Seminars and Colloquia at ESO Garching and on the campus

The Milky Way's stellar halo preserves the fossil record of past accretion events, but disentangling the debris of ancient mergers becomes increasingly difficult as their dynamical signatures phase-mix. In this talk, I will present a chemodynamical reconstruction of a possible disrupted progenitor associated with Omega Centauri, which we call the Omega Dwarf. Combining chemical abundances from APOGEE and GALAH with Gaia astrometry, we investigate whether Sequoia, Thamnos, Gaia–Enceladus, and Omega Centauri can be understood as different components (or different stages of disruption) of a single accreted dwarf galaxy. We recover a structured chemical sequence across the putative progenitor: chemically primordial populations dominate its outer debris, while the inner regions show signatures of more efficient and prolonged chemical enrichment. Within this picture, Sequoia emerges naturally as part of an outside-in sequence extending toward Omega Centauri, the surviving nucleus of the system. Thamnos, in contrast, appears consistent with material stripped at a later stage and shares chemical features otherwise seen primarily in Omega Centauri. Gaia-Enceladus, although often associated with Omega Centauri, remains less certain, leaving open the possibility that only part of its debris is associated with the same progenitor. This framework offers a new way to interpret stellar-halo substructures not simply as signatures of independent accretion events, but as different spatial components and stripping stages of disrupted galaxies.