Evolution in the Cluster Early - Type Galaxy Size - Surface Brightness Relation at Z ≃

We investigate the evolution in the distribution of surface brightness, as a function of size, for elliptical and S0 galaxies in the two clusters RDCS J1252.9-2927, z = 1.237 and RX J0152.7-1357, z = 0.837. We use multi-color imaging with the Advanced Camera for Surveys on the Hubble Space Telescope to determine these sizes and surface brightnesses. Using three different estimates of the surface brightnesses, we find that we reliably estimate the surface brightness for the galaxies in our sample with a scatter of < 0.2 mag and with systematic shifts of 0.05 mag. We construct samples of galaxies with early-type morphologies in both clusters. For each cluster, we use a magnitude limit in a band which closely corresponds to the rest-frame B, to magnitude limit of M B = −18.8 at z = 0, and select only those galaxies within the color-magnitude sequence of the cluster or by using our spectroscopic redshifts. We measure evolution in the rest-frame B surface brightness, and find −1.41 ± 0.14 mag from the Coma cluster of galaxies for RDCS J1252.9-2927 and −0.90 ± 0.12 mag of evolution for RX J0152.7-1357, or an average evolution of (−1.13 ± 0.15)z mag. Our statistical errors are dominated by the observed scatter in the size-surface brightness relation, σ = 0.42 ± 0.05 mag for RX J0152.7-1357 and σ = 0.76 ± 0.10 mag for RDCS J1252.9-2927. We find no statistically significant evolution in this scatter, though an increase in the scatter could be expected. Overall, the pace of luminosity evolution we measure agrees with that of the Fundamental Plane of early-type galaxies, implying that the majority of massive early-type galaxies observed at z ≃ 1 formed at high redshifts. The apparent evolution in the colors and magnitudes of early-type cluster galaxies has long been used as a test of the history of galaxy evolution. The relations between magnitude and size or velocity dispersion play an important role, as they give the observer a way to predict the apparent luminosity of a galaxy based on some other observable property Using these scaling relations, it has been observed that there is remarkable uniformity in cluster early-type galaxy properties at low redshifts, z 0.2, (Sandage & Perelmuter 1991; Jørgensen et al. 1996; Bernardi et al. 2003, for example). At redshifts up to ≃ 1, there have been a number of papers that have established a decrease in the mass-to-light ratio, …