The Structure of Galaxies: III. Two Structural Families of Ellipticals
  Using isophotal radius correlations for a sample of 2MASS ellipticals, we
have constructed a series of template surface brightness profiles to describe
the profile shapes of ellipticals as a function of luminosity. The templates
are a smooth function of luminosity, yet are not adequately matched to any
fitting function supporting the view that ellipticals are weakly non-homologous
with respect to structure. Through comparison to the templates, it is
discovered that ellipticals are divided into two families; those well matched
to the templates and a second class of ellipticals with distinctly shallower
profile slopes. We refer to these second type of ellipticals as D class, an old
morphological designation acknowledging diffuse appearance on photographic
material. D ellipticals cover the same range of luminosity, size and kinematics
as normal ellipticals, but maintain a signature of recent equal mass dry
mergers. We propose that normal ellipticals grow after an initial dissipation
formation era by accretion of low mass companions as outlined in hierarchical
formation scenarios, while D ellipticals are the result of later equal mass
mergers producing shallow luminosity profiles.
