The chemo-dynamical complexity of ω Centauri: Different kinematics for different populations
Year: 2026
Type: article
Abstract: Context . The origin of ω Centauri remains one of the key open questions in stellar dynamics and chemical evolution. Its large abundance spreads and multiple populations suggest a formation history more complex than that of a typical globular cluster. Aims . We investigate whether the chemical sub-populations identified in APOGEE DR17 also exhibit distinct spatial and kinematic signatures and the constraints these provide on the formation pathways of ω Cen. Methods . We analysed a sample of APOGEE DR17 red giant stars using a Gaussian mixture model in an 8D chemical-abundance space. The resulting chemical components were combined with Gaia proper motions and APOGEE line-of-sight velocities to derive intrinsic mean velocities and velocity dispersions in all three observable directions. We measured both global kinematic quantities and radial profiles for each chemically defined group, extending from the inner regions to ~4 half-light radii. Results . The Gaussian mixture model identifies five chemical components, which, when examined through their radial cumulative distributions, naturally group into two broader families characterised by lower and higher aluminium enrichment. The two families differ significantly in their spatial and kinematic properties: the Al-rich stars are more centrally concentrated and exhibit stronger radial anisotropy than the Al-poor stars, which remain closer to isotropy over the radial range probed. Despite these significant differences (>2 σ ), the two populations share a common rotation pattern, with comparable intrinsic rotation amplitudes and rotation-axis inclinations within the uncertainties (~0.5 km s −1 ). Both families span a wide range in metallicity, indicating that they do not simply correspond to a first- and second-generation dichotomy but rather trace chemically and dynamically complex substructures within ω Cen. Conclusions . This work represents the first chemo-dynamical study of ω Cen linking detailed chemical tagging to internal kinematics from the inner regions to the cluster outskirts and provides a key benchmark for models of its formation. A formation path involving both hierarchical assembly within a dwarf-galaxy potential and centrally concentrated, chemically enriched star formation offers a natural explanation for the observed chemo-dynamical complexity. Extending this approach to larger fields of view and to more numerous, fainter stars will be essential to robustly uncover the origin of this uniquely complex system.
Source: Astronomy and Astrophysics
Institutions: Centre National de la Recherche Scientifique, Centre National d'Études Spatiales, Observatoire astronomique de Strasbourg, Université de Strasbourg, Université Paris Cité, Université Paris Sciences et Lettres, Observatoire de Paris, Sorbonne Université, CY Cergy Paris Université, University of Padua, Osservatorio Astronomico di Padova, National Institute for Astrophysics
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Funders: Smithsonian Institution, U.S. Department of Energy, Alfred P. Sloan Foundation, Yale University, Carnegie Institution of Washington, Vanderbilt University, Ohio State University, University of Utah, University of Washington, Johns Hopkins University, Carnegie Mellon University, University of Notre Dame, University of Portsmouth, New Mexico State University, European Space Agency, York University, University of Oxford, Centre National d’Etudes Spatiales, Ministério da Ciência, Tecnologia e Inovação, Université de Strasbourg, Universidad Nacional Autónoma de México, Max-Planck-Institut für Astronomie, Instituto de Astrofísica de Canarias, Office of Science, University of Colorado Boulder, Leibniz-Gemeinschaft, Institut national des sciences de l'Univers, Lawrence Berkeley National Laboratory
OpenAlex ID: W7166046097