Chemical Taxonomy of ω Centauri: Ten Populations Reveal a Multi-Phase Enrichment History

Abstract ω Centauri, the most massive globular cluster-like system in the Milky Way, exhibits a level of stellar population complexity that has long resisted a unified chemical characterisation. We exploit high-resolution near-infrared spectroscopy from the Milky Way Mapper survey (MWM DR19) to construct one of the largest homogeneously analysed samples of ω Centauri members to date. Applying Ward-linkage hierarchical clustering in a seven-dimensional chemical abundance space, without prior assumptions on population number or boundaries, we identify ten chemically distinct stellar populations. Their nucleosynthetic signatures trace four enrichment channels: iron-peak, α-element, CNO-cycle, and high-temperature proton-capture processes. The populations organise into two dominant groups separated by a large light-element spread at a modest iron baseline, consistent with AGB-driven self-enrichment. This dichotomy reflects distinct enrichment pathways: core-collapse supernovae establish the iron baseline, while AGB stars dominate light-element and s-process enrichment. A decoupled rise in s-process abundances relative to iron-peak elements, together with sub-dominant Type Ia contributions across all metallicities, indicates evolution on timescales shorter than the characteristic Type Ia delay time. One intermediate-metallicity population retains a primordial composition, providing evidence for spatially segregated enrichment within the progenitor. The most metal-rich component may reflect star formation that persisted within the cluster’s nuclear remnant after its host dwarf galaxy merged with the Milky Way. All populations lie in the accreted regime of the [Al/Fe]–[Mg/Mn] plane, supporting an ex-situ origin. These results reinforce the interpretation of ω Cen as the remnant nucleus of an accreted dwarf galaxy and provide a framework for future chemo-dynamical studies.