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The photometric properties of brightest cluster galaxies

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Caltech Theses and Dissertations
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Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Photometry of a large sample of first-ranked cluster galaxies, obtained with SIT and CCD area photometers, is discussed. The absolute photometric results anchor the bright end of the Hubble diagram; essentially the entire formal error for the method is now due to the distant clusters used. New determinations of the systematic trend of galaxy absolute magnitude with the cluster properties of richness and Bautz-Morgan type are derived. Structural properties of the galaxies are derived from the surface photometric observations. All the structure data support and are interpreted on the dynamical friction evolution model. Twenty-eight percent of the galaxies have multiple component nuclei; the short lifetimes of such systems provide the best available evidence that ongoing evolution actually occurs. Average magnitude and structure evolution rates are derived and used to estimate corrections to the value of q[subscript o] derived from the Hubble diagram. When combined with the expected rate of evolution of the stellar population in the galaxies and accounting for known selection effects in the sample, a true value near the formal value of q[subscript o] = -0.5 is indicated, suggesting an open universe. Correlation of the absolute magnitudes with galaxy structure may be used to eliminate the magnitude dependence on cluster richness and Bautz-Morgan type, and remove the bias introduced into cluster samples by selection procedures. After removal of the trend due to differences in their volution the dispersion in the magnitudes of those brightest cluster galaxies is reduced to σ = 0[...]21 and the scatter in their core radii is σ = 22%.

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