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Virgo Supercluster

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Distances from the Local Group for selected groups and clusters within the Local Supercluster

The Virgo Supercluster (Virgo SC) or Local Supercluster (LSC or LS) is the irregular supercluster that contains the Virgo Cluster in addition to the Local Group, which in turn contains the Milky Way and Andromeda galaxies. At least 100 galaxy groups and clusters are located within its diameter of 33 megaparsecs (110 million light-years). It is one of millions of superclusters in the observable Universe.

Background

Beginning with the first large sample of nebulae published by William and John Herschel in 1863, it was known that there is a marked excess of nebular fields in the constellation Virgo (near the north galactic pole). In the 1950s French-American astronomer Gérard Henri de Vaucouleurs was the first to argue that this excess represented a large-scale galaxy-like structure, coining the term "Local Supergalaxy" in 1953 which he changed to "Local Supercluster" (LSC[1]) in 1958. (Harlow Shapley, in his 1959 book Of Stars and Men, suggested the term Metagalaxy.[2]) Debate went on during the 1960s and 1970s as to whether the Local Supercluster (LS) was actually a structure or a chance alignment of galaxies.[3] The issue was resolved with the large redshift surveys of the late 70's and early 80's, which convincingly showed the flattened concentration of galaxies along the supergalactic plane.[4]

Structure

In a comprehensive 1982 paper, R. Brent Tully presented the conclusions of his research concerning the basic structure of the LS. It consists of two components: an appreciably flattened disk containing two-thirds of the supercluster's luminous galaxies, and a roughly spherical halo containing the remaining one-third.[5] The disk itself is a thin (~1 Mpc) ellipsoid with a long axis / short axis ratio of at least 6 to 1, and possibly as high as 9 to 1.[6] Data released in June 2003 from the 5-year Two-degree-Field Galaxy Redshift Survey (2dF) has allowed astronomers to compare the LS to other superclusters. The LS represents a typical poor (that is, lacking a high density core) supercluster of rather small size. It has one rich galaxy cluster in the center, surrounded by filaments of galaxies and poor groups.[7] The Local Group is located on the outskirts of the LS in a small filament extending from the Fornax cluster to the Virgo cluster.[4] The Virgo Supercluster's volume is very approximately 7000 times that of the Local Group or 100 billion times that of the Milky Way. See volumes of similar orders of magnitude.

Galaxy distribution

The number density of galaxies in the LS falls off with the square of the distance from its center near the Virgo cluster, suggesting that this cluster is not randomly located. Overall, the vast majority of the luminous galaxies (greater than absolute magnitude -13) are concentrated in a small number of clouds (groups of galaxy clusters). Ninety-eight percent can be found in the following 11 clouds (given in decreasing order of number of luminous galaxies): Canes Venatici, Virgo cluster, Virgo II (southern extension), Leo II, Virgo III, Crater (NGC 3672), Leo I, Leo Minor (NGC 2841), Draco (NGC 5907), Antlia (NGC 2997) and NGC 5643. Of the luminous galaxies located in the disk, one third are in the Virgo cluster, while the remainder are found in the Canes Venatici Cloud and Virgo II Cloud, plus the somewhat insignificant NGC 5643 Group. The luminous galaxies in the halo are also concentrated in a small number of clouds (94% in 7 clouds). This distribution indicates that "most of the volume off the supergalactic plane is a great void."[6] A helpful analogy that matches the observed distribution is that of soap bubbles. Flattish clusters and superclusters are found at the intersection of bubbles, which are large, roughly spherical (on the order of 20-60 Mpc in diameter) voids in space.[8] Long filamentary structures seem to predominate. An example of this is the Hydra-Centaurus Supercluster, the nearest supercluster to the LS, which starts at a distance of roughly 30 Mpc and extends to 60 Mpc.[9]

Cosmology

Large scale dynamics

Since the late 1980s it has been apparent that not only the Local Group, but all matter out to a distance of at least 50 Mpc is experiencing a bulk flow on the order of 600 km/sec in the direction of the Norma cluster (Abell 3627).[10] Lynden-Bell et al. (1988) dubbed the cause of this "The Great Attractor". While astronomers are confident of the velocity of the LS, which has been measured against the Cosmic Microwave Background (CMB), the nature of what is causing it remains poorly understood.

Dark matter

The LS has a total mass M ≈ 1 x 1015Msolar and a total optical luminosity L ≈ 3 x 1012Lsolar.[7] This yields a mass-to-light ratio of about 300 times that of the solar ratio, a figure that is consistent with results obtained for other superclusters.[11][12] (By comparison, the mass-to-light ratio for the Milky Way is 2.7[citation needed].) These ratios are one of the main arguments in favor of the presence of large amounts of dark matter in the universe.

Maps

Virgo clusterCentaurus_A/M83_GroupM81 groupMaffei_GroupNGC 1023 GroupM101 groupNGC 2997 GroupCanes Venatici I GroupNGC 5033 groupUrsa_Major_ClusterLeo I GroupNGC 6744 GroupDorado GroupVirgo III GroupsNGC 4697Leo II GroupsNGC 7582Fornax clusterEridanus ClusterLocal GroupSculptor Group
The Virgo Supercluster in supergalactic coordinates (click on feature names for more information)
NGC 55Milky WayLarge Magellanic CloudNGC 3109Messier 31Messier 33NGC 247Circinus GalaxyNGC 5128NGC 5253NGC 5102NGC 5128 GroupIC4662Messier 83Virgo ClusterESO 274-01NGC 1313NGC 625NGC 7793NGC 4945NGC 45NGC 253Sculptor GroupLocal GroupNGC 1569NGC 300IC 342Maffei GroupNGC 404NGC 784Maffei IMaffei IIDwingeloo 1NGC 1560Messier 81IC 2574Messier 82NGC 3077NGC 2976NGC 4605NGC 6503NGC 5204NGC 3738NGC 4236NGC 2366NGC 2403NGC4305NGC5023Messier 94NGC 4244NGC 4214NGC 4449NGC 4395Canes I GroupM81 Group
The nearest galaxy groups projected onto the supergalactic plane (click on feature names for more information)

Diagrams

A diagram of our location in the observable Universe. (Click here for larger image.)

See also

References

  1. ^ cfa.harvard.edu, The Geometry of the Local Supercluster, John P. Huchra, 2007 (accessed 12-12-2008)
  2. ^ Shapley, Harlow Of Stars and Men (1959)
  3. ^ de Vaucouleurs, G. (March 1981). "The Local Supercluster of Galaxies". Bulletin of the Astronomical Society of India. 9: 6 (see note). Bibcode:1981BASI....9....1D.
  4. ^ a b Klypin, Anatoly; et al. (October 2003). "Constrained Simulations of the Real Universe: The Local Supercluster". The Astrophysical Journal. 596 (1): 19–33. arXiv:astro-ph/0107104. Bibcode:2003ApJ...596...19K. doi:10.1086/377574. {{cite journal}}: Explicit use of et al. in: |author= (help)
  5. ^ Hu, F. X.; et al. (April 2006). "Orientation of Galaxies in the Local Supercluster: A Review". Astrophysics and Space Science. 302 (1–4): 43–59. arXiv:astro-ph/0508669. Bibcode:2006Ap&SS.302...43H. doi:10.1007/s10509-005-9006-7. {{cite journal}}: Explicit use of et al. in: |author= (help)
  6. ^ a b Tully, R. B. (15 Jun 1982). "The Local Supercluster". Astrophysical Journal. 257 (1): 389–422. Bibcode:1982ApJ...257..389T. doi:10.1086/159999.
  7. ^ a b Einasto, M.; et al. (December 2007). "The richest superclusters. I. Morphology". Astronomy and Astrophysics. 476 (2): 697–711. Bibcode:2007A&A...476..697E. doi:10.1051/0004-6361:20078037. {{cite journal}}: Explicit use of et al. in: |author= (help)
  8. ^ An Introduction to Modern Astrophysics. New York: Addison-Wesley. 1996. p. 1136. ISBN 0201547309. {{cite book}}: Unknown parameter |name= ignored (help)
  9. ^ Fairall, A. P.; et al. (May 1989). "A wide angle redshift survey of the Hydra-Centaurus region". Astronomy and Astrophysics Supplement Series. 78 (2): 270. Bibcode:1989A&AS...78..269F. ISSN 0365-0138. {{cite journal}}: Explicit use of et al. in: |author= (help)
  10. ^ Plionis, Manolis; Valdarnini, Riccardo (March 1991). "Evidence for large-scale structure on scales about 300/h MPC". Royal Astronomical Society, Monthly Notices. 249: 46–61. Bibcode:1991MNRAS.249...46P.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  11. ^ Small, Todd A.; et al. (Jan 1998). "The Norris Survey of the Corona Borealis Supercluster. III. Structure and Mass of the Supercluster". Astrophysical Journal. 492 (1): 45–56. arXiv:astro-ph/9708153. Bibcode:1998ApJ...492...45S. doi:10.1086/305037. {{cite journal}}: Explicit use of et al. in: |author= (help)
  12. ^ Heymans, Catherine; et al. (April 2008). "The dark matter environment of the A901 abell A901/902 supercluster: a weak lensing analysis of the HST STAGES survey". Monthly Notices of the Royal Astronomical Society, Volume 385, Issue 3, pp. 1431-1442. 385 (3): 1431–1442. Bibcode:2008MNRAS.385.1431H. doi:10.1111/j.1365-2966.2008.12919.x. {{cite journal}}: Explicit use of et al. in: |author= (help)
  • The Atlas of the Universe, a website created by astrophysicist Richard Powell that shows maps of our local universe on a number of different scales (similar to above maps).
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