The Abell catalog of rich clusters of galaxies is an all-sky catalog of 4,073 rich galaxy clusters of nominal redshift z = 0. Galaxy groups and clusters are the largest Gravitationally bound objects to have arisen thus far in the process of cosmic structure formation In Physics and Astronomy, redshift occurs when Electromagnetic radiation – usually Visible light – emitted or reflected by 2. This catalog supplements a revision of George Ogden 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. George Ogden Abell ( March 1, 1927 &ndash October 7 1983) was an Astronomer at UCLA.

Contents 1 The Northern Survey 2 The Southern Survey 3 Format 4 Members 5 External links 6 References 7 See also

The Northern Survey

The original catalog of 2,712 rich clusters of galaxies was published in 1958 by George Ogden Abell (1927-83), who was then studying at the California Institute of Technology. The California Institute of Technology (commonly referred to as Caltech) is a private, Coeducational research university located in Pasadena 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. The Palomar Sky Survey is a complete Photographic survey of the whole sky which was made by the large Schmidt camera of the newly built Mount Palomar 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:

• 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. Hubble's law is the statement in Physical cosmology that the Redshift in light coming from distant galaxies is proportional to their distance 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 Way 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. The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply Like the richness criterion, this one was not applied rigorously, several clusters in or close to the Galactic Plane being included in the catalog where Abell was satisfied that they were genuine clusters that met the other criteria. 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

In the catalog as originally published the clusters were listed in increasing order of right ascension. Right ascension (abbrev RA; symbol α) is the Astronomical term for one of the two Coordinates of a point on the Celestial sphere Equatorial coordinates (right ascension and declination) were given for the equinox of 1855 (the epoch of the Bonner Durchmusterung) and galactic coordinates for 1900. The equatorial coordinate system is probably the most widely used Celestial coordinate system, whose equatorial coordinates are Declination (\delta Right ascension (abbrev RA; symbol α) is the Astronomical term for one of the two Coordinates of a point on the Celestial sphere In Astronomy, declination (abbrev dec or δ) is one of the two coordinates of the Equatorial coordinate system, the other being either In Astronomy, an epoch is a moment in time used as a reference for the Orbital elements of a Celestial body. In Astronomy, Durchmusterung or Bonner Durchmusterung ( BD) is the usual name for three comprehensive astrometric Star catalogues 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 Year 1900 ( MCM) was an exceptional Common year starting on Monday (link will display the full calendar of the Gregorian calendar

Also listed for each cluster were the following:

• The cluster's precession rate
• The magnitude 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. Precession refers to a change in the direction of the axis of a rotating object The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value 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’s 1. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located 2-metre Schmidt Telescope at Siding Spring Observatory, Australia, in the 1970s. A Schmidt camera, also referred to as the Schmidt telescope, is an astronomical Camera designed to provide wide fields of view with limited Siding Spring Observatory near Coonabarabran, Australia, part of the Research School of Astronomy & Astrophysics (RSAA at the Australian National For a topic outline on this subject see List of basic Australia topics. Abell began the survey during a sabbatical year in Edinburgh in 1976. Edinburgh ( ˈɛdɪnb(ərə Dùn Èideann) is the Capital of Scotland and is its second largest city after Glasgow. 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. The University of Edinburgh (Oilthigh Dhùn Èideann founded in 1582 is a renowned centre for teaching and research in Edinburgh, Scotland, UK. 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. Year 1983 ( MCMLXXXIII) was a Common year starting on Saturday (link displays the 1983 Gregorian calendar) University of Oklahoma, abbreviated OU, is a Coeducational public Research university located in the U Year 1989 ( MCMLXXXIX) was a Common year starting on Sunday (link displays 1989 Gregorian calendar)

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. Edinburgh ( ˈɛdɪnb(ərə Dùn Èideann) is the Capital of Scotland and is its second largest city after Glasgow.

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 (see SIMBAD). For the missile mounting see Mistral missile SIMBAD (the S et of I dentifications M easurements and B ibliography for

Members

Main article: List of Abell clusters

Some interesting members of Abell’s catalog include:

• A426, the Perseus Cluster
• A1367, the Leo Cluster
• A1656, the Coma Cluster
• A2151, the Hercules Cluster
• A3526, the Centaurus Cluster

About 10% of Abell clusters at redshift z < 0. The Abell catalogue is an almost complete catalogue of approximately 4000 Galaxy clusters with at least 30 members to a Redshift of z = 0 The Perseus Cluster (Abell 426 is a cluster of galaxies in the constellation Perseus. The Perseus Cluster (Abell 426 is a cluster of galaxies in the constellation Perseus. The Leo Cluster ( Abell 1367 is a galaxy cluster about 330 million Light-years distant ( z = 0 The Leo Cluster ( Abell 1367 is a galaxy cluster about 330 million Light-years distant ( z = 0 The Coma Cluster ( Abell 1656 is a large cluster of galaxies that contains over 1000 identified galaxies The Coma Cluster ( Abell 1656 is a large cluster of galaxies that contains over 1000 identified galaxies The Hercules Cluster ( Abell 2151 is a cluster of about 100 galaxies some 650 million Light-years distant ( z = 0 The Hercules Cluster ( Abell 2151 is a cluster of about 100 galaxies some 650 million Light-years distant ( z = 0 The Centaurus Cluster (A3526 is a cluster of hundreds of galaxies, located approximately 155 million Light years away in the Centaurus The Centaurus Cluster (A3526 is a cluster of hundreds of galaxies, located approximately 155 million Light years away in the Centaurus 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

References

• Abell, G O (1958). The distribution of rich clusters of galaxies. A catalogue of 2712 rich clusters found on the National Geographic Society Palomar Observatory Sky Survey, The Astrophysical Journal Supplement Series, 3, 211-288.  
• Abell, G O; Corwin, H G; Olowin, R P (1989). A Catalog of Rich Clusters of Galaxies, The Astrophysical Journal Supplement Series, 70, 1-138.  

See also

• List of Abell clusters
• List of galaxy clusters

The Abell catalogue is an almost complete catalogue of approximately 4000 Galaxy clusters with at least 30 members to a Redshift of z = 0 This page lists some of the more interesting Galaxy clusters and groups

---

© 2009 citizendia.org; parts available under the terms of GNU Free Documentation License, from http://en.wikipedia.org