Left: density plot (grey scale) of P/C vs. ε parameters for all the pixels in the sample for which P/C > 0.85. Contours that contain 68% (1σ), 95% (2σ) and 99% (3σ) of the points are overplotted. Red dots correspond to the values of the pre-selected regions, i.e. before imposing the grouping of at least 9 pixels. Middle: same as before, but this time the overplotted green dots correspond to selected regions, also obeying the grouping criterion. The orange vertical line indicates the cut used for ε (4), while the horizontal line denotes P/C ~ 2.1 parameter, having practically all the selected pixels a higher value than this limit. Right: histogram of ε for pixels with P/C > 0.85 (black), pre-selected pixels (red), selected pixels (green), and for those pre-selected pixels not satisfying the grouping criterion (dotted black). The curve resulting from a Gaussian fit of the black histogram is overplotted in blue.