# High-Resolution Observations of the Molecular Clouds Associated with the Huge HII Region CTB 102

## TL;DR

This study presents high-resolution mapping of molecular clouds around the HII region CTB 102, revealing their structure, star formation activity, and efficiency, including a potential embedded protocluster with unusually high star formation efficiency.

## Contribution

First high-resolution large-scale molecular cloud observations of CTB 102, combining molecular line and infrared data to analyze star formation and efficiency.

## Key findings

- Molecular clouds span 60x35 pc with mass 10^{4.8}-10^{5.0} M_sun.
- Detected 18 YSOs and 6 transition disks, showing age/class gradient.
- Overall star formation efficiency is 5-10%, with one region reaching 17-35%.

## Abstract

We report the first high-resolution (sub-arcminute) large-scale mapping $^{12}$CO and $^{13}$CO observations of the molecular clouds associated with the giant outer Galaxy HII 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 $60 \times 35$ pc and a total mass of $10^{4.8} - 10^{5.0}$ M$_\odot$. Infrared data from WISE and 2MASS were used to identify and classify the 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 HII 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 sub-regions of the cloud. We find that the overall SFE is between $\sim5 - 10$%, consistent with previous observations of giant molecular clouds. One of the sub-regions, 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 (sub-pc scale) star-forming cores, and we think region 1a is likely an embedded massive protocluster.