Galaxy population in distant galaxy clusters. I. Cl 0939+472 (z=0.41) and Cl 0016+161 (z=0.54)

¹ Max-Planck Institut fur Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
² Institut für Astronomie und Astrophysik, Scheinerstraße 1,81689 München, Germany e-mail: belloni@usm.uni-muenchen.de

Send offprint request to: P. Belloni

Received: 13 March 1995
Accepted: 14 December 1995

Abstract

We present results of a study of the galaxy population of Cl 0939+472 and Cl 0016+161 . We have used narrow-band filters (FWHM 90 – 200 Å) and broad band B, R, I filters covering the range from 3800 Å  to 9200 Å  to obtain low resolution spectra for all galaxies brighter than mag in a (Cl 0939+472) and a (Cl 0016+161) field. Template spectra for classical Hubble type and E + A galaxies were fitted to the low-resolution spectral energy distribution in order to determine the galaxies' redshift and the morphological type. We detected 160 cluster members in Cl 0939+472 and 100 in Cl 0016+161, with a success rate of about 80% in the determination of redshifts and corresponding classification of morphological types from spectral energy distributions. These results constitute a statistical improvement of at least a factor of 4 over the most complete study to date of these clusters. In particular, we provide a large sample of elliptical galaxies with secure membership, well suited for a study of evolutionary effects. The same E + A templates developed for the analysis of Cl 0939+472 were successful in recognizing almost all of the spectroscopically already known E + A galaxies in Cl 0016+161 and in identifying 10 new ones. Our results show that in this cluster, too, the fraction of E + A galaxies represents about 20% of the total galaxy population. This outlines the importance of taking into account galaxies with signs of recent star formation for a correct evaluation of the Butcher-Oemler effect in distant galaxy clusters.