The Atlas3D project - XX. Mass-size and mass-sigma distributions of
  early-type galaxies: bulge fraction drives kinematics, mass-to-light ratio,
  molecular gas fraction and stellar initial mass function
  We study the (M,sigma) and (M,Re) projections of the thin Mass Plane (MP)
(M,sigma,Re) which describes the distribution of the galaxy population. The
distribution of galaxy properties on the MP is characterized by: (i) a zone of
exclusion described by two power-laws joined by a break at M 3e10 Msun. This
results in a break in the mean M-sigma relation with Msigma^2.3 and M sigma^4.7
at small and large sigma respectively; (ii) a mass M 2e11 Msun which separates
a population dominated by flat fast rotator with disks and spiral galaxies at
lower masses, from one dominated by quite round slow rotators at larger masses;
(iii) below that mass the distribution of ETGs properties tends to be constant
along lines of constant sigma; (iv) it forms a parallel sequence with the
distribution of spiral galaxies; (v) at even lower masses, the distribution of
fast rotator ETGs and late spirals naturally extends to that of dwarf ETGs
(Sph) and dwarf irregulars (Im) respectively. We show via dynamical models that
sigma traces the bulge fraction, which drives the observed trends in M/L,
Hbeta, colour, IMF and molecular gas fraction. We interpret this as due to a
combination of two main effects: (i) an increase of the bulge fraction which
increases sigma and greatly enhances the likelihood for a galaxy to have its
star formation quenched, and (ii) dry merging, increasing galaxy mass along
lines of nearly constant sigma, while leaving the population unchanged.
[Abriged]
