Interaction between Ionized and Molecular Gas in the Active Star‐forming Region W31

We have carried out 21 cm radio continuum, H76_\alpha radio recombinationline, and various (CO, ^13CO, CS, & C^34S) molecular line observations of theW31 complex. Our radio continuum data show that W31 is composed of two extendedHII regions, G10.2-0.3 and G10.3-0.1, each of which comprises an ultracompactHII region, two or more compact components, and diffuse envelope. The W31 cloudappears as an incomplete shell on the whole and consists of southern sphericaland northern flat components, which are associated with G10.2-0.3 andG10.3-0.1, respectively. We detect two large and massive CS-emitting regions inthe northern and southern cloud components. The large amount of dense gas maysuggest that the W31 cloud has ability to form rich stellar clusters and thatstar formation has only recently begun. The extended envelopes of bothG10.2-0.3 and G10.3-0.1 are likely to be results of the champagne flows, basedon the distributions of ionized and molecular gas and the velocity gradient ofH76_\alpha line emission. We find strong evidence of bipolar molecular outflowsassociated with the two ultracompact HII regions. In the vicinity of theultracompact and compact HII regions in G10.3-0.1, the CO J=2-1/J=1-0 intensityratio is high (1.4) and a small but prominent molecular gas hollow exists.These observations strongly indicate that the HII regions and their ionizingstars are interacting with the molecular cloud. Therefore, it is most likelythat recently formed massive stars are actively disrupting their parentalmolecular cloud in the W31 complex.Comment: 26 pages, including 10 figures, accepted for publication in Ap