km s−larcmin−2. Open image in new window Figure 3 IRAS maps of the NGC 6334 cloud complex at 12 25, 60 and 100 µm.