2022ApJ...928...76S

We report results of observations of the GGD 12-15 region, where cluster formation is actively taking place, using various molecular emission lines. The C¹⁸O (J = 1-0) emission line reveals a massive clump in the region with a mass of ∼2800 M_☉ distributed over ∼2 pc. The distribution of the C¹⁸O (J = 3-2) emission is similar to that of a star cluster forming therein, with an elliptical shape of ∼1 pc in size. A bipolar molecular outflow driven by IRS 9Mc, a constituent star of the cluster, is blowing in the direction perpendicular to the elongated C¹⁸O (J = 3-2) distribution, covering the entire clump. There is a massive core with a radius of 0.3 pc and a mass of 530 M_☉ in the center of the clump. There are two velocity components around the core, which are prominent in a position-velocity (PV) diagram along the major axis of the clump. In addition, a PV diagram along the minor axis of the clump, which is parallel to the outflow, shows a velocity gradient opposite to that of the outflow. The velocity structure strongly indicates the infalling motion of the clump. Comparison of the observational data with a simple model of infalling oblate clumps indicates that the clump is undergoing gravitational contraction with rotation.