Radiation hydrodynamics simulations of massive star cluster formation in giant molecular clouds

TL;DR

This study uses 3D radiation hydrodynamics simulations to explore how surface density and metallicity influence the formation of massive star clusters in giant molecular clouds, revealing a critical density threshold for efficient star formation.

Contribution

It introduces a semi-analytical model linking surface density and star formation efficiency, explaining conditions for young massive star cluster formation.

Findings

Star formation is suppressed in low surface density clouds due to photoionization feedback.

A critical surface density (~100 M_sun/pc^2) determines whether clouds form bound massive clusters.

Star formation efficiency scales with surface density as a power law, matching observations.

Abstract

By performing three-dimensional radiation hydrodynamics simulations, we study the formation of young massive star clusters (YMCs, $M_{*}>10^4~M_{\odot}$) in clouds with the surface density ranging from $\Sigma_{\rm cl} = 80$ to $3200~M_{\odot}\;{\rm pc^{-2}}$. We find that photoionization feedback suppresses star formation significantly in clouds with low surface density. Once the initial surface density exceeds $\sim 100~M_{\odot}\;{\rm pc^{-2}}$ for clouds with $M_{\rm cl}=10^{6}~M_{\odot}$ and $Z= Z_{\odot}$, most of the gas is converted into stars because the photoionization feedback is inefficient in deep gravitational potential. In this case, the star clusters are massive and gravitationally bounded as YMCs. The transition surface density increases as metallicity decreases, and it is $\sim 350~M_{\odot}\;{\rm pc^{-2}}$ for $Z=10^{-2}~Z_{\odot}$. We show that more than 10 percent of star-formation efficiency (SFE) is needed to keep a star cluster gravitationally bounded even after the disruption of a cloud. Also, we develop a semi-analytical model reproducing the SFEs obtained in our simulations. We find that the SFEs are fit with a power-law function with the dependency $\propto \Sigma_{\rm cl}^{1/2}$ for low-surface density and rapidly increases at the transition surface densities. The conditions of the surface density and the metallicity match recent observations of giant molecular clouds forming YMCs in nearby galaxies.