A near-infrared/millimeter-wave study of six fourth-quadrant high-mass star formation regions

We present near-infrared and millimeter-wave observations of six high-mass star-forming regions in the fourth quadrant: RCW 108, G333.6, RCW 117, RCW 122, NGC 6334 I, and G351.6. These regions have heliocentric distances of 1.3-3.0 kpc and total luminosities ranging from 0.5 to 3 x 10(5) L-circle dot. Millimeter maps taken in transitions of (CO)-O-18, HC3N, (C16O)-C-12, and SiO with the Swedish-ESO Submillimetre Telescope 15 m telescope detail the structure and kinematics of the clouds. Near-infrared K-band images of the same regions obtained with the MPG/ESO 2.2 m telescope are used to map the stellar surface density. The (CO)-O-18 (1 --> 0) line shows extended high column density gas, with column densities ranging from 10(22) to 3 x 10(23) cm(-2); in contrast, the HC3N ( 15 ! 14) emission shows eight sharply peaked dense cores. We examine these cores for recent and ongoing star formation by searching for high-velocity, non-Gaussian wings on the CO (1 --> 0) and SiO (2 --> 1) lines, peaks in the surface density of stars, and positional coincidences with IRAS point sources, as well as masers and H II regions reported in the literature. All of the cores show evidence of ongoing star formation. NGC 6334 I(N) stands out as a unique case in which an outflow has formed and masers have appeared, but no IRAS source, K-band cluster, or UC H II region has yet appeared; our data support previous claims that this is a rare example of a core in the earliest stages of forming a cluster of high- and low-mass stars.