Velocity distributions of the WH15 cluster member galaxies in the four bins of projected transverse distance. These distributions were shifted vertically by an arbitrary amount (−0.2, 0, 0.2 and 0.35), for visual purposes. The coloured points represent the data of the binned background-corrected phase-space diagram and the error bars represent the Poisson noise combined with the error of the background-correction method. The solid lines and the shaded coloured areas show the best-fit models and their errors, respectively.