ABELL (G8): Abell Galaxy Cluster Catalogs (19911016)
FILES: abell.g8 (4076 galaxy clusters)
abellsup.g8 (1174 galaxy clusters)
CONTENTS: Abell Galaxy Cluster Catalog, version of 19880723
Abell Supplementary Southern Galaxy Clusters
DATASET: These files are part of HyperSky dataset G-3 (G-3.4), version 19911016 Availability on HyperSky CD-ROM: Vol. 1 (1993)
DESCRIPTION: File abell.g8 is a homogeneous all-sky catalog of rich galaxy clusters, nominally complete to redshift z = 0.2 for clusters with populations of 30 or more galaxies in the magnitude range m(3) to m(3) + 2.0, where m(3) is the magnitude of the third-brightest cluster galaxy. The catalog combines a northern survey, originally published by George Abell in 1958, and a southern survey begun by Abell and Harold Corwin in 1975, which (after Abell's unfortunate 1983 death) was completed by Corwin and Ronald Olowin in 1987.
The northern survey was based on visual scans of Palomar Sky Survey red plates to -27 degrees declination. The southern survey was based on visual scans of deep IIIa-J Southern Sky Survey plates taken by the United Kingdom's 1.2-meter Schmidt Telescope at Siding Spring in Australia, for declinations south of -17 degrees. The 275 clusters in the 10-degree overlap zone (-17 to -27 degrees) were used to reduce the southern survey data to the same systems used for the northern survey.
Corwin and Olowin caution that since the catalog is based on purely visual surveys of apparent areal densities of galaxies, it should NOT be taken as a definitive catalog of rich clusters, but rather as a finding list of APPARENT rich clusters which merit further investigation.
File abellsup.g8 contains supplementary clusters from the southern survey [declinations < -17 degrees] which are not rich enough [m(3) + 2 < 30] or too distant [m(3) + 2 > 21] for inclusion in the main catalog. More details on the Abell catalog may be found in Ap. J. Suppl. 70, 1, 1989.
DATA: The HyperSky datafile contains the following data from the catalog:
MAG: The magnitude is m(10)c, that of the 10th brightest cluster galaxy, corrected for interstellar extinction. The magnitudes estimated in the southern survey are total V magnitudes, rather than red magnitudes as estimated by Abell for the northern clusters. The southern V magnitudes have been converted to the system of the northern red magnitudes. The red magnitudes are used to determine the cluster Distance class, discussed below.
IDENTIFICATION: The Abell cluster number.
COMMENTS: The comment line contains the following additional information for each cluster:
* Richness class: Cluster richness is based on a count of galaxies in the magnitude range m(3) to m(3) + 2.0, where m(3) is the magnitude of the 3rd brightest cluster galaxy. The following table shows how richness class is derived from this count:
Population Class Population Class Population Class
30 - 49 0 80 - 129 2 200 - 299 4
50 - 79 1 130 - 199 3 300 or more 5
* Distance class: Cluster distances, needed to determine counting radii, were estimated solely from the magnitude, m(10)c, of the 10th brightest galaxy. This procedure was adopted to provide consistency with Abell's northern survey, and also as a matter of expediency. A table showing distance class as a function of m(10)c follows:
m(10)(c) Class m(10)(c) Class
< 13.3 0 15.7 - 16.4 4
13.3 - 14.0 1 16.5 - 17.2 5
14.1 - 14.8 2 17.3 - 18.0 6
14.9 - 15.6 3 > 18.0 7
* Count: The number of galaxies in the magnitude interval m(3) to m(3) + 2, falling within the "Abell radius". This "counting radius" was based on the distance estimated from the 10th brightest cluster galaxy.
* Diameter: The cluster diameters used on the HyperSky display are based on Distance class, as described in the following table, provided by Dr. Corwin. Diameters are in minutes of arc.
Diameter Class Diameter Class
110' 0 19' 4
65' 1 12' 5
45' 2 9' 6
25' 3 7' 7