We have obtained photometry and spectroscopy of 433 z \leq 0.08 brightest cluster galaxies ( BCGs ) in a full-sky survey of Abell clusters to construct a BCG sample suitable for probing deviations from the local Hubble flow .
The BCG Hubble diagram over 0 < z < 0.08 is consistent to within 2 % of the Hubble relation specified by a \Omega _ { m } = 0.3 , \Lambda = 0.7 cosmology .
This sample allows us to explore the structural and photometric properties of BCGs at the present epoch , their location in their hosting galaxy clusters , and the effects of the cluster environment on their structure and evolution .
We revisit the L _ { m } - \alpha relation for BCGs , which uses \alpha, the log-slope of the BCG photometric curve of growth , to predict the metric luminosity in an aperture with 14.3 kpc radius , L _ { m } , for use as a distance indicator .
Residuals in the relation are 0.27 mag rms .
We measure central stellar velocity dispersions , \sigma, of the BCGs , finding the Faber-Jackson relation to flatten as the metric aperture grows to include an increasing fraction of the total BCG luminosity .
A 3-parameter “ metric plane ” relation using \alpha and \sigma together gives the best prediction of L _ { m } , with 0.21 mag residuals .
The distribution of projected spatial offsets , r _ { x } of BCGs from the X-ray-defined cluster center is a steep \gamma = -2.33 power-law over 1 < r _ { x } < 10 ^ { 3 } kpc .
The median offset is \sim 10 kpc , but \sim 15 % of the BCGs have r _ { x } > 100 kpc .
The absolute cluster-dispersion normalized BCG peculiar velocity | \Delta V _ { 1 } | / \sigma _ { c } follows an exponential distribution with scale length 0.39 \pm 0.03. Both L _ { m } and \alpha increase with \sigma _ { c } . The \alpha parameter is further moderated by both the spatial and velocity offset from the cluster center , with larger \alpha correlated with the proximity of the BCG to the cluster mean velocity or potential center .
At the same time , position in the cluster has little effect on L _ { m } . Likewise , residuals from the metric plane show no correlation with either the spatial or velocity offset from the cluster center .
The luminosity difference between the BCG and second-ranked galaxy , M2 , increases as the peculiar velocity of the BCG within the cluster decreases .
Further , when M2 is a close luminosity “ rival ” of the BCG , the galaxy that is closest to either the velocity or X-ray center of the cluster is most likely to have the larger \alpha . We conclude that the inner portions of the BCGs are formed outside the cluster , but interactions in the heart of the galaxy cluster grow and extend the envelopes of the BCGs .