Chemodynamical signatures of bar resonances in the Galactic disk: current data and future prospects
Adam Wheeler et al 2022 ApJ 935 28
The Milky Way is a barred disk galaxy: the disk shows a prominent, elongated bar in the centre rotating like a solid body would. In this project, we aim to derive how fast the bar spins (the so-called pattern speed) to place further constraints on the evolution of our Galaxy.
Stars in the disk circulate around the centre describing almost circular orbits. Some of them have periods (or, conversely, frequencies) that agree with that of the bar’s. These are resonant stars, and the bar greatly perturbs their motions. Since astronomical missions only provide current positions and velocities of stars, previous studies had predicted instant dynamical signatures of resonances that are pattern-speed dependent (e.g. [1],[2]), and can therefore be used to derive the latter. We combined these dynamical signatures with the metallicity of stars, an orthogonal source of information yielding the star’s birthplace. We found a chemodynamical diagnostic that not only identifies, but also distinguishes between the different bar resonances that occur across the disk.
This result was applied to Gaia and LAMOST data. We find weak evidence for a slow bar, although constraints from current data are limited by their spatial footprint. Future data sets with greater azimuthal coverage, including the final Gaia data release, will allow reliable chemodynamical identification of bar resonances with this method.