Properties of massive star-forming clumps with infall motions
  In this work, we aim to characterise high-mass clumps with infall motions. We
selected 327 clumps from the Millimetre Astronomy Legacy Team 90-GHz (MALT90)
survey, and identified 100 infall candidates. Combined with the results of He
et al. (2015), we obtained a sample of 732 high-mass clumps, including 231
massive infall candidates and 501 clumps where infall is not detected. Objects
in our sample were classified as pre-stellar, proto-stellar, HII or
photo-dissociation region (PDR). The detection rates of the infall candidates
in the pre-stellar, proto-stellar, HII and PDR stages are 41.2%, 36.6%, 30.6%
and 12.7%, respectively. 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$\times$10$^{-3}$, 7.0$\times$10$^{-3}$, 6.5$\times$10$^{-3}$ and
5.5$\times$10$^{-3}$ M$_\odot$ yr$^{-1}$, 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 (ClMF) are 2.04$\pm$0.16 and 2.17$\pm$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).
