The Decrease of Specific Angular Momentum and the Hot Toroid Formation: The Massive Clump G10.6-0.4

TL;DR

This study uses high-resolution molecular line observations to confirm the presence of a rotating hot toroid in G10.6-0.4, revealing a significant decrease in specific angular momentum from outer to inner regions, advancing understanding of massive star formation.

Contribution

First high-resolution confirmation of a rotationally flattened hot toroid in G10.6-0.4 and detailed analysis of molecular accretion flow dynamics.

Findings

Confirmation of a hot toroid with perpendicular rotational axis.

Observation of decreasing specific angular momentum inward.

Insights into molecular accretion flow in UC HII regions.

Abstract

This is the first paper of our series of high resolution (1") studies of the massive star forming region G10.6--0.4. We present the emission line observations of the hot core type tracers (O$^{13}$CS, OCS, SO$_{2}$) with $\sim$0$"$.5 resolution. By comparing the results to the high--resolution NH$_{3}$ absorption line observation, we confirm for the first time the rotationally flattened hot toroid in the central $<$0.1 pc region, which has a rotational axis perpendicular to its geometrical major axis. In addition, we present the observations of NH$_{3}$, $^{13}$CS, and CH$_{3}$CN with $\sim$1$"$ resolution, and follow the dynamics of the molecular accretion flow from the 0.3 pc radius to the inner 0.03 pc radius. With reference to the rotational axis of the hot toroid, we measure the rotational velocity from the molecular emission in the region. The results are consistent with an envelope with a rapid decrease of the specific angular momentum from the outer to the inner region. These new results improve the current understanding of the molecular accretion flow in an ultracompact (UC) H\textsc{ii} region created by the embedded O-type cluster.