From short-lived to long-lived clouds: impact of star formation models on giant molecular cloud evolution in simulations of an NGC 300-like galaxy

TL;DR

This study uses radiation-hydrodynamic simulations of an NGC 300-like galaxy to compare star formation models, revealing their significant impact on GMC lifetimes and galactic star formation regulation.

Contribution

It demonstrates how different star formation prescriptions drastically alter GMC evolution and star formation rates in galaxy simulations.

Findings

Sink-particle model yields GMC lifetimes of 20-30 Myr, consistent with observations.

GTT model produces long-lived clouds over 200 Myr due to low star formation efficiency.

Cloud mergers extend GMC lifetimes and influence star formation efficiency.

Abstract

Multi-wavelength observations of molecular and ionized gas indicate that GMCs are short-lived, generally dispersing within one or two dynamical timescales. To investigate the physical origin of these short lifetimes and the role of star formation prescriptions, we conduct radiation-hydrodynamic simulations of an NGC 300-like disk galaxy with RAMSES-RT. We compare two distinct star formation models, one based on a local gravo-thermo-turbulent (GTT) condition and the other employing sink particles, to examine how star formation and feedback collectively regulate GMC evolution. The sink-particle-based model yields bursty yet self-regulated global star formation rates of $0.1$-$0.5$ $M_{\odot}\,yr^{-1}$ and produces GMC lifetimes of $\sim20$-$30$ Myr, with star formation efficiencies (SFEs) per free-fall time of a few percent, consistent with observations. In contrast, the GTT model generates a population of long-lived clouds with lifetimes $\gtrsim200$ Myr, owing to the extremely low SFEs per free-fall time $(\lesssim3\times10^{-3})$, which renders stellar feedback ineffective. With both models, cloud-cloud mergers extend the lifetimes of GMCs and increase their integrated SFEs by lengthening the star-forming duty cycle, while having only a minor impact on instantaneous efficiencies. On galactic scales, both models broadly reproduce the observed KS relation within its scatter, yielding gas depletion times of a few Gyr. In comparison, an extreme feedback model with the supernova energy boosted by a factor of five, combined with the GTT star formation model, excessively suppresses star formation and produces much longer depletion times ($6$-$20$ Gyr) for this isolated system. These results demonstrate that GMC lifecycles are strongly governed by the adopted star formation model, highlighting the need for improved prescriptions that realistically capture clump-scale star formation.