Surface photometry of the dominant galaxies in poor clusters

Abstract

Surface photometry in B and R is presented for seven brightest cluster galaxies (BCGs) in poor clusters. The primary goal was to detect diffuse envelopes around the BCGs to determine if they are genuine cD galaxies, which have a diffuse stellar envelope that manifests itself as a break in the brightness profile. The poor cluster BCGs did show breaks in their profiles, but these occurred at brighter magnitudes than in cDs and hence was likely produced by a systematic overestimation of the sky intensity. Based on the de Vaucouleurs parameters the poor cluster BCGs are D galaxies, which lack envelopes. Both poor cluster BCGs and rich cluster cD galaxies show similar isophotal flattening and major axis alignments, and therefore must share common formation processes independent of cluster richness. However, since the poor cluster BCGs likely do not have envelopes, a rich cluster environment is necessary for envelope formation.