A multi-transition molecular line study of inward motions towards massive star-forming cores

TL;DR

This study uses multi-transition molecular line observations to detect inward motions in 29 massive star-forming cores, identifying six strong infall candidates and establishing HCO$^+$(1-0) as the best tracer for inward motions.

Contribution

It provides the first comprehensive multi-transition survey to identify inward motions and infall candidates in massive star-forming regions, highlighting HCO$^+$(1-0) as the most effective tracer.

Findings

Inward motions are prominent in HCO$^+$(1-0), CS(2-1), or HNC(1-0) lines.

HCO$^+$(1-0) shows the highest occurrence of asymmetric profiles.

Six strong infall candidates were identified with extended infall signatures.

Abstract

A multi-transition 3$ $mm molecular line single-pointing and mapping survey was carried out towards 29 massive star-forming cores in order to search for the signature of inward motions. Up to seven different transitions, optically thick lines HCO$^+$(1-0), CS(2-1), HNC(1-0), HCN(1-0), $^{12}$CO(1-0) and optically thin lines C$^{18}$O(1-0), $^{13}$CO(1-0) were observed towards each source. The normalized velocity differences ($\delta$V$_{\rm CS}$, $\delta$V$_{\rm HCO^{+}}$) between the peak velocities of optically thick lines and optically thin line C$^{18}$O(1-0) for each source were derived. Prominent inward motions are probably present in either HCO$^+$(1-0) or CS(2-1) or HNC(1-0) observations in most sources. Our observations show that there is a significant difference in the incidence of blue shifted line asymmetric line profiles between CS(2-1) and HCO$^+$(1-0). The HCO$^+$(1-0) shows the highest occurrence of obvious asymmetric feature, perhaps owing to different optical depth between CS(2-1) and HCO$^+$(1-0). HCO$^+$(1-0) appears to be the best inward motion tracer. The mapping observations of multiple line transitions enable us to identify six strong infall candidates G123.07-6.31, W75(OH), S235N, CEP-A, W3(OH), NGC7538. The infall signature is extended up to a linear scale $>0.2 \:$pc.