Radial Distribution of Stellar Motions in Gaia DR2

TL;DR

This study utilizes Gaia DR2 data to map stellar rotation and vertical velocities across the Milky Way, revealing ridge features linked to spiral arms and oscillations in vertical velocities, enhancing understanding of Galactic dynamics.

Contribution

First detailed maps of stellar velocity distributions as a function of Galactocentric radius using Gaia DR2 data, linking features to Galactic structures.

Findings

Identification of diagonal ridge features in the $V_{rot}$ map.

Detection of radial wave-like oscillations in vertical velocities.

Correlation of features with spiral arms and Galactic bar resonances.

Abstract

By taking advantage of the superb measurements of position and velocity for an unprecedented large number of stars provided in Gaia DR2, we have generated the first maps of the rotation velocity, $V_{\rm rot}$, and vertical velocity, $V_{\rm z}$, distributions as a function of the Galactocentric radius, $R_{\rm gal}$, across a radial range of $5<R_{\rm gal}<12$~kpc. In the $R-V_{\rm rot}$ map, we have identified many diagonal ridge features, which are compared with the location of the spiral arms and the expected outer Lindblad resonance of the Galactic bar. We have detected also radial wave-like oscillations of the peak of the vertical velocity distribution.