Chemodynamical history of the Galactic Bulge

TL;DR

This review synthesizes observational evidence on the kinematics, chemical composition, and ages of the Galactic Bulge's stellar populations, highlighting its complex structure, formation scenarios, and the need for advanced chemodynamical models.

Contribution

It provides a comprehensive overview of the current understanding of the Galactic Bulge's stellar populations, dynamics, and formation models, emphasizing gaps in fully self-consistent chemodynamical modeling.

Findings

Bulge stars are predominantly old with a wide metallicity range.

The Bulge exhibits cylindrical rotation and a Box/Peanut structure.

Current models lack a fully self-consistent chemodynamical framework.

Abstract

The Galactic Bulge can uniquely be studied from large samples of individual stars, and is therefore of prime importance for understanding the stellar population structure of bulges in general. Here the observational evidence on the kinematics, chemical composition, and ages of Bulge stellar populations based on photometric and spectroscopic data is reviewed. The bulk of Bulge stars are old and span a metallicity range -1.5<~[Fe/H]<~+0.5. Stellar populations and chemical properties suggest a star formation timescale below ~2 Gyr. The overall Bulge is barred and follows cylindrical rotation, and the more metal-rich stars trace a Box/Peanut (B/P) structure. Dynamical models demonstrate the different spatial and orbital distributions of metal-rich and metal-poor stars. We discuss current Bulge formation scenarios based on dynamical, chemical, chemodynamical and cosmological models. Despite impressive progress we do not yet have a successful fully self-consistent chemodynamical Bulge model in the cosmological framework, and we will also need more extensive chrono-chemical-kinematic 3D map of stars to better constrain such models.