Deprojected PDF of the 3D true intervelocities between members of galaxy pairs in the IGP Catalog (all ρ >  2.5 values). The blue curves are obtained by the deprojection method using two-bin differences (bin of 30 km s⁻¹). The red curves indicate the result of deprojection by moving bins (see text and Nottale & Chamaraux 2018a). The ±1σ uncertainty curves (gray lines) are obtained from simulation of the deprojection process. Both methods agree within error bars. Upper panel: subsample of 11 259 pairs with errors < 70 km s⁻¹. The projected distribution of these pairs is given in Fig. 2. Lower panel: subsample of 6026 pairs having accurate velocities with errors < 20 km s⁻¹. Both subsamples confirm the existence of a large probability peak around ≈150 km s⁻¹, in agreement with the PDFs of fairly (Fig. 4) and highly isolated pair (Fig. 3) intervelocities.