Abell catalogue
Encyclopedia
The Abell catalog of rich clusters of galaxies is an all-sky catalog of 4,073 rich galaxy clusters of nominal redshift
z <= 0.2. This catalog supplements a revision of George O. Abell’s original “Northern Survey” of 1958, which had only 2,712 clusters, with a further 1,361 clusters – the “Southern Survey” of 1989 – from those parts of the south celestial hemisphere that had been omitted from the earlier survey.
. The catalog, which formed part of Abell’s PhD thesis, was prepared by means of a visual inspection of the red 103a-E plates of the Palomar Sky Survey (POSS), for which Abell was one of the principal observers. A. G. Wilson
, another of the principal observers, assisted Abell in the initial stages of the survey by routinely inspecting the plates as they were produced. After the completion of the survey, Abell went over the plates again and carried out a more detailed inspection. In both cases inspection was made with a 3.5x magnifying lens.
To qualify for inclusion in the catalog, a cluster had to satisfy four criteria:
In the catalog as originally published the clusters were listed in increasing order of right ascension
. Equatorial coordinates
(right ascension
and declination
) were given for the equinox of 1855 (the epoch
of the Bonner Durchmusterung) and galactic coordinates
for 1900.
Also listed for each cluster were the following:
The Southern Survey added a further 1,361 rich clusters to Abell’s original Northern Survey. The deep IIIa-J plates of the Southern Sky Survey (SSS) were used in the survey. These photographic plates were taken with the United Kingdom
’s 1.2-metre Schmidt Telescope at Siding Spring Observatory
, Australia
, in the 1970s. Abell began the survey during a sabbatical year in Edinburgh
in 1976. There he enlisted the assistance of Harold G Corwin of the University of Edinburgh
, who continued to work on the catalog until 1981, at which time he joined the Department of Astronomy at the University of Texas
. By then about half the survey had been completed. An interim paper on the Southern Survey was read at a symposium in 1983, about one month before Abell’s death; the catalog was completed by Ronald P Olowin of the University of Oklahoma
, and published in 1989.
Abell and Corwin worked from original plates stored at the Royal Observatory
in Edinburgh
, scanning the plates visually with a 3x wide-angle magnifier; Olowin used high-quality film copies, which he scanned both visually with a 7x magnifying lens and automatically with a backlit digitizer.
The criteria for inclusion in Abell’s Northern Survey were retained, as were Abell’s “richness” and “distance” classifications – but with the distance classes now being defined in terms of redshift rather than magnitude. As before, clusters were included if they had at least thirty bright galaxies, as it was estimated that this would all but eliminate the possibility of genuinely rich clusters (i.e. clusters with at least fifty bright members) being omitted. The Southern Survey retains the system of designation devised by Abell for his original catalog, with the numbers running from 2713 to 4076. (The catalog contains three duplicate entries: A3208 = A3207, A3833 = A3832, and A3897 = A2462.) The equatorial co-ordinates are for the equinoxes 1950 and 2000, while the galactic co-ordinates are calculated from the 1950 equatorial co-ordinates.
Abell’s original catalog – revised, corrected and updated – was included in the 1989 paper, as was the Abell Supplement, a supplementary catalog of 1,174 clusters from the Southern Survey which were not rich enough or were too distant to be included in the main catalog.
Alternative formats include: ABCG 1656; AC 1656; ACO 1656; A 1656, and A1656. Abell himself preferred the latter, but in recent years ACO 1656 has become the preferred format among professional astronomers and is the one recommended by the Centre de Données astronomiques de Strasbourg
(see SIMBAD
).
About 10% of Abell clusters at redshift z < 0.1 are not genuine rich clusters but, rather, the result of the superposition of sparser groupings.
Redshift
In physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum...
z <= 0.2. This catalog supplements a revision of George O. Abell’s original “Northern Survey” of 1958, which had only 2,712 clusters, with a further 1,361 clusters – the “Southern Survey” of 1989 – from those parts of the south celestial hemisphere that had been omitted from the earlier survey.
The Northern Survey
The original catalog of 2,712 rich clusters of galaxies was published in 1958 by George O. Abell (1927-83), who was then studying at the California Institute of TechnologyCalifornia Institute of Technology
The California Institute of Technology is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering...
. The catalog, which formed part of Abell’s PhD thesis, was prepared by means of a visual inspection of the red 103a-E plates of the Palomar Sky Survey (POSS), for which Abell was one of the principal observers. A. G. Wilson
Albert George Wilson
Albert George Wilson is an American astronomer.He was born in Houston, Texas. He received his Ph.D. in mathematics from Caltech in 1947; his thesis title was Axially Symmetric Thermal Stresses in a Semi-Infinite Solid....
, another of the principal observers, assisted Abell in the initial stages of the survey by routinely inspecting the plates as they were produced. After the completion of the survey, Abell went over the plates again and carried out a more detailed inspection. In both cases inspection was made with a 3.5x magnifying lens.
To qualify for inclusion in the catalog, a cluster had to satisfy four criteria:
- Richness: A cluster must have a minimum population of 50 members within a magnitude range of m3 to m3+2 (where m3 is the magnitude of the third brightest member of the cluster). To ensure a healthy margin or error, this criterion was not applied rigorously, and the final catalog included many clusters with fewer than fifty members (though these were excluded from Abell’s accompanying statistical study). Abell divided the clusters into six “richness groups,” depending on the number of galaxies in a given cluster that lie within the magnitude range m3 to m3+2 (the average number of galaxies per cluster for the entire catalog was 64):
- Group 0: 30-49 galaxies
- Group 1: 50-79 galaxies
- Group 2: 80-129 galaxies
- Group 3: 130-199 galaxies
- Group 4: 200-299 galaxies
- Group 5: more than 299 galaxies
- Compactness: A cluster must be sufficiently compact that its fifty or more members lie within one “counting radius” of the cluster’s centre. This radius, now known as the “Abell radius,” may be defined as 1.72/z arcminutes, where z is the cluster’s redshift, or as 1.5h-1 Mpc, where the Hubble constant is assumed to beH0 = 100 km s-1 Mpc-1, and h is a dimensionless scale parameter which usually takes value between 0.5 and 1. h = H0/100. The precise value of the Abell radius depends on the value taken for that parameter h. For h = 0.75 (same as H0 = 75 km s-1 Mpc-1), the Abell radius is 2 megaparsecs. This is more than twice the estimate Abell gave in 1958, when H0 was thought to be as high as 180 km s-1 Mpc-1.
- Distance: A cluster should have a nominal redshift of between 0.02 and 0.2 (i.e. a recessional velocity of between 6,000 and 60,000 km/s). Assuming H0 = 180 km s-1 Mpc-1, these values correspond to distances of about 33 and 330 Mpc respectively; but using today’s estimate for H0 (about 71 km s-1 Mpc-1) Abell’s upper and lower limits are actually set at about 85 and 850 Mpc. It has since been shown than many of the clusters in the catalog are more remote even than this, some being as far away as z = 0.4 (about 1,700 Mpc). Abell divided the clusters into seven “distance groups” according to the magnitudes of their tenth brightest members:
- Group 1: mag 13.3-14.0
- Group 2: mag 14.1-14.8
- Group 3: mag 14.9-15.6
- Group 4: mag 15.7-16.4
- Group 5: mag 16.5-17.2
- Group 6: mag 17.3-18.0
- Group 7: mag > 18.0
- Galactic-Latitude: Areas of the sky in the neighbourhood of the Milky WayMilky WayThe Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
were excluded from the study because the density of stars in those fields—not to mention interstellar obscuration—made it difficult to positively identify galaxy clusters. Like the richness criterion, this one was not applied rigorously, several clusters in or close to the Galactic PlaneGalactic coordinate systemThe galactic coordinate system is a celestial coordinate system which is centered on the Sun and is aligned with the apparent center of the Milky Way galaxy. The "equator" is aligned to the galactic plane...
being included in the catalog where Abell was satisfied that they were genuine clusters that met the other criteria.
In the catalog as originally published the clusters were listed in increasing order of right ascension
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
. Equatorial coordinates
Equatorial coordinate system
The equatorial coordinate system is a widely-used method of mapping celestial objects. It functions by projecting the Earth's geographic poles and equator onto the celestial sphere. The projection of the Earth's equator onto the celestial sphere is called the celestial equator...
(right ascension
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
and declination
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
) were given for the equinox of 1855 (the epoch
Epoch (astronomy)
In astronomy, an epoch is a moment in time used as a reference point for some time-varying astronomical quantity, such as celestial coordinates, or elliptical orbital elements of a celestial body, where these are subject to perturbations and vary with time...
of the Bonner Durchmusterung) and galactic coordinates
Galactic coordinate system
The galactic coordinate system is a celestial coordinate system which is centered on the Sun and is aligned with the apparent center of the Milky Way galaxy. The "equator" is aligned to the galactic plane...
for 1900.
Also listed for each cluster were the following:
- The cluster's precessionPrecessionPrecession is a change in the orientation of the rotation axis of a rotating body. It can be defined as a change in direction of the rotation axis in which the second Euler angle is constant...
rate - The magnitudeApparent magnitudeThe apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
of the cluster's tenth brightest member - The distance group of the cluster
- The richness group of the cluster
The Southern Survey
The sky-coverage of the 1958 catalog was limited to declinations north of –27°, the original southern limit of POSS. To rectify this and other shortcomings, the original catalog was later revised and supplemented with an additional catalog – the “Southern Survey” – of rich galaxy clusters from those parts of the south celestial hemisphere that had been omitted from the original catalog.The Southern Survey added a further 1,361 rich clusters to Abell’s original Northern Survey. The deep IIIa-J plates of the Southern Sky Survey (SSS) were used in the survey. These photographic plates were taken with the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
’s 1.2-metre Schmidt Telescope at Siding Spring Observatory
Siding Spring Observatory
Siding Spring Observatory near Coonabarabran, New South Wales, Australia, part of the Research School of Astronomy & Astrophysics at the Australian National University , incorporates the Anglo-Australian Telescope along with a collection of other telescopes owned by the Australian National...
, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, in the 1970s. Abell began the survey during a sabbatical year in Edinburgh
Edinburgh
Edinburgh is the capital city of Scotland, the second largest city in Scotland, and the eighth most populous in the United Kingdom. The City of Edinburgh Council governs one of Scotland's 32 local government council areas. The council area includes urban Edinburgh and a rural area...
in 1976. There he enlisted the assistance of Harold G Corwin of the University of Edinburgh
University of Edinburgh
The University of Edinburgh, founded in 1583, is a public research university located in Edinburgh, the capital of Scotland, and a UNESCO World Heritage Site. The university is deeply embedded in the fabric of the city, with many of the buildings in the historic Old Town belonging to the university...
, who continued to work on the catalog until 1981, at which time he joined the Department of Astronomy at the University of Texas
University of Texas at Austin
The University of Texas at Austin is a state research university located in Austin, Texas, USA, and is the flagship institution of the The University of Texas System. Founded in 1883, its campus is located approximately from the Texas State Capitol in Austin...
. By then about half the survey had been completed. An interim paper on the Southern Survey was read at a symposium in 1983, about one month before Abell’s death; the catalog was completed by Ronald P Olowin of the University of Oklahoma
University of Oklahoma
The University of Oklahoma is a coeducational public research university located in Norman, Oklahoma. Founded in 1890, it existed in Oklahoma Territory near Indian Territory for 17 years before the two became the state of Oklahoma. the university had 29,931 students enrolled, most located at its...
, and published in 1989.
Abell and Corwin worked from original plates stored at the Royal Observatory
Royal Observatory, Edinburgh
The Royal Observatory, Edinburgh is an astronomical institution located on Blackford Hill in Edinburgh, Scotland. The site is owned by the Science and Technology Facilities Council...
in Edinburgh
Edinburgh
Edinburgh is the capital city of Scotland, the second largest city in Scotland, and the eighth most populous in the United Kingdom. The City of Edinburgh Council governs one of Scotland's 32 local government council areas. The council area includes urban Edinburgh and a rural area...
, scanning the plates visually with a 3x wide-angle magnifier; Olowin used high-quality film copies, which he scanned both visually with a 7x magnifying lens and automatically with a backlit digitizer.
The criteria for inclusion in Abell’s Northern Survey were retained, as were Abell’s “richness” and “distance” classifications – but with the distance classes now being defined in terms of redshift rather than magnitude. As before, clusters were included if they had at least thirty bright galaxies, as it was estimated that this would all but eliminate the possibility of genuinely rich clusters (i.e. clusters with at least fifty bright members) being omitted. The Southern Survey retains the system of designation devised by Abell for his original catalog, with the numbers running from 2713 to 4076. (The catalog contains three duplicate entries: A3208 = A3207, A3833 = A3832, and A3897 = A2462.) The equatorial co-ordinates are for the equinoxes 1950 and 2000, while the galactic co-ordinates are calculated from the 1950 equatorial co-ordinates.
Abell’s original catalog – revised, corrected and updated – was included in the 1989 paper, as was the Abell Supplement, a supplementary catalog of 1,174 clusters from the Southern Survey which were not rich enough or were too distant to be included in the main catalog.
Format
The standard format used to refer to Abell clusters is: Abell X, where X = 1 to 4076. E.g. Abell 1656.Alternative formats include: ABCG 1656; AC 1656; ACO 1656; A 1656, and A1656. Abell himself preferred the latter, but in recent years ACO 1656 has become the preferred format among professional astronomers and is the one recommended by the Centre de Données astronomiques de Strasbourg
Centre de Données astronomiques de Strasbourg
The Centre de données astronomiques de Strasbourg is a data hub which collects and distributes astronomical information. It was established in 1972 under the name Centre de Données Stellaires...
(see SIMBAD
SIMBAD
SIMBAD is an astronomical database of objects beyond the Solar System...
).
Members
Some interesting members of Abell’s catalog include:- A426, the Perseus ClusterPerseus ClusterThe Perseus Cluster is a cluster of galaxies in the constellation Perseus. It has a recession speed of 5,366 km/s and a diameter of 863′...
- A1367, the Leo ClusterLeo ClusterThe Leo Cluster is a galaxy cluster about 330 million light-years distant in the constellation Leo. Along with the Coma Cluster, it is one of the two major clusters comprising the Coma Supercluster-External links:...
- A1656, the Coma Cluster
- A2151, the Hercules ClusterHercules ClusterThe Hercules Cluster is a cluster of about 100 galaxies some 650 million light-years distant in the constellation Hercules. It is rich in spiral galaxies and shows many interacting galaxies...
- A3526, the Centaurus ClusterCentaurus ClusterThe Centaurus Cluster is a cluster of hundreds of galaxies, located approximately 155 million light years away in the Centaurus constellation. The brightest member galaxy is the elliptical galaxy NGC 4696...
About 10% of Abell clusters at redshift z < 0.1 are not genuine rich clusters but, rather, the result of the superposition of sparser groupings.
External links
- Abell's 1958 paper and catalog
- Abell, Corwin and Olowin's 1989 paper and catalog
- Electronic form of the Abell catalog
See also
- List of Abell clusters
- List of galaxy clusters
- Hickson Compact GroupHickson Compact GroupA Hickson Compact Group is a collection of galaxies designated as published by Paul Hickson in 1982.The most famous group on Hickson’s list of 100 objects is HCG 92, Stephan's Quintet....
- Catalogue of Galaxies and Clusters of Galaxies