Multicolor photometry of clusters of galaxies: A3284, A3305, A1942

Abstract

We present complete multicolor photometry in the Gunn system for the three clusters of galaxies A3284, A3305 and A1942 at redshift z~0.2. INVENTORY magnitudes and colours have been obtained for over 1,000 objects in the three fields down to g=24, and with a good completeness level in the detections (85% or better) about one magnitude brighter. By fitting with King profiles the r counts we derived the total number of galaxies and the core radius down to the r magnitude limit in each cluster. These are N_TOT_=146 galaxies and R_c_=0.24 Mpc for A3284, N_TOT_=129 and R_c_=0.20 Mpc for A3305, N_TOT_=130 and R_c_=0.24 Mpc for A1942. The observed mean redshift of the clusters is z=0.150+/-0.001 for A3284, z=0.157+/-0.001 for A3305, and z=0.226+/-0.001 for A1942. The c-m diagrams and the g-i colour distribution as well as the two-colour diagrams are used to single out early-type galaxies and spirals on the basis of their different photometric properties. This approach aimed at a self-consistent classification of galaxies on the basis of photometric indicators will be further developed for a systematic study of the galaxy population in distant clusters.