Angular momenta, dynamical masses, and mergers of brightest cluster galaxies

Abstract

Using the VIMOS integral field unit (IFU) spectrograph on the Very Large Telescope, we have spatially mapped the kinematic properties of 10 nearby brightest cluster galaxies (BCGs) and 4 BCG companion galaxies located within a redshift of z = 0.1. In the hierarchical formation model, these massive galaxies (1010.5 M ⊙ < M dyn < 10 11.9 M ⊙) are expected to undergo more mergers than lower mass galaxies, and simulations show that dry minor mergers can remove angular momentum. We test whether BCGs have low angular momenta by using the λRe parameter developed by the SAURON and ATLAS3D teams and combine our kinematics with Sloan Digital Sky Survey photometry to analyze the BCGs' merger status. We find that 30% (3/10) of the BCGs and 100% of the companion galaxies (4/4) are fast rotators as defined by the ATLAS 3D criteria. Our fastest rotating BCG has a λ Re = 0.35 ± 0.05. We increase the number of BCGs analyzed from 1 in the combined SAURON and ATLAS3D surveys to 11 BCGs total and find that above Mdyn ∼ 11.5 M⊙, virtually all galaxies, regardless of environment, are slow rotators. To search for signs of recent merging, we analyze the photometry of each system and use the G-M 20 selection criteria to identify mergers. We find that 40% ± 20% of our BCGs are currently undergoing or have recently undergone a merger (within 0.2 Gyr). Surprisingly, we find no correlation between galaxies with high angular momentum and morphological signatures of merging. © 2013. The American Astronomical Society. All rights reserved.