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
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 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. 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. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2000
- DOI:
- 10.1086/308460
- arXiv:
- arXiv:astro-ph/9911065
- Bibcode:
- 2000ApJ...531..137K
- Keywords:
-
- GALAXIES: CLUSTERS: INDIVIDUAL: ALPHANUMERIC: CL 1358+62;
- GALAXIES: EVOLUTION;
- Astrophysics
- E-Print:
- 27 pages, 8 figures (2 jpg)