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 184

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.