The masses, structure and lifetimes of cold clouds in a high-resolution simulation of a low metallicity starburst

Abstract

We present an analysis of the cold gas phase in a low metallicity starburst generated in a high-resolution hydrodynamical simulation of a gas-rich dwarf galaxy merger as part of the griffin project. The simulations resolve (4 M⊙ gas phase mass resolution, ∼ 0.1 pc spatial resolution) the multi-phase interstellar medium with a non-equilibrium chemical heating/cooling network at temperatures below 104 K. Massive stars are sampled individually and interact with the ISM through the formation of HII regions and supernova explosions. In the extended starburst phase, the ISM is dominated by cold (Tgas < 300 K) filamentary clouds with self-similar internal structures. The clouds have masses of 102.6 - 105.6 M⊙ with a power law mass function, dN/dM∝Mα with α = −1.78( ± 0.08). They also follow the Larson relations, in good agreement with observations. We trace the lifecycle of the cold clouds and find that they follow an exponential lifetime distribution and an e-folding time of ∼ 3.5 Myr. Clouds with peak masses below 104 M⊙ follow a power law relation with their average lifetime $\tau _\mathrm{life} \propto M^{0.3}_\mathrm{max}$ which flattens out for higher cloud masses at <10 Myr. A similar relation exists between cloud size at peak mass and lifetime. This simulation of the evolution of a realistic galactic cold cloud population supports the rapid formation and disruption of star-forming clouds by stellar radiation and supernovae on a timescale less than 10 Myr.