Two-dimensional surface photometry has been done for 166 early-type galaxies ( bulge/total luminosity B / T > 0.6 ) in 3 fields of the Canadian Network for Observational Cosmology ( CNOC ) cluster survey .
These galaxies are either spectroscopically confirmed members of clusters at z = 0.23 ( 45 galaxies ) , 0.43 ( 22 ) , and 0.55 ( 16 ) or field galaxies in the same redshift range .
An additional 51 early-type galaxies in the rich cluster Abell 2256 at z = 0.06 were analysed with the same technique .
The resulting structural and surface brightness measurements show that , in the plane of absolute magnitude M _ { AB } ( B ) versus \log R _ { e } ( half-light radius ) , the locus of cluster ellipticals shifts monotonically with redshift so that at redshifts of ( 0.23 , 0.43 , 0.55 ) , galaxies of a given size are more luminous by ( -0.25 \pm 0.10 , -0.55 \pm 0.12 , -0.74 \pm 0.21 ) magnitudes with respect to the same relation measured at z = 0.06 ( adopting q _ { \circ } = 0.5 ) .
There is no evidence that early-type galaxies in the field evolve differently from those in clusters .
If dynamical processes do not substantially modify the size-luminosity relation for early-type galaxies over the observed redshift range , then these galaxies have undergone significant luminosity evolution over the past half of the age of the universe .
The amount of brightening is consistent with passive evolution models of old , single-burst stellar populations .