We identify close companions of Brightest Cluster Galaxies ( BCGs ) for the purpose of quantifying the rate at which these galaxies grow via mergers .
By exploiting deep photometric data from the CFHTLS , we probe the number of companions per BCG ( N _ { c } ) with luminosity ratios down to those corresponding to potential minor mergers of 20:1 .
We also measure the average luminosity in companions per galaxy ( L _ { c } ) .
We find that N _ { c } and L _ { c } rise steeply with luminosity ratio for both the BCGs , and a control sample of other bright , red , cluster galaxies .
The trend for BCGs rises more steeply , resulting in a larger number of close companions .
For companions within 50 kpc of a BCG , N _ { c } = 1.38 \pm 0.14 and L _ { c } =2.14 \pm 0.31 \times 10 ^ { 10 } L _ { \odot } and for companions within 50 kpc of a luminosity matched control sample of non-BCGs , N _ { c } =0.87 \pm 0.08 and L _ { c } =1.48 \pm 0.20 \times 10 ^ { 10 } L _ { \odot } .
This suggests that the BCGs are likely to undergo more mergers compared to otherwise comparable luminous galaxies .
Additionally , compared to a local sample of luminous red galaxies , the more distant sample presented in this study ( with redshifts between 0.15-0.39 , ) shows a higher N _ { c } , suggesting the younger and smaller BCGs are still undergoing hierarchical formation .
Using the Millennium Simulations we model and estimate the level of contamination due to unrelated cluster galaxies .
The contamination by interloping galaxies is 50 % within projected separations of 50 kpc , but within 30 kpc , 60 % of identified companions are real physical companions .
We conclude that the luminosity of bound merger candidates down to luminosity ratios of 20:1 could be adding as much as 10 % to the mass of a typical BCG over 0.5 Gyr at redshifts of z \sim 0.3 .