Disruption of a Giant: Spectroscopic Identification of Members in the Periphery and Tidal Tails of $ω$ Centauri

Abstract

$ω$ Centauri ($ω$ Cen, NGC\,5139) is one of the most enigmatic globular clusters in the Milky Way, with the recent detection of tidal tails adding further to its complexity. We report the results of a spectroscopic study of stars in the outer regions of $ω$ Cen, which provides an improved characterisation of the cluster periphery and confirms the existence of tidal tails. Our targets, which lie in six VLT/FLAMES fields sampling six degrees across the sky, are selected using a Bayesian inference technique. We confirm 157 members of $ω$ Cen based on line-of-sight velocity and [Fe/H] measurements, indicating an overall success rate of 93 per cent. We trace stars along the tidal tails to a cluster-centric radius of 3.2~deg, identifying five members in the debris and additional lower-probability candidates. The analysis of the kinematics and metallicities of the new members provides evidence of continuity in these properties from the bound component of the progenitor cluster into its tidal debris. We find that the metallicities of stars in the peripheral regions and tidal tails of $ω$ Cen are broadly consistent with those in the \textit{Fimbulthul} stream to which the cluster has been previously linked. Our study provides a glimpse of the promise of new and forthcoming wide-field multi-object spectrographs for advancing understanding of tidal structures around Milky Way globular clusters.