Cloud-cloud collision as origin of the G31.41+0.31 massive protocluster

TL;DR

This study reveals that the massive protocluster G31.41+0.31 formed through cloud-cloud collision, creating a large-scale hub-filament system with kinematics influenced by compression and shear, providing insights into star formation processes.

Contribution

It demonstrates that cloud-cloud collision can produce the large-scale filamentary structures and kinematic features observed in G31, linking large-scale dynamics to star formation.

Findings

Large-scale hub-filament system spanning 5 pc identified.

Velocity gradient consistent with cloud-cloud collision origin.

Filaments formed by compression from collision, influencing star formation.

Abstract

The G31.41+0.31 (G31) hot molecular core (HMC) is a high-mass protocluster showing accelerated infall and rotational spin-up that is well studied at high-angular resolution. To complement the accurate view of the small scale in G31, we have traced the kinematics of the large-scale material by carrying out N$_2$H$^+$\,(1--0) observations with the IRAM 30m telescope of an area of $\sim$6$\times6$\,arcmin$^2$ around the HMC. The N$_2$H$^+$ observations have revealed a large-scale (5\,pc) hub-filament system (HFS) composed by at least four filamentary arms and a NNE--SSW velocity gradient ($\sim$0.4\,km/s/pc) between the northern and southern filaments. The linewidth increases towards the hub at the center of the HFS reaching values of 2.5--3\,km\,s$^{-1}$ in the central 1\,pc. The origin of the large-scale velocity gradient is likely cloud-cloud collision. In this scenario, the filaments in G31 would have formed by compression resulting from the collision and the rotation of the HMC observed at scales of 1000\,au would have been induced by shear caused by the cloud-cloud collision at scales of a few pc. We conclude that G31 represents a HFS in a compressed layer with an orthogonal orientation to the plane of the sky, and represents a benchmark for the filaments-to-clusters paradigm of star formation.