Isolating signatures of major cloud-cloud collisions using position-velocity diagrams

TL;DR

This study identifies a distinctive broad bridge feature in position-velocity diagrams as a signature of high-velocity cloud-cloud collisions, aiding observational detection of such events linked to massive star formation.

Contribution

The paper introduces a method to distinguish cloud-cloud collisions from other phenomena using synthetic position-velocity diagrams, highlighting the broad bridge feature as a key signature.

Findings

Broad bridge feature indicates high-velocity cloud collisions.

Feature persists despite radiative feedback effects.

Observable from 20-30% of viewing angles in head-on collisions.

Abstract

Collisions between giant molecular clouds are a potential mechanism for triggering the formation of massive stars, or even super star clusters. The trouble is identifying this process observationally and distinguishing it from other mechanisms. We produce synthetic position-velocity diagrams from models of: cloud-cloud collisions, non-interacting clouds along the line of sight, clouds with internal radiative feedback and a more complex cloud evolving in a galactic disc, to try and identify unique signatures of collision. We find that a broad bridge feature connecting two intensity peaks, spatially correlated but separated in velocity, is a signature of a high velocity cloud-cloud collision. We show that the broad bridge feature is resilient to the effects of radiative feedback, at least to around 2.5Myr after the formation of the first massive (ionising) star. However for a head on 10km/s collision we find that this will only be observable from 20-30 per cent of viewing angles. Such broad-bridge features have been identified towards M20, a very young region of massive star formation that was concluded to be a site of cloud-cloud collision by Torii et al (2011), and also towards star formation in the outer Milky Way by Izumi et al (2014).