# Chemodynamical Modelling of the Galactic Bulge and Bar

**Authors:** Matthieu Portail, Christopher Wegg, Ortwin Gerhard, Melissa Ness  
**arXiv:** [1704.07821](https://arxiv.org/abs/1704.07821)  
**Date:** 2017-04-25  
**Summary page:** https://www.summarizepaper.com/en/paper/1704.07821v1/

## Key points

- Matthieu Portail, Christopher Wegg, Ortwin Gerhard, and Melissa Ness present a self-consistent chemodynamical model fitted to reproduce data for the galactic bulge, bar, and inner disk.
- The authors extend the Made-to-Measure method to an augmented phase-space that includes the metallicity of stars and show its first application to the bar region of the Milky Way.
- Using data from ARGOS and APOGEE (DR12) surveys, they adapt a recent dynamical model from Portail et al. to reproduce observed spatial and kinematic variations as a function of metallicity.
- Metal-rich stars with [Fe/H] > -0.5 are strongly barred and have dynamical properties consistent with a common disk origin while metal-poor stars with [Fe/H] < -0.5 exhibit strong kinematic variations with metallicity indicating varying contributions from underlying stellar populations.
- Outside the central kpc (kiloparsec), metal-poor stars are found to have the density and kinematics of a thick disk while in the inner kpc evidence for an extra concentration of metal-poor stars is detected.
- Combined orbit distributions of all metallicities in the model naturally reproduce observed vertex deviations in the bulge.
- Made-to-Measure chemodynamical models can be extended to other chemical dimensions making them powerful tools for maximizing information obtained from large spectroscopic surveys such as APOGEE, GALAH, and MOONS.

## Summary

In their paper titled "Chemodynamical Modelling of the Galactic Bulge and Bar," Matthieu Portail, Christopher Wegg, Ortwin Gerhard, and Melissa Ness present a self-consistent chemodynamical model that is fitted to reproduce data for the galactic bulge, bar, and inner disk. The authors extend the Made-to-Measure method to an augmented phase-space that includes the metallicity of stars and show its first application to the bar region of the Milky Way. Using data from the ARGOS and APOGEE (DR12) surveys, they adapt a recent dynamical model from Portail et al. to reproduce observed spatial and kinematic variations as a function of metallicity. The study allows for a detailed examination of 3D density distributions, kinematics, and orbital structure of stars in different metallicity bins. The authors find that metal-rich stars with [Fe/H] > -0.5 are strongly barred and have dynamical properties consistent with a common disk origin. In contrast, metal-poor stars with [Fe/H] < -0.5 exhibit strong kinematic variations with metallicity indicating varying contributions from underlying stellar populations. Outside the central kpc (kiloparsec), metal-poor stars are found to have the density and kinematics of a thick disk while in the inner kpc evidence for an extra concentration of metal-poor stars is detected. Finally, combined orbit distributions of all metallicities in the model naturally reproduce observed vertex deviations in the bulge. This paper demonstrates how Made-to-Measure chemodynamical models can be extended to other chemical dimensions making them powerful tools for maximizing information obtained from large spectroscopic surveys such as APOGEE, GALAH, and MOONS.