Infall motions in massive star-forming regions

The infall candidates have a higher H_2_ column density and volume density compared with the clumps where infall is not detected at every stage. For the infall candidates, the median values of the infall rates at the pre-stellar, proto-stellar, HII and PDR stages are 2.6 x 10^-3^, 7.0x10^-3^, 6.5x10^-3^ and 5.5x10^-3^M_{sun}_/yr, respectively. These values indicate that infall candidates at later evolutionary stages are still accumulating material efficiently.

It is interesting to find that both infall candidates and clumps where infall is not detected show a clear trend of increasing mass from the pre-stellar to proto-stellar, and to the HII stages. The power indices of the clump mass function are 2.04+/-0.16 and 2.17+/-0.31 for the infall candidates and clumps where infall is not detected, respectively, which agree well with the power index of the stellar initial mass function (2.35) and the cold Planck cores (2.0).