The kinematics of 30 Milky Way globular clusters and the multiple stellar populations within

¹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
² Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
³ School of Mathematics and Physics, The University of Queensland, St. Lucia, QLD 4072, Australia
⁴ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstraße 12–14, 69120 Heidelberg, Germany
⁵ Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (UB), Martí i Franquès, 1, 08028 Barcelona, Spain
⁶ Departament de Física Quàntica i Astrofísica (FQA), Universitat de Barcelona (UB), Martí i Franquès, 1, 08028 Barcelona, Spain
⁷ Institut d’Estudis Espacials de Catalunya (IEEC), Gran Capità, 2–4, 08034 Barcelona, Spain
⁸ ICREA, Pg. Lluís Companys 23, 08010 Barcelona, Spain
⁹ Institut für Astrophysik und Geophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
¹⁰ Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK

^★ Corresponding author; ellenivana.leitinger@unibo.it

Received: 3 October 2024
Accepted: 13 December 2024

Abstract

Aims. The spectroscopic and photometric classification of multiple stellar populations (MPs) in Galactic globular clusters (GCs) has enabled comparisons between contemporary observations and formation theories regarding the initial spatial configurations of the MPs. However, the kinematics of these MPs is an aspect that requires more attention. We investigated the 3D kinematics of 30 Galactic GCs, extending to 3–5 half-light radii, as well as their MPs, in order to uncover clues of the initial conditions of GCs and the MPs within.

Methods. We have combined Hubble Space Telescope and Gaia DR3 proper motions together with a comprehensive set of line-of- sight velocities to determine the 3D rotation amplitudes, rotation axes, and anisotropy profiles of the clusters. We include additional radial velocities from new IFU observations of NGC 5024 and an analysis of archival MUSE data of NGC 6101. We compare our kinematic results with structural and orbital parameters of each cluster, reporting the most significant correlations and common features.

Results. We find significant (>3σ) rotation in 21 GCs, with no significant differences between the total rotational amplitudes of the MPs, except for NGC 104. We find no significant differences in the position angles of the rotation axis or inclination angles. We find that the 3D rotational amplitude of the clusters in our sample is strongly correlated with their mass, relaxation time, enriched star fraction, and concentration. We determined the anisotropy profiles of each cluster and the MPs where possible. We investigated correlations with the structural parameters, orbital parameters, and accretion history of the clusters from their progenitor systems, finding that the dynamically young clusters with the highest central concentrations of primordial stars exhibit radial anisotropy in their outer regions (>2 half-light radii). The dynamically young clusters with a central concentration of enriched stars show significant tangential anisotropy or isotropy in their outer regions.