2011ApJ...729..100L

The massive clump G10.6-0.4 is an OB cluster-forming region, in which multiple ultracompact (UC) H II regions have been identified. In the present study, we report arcsecond resolution observations of the CS (1-0) transition, the NH₃(3,3) main hyperfine inversion transition, the CH₃ OH J = 5 transitions, and the centimeter free-free continuum emissions in this region. The comparisons of the molecular line emissions with the free-free continuum emissions reveal a 0.5 pc scale massive molecular envelope which is being partially dispersed by the dynamically expanding bipolar ionized cavity. The massive envelope is rotationally flattened and has an enhanced molecular density in the mid-plane. In the center of this massive clump lies a compact (<0.1 pc) hot (≳100 K) toroid, in which a cluster of O-type stars has formed. This overall geometry is analogous to the standard core collapse picture in a low-mass star-forming region, with a central (proto-)stellar object, a disk, an envelope, and a bipolar outflow and outflow cavity. However, G10.6-0.4 has a much larger physical size scale (≤0.1 pc for typical low-mass star-forming core). Based on the observations, we propose a schematic picture of the OB cluster-forming region, which incorporates the various physical mechanisms. This model will be tested with the observations of other embedded OB clusters, and with numerical simulations.