Outer Regions of the Milky Way

TL;DR

This paper reviews current knowledge and future prospects for understanding the structure, evolution, and star formation history of the Milky Way's outer disk regions, emphasizing Gaia's role.

Contribution

It summarizes existing knowledge and discusses how upcoming Gaia and ground-based surveys will improve understanding of the Milky Way's outer disk.

Findings

Gaia will provide precise data on stellar positions and velocities.

Upcoming surveys will help address key questions about spiral arms and warp formation.

Current understanding of the outer disk is limited by observational and theoretical challenges.

Abstract

With the start of the Gaia era, the time has come to address the major challenge of deriving the star formation history and evolution of the disk of our MilkyWay. Here we review our present knowledge of the outer regions of the Milky Way disk population. Its stellar content, its structure and its dynamical and chemical evolution are summarized, focussing on our lack of understanding both from an observational and a theoretical viewpoint. We describe the unprecedented data that Gaia and the upcoming ground-based spectroscopic surveys will provide in the next decade. More in detail, we quantify the expect accuracy in position, velocity and astrophysical parameters of some of the key tracers of the stellar populations in the outer Galactic disk. Some insights on the future capability of these surveys to answer crucial and fundamental issues are discussed, such as the mechanisms driving the spiral arms and the warp formation. Our Galaxy, theMilkyWay, is our cosmological laboratory for understanding the process of formation and evolution of disk galaxies. What we learn in the next decades will be naturally transferred to the extragalactic domain.