A New Set of Chisels for Galactic Archeology: Sc, V, and Zn as Taggers of Accreted Globular Clusters*

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-elements 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 element abundances to investigate the origin of a sample of metal-rich GCs. By homogeneously analyzing high-resolution UVES spectra of giant stars belonging to four metal-rich GCs (namely NGC 5927, NGC 6388, NGC 6441, and NGC 6496), we find that while the alpha-elements Si and Ca have similar abundance ratios for all 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 similar to 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 they provide robust evidence supporting an accreted origin from the same progenitor for NGC 6388 and NGC 6441.

Automated summary

Chemical tagging is a powerful tool to investigate the origin of stars and globular clusters. Using iron-peak element abundances, differences were found in the metal-rich globular clusters NGC 6388 and NGC 6441 compared to NGC 5927 and NGC 6496, indicating different formation environments and supporting an accreted origin for the former two clusters.