Cluster Formation in GGD12-15: Infall Motion with Rotation of the Natal Clump

Abstract

We report results of observations of the GGD12-15 region, where cluster formation is actively taking place, using various molecular emission lines. The C 18 O (J = 1 − 0) emission line reveals a massive clump in the region with a mass of ∼ 2800M distributed over ∼ 2 pc. The distribution of the C 18 O (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 a direction perpendicular to the elongated C 18 O (J = 3 − 2) distribution, covering the entire clump. There is a massive core with a radius of 0.3 pc and a mass of 530M in the center of the clump. There are two velocity components around the core, which are prominent in a positionvelocity (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.