ESO 383-76 within the Abell 3571 cluster, imaged by Dark Energy Spectroscopic Instrument in 2019

The type-cD galaxy[1] (also cD-type galaxy,[2] cD galaxy[3]) is a galaxy morphology classification, a subtype of type-D giant elliptical galaxy. Characterized by a large halo of stars,[4] they can be found near the centres of some rich galaxy clusters.[5] They are also known as supergiant ellipticals[6] or central dominant galaxies.[7]

Characteristics

The cD-type is a classification in the Yerkes galaxy classification scheme, one of two Yerkes classifications still in common use, along with D-type.[8] The "c" in "cD" refers to the fact that the galaxies are very large, hence the adjective supergiant, while the "D" refers to the fact that the galaxies appear diffuse.[9] A backformation of "cD" is frequently used to indicate "central Dominant galaxy".[7] cDs are also frequently considered the largest galaxies.[10][11]

cD galaxies are similar to lenticular galaxies (S0) or elliptical galaxies (E#), but many times larger, some having envelopes that exceed one million light years in radius.[12] They appear elliptical-like, with large low surface brightness envelopes[13] which may belong as much to the galaxy cluster as the cD galaxy. It is currently thought that cDs are the result of galaxy mergers.[14] Some cDs have multiple galactic nuclei.[15] cD galaxies are one of the types frequently found to be the brightest cluster galaxy (BCG) of a cluster.[16] Many fossil group galaxies are similar to cD BCG galaxies, leading some to theorize that the cD results from the creation of a fossil group, and then the new cluster accumulating around the fossil group.[17] However, cDs themselves are not found as field galaxies, unlike fossil groups.[13] cDs form around 20% of BCGs.[13]

Importance

Massive galaxies such as supergiant elliptical galaxies are important to understanding the evolution of the Universe, because they, along with other large-early type galaxies, account for half of the Universe's stellar mass, contribute a lot to its chemical enrichment and provide clues to the star formation history of the Universe.[18]

Growth

cD galaxies are believed to grow via mergers of galaxies that spiral in to the center of a galaxy cluster, a theory first proposed by Herbert J. Rood in 1965.[19] This "cannibalistic" mode of growth leads to the large diameter and luminosity of the cDs.[20] The second-brightest galaxy in the cluster is usually under-luminous, a consequence of its having been "eaten".[21] Remains of "eaten" galaxies sometimes appear as a diffuse halo of gas and dust,[20] or tidal streams, or undigested off-center nuclei in the cD galaxy. The envelope or halo may also consist of the "intra-cluster light", originating from stars stripped away from their original galaxy, and it can be up to 3 million light years in diameter.[14] It is estimated that the cD galaxy alone contributes 1–7%, depending on the cluster mass, of the total baryon mass within 12.5 virial radii.[22]

Dynamical friction

Dynamical friction is believed to play an important role in the formation of cD galaxies at the centres of galaxy clusters.[23] This process begins when the motion of a large galaxy in a cluster attracts smaller galaxies and dark matter into a wake behind it. This over-density follows behind the larger galaxy and exerts a constant gravitational force on it, causing it to slow down. As it loses kinetic energy, the large galaxy gradually spirals toward the centre of the cluster. Once there, the stars, gas, dust and dark matter of the large galaxy and its trailing galaxies will join with those of other galaxies who preceded them in the same fate.[24] A giant or supergiant diffuse or elliptical galaxy will result from this accumulation.[25] The centers of merged or merging galaxies can remain recognizable for long times, appearing as multiple "nuclei" of the cD galaxy.[26]

cD clusters

Type-cD galaxies are also used to define clusters. A galaxy cluster with a cD at its centre is termed a "cD cluster" or "cD galaxy cluster" or "cD cluster of galaxies".[27]

Examples

See also

References

  1. ↑ Sidereal Times, June 2002, page 3
  2. ↑ Proceedings of PATRAS 2008, page 59
  3. ↑ Galaxy Clusters, Jan Hartlap, page 3
  4. ↑ Surface Photometry and the Structure of Elliptical Galaxies, "Chapter 11. cD and Brightest Cluster Galaxies", John Kormendy, S. Djorgovski, 1989
  5. ↑ A Dictionary of Astronomy, "cD galaxy" (accessed 14 April 2010)
  6. ↑ encyclopedia.com "supergiant elliptical"
  7. 1 2 "Uncertainties on Clusters of Galaxies Distances", C. Adami, M.P. Ulmer, 18 July 2000, arXiv:astro-ph/0007265 (accessed 14 April 2010)
  8. ↑ An Atlas of DRAGNs, "Glossary", J. P. Leahy, 15 March 1997 (accessed 14 April 2010)
  9. ↑ Global Telescope Network, "Types of Galaxies" Archived 16 July 2010 at the Wayback Machine, Kevin McLin, 14 April 2010 (accessed 14 April 2010)
  10. ↑ Universe Today, "What is the Largest Galaxy?", Fraser Cain (accessed 14 April 2010)
  11. ↑ EurekAlert, "Scientists observe largest explosion in space", Andrea Gibson, 5 January 2005 (accessed 15 April 2010)
  12. ↑ Encyclopædia Britannica, "cD-galaxy" (accessed 14 April 2010)
  13. 1 2 3 Monthly Notices of the Royal Astronomical Society, "Intracluster light and the extended stellar envelopes of cD galaxies: an analytical description", Marc S. Seigar, Alister W. Graham, Helmut Jerjen, July 2007, Volume 378, Issue 4, pp. 1575–1588, doi:10.1111/j.1365-2966.2007.11899.x, Bibcode:2007MNRAS.378.1575S, arXiv:astro-ph/0612229v2 (accessed 15 April 2010)
  14. 1 2 COSMOS—The SAO Encyclopedia of Astronomy, "CD Galaxies", Swinburne University of Technology (accessed 14 April 2010)
  15. ↑ Internet Encyclopedia of Science, "D galaxy", David Darling (accessed 14 April 2010)
  16. ↑ IAU Symposium 245, "Star Formation in Bulges from GALEX", Sukyoung K. Yi, 5 September 2007, doi:10.1017/S174392130801819X, arXiv:0709.0177 (accessed 14 April 2010)
  17. ↑ Universe Today, "How Do Fossil Galaxy Clusters Form so Quickly?", Fraser Cain, 27 April 2006 (accessed 15 April 2010)
  18. ↑ Barbosa, C.E.; Spiniello, C.; Arnaboldi, M.; Coccato, L.; Hilker, M.; Richtler, T. (May 2021). "A preserved high-z compact progenitor in the heart of NGC 3311 revealed with MUSE 2D stellar population analysis". Astronomy & Astrophysics. 649: 19. arXiv:2012.11609. Bibcode:2021A&A...649A..93B. doi:10.1051/0004-6361/202039809. S2CID 232157305.
  19. ↑ Rood, Herbert J. (1965). The Dynamics of the Coma Cluster of Galaxies (PhD thesis). The University of Michigan. Bibcode:1965PhDT.........3R.
  20. 1 2 "Curious About Astronomy?". Retrieved 28 March 2007.
  21. ↑ Hausman, M. J.; Ostriker, J. P. (November 1977). "Cannibalism among the galaxies—Dynamically produced evolution of cluster luminosity functions". The Astrophysical Journal Letters. 217: L125–L128. Bibcode:1977ApJ...217L.125O. doi:10.1086/182554.
  22. ↑ Section 8 of Vikhlinin, A.; Kravtsov, A.; Forman, W.; Jones, C.; Markevitch, M.; Murray, S. S.; Van Speybroeck, L. (April 2006). "Chandra Sample of Nearby Relaxed Galaxy Clusters: Mass, Gas Fraction, and Mass-Temperature Relation". The Astrophysical Journal. Chicago, Illinois, USA. 640 (2): 691–709. arXiv:astro-ph/0507092. Bibcode:2006ApJ...640..691V. doi:10.1086/500288. S2CID 18940822.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  23. ↑ Merritt, David (January 1983). "Relaxation and tidal stripping in rich clusters of galaxies. I. Evolution of the mass distribution". The Astrophysical Journal. 264: 24–48. Bibcode:1983ApJ...264...24M. doi:10.1086/160571.
  24. ↑ Merritt, David (January 1984). "Relaxation and tidal stripping in rich clusters of galaxies. II. Evolution of the luminosity distribution". The Astrophysical Journal. 276: 26–37. Bibcode:1984ApJ...276...26M. doi:10.1086/161590.
  25. ↑ Merritt, David (February 1985). "Relaxation and tidal stripping in rich clusters of galaxies. III. Growth of a massive central galaxy". The Astrophysical Journal. 289: 18–32. Bibcode:1985ApJ...289...18M. doi:10.1086/162860.
  26. ↑ Merritt, David (May 1984). "The nature of multiple-nucleus cluster galaxies". The Astrophysical Journal. 280: L5–8. Bibcode:1984ApJ...280L...5M. doi:10.1086/184257.
  27. ↑ PDF, "'Tuning Fork' Classification of Rich Clusters of Galaxies", Herbert J.Rood, Gummuluru N. Sastry, June 1971, doi:10.1086/129128, Bibcode:1971PASP...83..313R (accessed 14 April 2010)
  28. ↑ Science, "The Central Galaxy in Abell 2029: An Old Supergiant", Juan M. Uson, Stephen P. Boughn, and Jeffrey R. Kuhn, 26 October 1990, Vol. 250, no. 4980, pp. 539–540, doi:10.1126/science.250.4980.539
  29. ↑ "Galaxy Found", Ellensburg Daily Record, United Press International, 27 October 1990, p. 16
  30. ↑ Lodi News-Sentinel, "Giant Galaxy Discovered", UPI, 26 October 1990, p. 9
  31. ↑ Nature, "FIGURE 3. The entropy of the intracluster medium in spherical shells of radius r." 9 July 2009, ISSN 0028-0836 ; E-ISSN 1476-4687 ; (accessed 15 April 2010)
  32. ↑ Nature, "FIGURE 4. Optical, radio and X-ray images of the Perseus cluster." 9 July 2009, ISSN 0028-0836 ; E-ISSN 1476-4687 ; (accessed 15 April 2010)

Further reading

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