Type-cD galaxy

Source: Wikipedia, the free encyclopedia.

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

The type-cD galaxy

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

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"[dead link] (accessed 14 April 2010)
  6. ^ encyclopedia.com "supergiant elliptical"
  7. ^
    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. ^
    arXiv:astro-ph/0612229v2
    (accessed 15 April 2010)
  14. ^ a b 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. 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. S2CID 232157305
    .
  19. Bibcode:1965PhDT.........3R
    .
  20. ^ a b "Curious About Astronomy?". Retrieved 28 March 2007.
  21. doi:10.1086/182554
    .
  22. S2CID 18940822.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  23. ^
    doi:10.1086/160571
    .
  24. ^
    doi:10.1086/161590
    .
  25. ^
    doi:10.1086/162860
    .
  26. doi:10.1086/184257
    .
  27. Bibcode:1971PASP...83..313R
    (accessed 14 April 2010)
  28. 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. ISSN 1476-4687
     ; (accessed 15 April 2010)
  32. ISSN 1476-4687
     ; (accessed 15 April 2010)

Further reading
Retrieved from "https://en.wikipedia.org/w/index.php?title=Type-cD_galaxy&oldid=1221552446"