Inflow Motions associated with High-mass Protostellar Objects
We performed a molecular line survey of 82 high-mass protostellar objects in search for inflow signatures associated with high-mass star formation. Using the H$^{13}$CO$^+$ (1$-$0) line as an optically thin tracer, we detected a statistically significant excess of blue asymmetric line profiles in the HCO$^+$ (1$-$0) transition, but nonsignificant excesses in the HCO$^+$ (3$-$2) and H$_2$CO (2$_{12}$$-$1$_{11}$) transitions. The negative blue excess for the HCN (3$-$2) transition suggests that the line profiles are affected by dynamics other than inflow motion. The HCO$^+$ (1$-$0) transition thus seems to be the suitable tracer of inflow motions in high-mass star-forming regions, as previously suggested. We found 27 inflow candidates that have at least one blue asymmetric profile and no red asymmetric profile, and derived the inflow velocities to be 0.23$-$2.00 km s$^{-1}$ for 20 of them using a simple two-layer radiative transfer model. Our sample is divided into two groups in different evolutionary stages. The blue excess of the group in relatively earlier evolutionary stages was estimated to be slightly higher than that of the other in the HCO$^+$ (1$-$0) transition.