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28-502: This group is sometimes identified as one group and sometimes identified as two groups. Hence, some references will refer to two objects named the Centaurus A Group and the M83 Group . However, the galaxies around Centaurus A and the galaxies around M83 are physically close to each other, and both subgroups appear not to be moving relative to each other. The Centaurus A/M83 Group is part of

56-480: A mass-to-light ratio of about 300 times that of the solar ratio ( M ☉ / L ☉ = 1), a figure that is consistent with results obtained for other superclusters. By comparison, the mass-to-light ratio for the Milky Way is 63.8 assuming a solar absolute magnitude of 4.83, a Milky Way absolute magnitude of −20.9, and a Milky Way mass of 1.25 × 10   M ☉ . These ratios are one of

84-410: A diameter of 1 to 2 megaparsecs (Mpc). Their mass is approximately 10 solar masses . The spread of velocities for the individual galaxies is about 150 km/s. However, this definition should be used as a guide only, as larger and more massive galaxy systems are sometimes classified as galaxy groups. Groups are the most common structures of galaxies in the universe, accounting for at least 50% of

112-509: A normal galaxy group, leaving behind the X-ray halo of the progenitor group. Galaxies within a group interact and merge. The physical process behind this galaxy-galaxy merger is dynamical friction . The time-scales for dynamical friction on luminous (or L*) galaxies suggest that fossil groups are old, undisturbed systems that have seen little infall of L* galaxies since their initial collapse. Fossil groups are thus an important laboratory for studying

140-416: 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

168-522: A small number of galaxies, typically around five, in close proximity and relatively isolated from other galaxies and formations. The first compact group to be discovered was Stephan's Quintet , found in 1877. Stephan's Quintet is named for a compact group of four galaxies plus an unassociated foreground galaxy. Astronomer Paul Hickson created a catalogue of such groups in 1982, the Hickson Compact Groups . Compact groups of galaxies readily show

196-621: Is a member of the Cen A group rather than of the distant Centaurus galaxy cluster as believed since 1983. Virgo Supercluster The Local Supercluster ( LSC or LS ), or Virgo Supercluster is a formerly defined supercluster containing the Virgo Cluster and Local Group , which itself contains the Milky Way and Andromeda galaxies, as well as others. At least 100 galaxy groups and clusters are located within its diameter of 33 megaparsecs (110 million light-years ). The Virgo Supercluster

224-669: Is one of about 10 million superclusters in the observable universe and is in the Pisces–Cetus Supercluster Complex , a galaxy filament . A 2014 study indicates that the Local Supercluster is only a part of an even greater supercluster, Laniakea , a larger group centered on the Great Attractor , thus subsuming the former Virgo Supercluster under Laniakea. Beginning with the first large sample of nebulae published by William and John Herschel in 1863, it

252-565: 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. Long filamentary structures seem to predominate. An example of this is the Hydra–Centaurus Supercluster , the nearest supercluster to the Virgo Supercluster, which starts at a distance of roughly 30 Mpc and extends to 60 Mpc. Since

280-668: The Fornax Cluster to the Virgo Cluster . The Virgo Supercluster's volume is roughly 7,000 times that of the Local Group, or 100 billion times that of the Milky Way. 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 (less than absolute magnitude −13) are concentrated in

308-621: The Local Group , and follow a similar metallicity–luminosity relation. One dwarf galaxy, KK98 203 (LEDA 166167), has an extended ring of Hα emission. The table below lists galaxies that have been identified as associated with the Centaurus A/M83 Group by I. D. Karachentsev and collaborators. Note that Karachentsev divides this group into two subgroups centered on Centaurus A and Messier 83 . Additionally, ESO 219-010 , PGC 39032 , and PGC 51659 are listed as possibly being members of

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336-527: The Parkes Radio Telescope and in the hydrogen -alpha spectral line with the Siding Spring 2.3 m Telescope . This identified 20 dwarf galaxies as members of the group. The HIPASS survey, which was a blind radio survey for hydrogen spectral line emission, found five uncatalogued galaxies in the group and also identified five previously-catalogued galaxies as members. An additional dwarf galaxy

364-582: The Virgo Supercluster , the local supercluster of which the Local Group is an outlying member. The brightest group members were frequently identified in early galaxy group identification surveys. However, many of the dwarf galaxies in the group were only identified in more intensive studies. One of the first of these identified 145 faint objects on optical images from the UK Schmidt Telescope and followed these up in hydrogen line emission with

392-425: 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. The Local Group is located on the outskirts of the LS in a small filament extending from

420-523: The Centaurus A Subgroup, and ESO 381-018 , NGC 5408 , and PGC 43048 are listed as possibly being members of the M83 Subgroup. Although HIPASS J1337-39 is only listed as a possible member of the M83 Subgroup in the later list published by Karachentsev, later analyses indicate that this galaxy is within the subgroup. Saviane and Jerjen found that NGC 5011C has an optical redshift of 647 km/s and thus

448-679: The Virgo Supercluster (including the Local Group) as well as the Hydra-Centaurus Supercluster, the Pavo-Indus Supercluster, and the Fornax Group. The Great Attractor, together with the entire supercluster, is found to be moving toward Shapley Supercluster , with center of Shapley Attractor . The LS has a total mass M ≈ 10 M ☉ and a total optical luminosity L ≈ 3 × 10 L ☉ . This yields

476-474: 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 third. 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. Data released in June 2003 from

504-543: The disk, one third are in the Virgo Cluster. 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 concentrated in a small number of clouds (94% in 7 clouds). This distribution indicates that "most of the volume of the supergalactic plane is a great void." A helpful analogy that matches the observed distribution

532-429: The effect of dark matter , as the visible mass is greatly less than that needed to gravitationally hold the galaxies together in a bound group. Compact galaxy groups are also not dynamically stable over Hubble time , thus showing that galaxies evolve by merger, over the timescale of the age of the universe. Fossil galaxy groups, fossil groups, or fossil clusters are believed to be the end-result of galaxy merging within

560-412: The formation and evolution of galaxies and the intragroup medium in an isolated system. Fossil groups may still contain unmerged dwarf galaxies , but the more massive members of the group have condensed into the central galaxy. This hypothesis is supported by studies of computer simulations of cosmological volumes. The closest fossil group to the Milky Way is NGC 6482 , an elliptical galaxy at

588-517: The galaxies in the local universe. Groups have a mass range between those of the very large elliptical galaxies and clusters of galaxies. In the local universe, about half of the groups exhibit diffuse X-ray emissions from their intracluster media . Those that emit X-rays appear to have early-type galaxies as members. The diffuse X-ray emissions come from zones within the inner 10–50% of the groups' virial radius, generally 50–500 kpc. There are several subtypes of groups. A compact group consists of

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616-513: 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/s in the direction of the Norma Cluster (Abell 3627) . Lynden-Bell et al. (1988) dubbed the cause of this the " Great Attractor ". The Great Attractor is now understood to be the center of mass of an even larger structure of galaxy clusters, dubbed " Laniakea ", which includes

644-517: The literature. From 2015 to 2017 a full optical survey was conducted using the Dark Energy Camera , covering 550 square degrees in the sky and doubling the number of known dwarf galaxies in this group. Another deep but spatially limited survey around Centaurus A revealed numerous new dwarfs. The dwarf spheroidal galaxies of the Centaurus A group have been studied and have been found to have old, metal-poor stellar populations similar to those in

672-477: The luminosity of the Sun ); collections of galaxies larger than groups that are first-order clustering are called galaxy clusters . The groups and clusters of galaxies can themselves be clustered, into superclusters of galaxies. The Milky Way galaxy is part of a group of galaxies called the Local Group . Groups of galaxies are the smallest aggregates of galaxies. They typically contain no more than 50 galaxies in

700-410: The main arguments in favor of the presence of large amounts of dark matter in the universe; if dark matter did not exist, much smaller mass-to-light ratios would be expected. Galaxy group A galaxy group or group of galaxies ( GrG ) is an aggregation of galaxies comprising about 50 or fewer gravitationally bound members, each at least as luminous as the Milky Way (about 10 times

728-419: The term Metagalaxy . 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. The issue was resolved with the large redshift surveys of the late 1970s and early 1980s, which convincingly showed the flattened concentration of galaxies along the supergalactic plane. In a comprehensive 1982 paper, R. Brent Tully presented

756-516: Was identified as a group member in the HIDEEP survey, which was a more intensive radio survey for hydrogen emission within a smaller region of the sky. Several optical surveys later identified 20 more candidate objects to the group. In 2007, the Cen A group membership of NGC 5011C was established. While this galaxy is a well-known stellar system listed with a NGC number, its true identity remained hidden because of coordinate confusion and wrong redshifts in

784-441: 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 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 ) in 1958. Harlow Shapley , in his 1959 book Of Stars and Men , suggested

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