The wobbly Galaxy: kinematics north and south with RAVE red clump giants

TL;DR

This study uses RAVE data to analyze stellar kinematics in the solar neighborhood, revealing velocity gradients and wave-like vertical motions, with detailed error analysis and North-South asymmetries.

Contribution

It provides new detailed measurements of 3D stellar velocity structures and gradients, highlighting wave-like vertical motions and North-South differences in the Galactic disk.

Findings

Confirmed a gradient in mean Galactocentric radial velocity VR, more pronounced below the plane.

Detected wave-like vertical velocity VZ with a rarefaction-compression pattern.

Identified North-South differences in VR and VZ velocities.

Abstract

The RAVE survey, combined with proper motions and distance estimates, can be used to study in detail stellar kinematics in the extended solar neighbourhood (solar suburb). Using the red clump, we examine the mean velocity components in 3D between an R of 6 and 10 kpc and a Z of -2 to 2 kpc, concentrating on North-South differences. Simple parametric fits to the R, Z trends for VPHI and the velocity dispersions are presented. We confirm the recently discovered gradient in mean Galactocentric radial velocity, VR, finding that the gradient is more marked below the plane, with a Z gradient also present. The vertical velocity, VZ, also shows clear structure, with indications of a rarefaction-compression pattern, suggestive of wave-like behaviour. We perform a rigorous error analysis, tracing sources of both systematic and random errors. We confirm the North-South differences in VR and VZ along the line-of-sight, with the VR estimated independent of the proper motions. The complex three-dimensional structure of velocity space presents challenges for future modelling of the Galactic disk, with the Galactic bar, spiral arms and excitation of wave-like structures all probably playing a role.