Top panel: rest-frame velocity vs. projected distance from the cluster center (here the BCGN(NW)). Small/black and large/red squares indicate the member galaxies and those rejected as interlopers by the shifting gapper procedure, respectively. Red crosses indicate ELGs. The two green circles indicate the BCGN(NW) and the BCGN(SE). The large/blue circle indicates the BCG of A1758S using the SDSS redshift. The cyan triangles and rotated triangles indicate galaxies detected as members of HT2 and HT12 subclusters detected through the Htree-method (see Sect. 3.5). Middle and bottom panels: differential (big circles) and integral (small points) profiles of mean velocity and LOS velocity dispersion, respectively. For the differential profiles, we plot the values for six annuli from the center of the cluster, each containing 15 galaxies (large green symbols). For the integral profiles, the mean and dispersion at a given (projected) radius from the cluster-center is estimated by considering all galaxies within that radius – the first value computed on the five galaxies closest to the center. The error bands at the 68% c.l. are also shown. In the lower panel, the horizontal line represents the X-ray temperature (7 keV) estimated from David & Kempner (2004) for the core of the two subclusters, see also Durret et al. (2011), transformed to σ_V assuming the density-energy equipartition between ICM and galaxies, i.e. β_spec = 1 (see Sect. 4).