Disentanglement of the chemodynamical assembly: mapping the Milky Way discs

Abstract

ABSTRACT The formation and structure of the Milky Way have a fundamental role in our understanding of the universe and its evolution, and thanks to the Gaia mission and large spectroscopic surveys, we live an exceptional moment of data availability, allowing us to trace the building blocks of the Galactic disc and their relations. In this sense, we propose here the exploration of a large data set in a top-down fashion, elaborating a similarity map of the local Galactic volume in order to segregate and characterize its main components, searching for hints about their relations. We have used the t-SNE algorithm with chemical, orbital and kinematic properties of the stars to produce 2D manifolds and dissect their structure by isolating populations to further analyse their behaviour. The young thin disc could be clearly separated from the older thick disc, also showing a puzzling transition zone with hints about the aftermath of the Gaia–Sausage–Enceladus merger. Moving groups and resonant features also appear prominently in the maps, splitting the disc into inner and outer portions as consequence of the resonances produced by the Galactic bar. The dynamical halo appears as an extreme end related to the heated portion of the thick disc, showing sub-structures corresponding to known accreted populations. Open and globular clusters also appear in their chemical/evolutionary context. We present details of the developed strategy, an overview of the different populations and their relations, as well as a discussion and insights of our results in the scenario of Galactic evolution.