BRIGHTEST CLUSTER GALAXIES AS STANDARD CANDLES

We investigate the use of brightest cluster galaxies (BCGs) as standar d candles for measuring galaxy peculiar velocities on large scales. We have obtained precise large-format CCD surface photometry and redshif ts for an all-sky, volume-limited (z less than or equal to 0.05) sampl e of 119 BCG. We reinvestigate the Hoessel (1980) relationship between the metric luminosity, L(m), within the central 10 h(-1) kpc of the B CGs and the logarithmic slope of the surface brightness profile, alpha . The L(m)-alpha relationship reduces the cosmic scatter in L(m) from 0.327 mag to 0.244 mag, yielding a typical distance accuracy of 17% pe r BCG. Residuals about the L(m)-alpha relationship are independent of BCG luminosity, BCG B-R(c) color, BCG location within the host cluster , and,richness of the host cluster. The metric luminosity is independe nt of cluster richness even before correcting for its dependence on al pha, which provides further evidence for the unique nature of the BCG luminosity function. Indeed, the BCG luminosity function, both before and after application of the alpha-correction, is consistent with a si ngle Gaussian distribution. Half the BCGs in the sample show some evid ence of small color gradients as a function of radius within their cen tral 50 h(-1) kpc regions but with almost equal numbers becoming redde r as becoming bluer. However, with the central 10 h(-1) kpc the colors are remarkably constant-the mean B-R(c) color is 1.51 with a dispersi on of only 0.06 mag. The narrow photometric and color distributions of the BCGs, the lack of ''second-parameter'' effects, as well as the un ique rich cluster environment of BCGs, argue that BCGs are the most ho mogeneous distance indicators presently available for large-scale stru cture research.