ABEL1400 (E0): 1400 MHz Abell Galaxy Cluster Survey (19950129)
FILE: abel1400.e0 (957 sources)
CONTENTS: 1400 MHz Abell Galaxy Cluster Survey; Owen et al, 1982
DATASET: This file comes in HyperSky dataset E-18, version 19950129 Availability on HyperSky CD-ROM: Vol. 2 (1995)
DESCRIPTION: This datafile contains the results of a radio survey of Abell galaxy clusters carried out by the Green Bank 91-meter telescope at 1400 MHz (1.4 GHz or 20cm) with an angular resolution of 10'x11' (RAxDEC). The catalog extends the sample of clusters originally published in Owen (1974). The primary survey goals were to observe all Abell clusters with m10 (magnitude of the tenth brightest cluster galaxy) less than or equal to 17.0 and declinations north of -19 degrees, to observe all clusters with a richness class GE 3 regardless of m10, and to obtain observations of a representative sample of the rest of the catalog (m10 GE 17.0; richness LE to 2).
It should be emphasized that within the set of 957 observed sources, there are a significant number of cases in which there are multiple 1400 MHz sources per Abell cluster. The total number of Abell clusters actually detected in this survey is about 440.
The HyperSky file is based on the version of the catalog available through the U.S. National Space Sciences Data Center (NSSDC) as Astronomical Data Center (ADC) catalog #8029. HyperSky dataset G-3 contains the Abell galaxy cluster catalog itself; see its associated manual page for further information on Abell clusters.
DATA: The HyperSky datafile contains the following data from the catalog:
POSITION: Right Ascension and Declination are based on the catalog 1950 radio source positions, precessed to equinox 2000. Catalog positions were provided to an accuracy of 0.1 second in Right Ascension and 1" in declination. Catalog cluster sources range in declination from -19.1 <= Dec < +83.1.
MAG: No true magnitudes can be provided for the 1400 MHz sources. A set of artificial magnitudes is provided, however, in the HyperSky catalog strictly to allow use of HyperSky's limiting-magnitude controls. In this way, you can display only those 1400 MHz sources above a desired threshold. The artificial magnitude system is based on the relation (from Pogson) used to define visual magnitudes:
m1 - m2 = 2.5 * log10(S1/S2)
where { m1, m2 } are magnitudes, and { S1, S2 } are source strengths. For the HyperSky catalog, the brightest source (S1 = 45.64 Jy) is arbitrarily assigned the magnitude m1 = 1.0. Given this, any other source S2 can have its relative magnitude, m2, derived using the relation:
1.0 - m2 = 2.5 * log10(45.64/S2)
or
m2 = 1.0 + 2.5 * log10 (45.64/S2)
In this system, the faintest catalog source (0.08 Jy) has a magnitude of 7.9. The following table summarizes the relation between magnitude and source strength for catalog extremes and intermediate magnitudes:
Magnitude Source Strength (Jy)
----------|----------------------
1.0 45.64 (brightest source; in Abell 780)
2.3 13.7
2.9 7.65
4.0 2.93
5.0 1.15
6.0 0.45
7.0 0.18
7.9 0.08 (faintest source)
With the above table, you can set HyperSky's limiting magnitude (for emission sources) to mask out catalog sources below a desired strength. Except for this use, the derived source magnitudes have NO significance. It should be emphasized again that the magnitudes are NOT provided in the original catalog; only the source strengths are fundamental catalog values.
IDENTIFICATION: The number of the Abell cluster containing the detected source. Since a cluster can contain multiple sources, this identification is not unique. Hence the actual source position must be used for unique identification of sources.
COMMENTS: The comment lines contain the following information, provided if available for each cluster radio source:
* The richness and distance classes of the associated Abell cluster. Cluster richness is related to the number of cluster galaxies, and ranges from 0 (30-49 galaxies) to 5 (300 or more). The cluster distance class is based solely from the magnitude, m(10)c, of the 10th brightest galaxy, ranging from 0 (mag<13.3) to 7 (mag>18.0).
For a more complete explanation of richness and distance classes, see the manual page for the HyperSky version of the Abell galaxy cluster catalog.
* A line giving the magnitude of the 10th brightest galaxy in the Abell cluster containing the radio source. This magnitude (and its galaxy) are characteristic of the cluster, but not related directly to the radio source.
* A line giving the estimated redshift, z, of the Abell galaxy cluster. This redshift was estimated using using the method of Corwin (1974) including a richness correction. This value is characteristic of the cluster, but not related directly to the radio source.
* A line giving the 1400 MHz flux strength of the radio source. Measurement units are janskys (Jy, originally flux units). One jansky equals 1E-26 watt per square meter per hertz.
* A line giving the approximate angular size of the 1400 MHz radio source. The values refer to source size after deconvolution with the radio telescope beam.
REFERENCES: A 1400-MHz Survey of 1478 Abell Clusters of Galaxies Owen, F. N, White, R. A., Hilldrup, K. C., and Hanisch, R. J. AJ, 87, 1083 (1982)