How non-linear scaling relations unify dwarf and giant elliptical
  galaxies
  Dwarf elliptical galaxies are frequently excluded from bright galaxy samples
because they do not follow the same linear relations in diagrams involving
effective half light radii R_e or mean effective surface brightnesses <mu>_e.
However, using two linear relations which unite dwarf and bright elliptical
galaxies we explain how these lead to curved relations when one introduces
either the half light radius or the associated surface brightness. In
particular, the curved <mu>_e - R_e relation is derived here. This and other
previously misunderstood curved relations, once heralded as evidence for a
discontinuity between faint and bright elliptical galaxies at M_B ~ -18 mag,
actually support the unification of such galaxies as a single population whose
structure (i.e. stellar concentration) varies continuously with stellar
luminosity and mass.
