Probability of detection for X-GAP-selected haloes as a function of observables. The three panels show different combinations of flux measured within R_500c, redshift, and velocity dispersion on the x-axis in different colours and with different symbols. The various line styles denote the selection function model in Eq. (15). The error bars account for the Poisson error on the number of total and detected sources. The lines in each panel were shifted by −0.02, −0.01, 0, and 0.01 dex for clarity.