  We have analyzed a sample of galaxies belonging to three clusters: Coma,
Abell 85, and Abell 496 (real galaxies) and a sample of simulated elliptical
galaxies formed in a hierarchical merging scheme (virtual galaxies). We use the
Sersic law to describe their light profile. The specific entropy
(Boltzmann-Gibbs definition) is then calculated supposing that the galaxies
behave as spherical, isotropic, one-component systems. We find that, to a good
approximation (about 10%), both real and virtual galaxies have an almost unique
specific entropy. Within this approximation the galaxies are distributed in a
thin plane in the space defined by the three Sersic law parameters, which we
call the Entropic Plane. A further analysis shows that both real and virtual
galaxies are in fact located on a thin line, therefore indicating the existence
of another - and yet unknown - physical property, besides the uniqueness of the
specific entropy. A more careful examination of the virtual galaxies sample
indicates a very small increase of their specific entropy with merging
generation. In a hierarchical scenario, this implies a correlation between the
specific entropy and the total mass, which is indeed seen in our data. The
scatter and tilt of the Entropic Line, defined by Lima Neto et al. (1999a), are
reduced when this correlation is taken into account. Although one cannot
distinguish between various generations for real galaxies, the distribution of
their specific entropy is similar to that in the virtual sample, suggesting
that hierarchical merging processes could be an important mechanism in the
building of elliptical galaxies.
