Climbing to the top of the galactic mass ladder: evidence for frequent
  prolate-like rotation among the most massive galaxies
  We present the stellar velocity maps of 25 massive early type galaxies
located in dense environments observed with MUSE. Galaxies are selected to be
brighter than M_K=-25.7 magnitude, reside in the core of the Shapley Super
Cluster or be the brightest galaxy in clusters richer than the Virgo Cluster.
We thus targeted galaxies more massive than 10^12 Msun and larger than 10 kpc
(half-light radius). The velocity maps show a large variety of kinematic
features: oblate-like regular rotation, kinematically distinct cores and
various types of non-regular rotation. The kinematic misalignment angles show
that massive galaxies can be divided into two categories: those with small or
negligible misalignment, and those with misalignment consistent with being 90
degrees. Galaxies in this latter group, comprising just under half of our
galaxies, have prolate-like rotation (rotation around the major axis). Among
the brightest cluster galaxies the incidence of prolate-like rotation is 50 per
cent, while for a magnitude limited sub-sample of objects within the Shapley
Super Cluster (mostly satellites), 35 per cent of galaxies show prolate-like
rotation. Placing our galaxies on the mass - size diagram, we show that they
all fall on a branch extending almost an order of magnitude in mass and a
factor of 5 in size from the massive end early-type galaxies, previously
recognised as associated with major dissipation-less mergers. The presence of
galaxies with complex kinematics and, particularly, prolate-like rotators
suggests, according to current numerical simulations, that the most massive
galaxies grow predominantly through dissipation-less equal-mass mergers.
