Westerlund 1 and its Galactic siblings -Observation confronts Theory

TL;DR

This study analyzes near-infrared data of Westerlund 1, a massive Galactic starburst cluster, to test stellar evolution models and explore its dissolution, survival, and relation to proto-globular clusters.

Contribution

It provides the first detailed analysis of the lower-mass stellar population in Westerlund 1 using near-infrared data, testing evolutionary tracks and cluster dissolution.

Findings

Westerlund 1's properties support rapid dissolution of starburst clusters.

Comparison suggests Galactic starburst clusters may resemble proto-globular clusters.

Data constrains models of stellar evolution and cluster dynamics.

Abstract

Because of their large number of stars spread over the entire stellar mass spectrum, starburst clusters are highly suitable to benchmark and calibrate star formation models and theories. Among the handful of Galactic starburst clusters, Westerlund 1 with its estimated 150 O-stars, W-R stars, supergiants and hypergiants is the most massive young cluster identified to date in the Milky Way. While previous studies of Westerlund 1 focused largely on optical and X-ray observations of its evolved massive stellar population, we have analyzed near-infrared data, resulting in the first in depth study of the ``lower-mass'' main sequence and pre-main sequence cluster population, i.e., of stars in the mass range 0.4 to 30 solar masses. The derived properties of the cluster population allow us to test theoretical evolutionary tracks. By comparison of Westerlund 1's half-mass radius with younger starburst clusters like NGC 3603 YC and Arches, and somewhat older massive clusters like RSGC1 and RSGC2, we find evidence for a rapid dissolution of Galactic starburst clusters, which has interesting implications for the long-term survival of starburst clusters, and the question to which extent Galactic starburst clusters might mimic proto-globular clusters.