A deep imaging survey of brightest cluster galaxies

grantor: University of TorontoA deep imaging survey of brightest cluster galaxies (BCGs) has been completed. We present results of B and R band surface photometry for 25 BCGs, many of which have been classified as "cD" galaxies. Data were obtained using a large format CCD (2048 x 2048 pixels) and 0.9 m telescope. This arrangement was capable of imaging the enormous spatial extent of these objects. The isophotes of the BCGs were modeled with elliptical contours, and used to produce a set of surface brightness profiles. Fits of the profiles showed that the Sersic (1968) law best described our data. Two-component models of the "cD" profiles also showed a good agreement between the models and the data. Parametrisations of our profiles have yielded two distinct classes of BCGs based upon the amplitude of their effective radii, $r\sb{e}.$ The large $r\sb{e}$ BCGs are called diffuse BCGs, and are similar, but not identical, to the classical definition of a cD. The parent clusters of our diffuse BCGs coincides with the list of clusters with flat, faint-end luminosity functions (Lopez-Cruz 1997), suggesting that the two properties may be related. We present a model in which the growth of these galaxies is governed by the destruction of dwarf galaxies within the cluster. The remaining BCGs form a class of objects with a different formation history, possibly linked to the merging of several large galaxy units early in the cluster collapse. The colour profiles have shown that there are detectable blueward colour gradients in BCGs, in agreement with the data seen in ordinary ellipticals. We have confirmed that BCGs are aligned with their parent clusters by estimating the orientations of these clusters from their distribution of galaxies. This alignment suggests that cluster formation and BCG formation are linked, and is predicted from formation mechanisms of both types of BCGs.Ph.D