Upper panel: probability distribution function of the 3D true intervelocities between members of galaxy pairs (i.e., orbital velocities of the galaxies in the pairs) in the IGP Catalog, deprojected from the radial velocity differences, for the subsample of 4268 highly isolated pairs ρ >  10 (see text). The deprojection method used here is the two-bin difference, with bins of 28, 30, 32, and 34 km s⁻¹. Whatever the bin width, probability peaks at ≈150 km s⁻¹ and ≈360 km s⁻¹ appear in a stable way. Lower panel: deprojected PDF of the 3D true intervelocities between members of galaxy pairs in the IGP Catalog, for the subsample of highly isolated pairs ρ >  10, where an additional selection has accurate velocities (errors < 20 km s⁻¹, 1859 pairs). The deprojection uses the moving bin method; the numbers are the density in effective bins of 1 km s⁻¹. The error is estimated from 50 numerical simulations (see text). The upper and lower panels agree on the existence of the main peak at 150 km s⁻¹ and possibly another lower one at ≈360 km s⁻¹.