Cluster Ages to Reconstruct the Milky Way Assembly (CARMA)

IV. Chrono-dynamics of seven old star clusters in the Large Magellanic Cloud and the peculiar origin of NGC 1841

¹ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
² INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
³ atlanTTic, Universidade de Vigo, Escola de Enxeñaría de Telecomunicación, 36310 Vigo, Spain
⁴ Universidad de La Laguna, Avda. Astrofísico Fco. Sánchez, 38205 La Laguna, Tenerife, Spain
⁵ INAF – Osservatorio Astronomico d’ Abruzzo, Via M. Maggini, 64100 Teramo, Italy
⁶ INFN – Sezione di Pisa, Università di Pisa, Largo Pontecorvo 3, 56127 Pisa, Italy
⁷ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁸ Eureka Scientific, Inc., 2452 Delmer Street Suite 100, Oakland, CA 94602-3017, USA
⁹ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, Padova 35122, Italy
¹⁰ Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, via Gobetti 93/2, 40129 Bologna, Italy
¹¹ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone, Roma, Italy
¹² Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal, 4, 20018 Donostia-San Sebastián, Guipuzkoa, Spain
¹³ IKERBASQUE, Basque Foundation for Science, 48013 Bilbao, Spain
¹⁴ Vyoma GmbH, Karl-Theodor-Straße 55, 80803 Munich, Germany
¹⁵ Lennard-Jones Laboratories, School of Chemical and Physical Sciences, Keele University, Keele ST5 5BG, UK
¹⁶ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹⁷ Aix Marseille Université, CNRS, CNES, LAM, Marseille, France
¹⁸ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
¹⁹ Astrophysics Research Institute, Liverpool John Moores University, IC2 Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF, UK

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

Received: 5 March 2025
Accepted: 15 August 2025

Abstract

In this study, we report conclusive evidence of an ancient star cluster accreted by the Large Magellanic Cloud (LMC). By leveraging observations from the Hubble Space Telescope (HST), we investigated the chrono-dynamical structure of a sample of seven old star clusters within the LMC in a self-consistent way. The multi-epoch nature of the dataset made it possible to determine high-precision proper motions for the clusters. By employing an isochrone-fitting methodology, we also inferred homogeneous and robust estimates for their distances, ages, and metallicities from the deep high-resolution HST data. Supplementing these data with line-of-sight velocities from the literature, we investigated the full 3D dynamics of the clusters within the frame of the LMC. With respect to the other clusters in our sample, NGC 1841 depicts a peculiar case. Its position in the age-metallicity plane makes it about 1 Gyr younger than the other metal-poor LMC clusters. This offset in age, along with its dynamical properties, with a radial orbit that is nearly perpendicular to the LMC disc plane, clearly advocate for a different origin scenario. Thus, we conclude that NGC 1841 has likely been accreted by the LMC from a smaller galaxy. The other clusters in our sample show disc-like kinematics, with the case of NGC 2210 standing out as peculiar, based on its inclined orbit. Their coherent age-metallicity relation closely resembles that of Gaia-Sausage-Enceladus globular clusters, suggesting a similar early evolution for the two dwarf galaxies. We did not find any clear-cut chrono-kinematic evidence that NGC 2005 has been accreted by the LMC, as suggested by a previous study based on its chemical abundance pattern. Regardless of its nature, its very old age illustrates that peculiar chemical evolutions had already emerged at very early times in cosmic evolution.