A new set of chisels for Galactic archaeology: Sc, V and Zn as taggers of accreted globular clusters

TL;DR

This study uses iron-peak element abundances in globular clusters to identify their origins, revealing that certain clusters likely originated from external accreted environments rather than the Milky Way itself.

Contribution

It introduces a novel chemical tagging method using Sc, V, and Zn abundances to distinguish between in-situ and accreted globular clusters.

Findings

NGC 6388 and NGC 6441 have lower iron-peak element ratios than in-situ clusters.

Chemical signatures support an accreted origin for NGC 6388 and NGC 6441.

Alpha and neutron capture elements show minimal variation among studied clusters.

Abstract

Chemical tagging is a powerful tool to reveal the origin of stars and globular clusters (GCs), especially when dynamics alone cannot provide robust answers. So far, mostly $\alpha$- and neutron capture elements have been used to distinguish stars born in the Milky Way (MW) from those born in external environments such as that of dwarf galaxies. Here, instead, we use iron-peak elements abundances to investigate the origin of a sample of metal-rich globular clusters. By homogeneously analyzing high-resolution UVES spectra of giant stars belonging to four metal-rich GCs (namely NGC 5927, NGC 6388, NGC 6441, NGC 6496), we find that while the $\alpha$-elements Si and Ca have similar abundance ratios for all the four GCs, and Ti and neutron capture elements (La, Ba and Eu) only show a marginal discrepancy, a stark difference is found when considering the abundances of some iron-peak elements (Sc, V and Zn). In particular, NGC 6388 and NGC 6441 have abundance ratios for these iron-peak elements significantly lower (by ~ 0.5 dex) than those measured in NGC 5927 and NGC 6496, which are clearly identified as born in-situ MW clusters through an analysis of their orbital properties. These measurements indicate that the environment in which these clusters formed is different, and provide robust evidence supporting an accreted origin from the same progenitor for NGC 6388 and NGC 6441.