Searching for Inflow Towards Massive Starless Clump Candidates Identified in the Bolocam Galactic Plane Survey

TL;DR

This study searches for inflow signatures in massive starless clump candidates using HCO+ spectroscopy, finding rare evidence of inflow that could lead to massive star formation, with some clumps potentially doubling their mass quickly.

Contribution

First systematic search for inflow signatures in massive starless clumps using HCO+ spectroscopy, identifying candidate inflow motions and estimating mass inflow rates.

Findings

Small blue excess observed in the survey.

Six clumps identified as good inflow candidates.

Mass inflow rates estimated between 500-2000 M/Myr.

Abstract

Recent Galactic plane surveys of dust continuum emission at long wavelengths have identified a population of dense, massive clumps with no evidence for on-going star formation. These massive starless clump candidates are excellent sites to search for the initial phases of massive star formation before the feedback from massive star formation effects the clump. In this study, we search for the spectroscopic signature of inflowing gas toward starless clumps, some of which are massive enough to form a massive star. We observed 101 starless clump candidates identified in the Bolocam Galactic Plane Survey (BGPS) in HCO+ J = 1-0 using the 12m Arizona Radio Observatory telescope. We find a small blue excess of E = (Nblue - Nred)/Ntotal = 0.03 for the complete survey. We identified 6 clumps that are good candidates for inflow motion and used a radiative transfer model to calculate mass inflow rates that range from 500 - 2000 M /Myr. If the observed line profiles are indeed due to large-scale inflow motions, then these clumps will typically double their mass on a free fall time. Our survey finds that massive BGPS starless clump candidates with inflow signatures in HCO+ J = 1-0 are rare throughout our Galaxy.