Effect of environment on galaxies mass-size distribution: unveiling the
  transition from outside-in to inside-out evolution
  The distribution of galaxies on the mass-size plane as a function of redshift
or environment is a powerful test for galaxy formation models. Here we use
integral-field stellar kinematics to interpret the variation of the mass-size
distribution in two galaxy samples spanning extreme environmental densities.
The samples are both identically and nearly mass-selected (stellar mass M*>6e9
Msun) and volume-limited. The first consists of nearby field galaxies from the
Atlas3D parent sample. The second consists of galaxies in the Coma Cluster
(Abell 1656), one of densest environments for which good resolved spectroscopy
can be obtained. The mass-size distribution in the dense environment differs
from the field one in two ways: (i) spiral galaxies are replaced by
bulge-dominated disk-like fast-rotator early-type galaxies (ETGs), which follow
the SAME mass-size relation and have the SAME mass distribution as in the field
sample; (ii) the slow rotator ETGs are segregated in mass from the fast
rotators, with their size increasing proportionally to their mass. A transition
between the two processes appears around the stellar mass M_crit=2e11 Msun. We
interpret this as evidence for bulge growth (outside-in evolution) and
bulge-related environmental quenching dominating at low masses, with little
influence from merging, while significant dry mergers (inside-out evolution)
and halo-related quenching driving the mass and size growth at the high-mass
end. The existence of these two processes naturally explains the diverse size
evolution of galaxies of different masses and the separability of mass and
environmental quenching.
