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

Abstract

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. The mean vertical motions induced by the Milky Way bar are small (mean velocity of less than 1 km/sec) and cannot be responsible alone for the observed breathing mode, but they are existing. Our analytical treatment is valid close to the plane for all the non-axisymmetric perturbations of the disc that can be described by small-amplitude Fourier modes. Further work should study how the coupling of multiple internal perturbers and external perturbers is affecting the present analytical results.

9 pages, 6 figures, accepted for publication in MNRAS. Error corrected, figures updated, added term in Eqs. 10 and 18 with no consequences on the conclusions

References in corpus (8)

• The Local Dark Matter Density
• Rings and Radial Waves in the Disk of the Milky Way
• Bending and Breathing Modes of the Galactic Disk
• Radial and vertical flows induced by galactic spiral arms: likely contributors to our "wobbly Galaxy''
• Origin and evolution of moving groups I. Characterization in the observational kinematic-age-metallicity space
• Weighing the local dark matter with RAVE red clump stars
• The power spectrum of the Milky Way: Velocity fluctuations in the Galactic disk
• The Vertical Structure and Kinematics of Grand Design Spirals

Cited by in corpus (6)

• The Canada-France Imaging Survey: First results from the u-band component
• Staying away from the bar: the local dynamical signature of slow and fast bars in the Milky Way
• Spontaneous generation of bending waves in isolated Milky Way-like discs
• Milky Way Tomography with K and M Dwarf Stars: the Vertical Structure of the Galactic Disk
• Distribution functions for resonantly trapped orbits in the Galactic disc
• A Map of the Local Velocity Substructure in the Milky Way Disk