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

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 2σ confidence level. While our data further suggest that the intermediate population shows the least amount of rotation, this trend is rather marginal (1 − 2σ). 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.

Linking globular cluster structural parameters and their evolution: multiple stellar populations

“…Therefore, a more significant 1P mass loss is expected compared with less concentrated clusters. As previously also pointed out by Richer et al (2013), Bellini et al (2015, Cordero et al (2017), Kamann et al (2020), andDalessandro et al (2019), the correlation existing between F 2 and the concentration parameter supports the idea that 2P stars are born concentrated at the centre of the cluster, while the initial radial distribution of 1P stars is more extended. The more the cluster is concentrated, the more 1P stars will be stripped away.…”

“…Moreover, simulations predict kinematic differences between the two populations, including differential rotation and discrepancies in the velocity dispersions (Mastrobuono-Battisti & Perets 2013, 2016Vesperini et al 2013;Hénault-Brunet et al 2015;Tiongco et al 2019). This kind of differences have been observed in Galactic GCs (Richer et al 2013;Bellini et al 2015Bellini et al , 2018Cordero et al 2017;Lee 2017Lee , 2018Dalessandro et al 2018;Milone et al 2018;Cordoni et al 2020c;Kamann et al 2020), however, the strength and variety of the signatures hamper the interpretation of the results. Carretta et al (2010) used principal component analysis and multivariate relations to study the phase of transition between 1P and 2P, finding that the main parameters driving the chemical signatures found in GCs are the metallicity, mass, and cluster age (see also Martocchia et al 2018Martocchia et al , 2019Lagioia et al 2019).…”

“…Centrally concentrated 2P stars have been indeed observed in a number of clusters (see e.g. Norris & Freeman 1979;Milone et al 2012a;Richer et al 2013;Cordero et al 2014Cordero et al , 2017Bellini et al 2015;Dalessandro et al 2019;Kamann et al 2020;Dondoglio et al 2021;Szigeti et al 2021). The observed differences are milder for more dynamically evolved systems (Dalessandro et al 2019).…”

MUSE narrow field mode observations of the central kinematics of M15

“…We analysed the spatial resolved kinematics in a similar manner as in Kamann et al (2018aKamann et al ( , 2020 by deriving 1D radial profiles and 2D Voronoi maps of the first and second moments of the line-of-sight velocity distribution. The radial profiles are depicted in Fig.…”

Black holes and rotation: Internal kinematics of star clusters with MUSE

“…Hénault-Brunet et al 2015). A first study on the peculiar cluster NGC 6093 (M80, see Dalessandro et al 2018) already revealed remarkable differences in the rotation patterns of the populations (Kamann et al 2020).…”