The Structure of Brightest Cluster Members. III. cD Envelopes

Single-band photographic and CCD surface photometry is used to determine luminosity and structural properties of the extended, faint envelopes around 27 cD galaxies. The distribution of envelope light follows a similar slope (I proportional to r^-1.6^) as other cluster luminous material (i.e., galaxies). Several correlations between envelope luminosity and cluster properties (richness, cluster X-ray luminosity, Bautz-Morgan type, and Rood-Sastry type) substantiate arguments for the dynamical formation of envelopes. A correlation between underlying galaxy luminosity and envelope luminosity implies a parallel but separate process between the growth of the first-ranked elliptical by mergers and cD envelope formation. Strong color gradients, in particular the blue disk colors as predicted by other studies, were not found upon examination of multicolor profiles for three cD envelopes.