An Overall Picture of the Gas Flow In Massive Cluster Forming Region: The Case of G10.6-0.4

TL;DR

This study provides high-resolution observations of the massive cluster-forming region G10.6-0.4, revealing a complex structure with a rotating envelope, hot toroid, and expanding bipolar cavity, offering insights into massive star formation processes.

Contribution

It presents a detailed observational model of G10.6-0.4, illustrating the physical mechanisms involved in massive OB cluster formation, and compares it to low-mass star formation structures.

Findings

Identification of a 0.5 pc scale massive molecular envelope

Detection of a hot, compact toroid with O-type stars

Observation of a bipolar ionized cavity dispersing the envelope

Abstract

The massive clump G10.6-0.4 is an OB cluster forming region, in which multiple UC HII regions have been identified. In the present study, we report arcsecond resolution observations of the CS (1-0) transition, the NH$_{3}$ (3,3) main hyperfine inversion transition, the CH$_{3}$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 ($<$0.1 pc) hot ($\gtrsim$100 K) toroid, in which a cluster of O--type stars has formed. This overall geometry is analogous to the standard core collapse picture in the low-mass star forming region, with a central (proto-)stellar object, a disk, an envelope, and a bipolar outflow and outflow cavity. However, G10.6-0.4 has a much larger physical size scale ($\le$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.