Abstract In this work, we perform a statistical investigation towards 50 high-mass clumps using data from the Bolocam Galactic Plane Survey (BGPS) and Millimetre Astronomy Legacy Team 90-GHz survey (MALT90). Eleven dense molecular lines (N2H+ (1–0), HNC(1–0), HCO+ (1–0), HCN(1–0), HN13C(1–0), H13CO+ (1–0), C 2H(1–0), HC3 N(10–9), SiO(2–1),13CS(2-1)and HNCO(44,0 − 30,3)) are detected. N2H + and HNC are shown to be good tracers for clumps in various evolutionary stages since they are detected in all the fields. The detection rates of N-bearing molecules decrease as the clumps evolve, but those of O-bearing species increase with evolution. Furthermore, the abundance ratios [N2H+]/[HCO+] and log([HC3N]/[HCO+]) decline with log([HCO+]) as two linear functions, respectively. This suggests that N2H+ and HC3N transform to HCO+ as the clumps evolve. We also find that C2H is the most abundant molecule with an order of magnitude 10−8. In addition, three new infall candidates, G010.214–00.324, G011.121–00.128 and G012.215–00.118(a), are discovered to have large-scale infall motions and infall rates with an order of magnitude 10−3M⊙ yr−1.

Keywords stars: formation — ISM: abundance — ISM: molecules — radio lines: ISM — ISM: kinematics and dynamics

https://doi.org/10.1088/1674–4527/18/1/4