The Inception of Star Cluster Formation Revealed by [CII] Emission Around an Infrared Dark Cloud

TL;DR

This study uses [CII] emission observations to investigate the atomic gas envelope of an Infrared Dark Cloud, providing evidence that its formation is likely due to giant molecular cloud collisions, which could trigger star cluster formation.

Contribution

It presents new [CII] emission data and compares it with simulations, supporting the GMC-GMC collision model for IRDC formation, a novel approach in this context.

Findings

[CII] emission traces the IRDC's atomic gas envelope.

Spatial and velocity offsets support GMC collision origin.

Results align with magnetized filament formation simulations.

Abstract

We present SOFIA-upGREAT observations of [CII] emission of Infrared Dark Cloud (IRDC) G035.39-00.33, designed to trace its atomic gas envelope and thus test models of the origins of such clouds. Several velocity components of [CII] emission are detected, tracing structures that are at a wide range of distances in the Galactic plane. We find a main component that is likely associated with the IRDC and its immediate surroundings. This strongest emission component has a velocity similar to that of the $^{13}$CO(2-1) emission of the IRDC, but offset by $\sim3\:{\rm km\:s}^{-1}$ and with a larger velocity width of $\sim9\:{\rm km\:s}^{-1}$. The spatial distribution of the [CII] emission of this component is also offset predominantly to one side of the dense filamentary structure of the IRDC. The CII column density is estimated to be of the order of $\sim10^{17}-10^{18}\,{\rm cm}^{-2}$. We compare these results to the [CII] emission from numerical simulations of magnetized, dense gas filaments formed from giant molecular cloud (GMC) collisions, finding similar spatial and kinematic offsets. These observations and modeling of [CII] add further to the evidence that IRDC G035.39-00.33 has been formed by a process of GMC-GMC collision, which may thus be an important mechanism for initiating star cluster formation.