Relation between diagonal ridges and the moving groups in N-body simulation. (a): density distribution in the (R, v_ϕ) plane for stars selected in a 10° azimuthal cone (see Fig. 3). Coloured lines represent the selected spiral arm regions in guiding coordinates (see Fig. 3d). White vertical lines limit the SNd-like region at 8 ± 0.2 kpc. (b): same as in (a), but transformed into R_g-v_ϕ coordinates. (c): phase-space (v_R,v_ϕ) density distribution for stars in the SNd-like region between the white lines in (a). (d): coloured density contours highlight the positive overdensities in (v_R,v_ϕ) coordinates after unsharp masking of the density distribution in (c). The colours of the (v_R,v_ϕ) overdensities are chosen to match the angular momentum (guiding radius) of the large-scale selections made in (X_g,Y_g) (see Fig. 3d) and thus provide correspondence between the local SNd-like (v_R,v_ϕ) features and large-scale (R, v_ϕ) ridges shown in (panel a).