# Rotation in young massive star clusters

## TL;DR

This study uses hydrodynamical simulations to show that massive star clusters commonly inherit significant rotation from their parent gas, supporting hierarchical assembly as a key formation process.

## Contribution

It demonstrates through simulations that hierarchical merging leads to rotation in massive star clusters, a novel insight into their formation dynamics.

## Key findings

- Massive star clusters inherit rotation from parent gas.
- Clusters with mass > few hundred Msun show clear rotation.
- Simulated clusters are highly elliptical and subvirial.

## Abstract

Hydrodynamical simulations of turbulent molecular clouds show that star clusters form from the hierarchical merger of several sub-clumps. We run smoothed-particle hydrodynamics simulations of turbulence-supported molecular clouds with mass ranging from 1700 to 43000 Msun. We study the kinematic evolution of the main cluster that forms in each cloud. We find that the parent gas acquires significant rotation, because of large-scale torques during the process of hierarchical assembly. The stellar component of the embedded star cluster inherits the rotation signature from the parent gas. Only star clusters with final mass < few X 100 Msun do not show any clear indication of rotation. Our simulated star clusters have high ellipticity (~0.4-0.5 at t=4 Myr) and are subvirial (Q_vir<~0.4). The signature of rotation is stronger than radial motions due to subvirial collapse. Our results suggest that rotation is common in embedded massive (>~1000 Msun) star clusters. This might provide a key observational test for the hierarchical assembly scenario.