Reduced χ² contours for models using mass-to-light ratios determined from the photometry projected on the six planes corresponding to the four-dimensional space M/L_Disc, M/L_Bulge, R_c and σ. Each plane is chosen to match the parameters derived for model (b). The forbidden area delimited by the condition M/L_Bulge ≤ M/L_Disc is represented as a red triangle in the top left panel. The contours correspond to the following percentile levels [0, 1, 2, 3, 5, 10, 20, 30, 40, 50, 60, 75, 90] of the distribution; these are labelled by reduced χ² values. The different symbols, except the large magenta cross, plotted on the six sub-panels, correspond to 10 of the 12 models presented in Table 5 because models (c) and (d) do not fit within the plot limits. Symbols and their colour are described for each model in Table 5. The size of the symbols is random in order to distinguish the different models when they are superimposed. The large white plus symbols used for model (b), do not match with the isocontour centre because of the forbidden volume. The large magenta cross symbols correspond to the median of the 5 percentile of the χ² distribution.