Global and Local Infall in the ASHES Sample (GLASHES). II. Asymmetric Line Profiles around Dense Cores in 70 $\mu$m Dark Massive Clumps

TL;DR

This study uses ALMA observations to statistically analyze infall signatures in dense cores of massive, dark clumps, revealing prevalent gravitational collapse across different evolutionary stages and supporting a hierarchical star formation model.

Contribution

First large-scale statistical analysis of infall signatures in dense cores within massive dark clumps, demonstrating widespread collapse and hierarchical dynamics in high-mass star formation.

Findings

Infall signatures detected in approximately 50-60% of cores.

Infall signatures increase with core mass and surface density.

Evidence supports hierarchical collapse from prestellar to more evolved stages.

Abstract

Gravitational collapse is fundamental to star formation, yet direct kinematic evidence of infall at the core scale in high-mass star-forming regions remains poorly constrained. We present the first large-scale statistical study of infall signatures in 304 dense cores within 24 massive 70 $\mu$m-dark clumps from the GLASHES (Global and Local Infall in the ASHES Sample) survey. Using ALMA Band 6 observations of the optically thick tracers HCO$^+$ and HNC (J=3-2), we systematically characterize blue asymmetry line profiles indicative of infalling motions. We employ two complementary metrics, the velocity difference parameter ($\delta_v$) and the asymmetry parameter ($A$), to quantify infall signatures, finding consistent results across both tracers. Blue asymmetry profiles are detected in $\sim$50-60% of cores ($\delta_v<$0 or A>0). Spectral classification reveals that $\sim$60% of cores exhibit double-peaked profiles, and 34% and 39% show blue asymmetry profiles in HCO$^+$ and HNC, respectively, with the percentage increasing with core mass and surface density. Accounting for geometric effects that can obscure infall signatures, our results suggest that gravitational collapse is prevalent in and around the cores. Importantly, infall signatures are detected from the prestellar stage and become more dominant as cores' evolution proceeds. Even cores with virial parameters $\alpha_{vir} > 2$ show infall signatures, suggesting that external compression may trigger collapse in addition to self-gravity or that linewidth may include inward motion in addition to turbulence. Furthermore, a moderate correlation between clump-scale and core-scale asymmetry supports a hierarchical collapse scenario, implying a dynamic and multi-scale process of high-mass star formation.