Observed correlations, evolution, and environment dependence of 9000 early-type galaxies in the SDSS

A sample of nearly 9000 early-type galaxies, observed in the g*,r*,i*, and z* bands, was selected from the Sloan Digital Sky Survey using morphological and spectral criteria. The sample spans the redshift range 0 < z < 0.3, and was used to study how early-type galaxy observables, including luminosity, effective radius, surface brightness, color, velocity dispersion, and chemical abundances are correlated with one another, how they evolve, and whether they depend on environment. Relative to the population at z~0.1, the median redshift of the sample, galaxies at lower and higher redshifts have evolved little. The luminosities and colors, the Fundamental Plane, and absorption- line strengths (obtained from co-added spectra of similar objects) suggest that the population is evolving passively, having formed the bulk of its stars about 9 Gyrs ago. While the Fundamental Plane suggests that galaxies in dense regions are slightly different from galaxies in less dense regions, the chemical abundances and color-velocity dispersion relations show no statistically significant environmental dependence. That we are able to measure velocity dispersions at all is a tribute to the quality of the SDSS spectrographs: they exceed the goals for which they were designed.