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2.2. Redshifts

The clusters in the Abell (1958) catalog were assigned to distance groups, based on the redshift estimated from the magnitude of the tenth brightest galaxy in the cluster. Leir and van den Bergh (1977) have given improved estimates of redshifts for 1889 rich Abell clusters, using the magnitudes of the first and tenth brightest galaxies, and an estimate of the cluster radius. Their distance scale is calibrated using measured redshifts for 101 clusters. Photometric distance estimators derived from a larger sample of redshifts have been given by Sarazin et al. (1982). Similarly, clusters in the Zwicky catalog were placed in distance groups, based on the magnitudes and sizes of the brightest cluster galaxies.

Spectroscopic redshifts are now available for about 500 Abell clusters. Sarazin (1986a, Table I) gives an extensive list of the redshifts for Abell clusters, taken primarily from Sarazin et al. (1982), Noonan (1981), Struble and Rood (1982, 1985), and Hoessel, Gunn, and Thuan (1980).

Of course, many redshifts are known for non-Abell clusters as well. The compilation of Noonan (1981) includes many such redshifts.

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