Radial asymmetrical structures in the R, Z plane of LAMOST-Gaia stars in different age populations. Bins in each panel are color-coded as the median radial velocity V_R, with the panels showing different age bins as labeled. The red/blue difference between above-the-plane and below-the-plane represents the asymmetry in radial velocity. The panels showing ages between 2 and 8 Gyr have clear North/South asymmetries in V_R, and these are still apparent at ages of 10–14 Gyr. Each pixel plotted in this figure has at least five stars and the total number is shown in each panel.