The peculiar kinematics of the multiple populations in the globular cluster Messier 80 (NGC 6093)

TL;DR

This study combines spectroscopy and UV photometry to analyze the chemical and kinematic properties of multiple stellar populations in M80, revealing differences in rotation and angular momentum that inform its complex formation history.

Contribution

It provides the first detailed kinematic analysis of M80's multiple populations, showing they have distinct angular momenta and rotational behaviors, indicating primordial kinematic differences.

Findings

N-enriched population rotates faster than others

Intermediate population shows marginally less rotation

Populations have different angular momenta explained by their radial distributions

Abstract

We combine MUSE spectroscopy and Hubble Space Telescope ultraviolet (UV) photometry to perform a study of the chemistry and dynamics of the Galactic globular cluster Messier 80 (M80, NGC 6093). Previous studies have revealed three stellar populations that not only vary in their light-element abundances, but also in their radial distributions, with concentration decreasing with increasing nitrogen enrichment. This remarkable trend, which sets M80 apart from the other Galactic globular clusters, points towards a complex formation and evolutionary history. To better understand how M80 formed and evolved, revealing its internal kinematics is key. We find that the most N-enriched population rotates faster than the other two populations at a 2 sigma confidence level. While our data further suggest that the intermediate population shows the least amount of rotation, this trend is rather marginal (1 - 2 sigma). Using axisymmetric Jeans models, we show that these findings can be explained from the radial distributions of the populations if they possess different angular momenta. Our findings suggest that the populations formed with primordial kinematical differences.