available, we switched to using this due to several advantages it offered, such as explicit BCG probabilities, candidate member galaxy probabilities, etc. However, spectroscopic follow-up was already well underway for the GMBCG sample. In this work, we treat them as two independent cluster samples, in the same way as comparing our redMaPPer work with those of others in the literature, and will show that our results are compatible.

We refer the reader to [@Hao2010] for details on the GMBCG catalogue. Briefly, the catalogue spans a redshift range of $0.1 < z < 0.55$ and contains 55 000 clusters, optically identified from the SDSS DR7 [@Abazajian2009] as overdensities of red-sequence galaxies. The positions of the BCGs and the photometric redshifts of their host clusters are provided in the catalogue. Here we are interested in the 4814 BCGs that are found in the redshift range $0.4 \leq z \leq 0.5$.

We use the method outlined in Section \[sec:pair\_selection\] to select the close pairs that are included in the SALT sample. Briefly, all companions within a physical separation distance of 50 kpc and 1.5 magnitudes (in the $i$-band) of the BCGs were retrieved from the DR7 database. The spectroscopic redshifts (if available) of 