The Nephele ecosystem: Stars, globular clusters, and stellar streams associated with the progenitor galaxy of ω Centauri

¹ LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS, 92190 Meudon, France
² Université de Strasbourg, CNRS, Observatoire Astronomique de Strasbourg, 67000 Strasbourg, France
³ Dipartimento di Fisica, Università di Roma “La Sapienza”, Piazza Aldo Moro, Italy
⁴ Institute for Complex Systems CNR, Piazzale Aldo Moro 2, 00185 Rome, Italy
⁵ Dipartimento di Fisica e Astronomia “Galileo Galilei”, Università di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁶ Dipartimento di Tecnica e Gestione dei Sistemi Industriali, Università degli Studi di Padova, Stradella S. Nicola 3, 36100 Vicenza, Italy
⁷ Istituto Nazionale di Astrofisica - Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, Padova 35122, Italy
⁸ Division of Astrophysics, Department of Physics, Lund University, Box 118, 221 00 Lund, Sweden
⁹ Leibniz Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482, Potsdam, Germany
¹⁰ University of Strasbourg Institute for Advanced Study, 5 allée du Général Rouvillois, 67083 Strasbourg, France

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

Received: 14 October 2025
Accepted: 25 February 2026

Abstract

Context. Globular clusters (GCs) and their associated stellar streams are key tracers of the hierarchical assembly history of the Milky Way. ω Centauri, the most massive and chemically complex GC in the Galaxy, is widely believed to be the remnant nucleus of an accreted dwarf galaxy. Identifying its associated debris and that of chemically similar clusters can provide important constraints on the nature of this progenitor system.

Aims. We aim to identify stars in the Galactic field that are chemically and kinematically associated with ω Cen and with a group of GCs hypothesised to share a common origin. This group, recently proposed to form a coherent system named Nephele, may represent the remnants of a single, massive accretion event.

Methods. We analysed APOGEE DR17 data to select field stars with high-quality chemical abundances. We applied a Gaussian mixture model (GMM) in an 8D chemical abundance space to identify stars compatible with ω Cen chemistry. We then computed the orbital energy and angular momentum of these stars and applied a second GMM, calibrated on simulations from the e-TidalGCs project, to determine the kinematic compatibility with the predicted streams of ω Cen and the associated Nephele GCs.

Results. We identify 470 stars chemically compatible with ω Cen, of which 58 are also Al-rich, consistent with second-generation stars found in GCs. Of these, six stars show kinematics consistent with the predicted ω Cen stream, and additional stars are linked to the tidal streams of NGC 6205, NGC 6254, NGC 6273, NGC 6656, and NGC 6809. These findings suggest the presence of extended stellar streams that have not been previously detected. We also find overlap in chemical and kinematic properties between Nephele stars and the Gaia Sausage-Enceladus population.

Conclusions. Our results suggest the presence of stellar debris associated with ω Cen and its candidate family of GCs. The combined chemical and kinematic analysis supports the scenario in which these systems originated in a common progenitor, which has now been disrupted. While uncertainties remain—particularly due to disc contamination and limited sky coverage—this work illustrates the potential of chemical and dynamical methods to trace the remnants of past accretion events in the inner Galaxy.