Radial Distribution of Stellar Motions in Gaia DR2
  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.
