The Fundamental Plane of Gravitational Lens Galaxies and The Evolution of Early‐Type Galaxies in Low‐Density Environments

Most gravitational lenses are early-type galaxies in relatively low densityenvironments -- a ``field'' rather than a ``cluster'' population. We show thatfield early-type galaxies with 0 < z < 1, as represented by the lens galaxies,lie on the same fundamental plane as those in rich clusters at similarredshifts. We then use the fundamental plane to measure the combinedevolutionary and K-corrections for early-type galaxies in the V, I and H bands.Only for passively evolving stellar populations formed at z > 2 (H_0=65 km/sMpc, Omega_0=0.3, Lambda_0=0.7) can the lens galaxies be matched to the localfundamental plane. The high formation epoch and the lack of significantdifferences between the field and cluster populations contradict many currentmodels of the formation history of early-type galaxies. Lens galaxy colors andthe fundamental plane provide good photometric redshift estimates with anempirical accuracy of -0.03 +/- 0.11 for the 17 lenses with known redshifts. Amass model dominated by dark matter is more consistent with the data thaneither an isotropic or radially anisotropic constant M/L mass model, and aradially anisotropic model is better than an isotropic model.Comment: 36 pages, 9 figures, 6 tables. ApJ in press. Final version contains more observational dat