Properties of massive star-forming clumps with infall motions

Abstract

In this work, we aim to characterise high-mass clumps with infall motions. We\nselected 327 clumps from the Millimetre Astronomy Legacy Team 90-GHz (MALT90)\nsurvey, and identified 100 infall candidates. Combined with the results of He\net al. (2015), we obtained a sample of 732 high-mass clumps, including 231\nmassive infall candidates and 501 clumps where infall is not detected. Objects\nin our sample were classified as pre-stellar, proto-stellar, HII or\nphoto-dissociation region (PDR). The detection rates of the infall candidates\nin the pre-stellar, proto-stellar, HII and PDR stages are 41.2%, 36.6%, 30.6%\nand 12.7%, respectively. The infall candidates have a higher H$_{2}$ column\ndensity and volume density compared with the clumps where infall is not\ndetected at every stage. For the infall candidates, the median values of the\ninfall rates at the pre-stellar, proto-stellar, HII and PDR stages are\n2.6$\\times$10$^{-3}$, 7.0$\\times$10$^{-3}$, 6.5$\\times$10$^{-3}$ and\n5.5$\\times$10$^{-3}$ M$_\\odot$ yr$^{-1}$, respectively. These values indicate\nthat infall candidates at later evolutionary stages are still accumulating\nmaterial efficiently. It is interesting to find that both infall candidates and\nclumps where infall is not detected show a clear trend of increasing mass from\nthe pre-stellar to proto-stellar, and to the HII stages. The power indices of\nthe clump mass function (ClMF) are 2.04$\\pm$0.16 and 2.17$\\pm$0.31 for the\ninfall candidates and clumps where infall is not detected, respectively, which\nagree well with the power index of the stellar initial mass function (2.35) and\nthe cold Planck cores (2.0).\n