Death of the Immortal Molecular Cloud: Resolution Dependence of the Gas-Star Formation Relation Rules out Decoupling by Stellar Drift

TL;DR

This study investigates whether giant molecular clouds (GMCs) are destroyed by stellar feedback or become 'immortal' by decoupling from stars through stellar drift, finding strong evidence for feedback-driven destruction across multiple galaxies.

Contribution

The paper provides observational evidence that stellar feedback, not stellar drift, predominantly destroys GMCs, challenging the idea of GMC immortality and clarifying their lifecycle.

Findings

GMCs are rarely found near young stars, regardless of scale.

Stellar feedback is about 2,000 times more likely to end GMCs than stellar drift.

GMC lifecycle is primarily driven by feedback, not decoupling from stars.

Abstract

Recent observations have demonstrated that giant molecular clouds (GMCs) are short-lived entities, surviving for the order of a dynamical time before turning a few percent of their mass into stars and dispersing, leaving behind an isolated young stellar population. The key question has been whether this GMC dispersal actually marks a point of GMC destruction by stellar feedback from the new-born stars, or if GMCs might be `immortal' and only dynamically decouple from their nascent stars due to stellar drift. We address this question in six nearby galaxies, by quantifying how the gas-star formation relation depends on the spatial scale for scales between the GMC diameter and the GMC separation length, i.e. the scales where an excess of GMCs would be expected to be found in the stellar drift scenario. Our analysis reveals a consistent dearth of GMCs near young stellar populations regardless of the spatial scale, discounting the notion of `immortal' GMCs that decouple from their nascent stars through stellar drift. Instead, our findings demonstrate that stellar feedback destroys most GMCs at the end of their lifecycle. Employing a variety of statistical techniques to test both hypotheses, we find that the probability that stellar feedback concludes the GMC lifecycle is about 2,000 times higher than the probability that stellar drift separates GMCs and young stellar regions. This observation strengthens the emerging picture that galaxies consist of dynamic building blocks undergoing vigorous, feedback-driven lifecycles that collectively regulate star formation and drive the baryon cycle within galaxies.