Mean redshift values with respect to the optical G magnitudes for the 2198 sources with available redshifts. The blue curve is for the sources with X_ρ ≤ 4, and the red curve is for the sources with X_ρ > 4. The error bars show the estimated uncertainties of the mean values. The bin windows of G are shown in the first column in Table 4. The sources with X_ρ > 4 have substantially lower Z at G > 18.5 mag, but higher z at G ≃ 16.5 mag than the sources with X_ρ ≤ 4. The statistics are shown in Tables 4 and 5.