2007ApJ...663.1092K

We present single-pointing observations of SiO, HCO⁺, and H¹³CO⁺ from the James Clerk Maxwell Telescope toward 23 massive star-forming regions previously known to contain molecular outflows and ultracompact H II regions. We detected SiO toward 14 sources and suggest that the nondetections in the other nine sources could be due to those outflows being older and without ongoing shocks to replenish the SiO. We serendipitously detected SO₂toward 17 sources in the same tuning as HCO⁺. We detected HCO⁺ toward all sources, and suggest that it is tracing infall in nine cases. For seven infall candidates, we estimate mass infall rates between 1x10^–2 and 2x10^–5 M_☉/yr. Seven sources show both SiO detections (young outflows) and HCO⁺ infall signatures. We also find that the abundance of H¹³ CO⁺ tends to increase along with the abundance of SiO in sources for which we could determine abundances. We discuss these results with respect to current theories of massive star formation via accretion. From this survey, we suggest that perhaps both models of ionized accretion and halted accretion may be important in describing the evolution of a massive protostar (or protostars) beyond the formation of an H II region.