Friske, JKS; Schönrich, R; (2019) More than just a wrinkle: a wave-like pattern in Ug versus Lz from Gaia data. Monthly Notices of the Royal Astronomical Society , 490 (4) pp. 5414-5423. 10.1093/mnras/stz2951.

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Abstract

We present a newly found wave-like pattern in mean Galactocentric radial velocity U¯¯¯¯g versus guiding centre radius Rg or angular momentum Lz of stars in the RV subsample of Gaia DR2. The short-wave pattern has a wavelength of order 1.2kpc in Rg or 285kpckms−1 in Lz. The pattern shows only weak changes with Galactocentric radius R and little change in strength in particular with the vertical energy Ez of the stars or the distance to the Galactic plane |z|. The pattern is to first order symmetric around the plane, i.e. has no significant odd terms in z. There is a weak phase shift with the pattern moving towards slightly lower Lz (i.e. trailing) with |z| and Ez. However, we observe a highly significant phase shift in Galactic azimuth ϕ, which is different for different peaks. The peak around Lz∼2100kpckms−1 only shows a weak change with ϕ, while the rest of the pattern shows a clearly detectable shift of dLz/dϕ=(200±22)kpckms−1rad−1⁠. If we consider all peaks to belong to the same pattern, this would suggest a wavenumber m = 4. We further find that the wave-like pattern in Ug appears to be related to the W¯¯¯¯¯ versus Lz pattern detected in Gaia DR1. A comparison of the U¯¯¯¯g−Lz wave pattern with changes of U¯¯¯¯g versus R, which have been previously discussed, suggests that the latter can be understood as just the U¯¯¯¯g−Lz pattern washed out by blurring (i.e. orbital excursions around their guiding centre) of disc stars.

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