The power of chemical tagging for studying Galactic evolution

Abstract

Chemical tagging is a relatively new technique in Galactic Archaeology, designed to find unique stellar groups among the Galactic field stars. Each small galaxy accreted by a large galaxy like the Milky Way leaves its own tidal stream of debris which is stripped off during its gravitational interaction with our Galaxy. The stars in these tidal streams retain kinematic and chemical signatures of their parent galaxy and are essentially fossil remnants of merger events which happened long ago. Stars from the same stellar nursery formed from the same material and will retain their unique chemical signatures compared with other field stars. The idea is that, with highly detailed abundance analysis and by using chemical tagging, we can identify which stars formed together. Some systems retain both their chemical and kinematical signatures (like the examples given here). However, in some cases the kinematical signatures will be lost after a while leaving only the chemical signatures. The following examples show the power of chemical tagging in identifying tidal debris of a globular cluster (the Aquarius Stream), tidal debris from satellite mergers (Omega Centauri) as well as identifying members of the Hyades supercluster. In each of these cases, kinematics has hinted at a relationship and existence of a stellar group, while the chemical tagging has confirmed the existence. In addition, chemical tagging has enabled the determination of the origin of the stellar group.