Some new observed properties of elliptical galaxies

We suggest that elliptical galaxies, as stellar systems in a stage of quasi-equilibrium, may have a specific entropy. We use the Sersic law to describe the light profile. The specific entropy (the Boltzmann-Gibbs definition) is then calculated assuming that the galaxy behaves as a spherical, isotropic, one-component system. We predict a relation between the three parameters of the Sersic law linked to the specific entropy, defining a surface in the parameter space, an `entropic plane'. We have analysed a sample of simulated merging elliptical galaxies (virtual) and a sample of galaxies belonging to the Coma Cluster (real). Both virtual and real galaxies are: 1) located in their own `entropic plane' and 2) in this plane, they are located on a straight line, indicating constant entropy: another physical property. A careful examination of the value of the specific entropy indicates a very small increase in the specific entropy with the generation after merging (virtual sample). Although one cannot distinguish between various generations for real galaxies, the distribution of specific entropy in this sample is very similar to that in the virtual sample.