Spatial kinematics of Brightest Cluster Galaxies and their close companions from Integral Field Unit spectroscopy

We present Integral Field Unit (IFU) spectroscopy of four brightest cluster galaxies (BCGs) at z ~ 0.1. Three of the BCGs have close companions within a projected radius of 20 kpc and one has no companion within that radius.We calculate the dynamical masses of the BCGs and their companions to be 1.4 × 10¹¹ < M_dyn(M⊙) < 1.5 × 1012. We estimate the probability that the companions of the BCGs are bound using the observed masses and velocity offsets. We show that the lowest mass companion (1:4) is not bound while the two nearly equal mass (1:1.45 and 1:1.25) companions are likely to merge with their host BCGs in 0.35 Gyr in major, dry mergers. We conclude that some BCGs continue to grow from major merging even at z ~ 0. We analyse the stellar kinematics of these systems using the λ_R parameter developed by the SAURON team. This offers a new and unique means to measure the stellar angular momentum of BCGs and make a direct comparison to other early-type galaxies. The BCGs and their companions have similar ellipticities to those of other early-type galaxies but are more massive. We find that not all these massive galaxies have low λ_Re as one might expect. One of the four BCGs and the two massive companions are found to be fast-rotating galaxies with high angular momentum, thereby providing a new test for models of galaxy evolution and the formation of intracluster light.