The GALAH Survey: Chemically tagging the Fimbulthul stream to the globular cluster $ω$ Centauri

Abstract

Using kinematics from Gaia and the large elemental abundance space of the second data release of the GALAH survey, we identify two new members of the Fimbulthul stellar stream, and chemically tag them to massive, multi-metallic globular cluster $ω$ Centauri. Recent analysis of the second data release of Gaia had revealed the Fimbulthul stellar stream in the halo of the Milky Way. It had been proposed that the stream is associated with the $ω$ Centauri, but this proposition relied exclusively upon the kinematics and metallicities of the stars to make the association. In this work, we find our two new members of the stream to be metal-poor stars that are enhanced in sodium and aluminium, typical of second population globular cluster stars, but not otherwise seen in field stars. Furthermore, the stars share the s-process abundance pattern seen in $ω$ Centauri, which is rare in field stars. Apart from one star within 1.5 deg of $ω$ Centauri, we find no other stars observed by GALAH spatially near $ω$ Centauri or the Fimbulthul stream that could be kinematically and chemically linked to the cluster. Chemically tagging stars in the Fimbulthul stream to $ω$ Centauri confirms the earlier work, and further links this tidal feature in the Milky Way halo to $ω$ Centauri.