The VLT-FLAMES Tarantula Survey VI: Evidence for rotation of the young massive cluster R136

TL;DR

This study provides evidence that the young massive cluster R136 exhibits rotation, with about 20% of its kinetic energy in rotational motion, based on spectroscopic data of its stars.

Contribution

First detection of rotation in the young cluster R136 using multi-epoch spectroscopic data and a maximum likelihood fitting approach.

Findings

Evidence for cluster rotation at 95% confidence level

Typical rotational velocity around 3 km/s

At least 20% of kinetic energy in rotation

Abstract

Although it has important ramifications for both the formation of star clusters and their subsequent dynamical evolution, rotation remains a largely unexplored characteristic of young star clusters (few Myr). Using multi-epoch spectroscopic data of the inner regions of 30 Doradus in the Large Magellanic Cloud (LMC) obtained as part of the VLT-FLAMES Tarantula Survey, we search for rotation of the young massive cluster R136. From the radial velocities of 36 apparently single O-type stars within a projected radius of 10 pc from the centre of the cluster, we find evidence, at the 95% confidence level, for rotation of the cluster as a whole. We use a maximum likelihood method to fit simple rotation curves to our data and find a typical rotational velocity of ~3 km/s. When compared to the low velocity dispersion of R136, our result suggests that star clusters may form with at least ~20% of the kinetic energy in rotation.