Kinematics of metallicity populations in Omega Centauri using Gaia Focused Product Release and Hubble Space Telescope

TL;DR

This study investigates the kinematics of different metallicity populations in Omega Centauri using Gaia and Hubble data, revealing similar proper motions and rotation across populations, which informs the cluster's formation history.

Contribution

It provides a detailed kinematic analysis of Omega Centauri's metallicity populations using new Gaia data, highlighting the uniformity in their motions and rotation.

Findings

No significant difference in proper motions among metallicity populations.

All populations exhibit clear rotation signatures.

Proper motions are consistent regardless of the population number estimation method.

Abstract

Context. Omega Cen is the largest known globular cluster in the Milky Way. It is also quite a complex object with a large metallicity spread and multiple stellar populations. Despite a number of studies over the past several decades, the series of events that led to the formation of this cluster is still poorly understood. One of its peculiarities is the presence of a metal-rich population which does not show the phenomenon of light-element anti-correlations (C-N, Na-O, Mg-Al), a trait that is considered as characteristic of Galactic Globular Clusters, and is in fact present among more metal-poor Omega Cen stars, leading to speculations that such anomalous population was accreted by the cluster. In this paper, we aim at investigating the kinematics of Omega Cen populations to gain insight on the formation scenario of the cluster. Using the newly released Gaia FPR and DR3 catalogue, we conducted a detailed kinematical analysis of cluster members within Omega Cen. The cluster members were divided into four metallicity populations and their mean proper motion in radial and tangential components were compared with each other. We also performed Gaussian Mixture Model fitting on the metallicity distribution to estimate the number of populations within our sample and an independent analysis of the HST catalogue as confirmation. The mean proper motions (mu_r and mu_t) of the metallicity populations do not show any significant differences. It is also not dependent on the approach chosen to determine the number of metallicity populations. We do find clear signature of rotation in all of the populations (including the metal-rich) with similar velocities.