Global and Local Infall in the ASHES Sample (GLASHES). I. Pilot Study in G337.541

TL;DR

This study uses ALMA observations of a massive, cold clump to detect infall motions, revealing high infall rates and velocities that support core growth models for high-mass star formation.

Contribution

It provides direct measurements of infall velocities and rates in a massive clump, demonstrating their significance in early high-mass star formation.

Findings

Infall velocities range from 0.28 to 1.45 km/s.

Infall rates are 10^{-4} to 10^{-3} solar masses per year.

High infall rates support core growth in high-mass star formation.

Abstract

Recent high-angular-resolution observations indicate the need for core growth to form high-mass stars. To understand the gas dynamics at the core scale in the very early evolutionary stages before being severely affected by feedback, we have conducted Atacama Large Millimeter/submillimeter Array (ALMA) observations toward a 70 $\mu$m dark massive clump, G337.541-00.082 as part of the Global and Local infall in the ASHES sample (GLASHES) program. Using dense gas tracers such as N$_2$H$^+$ ($J = 1-0$) and HNC ($J = 3-2$), we find signs of infall from the position-velocity diagram and more directly from the blue asymmetry profile in addition to the clump-scale velocity gradient. We estimate infall velocities from intermediate and low-mass cores to be 0.28-1.45 km s$^{-1}$, and infall rates to be on the order of 10$^{-4}$ to 10$^{-3}$ $M_\odot$ yr$^{-1}$, both are higher than those measured in low-mass star-forming regions by more than a factor of five and an order of magnitude, respectively. We find a strong correlation of the infall velocity with the nonthermal velocity dispersion, suggesting that infall may contribute significantly to the observed line width. Consistent with clump-fed scenarios, we show that the mass infall rate is larger for larger core masses and shorter distances to the clump center. Such high infall rates in cores embedded in IRDCs can be considered as strong signs of core growth, allowing high-mass star formation from intermediate-mass cores that would not initially form high-mass stars at their current mass.