Milky Way disc & Bulge in situ populations: ESO white paper - Expanding horizons call

TL;DR

This paper emphasizes the need for a new wide-field spectroscopic facility to create a comprehensive chemo-dynamical map of the Milky Way, crucial for understanding its formation, evolution, and structure.

Contribution

It advocates for a novel large-aperture, multiplexed spectroscopic instrument to obtain homogeneous data across the Galaxy, enabling breakthroughs in galactic archaeology.

Findings

Current surveys lack comprehensive, high-quality data for the entire Milky Way.

A new facility would enable detailed chemo-dynamical mapping of the Galaxy.

Such data would significantly advance understanding of galactic formation and evolution.

Abstract

The formation and evolution of the Milky Way's disc, bar, and bulge remain fundamentally limited by the lack of a contiguous, Galaxy-wide, high-precision chemo-dynamical map. Key open questions - including the survival or destruction of the primitive discs, the origin of the bulge's multi-component structure, the role of mergers and secular processes, and the coupling between stellar chemistry, dynamics, and the Galactic potential - cannot be fully resolved with current or planned facilities. Existing spectroscopic surveys provide either high resolution for small samples or wide coverage at insufficient resolution and depth, and none can obtain homogeneous abundances, precise 3D kinematics, and reliable ages for the millions of stars required, particularly in the obscured midplane, the far side of the bar, or the outer, low-density disc. A new wide-field, massively multiplexed, large-aperture spectroscopic facility, capable of both high- and low-resolution spectroscopy over tens of thousands of square degrees, is therefore essential. Such a facility would deliver the statistical power, sensitivity, and completeness needed to reconstruct the Galaxy's assembly history, constrain its gravitational potential, and establish the Milky Way as the definitive benchmark for galaxy evolution.