A Pristine View of Galactic Globular Clusters and their Peripheries: Omega Centauri

TL;DR

This study combines Gaia data, synthetic photometry, and metallicity measurements to map and analyze the tidal tails and stellar populations of Omega Centauri, revealing complex structures and multiple populations extending beyond the cluster.

Contribution

It introduces a probabilistic method to identify Omega Centauri-like stars and characterizes the metallicity and population structure of its outer regions and tidal tails.

Findings

Recovered Omega Centauri's tidal tails using proper motion and photometry.

Identified two main metallicity populations in the outer regions and tails.

First evidence of similar populations beyond the tidal radius into the tails.

Abstract

The central regions of the globular cluster Omega Centauri ($\omega$ Cen) have been extensively studied, but its outer regions and tidal structure have been less so. Gaia's astrometry uncovered substantial tidal substructure associated with $\omega$ Cen, yet the lack of chemical tagging makes these associations tenuous. In this paper, we utilise the Gaia-Synthetic CaHK-band photometry, metallicities from the Pristine survey and Gaia's astrometry to explore up to a clustercentric radius of 5 degrees from $\omega$ Cen. We identify $\omega$ Cen-like stars based on proper motion, colour-magnitude and colour-colour space, exploring the morphology, and stellar populations of the outer regions. Our probabilistic approach recovers the tidal tails of $\omega$ Cen, and we investigate the metallicity distribution of $\omega$ Cen ranging from a radius of 15 arcmin to the tidal radius, and beyond into the tidal tails. We present (1) two components between 15 arcmin and tidal radius at -1.83 and -1.45 dex which are also the dominant populations within 15 arcmin, and (2) the first evidence that the same two populations in the outer regions of the cluster are present outside the tidal radius and into the tidal tails. These populations are mixed about the stream, and are typically amongst the faintest stars in our sample; all indicating that the tidal tails are made of tidally stripped $\omega$ Cen stars.