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Description
We investigate the use of Brightest Cluster Galaxies (BCGs) as standard candles for measuring galaxy peculiar velocities on large scales. We have obtained precise large-format CCD surface photometry and redshifts for an all-sky, volume-limited (z<=0.05) sample of 119 BCG. We reinvestigate the Hoessel (1980ApJ...241..493H) relationship between the metric luminosity, L_m_, within the central 10h^-1^kpc of the BCGs and the logarithmic slope of the surface brightness profile, {alpha}. The L_m_-{alpha} relationship reduces the cosmic scatter in L_m_ from 0.327mag to 0.244mag, yielding a typical distance accuracy of 17% per 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 independent of cluster richness even before correcting for its dependence on {alpha}, 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 single Gaussian distribution. Half the BCGs in the sample show some evidence of small color gradients as a function of radius within their central 50h^-1^kpc regions but with almost equal numbers becoming redder as becoming bluer. However, with the central 10h^-1^kpc the colors are remarkably constant, the mean B-R_c_ color is 1.51 with a dispersion of only 0.06mag. The narrow photometric and color distributions of the BCGs, the lack of "second-parameter" effects, as well as the unique rich cluster environment of BCGs, argue that BCGs are the most homogeneous distance indicators presently available for large-scale structure research.
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