A New Model for the Milky Way Bar

TL;DR

This paper develops a self-consistent dynamical model of the Milky Way's bar using Schwarzschild's method, fitting observational data and predicting proper motions, with implications for future Gaia observations.

Contribution

It introduces a new dynamical model of the Galactic bar that matches multiple observational datasets and predicts proper motions, advancing understanding of the bar's structure and dynamics.

Findings

Best-fit pattern speed: 60 km/s/kpc

Model reproduces density and velocity data from BRAVA

Proper motion predictions exceed current observations in some regions

Abstract

We use Schwarzschild's orbit-superposition technique to construct self-consistent models of the Galactic bar. Using $\chi^2$ minimisation, we find that the best-fit Galactic bar model has a pattern speed $\Omega_{\rm p}=60 \rm{km s^{-1} kpc^{-1}}$, disk mass $\rm{M_{\rm d}=1.0\times10^{11}M_{\odot}}$ and bar angle $\theta_{\rm bar}=20^{\circ}$ for an adopted bar mass $\rm{M_{\rm bar}=2\times10^{10}M_{\odot}}$. The model can reproduce not only the three-dimensional and projected density distributions but also velocity and velocity dispersion data from the BRAVA survey. We also predict the proper motions in the range $l=[-12^{\circ},12^{\circ}]$, $b=[-10^{\circ},10^{\circ}]$, which appear to be higher than observations in the longitudinal direction. The model is stable within a timescale of 0.5 Gyr, but appears to deviate from steady-state on longer timescales. Our model can be further tested by future observations such as those from GAIA.