Massive molecular outflows associated with UCHII/HII regions

Abstract

Aims: We searched for the molecular outflows from fifteen molecular clouds associated with ultra-compact and compact HII (UCHII/HII) regions and discussed possible gas heating mechanism. Methods: Mapping observations of CO $J=3-2$ and $J=2-1$ lines were carried out with the KOSMA 3m-Telescope towards the 15 HII regions/molecular cloud complexes. Results: Ten molecular outflows were identified out of the fifteen HII region/molecular cloud complexes. The higher outflow detection rate (67%) suggested that such outflows are as common in high mass star forming regions as those in low mass star forming regions, which is consistent with the results of other authors. The observations also showed that the outflow might occur in the HII region. The integrated CO line intensity ratios (${\rm R_{I_{CO(3-2)}/I_{CO(2-1)}}}$) were determined from the core component of the spectra as well as from both the blue and red wings. Maximum line intensity ratios from the wings and core components appeared to be related to the mid-infrared sources imaged by Midcourse Space Experiment (MSX). The relationship between the maximum line intensity ratios and MSX sources indicates that the molecular gas could be heated by the emission of dust associated with massive stars. Based on maser observations reported in the literature, we found that ${\rm H_{2}O}$ masers were only detected in seven regions. The ${\rm H_{2}O}$ masers in these regions are located near the MSX sources and within the maximum line intensity ratio regions, suggesting that ${\rm H_{2}O}$ masers occur in relatively warm environments.