Luminosity Dependence in the Fundamental Plane Projections of Elliptical Galaxies

We analyze the fundamental plane projections of elliptical galaxies as a function of luminosity, using a sample of approximately 80,000 galaxies drawn from Data Release 4 (DR4) of the Sloan Digital Sky Survey (SDSS). We exclude brightest cluster galaxies (BCGs) from our sample because of a problem with the default pipeline sky subtraction for BCGs. The observables we consider are effective radius (R_o), velocity dispersion (sigma), dynamical mass (M_dyn ~ R_o sigma^2), effective density (sigma^2/R_o^2), and effective surface brightness (mu_o). With the exception of the L-M_dyn correlation, we find evidence of variations in the slope of the fundamental plane projections with luminosity. In particular, the radius-luminosity and Faber-Jackson relations are steeper at high luminosity relative to low luminosity, and the more luminous ellipticals become progressively less dense and have lower surface brightnesses than lower luminosity ellipticals. These variations can be understood as arising from differing formation histories, with more luminous galaxies having less dissipation. Data from the literature on BCGs show that BCGs have radius-luminosity and Faber-Jackson relations steeper than the brightest non-BCG ellipticals in our sample, consistent with significant growth of BCGs via dissipationless mergers. The curvature we find in the Faber-Jackson relation is qualitatively similar to reported curvature in the black hole mass-velocity dispersion (M_BH-sigma) correlation. This similarity is consistent with a roughly constant value of M_BH/M_star over a wide range of early type galaxies, where M_star is the stellar mass