Wikipedia:Virgo Supercluster
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The Virgo Supercluster (Virgo SC) or Local Supercluster (LSC or LS) is the irregular supercluster that contains 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.
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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. Debate went on during the 1960s and 1970's as to whether the Local Supercluster (LS) was actually a structure or a chance alignment of galaxies.[2] 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.[3]
Structure
In a comprehensive 1982 paper R. Brent Tully laid out much of the LS's basic structure. It consists of two components: an appreciably flattened disk (containing 2/3rds of the supercluster's luminous galaxies), and a roughly spherical halo (containing the remaining 1/3rd of the luminous galaxies).[4] 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.[5] Recent data (released Jun 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 (i.e., 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.[6] The Local Group is located on the outskirts of the LS in a small filament extending from the Fornax cluster to the Virgo cluster.[3]
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."[5] 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.[7] 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.[8]
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).[9] 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.[6] 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.[10][11] (By comparison, the mass-to-light ratio for the Milky Way is 2.7.) These ratios are one of the main arguments in favor of the presence of large amounts of dark matter in the universe.
Maps
See also
References
- ^ cfa.harvard.edu, The Geometry of the Local Supercluster, John P. Huchra, 2007 (accessed 12-12-2008)
- ^ de Vaucouleurs, G. (Mar 1981). "The Local Supercluster of Galaxies". Bulletin of the Astronomical Society of India 9: 6 (see note). http://adsabs.harvard.edu/abs/1981BASI....9....1D.
- ^ a b Klypin, Anatoly, et al. (Oct 2003). "Constrained Simulations of the Real Universe: The Local Supercluster". The Astrophysical Journal 596 (1): 19-33. doi:. http://adsabs.harvard.edu/abs/2003ApJ...596...19K.
- ^ Hu, F. X., et al. (Apr 2006). "Orientation of Galaxies in the Local Supercluster: A Review". Astrophysics and Space Science 302 (1-4): 43-59. doi:. http://adsabs.harvard.edu/abs/2006Ap%26SS.302...43H.
- ^ a b Tully, R. B. (15 Jun 1982). "The Local Supercluster". Astrophysical Journal 257 (1): 389-422. doi:. http://adsabs.harvard.edu/abs/1982ApJ...257..389T.
- ^ a b Einasto, M., et al. (Dec 2007). "The richest superclusters. I. Morphology". Astronomy and Astrophysics 476 (2): 697-711. doi:. http://adsabs.harvard.edu/cgi-bin/bib_query?2007A%26A...476..697E.
- ^ An Introduction to Modern Astrophysics. New York: Addison-Wesley. 1996. p. 1136. ISBN 0201547309.
- ^ 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. doi:. http://adsabs.harvard.edu/cgi-bin/bib_query?1989A%26AS...78..269F&db_key=AST.
- ^ Plionis, Manolis; Valdarnini, Riccardo (Mar 1991). "Evidence for large-scale structure on scales about 300/h MPC". Royal Astronomical Society, Monthly Notices 249: 46-61. http://adsabs.harvard.edu/cgi-bin/bib_query?1991MNRAS.249...46P.
- ^ 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: 45-56. doi:. http://adsabs.harvard.edu/abs/1998ApJ...492...45S.
- ^ Heymans, Catherine, et al. (Apr 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. doi:. http://adsabs.harvard.edu/abs/2008MNRAS.385.1431H.
- Brent Tully: The Local Supercluster, Astrophys. J., vol. 257, pp. 389–422 (1982)
- Oscar Monchito: Superclusters and Other Stuff, Colton, vol. 12, pp. 124–118 (1992)
- Lynden-Bell, D., et al.: Spectroscopy and photometry of elliptical galaxies. V - Galaxy streaming toward the new supergalactic center, Astrophysical Journal, Part 1, vol. 326, pp. 19–49 (Mar 1988)
External links
- 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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