R-band luminosity function of members considered galaxies (see Fig. 7). The black histogram represents the observed data (bin width: 1 mag). The red dotted line is a binning-independent representation of the counts (Epanechnikov kernel of 1 mag bin width), while the red solid line is its completeness-corrected (see Sect. 3.1) counterpart with the 1σ uncertainty limits (dashed). The vertical dotted line is our 50% completeness limit at M_R = −10.5  mag. For comparison, some faint end slopes are illustrated in the top left corner of the plot. The best fit slope to our data is α ~ −1.3, see text.