A joint JWST and HST view of Omega Centauri: Multiple stellar populations and their kinematics

¹ Dipartimento di Fisica e Astronomia “Galileo Galilei”, Univ. di Padova, Vicolo dell’Osservatorio 3, Padova 35122, Italy
² Istituto Nazionale di Astrofisica – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, Padova 35122, Italy
³ Research School of Astronomy & Astrophysics, Australian National University, Canberra, ACT 2611, Australia

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

Received: 26 June 2025
Accepted: 16 December 2025

Abstract

We combine F115W and F277W images collected with the Near Infrared Camera of the James Webb Space Telescope with multiband, multi-epoch Hubble Space Telescope observations of ω Centauri to investigate its multiple stellar populations and internal kinematics. Our study focuses on a region spanning ∼0.9 to ∼2.3 half-light radii from the cluster center, which is largely unexplored by these telescopes. Using chromosome maps, we identified the principal populations along the upper main sequence and among M dwarfs, distinguishing lower-stream stars chemically akin to first-generation globular cluster stars with similar metallicities from upper-stream stars enriched in helium and nitrogen but that are oxygen poor. Both streams also host subpopulations with varying metallicities. We found radially anisotropic motions, with upper-stream stars exhibiting significantly stronger anisotropy than lower-stream stars. Subdividing the upper stream into extreme and intermediate light-element populations revealed a gradient in anisotropy, with intermediate stars lying between the lower-stream stars and extreme upper-stream populations. However, metal-rich and metal-poor stars within each stream show moderate kinematic differences. The lower-stream stars show a higher angular momentum dispersion compared to upper-stream stars, and they also exhibit stronger systemic rotation and proper motion skewness, further highlighting their kinematic divergence. Finally, leveraging a mass range of ∼0.15–0.7 M_⊙, we detected a low degree of energy equipartition for all cluster stars, which decreases with radial distance from the cluster center.