Left panel: result of the Monte Carlo calculations. The histogram shows the distribution of the radio-loud BCGs in relaxed clusters after 10⁵ trials. The red dots shows the 3.4σ location of our observed result compared to the random distribution. Right panel: distribution of the BCGs in the w₅₀₀–c₁₀₀ space. Relaxed clusters are shown as blue circles, and are all located in the upper left quadrant; merging clusters are shown as red cicles and occupy the lower right portion. Filled black circles are the radio-loud BCGs, the black crosses show the BCGs with radio emission that have been removed from the analysis (Sect. 3.1). The threshold values to classify clusters as mergers are the same as in C10, i.e., P₃/P₀> 1.2 × 10^-7, w₅₀₀> 0.012 and c₁₀₀< 0.20.