oMEGACat. VIII. A Subpopulation Census of ω Centauri

Abstract An understanding of the assembly history of the complex star cluster Omega Centauri has long been sought after, with many studies separating the stars on the color–magnitude diagram into multiple groupings across small magnitude ranges. Utilizing the oMEGACat combined astro-photometric and spectroscopic data set, we parse 14 subpopulations from the upper red giant branch to below the main-sequence turnoff. We combine our results with previous works to estimate the age and age spread of each population. We find that the chemically enhanced (P2) populations are all ∼1 Gyr younger (∼11.6 Gyr old) and have significantly higher intrinsic age spreads (0.6 Gyr) than the primordial (P1) populations (∼12.6 Gyr old, 0.3 Gyr spread), with the intermediate (Im) populations falling in between the two. Additionally, we connect for the first time the chromosome diagram to the two-stream age–metallicity relation, allowing us to link the P1 and P2 stars to the distinct star formation tracks, proposed to be in situ and ex situ contributions to the cluster’s assembly. Our results are consistent with some suggested formation models and rule out others, but no current model can explain all observed features of the subpopulations.