The EFIGI catalogue of 4458 nearby galaxies with morphology II.
  Statistical properties along the Hubble sequence
  The EFIGI catalogue of 4458 galaxies provides a reference database of the
morphological properties of nearby galaxies, with 16 shape attributes
describing their various dynamical components, their texture and environment,
and with a dense sampling of all Hubble types. This catalogue allows us to
derive a quantitative description of the Hubble Sequence in terms of the
specific morphological features of the various types. The variations of the
EFIGI morphological attributes with type confirm that the visual Hubble
sequence is a decreasing sequence of bulge-to-total ratio and an increasing
sequence of disk contribution to the total flux. There is nevertheless a large
dispersion of approximately 5 types for a given bulge-to-total ratio, due to
the fact that the Hubble sequence is primarily based on the strength and pitch
angle of the spiral arms, independently from the bulge-to-total ratio. The
grand spiral design is also related to a steep decrease in visible dust from
types Sb to Sbc-Sc. In contrast, the scattered and giant HII regions show
different strength variation patterns; hence, they do not appear to directly
participate in the establishment of the Hubble sequence. The distortions from a
symmetric profile also incidentally increase along the sequence. Bars and inner
rings are frequent and occur in 41% and 25% of disk galaxies resp. Outer rings
are twice less frequent than inner rings, and outer pseudo-rings occur in 11%
of barred galaxies. Finally, we find a smooth decrease in mean surface
brightness and intrinsic size along the Hubble sequence. The largest galaxies
are cD, Ellipticals and Sab-Sbc spirals, whereas Sd and later spirals are
nearly twice smaller. S0 are intermediate in size, and Im, cE and dE are
confirmed as small objects. Dwarf spiral galaxies of type Sa to Scd are rare in
the EFIGI catalogue, we only find 2 such objects.
