The Milky Way thin disk structure as revealed by stars and young open clusters

TL;DR

This paper reviews the structure of the Milky Way's thin disk, focusing on spiral structure, disk size, and the Local arm, highlighting current uncertainties and the impact of upcoming data from GAIA and LAMOST.

Contribution

It provides an updated synthesis of the Milky Way thin disk structure, emphasizing unresolved issues and the potential of new astronomical surveys.

Findings

Poor knowledge of the Milky Way spiral structure

Galactic disk lacks a clear luminous cutoff at 14 kpc

The Local arm is likely an inter-arm structure

Abstract

In this contribution I shall focus on the structure of the Galactic thin disk. The evolution of the thin disk and its chemical properties have been discussed in detail by T. Bensby's contribution in conjunction with the properties of the Galactic thick disk, and by L.Olivia in conjunction with the properties of the Galactic bulge. I will review and discuss the status of our understanding of three major topics, which have been the subject of intense research nowadays, after long years of silence: (1) the spiral structure of the Milky Way, (2) the size of the Galactic disk, and (3) the nature of the Local arm (Orion spur), where the Sun is immersed. The provisional conclusions of this discussion are that : (1) we still have quite a poor knowledge of the Milky Way spiral structure, and the main dis-agreements among various tracers are still to be settled; (2) the Galactic disk does clearly \textit{not} have an obvious luminous cut-off at about 14 kpc from the Galactic center, and next generation Galactic models need to be updated in this respect, and (3) the Local arm is most probably an inter-arm structure, similar to what we see in several external spirals, like M~74. Finally, the impact of GAIA and LAMOST in this field will be briefly discussed as well.