The vertical effects of disc non-axisymmetries from perturbation theory: the case of the Galactic bar

Understand

Evidence for non-zero mean stellar velocities in the direction perpendicular to the Galactic plane has been accumulating from various recent large spectroscopic surveys.

• Previous analytical and numerical work has shown that a "breathing mode" of the Galactic disc, similar to what is observed in the Solar vicinity, can be the natural consequence of a non-axisymmetric internal perturbation of the disc.
• Here we provide a general analytical framework, in the context of perturbation theory, allowing us to compute the vertical bulk motions generated by a single internal perturber (bar or spiral pattern).
• In the case of the Galactic bar, we show that these analytically predicted bulk motions are well in line with the outcome of a numerical simulation.