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We present a newly found wave--like pattern in mean Galactocentric radialvelocity U_g vs. guiding centre radius R_g or angular momentum L_z of stars inthe RV subsample of Gaia DR2. The short-wave pattern has a wavelength of order1.2 kpc in R_g or 285 kpc km/s in L_z. The pattern shows only weak changes withGalactocentric radius R and little change in strength in particular with thevertical energy E_z of the stars or respectively the distance to the Galacticplane |z|. The pattern is to first order symmetric around the plane, i.e. hasno significant odd terms in z. There is weak phase shift with the patternmoving towards slightly lower L_z (i.e. trailing) with |z| and E_z. However, weobserve a highly significant phase shift in Galactic azimuth phi, which isdifferent for different peaks. The peak around L_z ~ 2100 kpc km/s only shows aweak change with galactic azimuth, while the rest of the pattern shows aclearly detectable shift of d L_z /d phi = (200 +/- 22) kpc km/s/rad. If weconsider all peaks to belong to the same pattern, this would suggest awavenumber m = 4. We further find that the wave-like pattern in U_g appears tobe related to the W vs. L_z pattern detected in Gaia DR1. A comparison of theU_g-L_z wave pattern with changes of U_g vs. R, which have been previouslydiscussed, suggests that the latter can be understood as just the U_g-L_zpattern washed out by blurring (i.e. orbital excursions around theirguiding-centre) of disc stars.

More than just a wrinkle: A wave-like pattern in radial velocity vs. angular momentum from Gaia Data