The Evolution of Early-Type Galaxies in Distant Clusters I.: Surface Photometry and Structural Parameters for 53 Galaxies in the z=0.33 Cluster CL1358+62

Abstract

Using HST imaging of CL1358+62 (z=0.33) structural parameters are derived for 53 cluster members. We fit integrated r^{1/4}-laws to the integrated S.B. profiles, and fit two-dimensional r^{1/4}-law model galaxies to the images directly. The results from the two methods agree very well, with an rms scatter of 13% in r_e. The half-light radii range from 1 to 20 kpc, with a median of 3 kpc. We compared r_e from the r^{1/4}-law fits to r_{1/2} derived using other profiles. In particular, we fit Sersic r^{1/n}-laws and superpositions of r^{1/4}-law bulges with exponential disks. The r_{1/2} derived from the best-fit Sersic profiles varied with respect to r_e from the r^{1/4}-law fits by 1% in the median, but with a standard deviation of more than 40%. For the bulge-plus-disk fits, the derived r_{1/2} were offset from r_e of the r^{1/4}-law fits by 10% in the mean, also with a standard deviation of more than 40%. By comparing the Sersic r_{1/2} with those derived from the bulge-plus-disk fitting, that scatter is also large, at 30%. We conclude that r_{1/2} is generally measured with a typical accuracy of 30-40%. The large uncertainties in r_{1/2} do not impact the fundamental plane analysis because the combination r<I>^{0.76}, which enters the fundamental plane, is extremely stable. The rms scatter in r<I>^{0.76} is less than 3%, regardless of the form of the profile fit to the galaxies. We find that the median bulge fraction of the sample is 84% and that the few E+A galaxies in this sample have disks which make up about 10-35% of their total light. These results are consistent with residuals from fitting 2D r^{1/4}-law models directly to the galaxies, in which disk-like structures are revealed in about half of the sample. Two of the three E+A galaxies show spiral arm structure.