EVOLUTION OF CLUSTER ELLIPTICALS AT 0.2-LESS-THAN-Z-LESS-THAN-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 b y 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 repre sent 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 evolu tion since z = 1, consistent with expectations based on models of pass ively evolving old stellar populations.