Cluster Formation in GGD12-15: Infall Motion with Rotation of the Natal
  Clump
  We report results of observations of the GGD12-15 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 Mo 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 a 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 Mo 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.
