The Evolution of Early-Type Galaxies in Distant Clusters. I. Surface Photometry and Structural Parameters for 53 Galaxies in the z = 0.33 Cluster Cl 1358+62*

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Abstract
Using wide-field, two-color Hubble Space Telescope (HST) imaging of the cluster Cl 1358+62 (z = 0.33), we derive structural parameters for a large, magnitude-limited sample of cluster members. These structural parameters are combined with accurate velocity dispersions in another paper to investigate the fundamental plane in the cluster. We fit integrated r1/4 laws to the integrated surface brightness profiles and fit two-dimensional r1/4-law model galaxies to the images directly. A comparison of the results from the two methods shows that the derived half-light radii, re, agree very well, with an rms scatter of only 13%. The half-light radii range from approximately 1 to 20 kpc with a median of about 3 kpc (H0 = 65 km s-1 Mpc-1, q0 = 0.1). We investigated the stability of re by comparing the r1/4-law fits to the half-light radii derived using other commonly used surface brightness profiles. In particular, we fit Sersic r1/n laws (finding the best-fit n in the range n = 1-6) and superpositions of r1/4-law bulges with exponential disks. The half-light radii derived from the best-fit Sersic profiles varied with respect to re from the r1/4-law fits by only 1% in the median, but with a standard deviation of more than 40% in re. For the bulge + disk fits, the derived half-light radii were offset from re of the r1/4-law fits by 10% in the mean, also showing a large standard deviation of more than 40%. By comparing the fitted half-light radii from the Sersic laws with those derived from the bulge + disk fitting, one also finds a large scatter of 30%. Based on these tests, we conclude that, in general, half-light radii are only measured with a typical accuracy of 30%-40%. While there are large uncertainties in half-light radii, these do not impact the subsequent fundamental plane analysis because the combination rI0.76, which enters the fundamental plane, is extremely stable. The rms scatter in rI0.76 is less than 3%, regardless of the form of the profile fit to the galaxies. By fitting bulge + disk profiles, 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 the residuals from fitting two-dimensional r1/4-law models directly to the galaxies, in which disklike structures are revealed in about half of the sample. Two of the three E + A galaxies show spiral arm structure.
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