Histogram of X_ρ for the 2490 sources (top), the sources with CARMS < 0.10 (middle), and the sources with CARMS > 0.40 (bottom). The sources with X_ρ > 10 are accounted for in the last bin. The blue curves show the Rayleigh distributions with unit standard deviation. The total number of sources in each of the three samples is shown in black in each panel (top right), and the number of the sources with X_ρ > 3.0 is in red. The straight red lines correspond to X_ρ = 3. The remarkable differences in the distributions of X_ρ between these three groups of sources are the numbers of sources in the last bins, X_ρ > 9.8.