The importance of major mergers in the build up of stellar mass in
  brightest cluster galaxies at z=1
  Recent independent results from numerical simulations and observations have
shown that brightest cluster galaxies (BCGs) have increased their stellar mass
by a factor of almost two between z~0.9 and z~0.2. The numerical simulations
further suggest that more than half this mass is accreted through major
mergers. Using a sample of 18 distant galaxy clusters with over 600
spectroscopically confirmed cluster members between them, we search for
observational evidence that major mergers do play a significant role. We find a
major merger rate of 0.38 +/- 0.14 mergers per Gyr at z~1. While the
uncertainties, which stem from the small size of our sample, are relatively
large, our rate is consistent with the results that are derived from numerical
simulations. If we assume that this rate continues to the present day and that
half of the mass of the companion is accreted onto the BCG during these
mergers, then we find that this rate can explain the growth in the stellar mass
of the BCGs that is observed and predicted by simulations. Major mergers
therefore appear to be playing an important role, perhaps even the dominant
one, in the build up of stellar mass in these extraordinary galaxies.
