The Evolution of a Mass-selected Sample of Early-Type Field Galaxies

We investigate the evolution of mass-selected early-type field galaxies using a sample of 28 gravitational lenses spanning the redshift range 0 ≲ z ≲ 1. Based on the redshift-dependent intercept of the fundamental plane in the rest-frame B band, we measure an evolution rate of d log(M/L)B/dz = -0.56 ± 0.04 (all errors are 1 σ unless noted) if we directly compare to the local intercept measured from the Coma Cluster. Refitting the local intercept helps minimize potential systematic errors and yields an evolution rate of d log(M/L)B/dz = -0.54 ± 0.09. An evolution analysis of properly corrected aperture mass-to-light ratios (defined by the lensed image separations) is closely related to the Faber-Jackson relation. In the rest-frame B band, we find an evolution rate of d log(M/L)B/dz = -0.41 ± 0.21, a present-day characteristic magnitude of M*0 = -19.70 + 5 log h ± 0.29 (assuming a characteristic velocity dispersion of σDM* = 225 km s-1), and a Faber-Jackson slope of γFJ = 3.29 ± 0.58. The measured evolution rates favor old stellar populations (mean formation redshift ⟨zf⟩ > 1.8 at 2 σ confidence for a Salpeter initial mass function and a flat Ωm = 0.3 cosmology) among early-type field galaxies and argue against significant episodes of star formation at z < 1.