The bright galaxy population of five medium redshift clusters^*

I. Color–magnitude relation, blue fractions, and visual morphology

¹ Instituto de Astrofísica de Andalucía-CSIC, Camino Bajo de Huetor 50, CP 18008 Granada, Spain e-mail: [ascaso;moles;jesusvl]@iaa.es
² Instituto de Astrofísica de Canarias, C/ via Láctea S/N CP La Laguna, Spain e-mail: [jalfonso;ruben]@iac.es

Received: 18 February 2008
Accepted: 28 May 2008

Abstract

Aims. Using data from five clusters of galaxies within the redshift range , imaged with the Nordic Optical Telescope (NOT) in the central ≈1 Mpc² in very good seeing conditions, we have performed an exhaustive inspection of their bright galaxy population. That range of redshift, where only a small amount of data with the required resolution and quality is available, is particularly important for the understanding of the formation and evolution of clusters of galaxies.

Methods. We have inspected the color-magnitude relation (CMR) for those clusters and measured the blue fraction of galaxies in their cores to check for evidence of evolution as found in other works. Visual classification of the galaxy morphology has been performed and the morphology-radius relation examined.

Results. We have not found signs of evolution either in the slope of the CMR or in the blue fraction of galaxies. A diversity of situations regarding those parameters and in the morphological mixing has been noticed, with two out of five clusters containing a dominant late-type core population. The cluster A1878 stands out as some of its properties differ from those of the other clusters in the sample.

Conclusions. No clear signs of evolution appear in our analysis. The data support the view that the morphology and the stellar content of the galaxies in our clusters already have been settled at . Only the fraction of interacting galaxies in the clusters appear to be larger than in clusters like Coma, although the number of clusters in the sample is too small to give a definitive conclusion.