Unveiling the formation route of the largest galaxies in the universe
  Observational evidence indicates that the role of gas is secondary to that of
gravity in the formation of the most luminous spheroids inhabiting the centres
of galaxy associations, as originally conjectured in the late 80's/early 90's.
However, attempts to explain the origin of the Fundamental Plane (FP) of
massive early-type galaxies (ETGs) -- a tilted version of the scaling relation
connecting the size, velocity dispersion and mass of virialized homologous
systems -- based on sequences of pairwise mergers, have systematically
concluded that dissipation cannot be ignored. We use controlled simulations of
the previrialization stage of galaxy groups to show that multiple collisionless
merging is capable of creating realistic first-ranked galaxies. Our mock
remnants define a thin FP that perfectly fits data from all kinds of giant ETGs
in the local volume, showing the existence of a unified relationship for these
systems. High-ranked galaxies occupy in the FP different areas than standard
objects, a segregation which is viewed essentially as zero-point offsets in the
2D correlations arising from standard projections of this plane. Our findings
make a strong case for considering hierarchical dissipationless merging a
viable route for the formation of the largest galaxies in the universe.
