2004ApJ...606..929H

We present high-resolution, multiwavelength-continuum, and molecular-line images of the massive star forming region IRAS 18317-0757. The global infrared through millimeter spectral energy distribution can be approximated by a two-temperature model (25 and 63 K) with a total luminosity of approximately log(L/L_☉)=5.2. Previous submillimeter imaging resolved this region into a cluster of five dust cores, one of which is associated with the ultracompact H II region G23.955+0.150, and another with a water maser. In our new 2.7 mm continuum image obtained with BIMA, only the UCH II region is detected, with total flux and morphology in good agreement with the free-free emission in the VLA centimeter-wave maps. For the other four objects, the nondetections at 2.7 mm and in the MSX mid-infrared bands are consistent with cool dust emission with a temperature of 13-40 K and a luminosity of 1000-40,000 L_☉. By combining single-dish and interferometric data, we have identified over two dozen virialized C¹⁸O cores in this region that contain ~40% of the total molecular gas mass present. While the overall extent of the C¹⁸O and dust emission is similar, the emission peaks do not correlate well in detail. At least 11 of the 123 infrared stars identified by 2MASS in this region are likely to be associated with the star-forming cluster. Two of these objects (both associated with the UCH II region) were previously identified as O stars via infrared spectroscopy. Most of the rest of the reddened stars have no obvious correlation with the C¹⁸O cores or the dust continuum sources. In summary, our observations indicate that considerable fragmentation of the molecular cloud has taken place during the time required for the UCH II region to form and for the O stars to become detectable at infrared wavelengths. Additional star formation appears to be ongoing on the periphery of the central region, where up to four B-type (proto)stars have formed among a substantial number of C¹⁸O cores.