Fall relation colour coded by η (see Sect. 2.3). Galaxies in rich groups with more than ten members are shown as circles and field galaxies as black squares (both have the redshift cut 0.5 < z < 0.9 applied). The mass model rotation curve is used (see Fig. A.2 for the flat model rotation curve instead). As an indication, the best-fit linear relations (with redshift cut applied, see also Table 1) for the field and rich groups sub-samples are shown as grey and black plain lines, respectively. The typical uncertainty is shown as the black error-bar on the bottom right corner.