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Astron. Astrophys. 323, 337-348 (1997)

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The morphological segregation of galaxies in clusters

III. The distant cluster Cl 0939+4713 (Abell 851) *

S. Andreon ** 1, 2, E. Davoust 2 and T. Heim 2, 3

1 IFCTR-CNR, via Bassini 15, I-20133 Milano, Italy
2 UMR 5572, Observatoire Midi-Pyrénées, 14 Avenue E. Belin, F-31400 Toulouse, France (davoust@obs-mip.fr)
3 Ecole Nationale Supérieure de Lyon, 46 Allées d'Italie, F-69364 Lyon Cedex 07, France (Thomas.Heim@ens.ens-lyon.fr)

Received 2 August 1996 / Accepted 26 November 1996

Abstract

We have performed an isophotal analysis of galaxies in the distant ([FORMULA]) cluster Cl0939+4713 (Abell 851), using post-refurbished Hubble Space Telescope images. Morphological type estimates for the galaxies are given. A rigorous comparison of the properties of the types shows that early-type galaxies in Cl0939+4713 are, within the present statistical or systematic errors, indistinguishable from their counterparts in Coma in all their studied properties, namely ellipticity profile, slope of the color-magnitude relation from the near-ultraviolet to the near-infrared colors, mean surface brightness and luminosity function in the restframe photographic J band, homogeneity in color (around the color-magnitude relation). Furthermore ellipticals and lenticulars are separately homogeneous in their mean surface brightness, and have similar relative mean surface brightnesses in both clusters.

Spirals are overabundant in Cl0939+4713 with respect to Coma, but twice less than previously estimated, and are more similar to field spirals than to cluster spirals. We suggest that the differences in the photometric properties of the spirals in the two clusters arise from differences in cluster gas density distribution which ultimately bring star formation in the spirals to a stop in Coma, but not in Cl0939+4713.

The morphological types are segregated along a privileged direction that coincides with the position angle of the major axis of the outer X-ray isophotes in the cluster, just like in Coma and Perseus.

Key words: galaxies: fundamental parameters; luminosity function, mass function; evolution; cluster: individual: Cl 0939+4713 (Abell 851) – Coma cluster

* Based on observations made with the NASA/ESA Hubble Space Telescope. Table 1 is only available in electronic form at the CDS anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
** Present adress: Osservatorio di Capodimonte, via Moiariello 16, I-80131 Naples, Italy (andreon@cerere.na.astro.it)

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© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998

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