oMEGACat. VIII. A Subpopulation Census of {\omega} Centauri

TL;DR

This study dissects the complex star populations of Omega Centauri, revealing age differences and formation histories that inform cluster assembly models using combined photometric and spectroscopic data.

Contribution

It provides a detailed subpopulation census of Omega Centauri, linking chemical and age properties to formation scenarios for the first time.

Findings

Chemically enhanced populations are ~1 Gyr younger with larger age spreads.

Primordial populations are older (~12.6 Gyr) with smaller age spreads.

The study connects the Chromosome Diagram to the age-metallicity relation.

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 dataset 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.