AAS Meeting #193 - Austin, Texas, January 1999
Session 38. Galaxy Clusters
Display, Thursday, January 7, 1999, 9:20am-6:30pm, Exhibits Hall 1

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[38.19] Quantitative Measurements of E/S0 Morphology: HST Observations of a cluster at z=0.39

M. Bergmann (University of Texas, Austin), I. Jorgensen (University of Texas, Austin, and Gemini 8-m Telescopes Project, Hilo, HI)

Two-dimensional surface photometry has been derived in two colors for a sample of 88 E and S0 galaxies in the galaxy cluster CL0024+16 at z=0.39. The photometry is based on Hubble Space Telescope archival data. CL0024+16 is one of the original ``Butcher-Oemler'' clusters. It has also been found to have fewer S0 galaxies than are found in nearby rich clusters. We have used the surface photometry to derive effective radii and surface brightnesses, color gradients, ellipticities, as well as Fourier coefficients quantifying the deviations of the isophots from ellipses. We use the mean fourth order cosine coefficient, < c4>, and the apparent ellipticity, to estimate the relative disk luminosity (Ldisk/Ltot) and inclination for each of the galaxies. The relative disk luminosities have a very broad distribution between zero and one. A Kolmogorov-Smirnoff test show that the distribution is best fit with a model distribution where 37% of the galaxies are diskless, and 63% of the galaxies are drawn from a distribution that is uniform in relative disk luminosities from zero to one. We also compare the distribution with the distribution of relative disk luminosities for galaxies in the Coma cluster (Jorgensen & Franx, 1994, ApJ 433,553) and find a 31% probability that the two distributions are drawn from the same parent population. However, the best fitting distribution of relative disk luminosites for the CL0024+16 sample has 37% diskless galaxies, while the best fitting distribution for the Coma sample has only 10 galaxies.


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