A statistical study towards the high-mass BGPS clumps with the MALT90 survey

TL;DR

This study statistically analyzes 50 high-mass molecular clumps using BGPS and MALT90 data, revealing molecular tracers' evolution and discovering three new infall candidates with significant infall rates.

Contribution

It provides new insights into molecular evolution in high-mass clumps and identifies three new large-scale infall candidates with notable infall rates.

Findings

N$_2$H$^+$ and HNC are universal tracers across evolutionary stages.

Detection rates of N-bearing molecules decrease with evolution, O-bearing increase.

Three new infall candidates with infall rates around 10^{-3} M$_\ ext{\odot}$ yr$^{-1}$.

Abstract

In this work, we perform a statistical investigation towards 50 high-mass clumps using the data from the Bolocam Galactic Plane Survey (BGPS) and the Millimetre Astronomy Legacy Team 90-GHz survey (MALT90). Eleven dense molecular lines (N$_2$H$^+$(1-0), HNC(1-0), HCO$^+$(1-0), HCN(1-0), HN$^{13}$C(1-0), H$^{13}$CO$^+$(1-0), C$_2$H(1-0), HC$_3$N(10-9), SiO(2-1), $^{13}$CS(2-1) and HNCO$(4_{4,0}-3_{0,3}))$ are detected. N$_2$H$^+$ and HNC are shown to be good tracers for clumps in virous evolutionary stages since they are detected in all the fields. And 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 [N$_2$H$^+$]/[HCO$^+$] and Log([HC$_3$N]/[HCO$^+$]) decline with Log([HCO$^+$]) as two linear functions, respectively. This suggests the transformation of N$_2$H$^+$ and HC$_3$N to HCO$^+$ as the clumps evolve. We also find that C$_2$H is the most abundant molecule with an order of $10^{-8}$. Besides, three new infall candidates G010.214-00.324, G011.121-00.128, and G012.215-00.118(a) are discovered to have large-scaled infall motions and infall rates in the magnitude of $10^{-3}$ M$_\odot$ yr$^{-1}$.