High-resolution Observations of the Molecular Clouds Associated with the Huge H ii Region CTB 102

Abstract

Abstract We report the first high-resolution (subarcminute) large-scale mapping 12CO and 13CO observations of the molecular clouds associated with the giant outer Galaxy H ii region CTB 102 (KR 1). These observations were made using a newly commissioned receiver system on the 13.7 m radio telescope at the Taeduk Radio Astronomy Observatory. Our observations show that the molecular clouds have a spatial extent of 60 × 35 pc and a total mass of 104.8–105.0 M ⊙. Infrared data from the Wide-field Infrared Survey Explorer and Two Micron All Sky Survey were used to identify and classify the young stellar object (YSO) population associated with ongoing star formation activity within the molecular clouds. We directly detect 18 class I/class II YSOs and six transition disk objects. Moving away from the H ii region, there is an age/class gradient consistent with sequential star formation. The infrared and molecular-line data were combined to estimate the star formation efficiency (SFE) of the entire cloud as well as the SFE for various subregions of the cloud. We find that the overall SFE is between ∼5% and 10%, consistent with previous observations of giant molecular clouds. One of the subregions, region 1a, is a clear outlier, with a SFE of 17%–35% on a 5 pc spatial scale. This high SFE is more typical for much smaller (subparsec scale) star-forming cores, and we think region 1a is likely an embedded massive protocluster.