Revealing the Origins of Galactic Globular Clusters via Their Mg-Al Abundances

TL;DR

This study uses Mg-Al abundance patterns in globular clusters to trace their origins, distinguishing between in-situ and accreted populations and offering a new chemical classification method for Galactic archaeology.

Contribution

It introduces a chemically driven classification based on Mg-Al abundances to identify the birth environments of globular clusters, improving upon dynamical methods.

Findings

Clear chemical dichotomy between in-situ and accreted GCs at [Fe/H] > -1.5.

Primordial populations with lower [Al/Fe] are reliable tracers of birth environments.

Some clusters are reclassified compared to dynamical methods, highlighting the method's effectiveness.

Abstract

Many Galactic globular clusters (GCs) originated in diverse host galaxies before being subsequently incorporated into the Milky Way through hierarchical galaxy assembly. Identifying their origins is crucial for revealing galaxy properties at early times. Traditional classification methods relying on dynamical properties face inherent uncertainties stemming from the evolving Galactic potential and complex merger histories. Chemically driven classification confronts a distinct obstacle: multiple populations - abundance variations in light elements of GC members. In this Letter, we identify primordial populations exhibiting lower [Al/Fe] as reliable tracers of their birth environments' chemical evolution. A clear chemical dichotomy emerges between in-situ and accreted GC populations at [Fe/H] > -1.5, particularly in the [Mg/Fe]-[Al/Fe] plane, indicating that their progenitor galaxies have experienced fundamentally different enrichment histories. While our chemically driven classification demonstrates general consistency with dynamically driven classifications, notable discrepancies emerge: NGC 288 and M4 are reclassified as in-situ, and Terzan 9 as accreted. This chemically driven GC classification provides promising application for Galactic archaeology.