FIRESTORM I: Stellar Feedback and Gas Kinematics in the Evolved W40 Hub-Filament System

TL;DR

This study investigates the gas dynamics and filament structures in the W40 star-forming region, revealing evidence of past cloud-cloud collision triggering the formation of a hub-filament system and a massive star cluster.

Contribution

It provides detailed multiwavelength analysis of filaments, turbulence dissipation, and evidence for cloud-cloud collision in the W40 region, advancing understanding of high-mass star formation processes.

Findings

Identification of six velocity-coherent filaments converging at the cluster

Detection of turbulence dissipation from filaments to dense clumps

Evidence of cloud-cloud collision triggering star formation

Abstract

The FIRESTORM project--Feedback-Induced Regions and Emission from Star-forming Tracers of ObseRvable Molecular Gas--has targeted four star-forming regions to quantify the impact of stellar feedback on star formation. In this paper, we present multiwavelength results for one of the targets, the nearby high-mass star-forming region W40. Using dense-gas tracers C$^{18}$O(1--0) and H$^{13}$CO$^+$(1--0), we identified six velocity-coherent filaments: five at \vlsr $\sim$\,7.5\kms\! and one at \vlsr $\sim$\,5\kms. Four of these converge towards an infrared-bright cluster hosting the most massive star of the region (IRS 1A South, O9.5V), forming a hub-filament system (HFS). Key physical parameters, including filament lengths, widths, masses, velocity dispersions, and line masses, are derived. Five dense clumps traced by N$_2$H$^+$(1--0) exhibit subsonic to transonic turbulence, contrasting with the supersonic motions of their parental filaments, indicating turbulence dissipation. A deficit of emission at \vlsr $\sim$\,7\kms\! in several molecular lines, along with a blueshifted absorption dip in the HCN(1--0) profile, suggests that emission from OB-heated gas is being absorbed by a cold foreground cloud. A bridge-like feature in position-velocity space connects the \vlsr $\sim$\,5 and $\sim$\,7.5\kms\! filaments, and spatially coinciding with dense condensations and radio continuum peaks. These findings suggest that a past interaction--likely a cloud-cloud collision--triggered the formation of HFS and ultimately the central massive cluster.