Characterization of the noise in the Faraday volumes of the two polarized sources, J132626+473741 (in blue, also presented in Fig. 7) and 4C+47.38 (in green). The measurements were extracted in the range of Faraday depths 100 rad m⁻² ≤ |ϕ | ≤ 450 rad m⁻² where no polarized signal is expected. Upper panel: histograms of local maxima. The histograms were not normalized since the two regions contain the same number of voxels. The shaded areas correspond to flux values in the top 5% of the distribution. The noise in the Faraday cube of 4C+47.38 is higher than for the other source (the histogram is broader) because the source lies at a greater distance from the center of the field. Lower panel: complementary cumulative distribution function (CCDF) for the same sources as in the first panel. The dots show the actual CCDF and the solid line is the Gaussian fit used to model the distribution at high F (calculated at CCDF(F) ≤ 10⁻², as indicated by the dashed line). The horizontal solid line at CCDF = 0.05 corresponds to the lower limit of the shaded distributions in the upper panel.