M0.20-0.033: An Expanding Molecular Shell in the Galactic Center Radio Arc

We present high-frequency Karl G. Jansky Very Large Array (VLA) continuum and spectral line (NH3, H64 , and H63 ) observations of the Galactic Center Radio Arc region, covering the Sickle H ii region, the Quintuplet cluster, and molecular clouds M0.20−0.033 and M0.10−0.08. These observations show that the two velocity components of M0.20−0.033 (∼25 and 80 km s−1), previously thought to be separate clouds along the same line-of-sight, are physically connected in position-velocity space via a third southern component around 50 km s−1. Further position-velocity analysis of the surrounding region, using lower-resolution survey observations taken with the Mopra and ATCA telescopes, indicates that both molecular components in M0.20−0.033 are physically connected to the M0.10−0.08 molecular cloud, which is suggested to be located on stream 1 in the Kruijssen et al. orbital model. The morphology and kinematics of the molecular gas in M0.20−0.033 indicate that the two velocity components in M0.20−0.033 constitute an expanding shell. Our observations suggest that the M0.20−0.033 expanding shell has an expansion velocity of 40 km s−1, with a systemic velocity of 53 km s−1, comparable to velocities detected in M0.10−0.08. The origin of the expanding shell is located near the Quintuplet cluster, suggesting that the energy and momentum output from this massive stellar cluster may have contributed to the expansion.