Star cluster formation from giant molecular clouds in the Small Magellanic Cloud about 2 Gyr ago: their origin, structures, and kinematics

TL;DR

This study uses simulations to show that tidal interactions between the Small and Large Magellanic Clouds around 2 Gyr ago likely triggered the formation of massive star clusters from giant molecular clouds, explaining observed cluster properties.

Contribution

It demonstrates that galaxy interactions can significantly enhance GMC and star cluster formation, incorporating molecular hydrogen physics and cluster merging processes in the simulations.

Findings

GMC formation is enhanced by tidal forces during galaxy interaction.

Massive star clusters can form with lower densities than globular clusters.

Simulated clusters exhibit internal rotation and substructures.

Abstract

Recent observations have found that the age distribution of star clusters (SCs) in the Small Magellanic Cloud (SMC) shows a sharp peak around 2 Gyr ago. However, it is theoretically unclear what physical processes are responsible for such sudden formation of SCs in the SMC. Here we investigate whether massive SCs with initial masses more than $10^5$ $\text{M}_\odot$ can be formed during tidal interaction of the SMC with the Large Magellanic Cloud (LMC) about 2 Gyr ago, based on our new simulations, which include molecular hydrogen formation on dust grains and SC formation within giant molecular clouds (GMCs). We find that the formation of GMCs with masses more than $10^5$ $\text{M}_\odot$ can be dramatically enhanced due to the tidal force of the LMC-SMC interaction. We also find that gravitationally bound massive SCs can be formed within these GMCs, though their mean stellar densities ($10^4$ $\text{M}_\odot \text{pc}^{-3}$) are systematically lower than those of the genuine globular clusters (GCs). All simulated SCs have diffuse extended stellar envelopes that were formed from multiple merging of sub clusters within their natal GMCs. Furthermore, we find that some of the simulated SCs can have considerable global internal rotation and substructures surrounding them. Based on these simulation results, we discuss the origin of the observed diverse properties of SCs in the SMC and the physical roles of galaxy interaction in the formation of massive SCs from GMCs.