stellar mass estimates using version 4.1 of the [kcorrect]{} code [@Blanton2007] which uses templates based on the [@Bruzual2003] models. Briefly, spectral energy distribution fitting is used to derive the $M_{\star}$ of the galaxies by fitting their observed `modelMag` magnitudes (in the $u, g, r, i $ and $z$-bands) against a range of spectral templates from [@Bruzual2003] assuming a [@Chabrier2003] initial mass function. The best-fitting stellar template is determined through $\chi^{2}$-minimization, whereafter a mass-to-light ratio is determined from this template and used to convert the luminosity of the galaxy to stellar mass.

The SALT sample
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We extend the BCG pair fraction analysis out to moderately high redshifts ($0.4 \leq z \leq 0.5$) using the Gaussian Mixture Brightest Cluster Galaxy catalogue [GMBCG[^8]; @Hao2010] with follow-up spectroscopy from the Southern African Large Telescope [SALT; @Buckley2006; @ODonoghue2006]. We require a sample with a high spectroscopic completeness in order to identify pairs that are likely to merge. The spectroscopic completeness of the SDSS drops significantly around $z=0.4$, so we have supplemented the SDSS data with additional redshifts from SALT.

The GMBCG cluster catalogue is a photometrically-identified cluster sample similar to redMaPPer and was used in the early stages of this work. When redMaPPer became 