A Unified Exploration of the Chronology of the Galaxy

TL;DR

This study uses a large, high-quality stellar dataset to identify and characterize the structural components of the Milky Way's disc and halo through unsupervised clustering, revealing new insights into Galactic formation and evolution.

Contribution

It introduces a comprehensive analysis combining spectroscopic, astrometric, and asteroseismic data with Gaussian mixture models to identify four main Galactic components and measure age gradients.

Findings

Identification of four distinct Galactic components: thin disc, heated thin disc, thick disc, and halo.

Detection of an age asymmetry between Northern and Southern Galactic hemispheres.

Measurement of vertical and radial age gradients extending previous studies.

Abstract

The Milky Way has distinct structural stellar components linked to its formation and subsequent evolution, but disentangling them is nontrivial. With the recent availability of high-quality data for a large numbers of stars in the Milky Way, it is a natural next step for research in the evolution of the Galaxy to perform automated explorations with unsupervised methods of the structures hidden in the combination of large-scale spectroscopic, astrometric, and asteroseismic data sets. We determine precise stellar properties for 21,076 red giants, mainly spanning 2-15 kpc in Galactocentric radii, making it the largest sample of red giants with measured asteroseismic ages available to date. We explore the nature of different stellar structures in the Galactic disc by using Gaussian mixture models as an unsupervised clustering method to find substructure in the combined chemical, kinematic, and age subspace. The best-fit mixture model yields four distinct physical Galactic components in the stellar disc: the thin disc, the kinematically heated thin disc, the thick disc, and the stellar halo. We find hints of an age asymmetry between the Northern and Southern hemisphere and we measure the vertical and radial age gradient of the Galactic disc using the asteroseismic ages extended to further distances than previous studies.