Impact of distance determinations on Galactic structure. II. Old tracers

TL;DR

This paper reviews how old stellar tracers like RR Lyrae stars are used to understand the structure, evolution, and history of the Milky Way galaxy, focusing on the bulge, halo, and dwarf galaxies.

Contribution

It synthesizes recent methods and findings on using old tracers to measure distances and analyze the Galactic structure and evolution.

Findings

Old tracers reveal detailed Galactic bulge structure.

RR Lyrae stars help map the Galactic halo and dwarf galaxies.

Various methods improve age estimates of stellar clusters.

Abstract

Here we review the efforts of a number of recent results that use old tracers to understand the build up of the Galaxy. Details that lead directly to using these old tracers to measure distances are discussed. We concentrate on the following: (1) the structure and evolution of the Galactic bulge and inner Galaxy constrained from the dynamics of individual stars residing therein; (2) the spatial structure of the old Galactic bulge through photometric observations of RR Lyrae-type stars; (3) the three\--dimensional structure, stellar density, mass, chemical composition, and age of the Milky Way bulge as traced by its old stellar populations; (4) an overview of RR Lyrae stars known in the ultra-faint dwarfs and their relation to the Galactic halo; and (5) different approaches for estimating absolute and relative cluster ages.