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Groups and Clusters of Galaxies

Groups and Clusters of Galaxies - redshift more or less 1...

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Groups and Clusters of Galaxies The earliest studies (back to the Messier catalog, had anyone known what all those blobs in the spring sky meant) showed that clumps of galaxies exist - such as the prominent ones in Virgo and Coma. It was long held that only a small fraction of galaxies were involved, so that clusters would be rare collections superimposed on a smooth "field". All-sky surveys (such as those from large Schmidt telescopes) changed this view. The distribution of galaxies to a given magnitude shows considerable structure, as shown in this map from Sharp 1986 (PASP 98, 740, from the ADS) for galaxies to B=14.5 (merging the UGC, ESO, and MCG catalogs): Abell (1958, ApJSuppl 3, 211) identified 2712 rich clusters on the Palomar survey plates, producing the basic sample for later statistical studies. Abell based his rough classifications on the number of cluster members within an Abell radius (which scales with the expected cluster
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Unformatted text preview: redshift, more or less 1 Mpc) and the number of members within 3 magnitudes of the brightest galaxy, assigning richness and distance classes to each cluster. Zwicky and coworkers ( Catalog of Galaxies and Clusters of Galaxies = CGCG, vols. 1-6, 1961-68) found many looser clusters. The Abell clusters have been tabulated with up-to-date information by Struble and Rood 1987 (ApJSuppl 63, 543 and 555). The survey of clusters was extended to the southern sky by Abell, Corwin, and Olowin 1989 (ApJSuppl 70, 1; CDS digital version ), producing the first reasonably complete all-sky catalog of nearby clusters (some as far away as z =0.4). The Abell survey was remarkably reliable, with only about 10% of the clusters at z < 0.1 being fakes produced by superpositions of sparser groupings (Katgert et al. 1996 A&A 310, 8)....
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