# GMC Collisions as Triggers of Star Formation. V. Observational Signatures

## TL;DR

This study models molecular, atomic, and ionic line emissions from simulations of giant molecular cloud collisions, identifying [CII] 158μm as a key observational signature for detecting such collisions.

## Contribution

It introduces a method to identify GMC collisions using specific line emissions, especially [CII], even in evolved systems where molecular line signatures fade.

## Key findings

- [CII] 158μm line effectively traces GMC collisions.
- Fine-structure lines remain detectable in evolved collision systems.
- Simulations show distinct emission patterns for colliding and non-colliding GMCs.

## Abstract

We present calculations of molecular, atomic and ionic line emission from simulations of giant molecular cloud (GMC) collisions. We post-process snapshots of the magneto-hydrodynamical simulations presented in an earlier paper in this series by Wu et al. (2017) of colliding and non-colliding GMCs. Using photodissociation region (PDR) chemistry and radiative transfer we calculate the level populations and emission properties of $^{12}$CO $J=1-0$, [CI] $^3{\rm P}_1\rightarrow{^3{\rm P}}_0$ at $609\,\mu$m, [CII] $158\,\mu$m and [OI] $^3{\rm P}_1\rightarrow{^3{\rm P}}_0$ transition at $63\,\mu$m. From integrated intensity emission maps and position-velocity diagrams, we find that fine-structure lines, particularly the [CII] $158\,\mu$m, can be used as a diagnostic tracer for cloud-cloud collision activity. These results hold even in more evolved systems in which the collision signature in molecular lines has been diminished.