Distribution of the eight overdensity members in rest-frame radial velocity space (lower x-axis) and in radial separations (upper x-axis), assuming the median redshift of the sample as the zero point. Radial separations are computed assuming that the overdensity members have negligible peculiar velocities. Velocity bins are 5 km s⁻¹ wide. Green and yellow bars refer to redshifts measured by MUSE and LUCI, respectively, and the position of the FRII host is also labeled. The four MUSE sources in the arc around the diffuse X-ray emission (m1 − m4) are all concentrated within 450 kpc radial, and the three of them that lie within 60 kpc on the plane of the sky (m2 − m4), also lie within 60 kpc in the radial direction. The typical uncertainty introduced by redshift errors (Δz ± 0.0004, see Table 1) is shown by the horizontal bar.