We investigate the infall properties in a sample of 11 infrared dark clouds (IRDCs) showing blue-asymmetry signatures in HCO+ J=1--0 line profiles. We used JCMT to conduct mapping observations in HCO+ J=4--3 as well as single-pointing observations in HCO+ J =3--2, towards 23 clumps in these IRDCs. We applied the HILL model to fit these observations and derived infall velocities in the range of 0.5-2.7 km s−1, with a median value of 1.0 km s−1, and obtained mass accretion rates of 0.5-14×10−3 Msun yr−1. These values are comparable to those found in massive star forming clumps in later evolutionary stages. These IRDC clumps are more likely to form star clusters. HCO+ J =3--2 and HCO+ J =1--0 were shown to trace infall signatures well in these IRDCs with comparable inferred properties. HCO+ J=4--3, on the other hand, exhibits infall signatures only in a few very massive clumps, due to smaller opacties. No obvious correlation for these clumps was found between infall velocity and the NH3/CCS ratio.
@article{arxiv.2104.07231,
title = {Studying Infall in Infrared Dark Clouds with Multiple HCO+ Transitions},
author = {Jinjin Xie and Jingwen Wu and Gary A. Fuller and Nicolas Peretto and Zhiyuan Ren and Longfei Chen and Yaoting Yan and Guodong Li and Yan Duan and Jifeng Xia and Yongxiong Wang and Di Li},
journal= {arXiv preprint arXiv:2104.07231},
year = {2022}
}