The importance of major mergers in the build up of stellar mass in brightest cluster galaxies at z=1

TL;DR

This study provides observational evidence that major mergers significantly contribute to the stellar mass growth of brightest cluster galaxies at z=1, aligning with simulation predictions.

Contribution

It offers the first observational estimate of the major merger rate at z=1 and links it to the stellar mass growth of BCGs.

Findings

Major merger rate at z~1 is 0.38 +/- 0.14 mergers per Gyr.

The observed merger rate can explain the stellar mass increase in BCGs.

Results are consistent with numerical simulation predictions.

Abstract

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.