Evolution of cluster ellipticals at 0.2<z<1.2 from Hubble Space Telescope imaging

Two-dimensional surface photometry derived from Hubble Space Telescope imaging is presented for a sample of 225 early-type galaxies (assumed to be cluster members) in the fields of nine clusters at redshifts 0.17 < z < 1.21. The 94 luminous ellipticals (M(AB)(B) < -20; selected by morphology alone with no reference to color) form tight sequences in the size-luminosity plane. The position of these sequences shifts, on average, with redshift, so that an object of a given size at z = 0.55 is brighter by Delta M(B) = -0.57 +/- 0.13 mag than its counterpart (measured with the same techniques) in nearby clusters. At z = 0.9 the shift is Delta M(B) = -0.96 +/- 0.22 mag. If the relation between size and luminosity is universal, so that the local cluster galaxies represent the evolutionary endpoints of those at high redshift, and if the size-luminosity relation is not modified by dynamical processes, then this population of galaxies has undergone significant luminosity evolution since z = 1, consistent with expectations based on models of passively evolving old stellar populations.