GMM analysis of the proper motion distributions. Upper panels: GMM modelling for the proper motion distribution (μ_l and μ_b, left and right panels, respectively) of the low-extinction group of stars that corresponds to the NSD. The blue lines show the total GMM model whereas the coloured dashed lines indicate each individual Gaussian contributing to the total model. Lower panels: similar to the upper panels but for the high-extinction group of stars corresponding to the NSC.