Isolating signatures of major cloud-cloud collisions II: The lifetimes of broad bridge features

TL;DR

This paper analyzes the lifetimes of broad bridge features caused by cloud-cloud collisions, showing that for larger clouds, collision duration dominates, while feedback effects are more significant for smaller clouds, supported by simulations.

Contribution

It provides analytic estimates for broad bridge lifetimes and compares them with numerical simulations, offering new insights into cloud collision dynamics and feedback effects.

Findings

Broad bridge lifetime is mainly determined by collision duration for clouds >10 pc.

Feedback effects become dominant in smaller clouds due to scaling of radiative feedback.

Collision rate estimates align with previous models for large clouds but are higher for smaller clouds.

Abstract

We investigate the longevity of broad bridge features in position-velocity diagrams that appear as a result of cloud-cloud collisions. Broad bridges will have a finite lifetime due to the action of feedback, conversion of gas into stars and the timescale of the collision. We make a series of analytic arguments with which to estimate these lifetimes. Our simple analytic arguments suggest that for collisions between clouds larger than R~10 pc the lifetime of the broad bridge is more likely to be determined by the lifetime of the collision rather than the radiative or wind feedback disruption timescale. However for smaller clouds feedback becomes much more effective. This is because the radiative feedback timescale scales with the ionising flux Nly as R^{7/4}Nly^{-1/4} so a reduction in cloud size requires a relatively large decrease in ionising photons to maintain a given timescale. We find that our analytic arguments are consistent with new synthetic observations of numerical simulations of cloud-cloud collisions (including star formation and radiative feedback). We also argue that if the number of observable broad bridges remains ~ constant, then the disruption timescale must be roughly equivalent to the collision rate. If this is the case our analytic arguments also provide collision rate estimates, which we find are readily consistent with previous theoretical models at the scales they consider (clouds larger than about 10 pc) but are much higher for smaller clouds.