Column-normalised (by sum) 2D histogram of stars in the [M/H]–v_ϕ plane (azimuthal velocity vs metallicity) for all the stars (top), high-α selection (bottom left), and low-α selection (bottom right). The running median track is shown as dashed black line and the 16th and 84th percentile tracks are shown as black lines in all panels. The running median tracks for the low-α panel look more like a step-function, while high-α tracks is shallower, supporting the gradual monotonic increase, that can be interpreted as a gradual spin-up from old proto-Galactic populations to the present day high-α disc with respect to metallicities.