2012A&A...538A.140K

Many physical parameters change with time in star-forming regions. Here we attempt to correlate changes in the infall and outflow motions in high-mass star-forming regions with evolutionary stage using JCMT observations. From a sample of 45 high-mass star-forming regions in three phases of evolution, we investigate the presence of established infall and outflow tracers to determine whether there are any trends attributable to the age of the source. We obtained JCMT observations of HCO⁺/H¹³CO⁺ J=4-3 to trace large-scale infall, and SiO J=8-7 to trace recent outflow activity. We compared the infall and outflow detections to the evolutionary stage of the host source (high-mass protostellar objects, hypercompact HII regions, and ultracompact HII regions). We find a surprising lack of SiO detections in the middle stage (hypercompact HII regions), which may be an observational bias. When SiO is detected, we find that the integrated intensity of the line increases with evolutionary stage. The integrated intensity of SiO varies with the full width at half maximum of the H¹³CO⁺. All of the sources with infall signatures onto ultracompact HII regions have corresponding outflow signatures as well.