Globular clusters in ORBIT: Complete dynamical characterisation of the Milky Way globular cluster population through updated orbital reconstruction

¹ Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, Via Piero Gobetti 93/2, Bologna 40129, Italy
² Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, INAF, Via Piero Gobetti 93/3, Bologna 40129, Italy
³ Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
⁴ Instituto Milenio de Astrofísica MAS, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
⁵ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, 06304 Nice, France

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 3 July 2025
Accepted: 2 December 2025

Abstract

Context. In hierarchical structure formation, the content of a galaxy is determined both by its in-situ processes and by material added via accretions. Globular clusters, in particular, represent a window into the study of the different merger events that a galaxy has undergone. Establishing the correct classification of in-situ and accreted tracers, and distinguishing the various progenitors that contributed to the accreted population are important tools to deepen our understanding of galactic formation and evolution.

Aims. This study aims to refine our knowledge of the Milky Way’s assembly history by examining the dynamics of its globular cluster population and establishing an updated classification among in-situ objects and the different merger events identified.

Methods. We used a custom-built orbit integrator to derive precise orbital parameters, integrals of motions and adiabatic invariants for the globular cluster sample studied. By properly accounting for the rotating bar, which transforms the underlying model into a time-varying potential, we performed a complete dynamical characterisation of the globular clusters.

Results. We present a new catalogue of clear associations between globular clusters and structures (both in-situ and accreted) in the Milky Way, along with a full table of derived parameters. Using all available dynamical information, we attributed previously unassociated or misclassified globular clusters to different progenitors, including those responsible for the Aleph, Antaeus, Cetus, Elqui, and Typhon merger events.

Conclusions. Using a custom-built orbit integrator and properly accounting for the time-varying nature of the Milky Way potential, we demonstrate the depth of information that can be extracted from a purely dynamical analysis of the Galaxy’s globular clusters. Merging our dynamical analysis with complementary chronochemical studies, will allow us to uncover the remaining secrets of the accretion history of the Milky Way.