The Chemical Diversity of the Metal-Poor Milky Way

TL;DR

This study uses advanced statistical techniques on GALAH DR3 data to uncover detailed chemical substructures in the metal-poor Milky Way, revealing new insights into its formation and evolution.

Contribution

It introduces a novel combination of PCA and Extreme Deconvolution to identify stellar populations without prior cuts, highlighting key elemental differences in Galactic components.

Findings

Identified 10 distinct stellar groups in the Milky Way.

Found that elements Ba, Al, Cu, and Sc are crucial for distinguishing populations.

Showed the thick disc contains multiple substructures, indicating diverse origins.

Abstract

We present a detailed study of the chemical diversity of the metal-poor Milky Way (MW) using data from the GALAH DR3 survey. Considering 17 chemical abundances relative to iron ([X/Fe]) for 9,923 stars, we employ Principal Component Analysis (PCA) and Extreme Deconvolution (XD) to identify 10 distinct stellar groups. This approach, free from chemical or dynamical cuts, reveals known populations, including the accreted halo, thick disc, thin disc, and in-situ halo. The thick disc is characterised by multiple substructures, suggesting it comprises stars formed in diverse environments. Our findings highlight the limited discriminatory power of magnesium in separating accreted and disc stars. Elements such as Ba, Al, Cu, and Sc are critical in distinguishing disc from accreted stars, while Ba, Y, Eu and Zn differentiate disc and accreted stars from the in-situ halo. This study demonstrates the potential power of combining a latent space representation of the data (PCA) with a clustering algorithm (XD) in Galactic archaeology, in providing new insights into the galaxy's assembly and evolutionary history.