Results from the CASTLES survey of gravitational lenses

We show that most gravitational lenses lie on the passively evolving fundamental plane for early-type galaxies. For burst star formation models (1 Gyr of star formation, then quiescence) in low Ω0 cosmologies, the stellar populations of the lens galaxies must have formed at zf≳2. Typical lens galaxies contain modest amounts of patchy extinction, with a median differential extinction for the optical (radio) selected lenses of ΔE(B−V)=0.04(0.07) mag. The dust can be used to determine both extinction laws and lens redshifts. For example, the zl=0.96 elliptical lens in MG0414+0534 has an RV=1.7±0.1 mean extinction law. Arc and ring images of the quasar and AGN source host galaxies are commonly seen in NICMOS H band observations. The hosts are typically blue, L≲L* galaxies.