Roughly 80% of all galaxies located within 5 Mpc (16 Mly) of the Milky Way are in groups or clusters of galaxies. Most low-surface-brightness galaxies are field galaxies. The median Hubble-type of field galaxies is Sb, a type of spiral galaxy.
|NGC 404||SA(s)0||Andromeda||01h 09m 27.0s||+35° 43′ 04″||11.2 Mly (3.4 Mpc)|||
|NGC 1313||SB(s)d||Reticulum||03h 18m 15.4s||−66° 29′ 50″||12.89 Mly (3.95 Mpc)||Nicknamed the "Topsy Turvy Galaxy" due to its uneven shape|||
|NGC 2188||Sm||Columba||06h 10m 09.7s||−34° 06′ 50″||27.5 Mly (8.4 Mpc)|||
|NGC 2683||Sc||Lynx||08h 52m 41.3s||+33° 25′ 18″||32.9 Mly (10.1 Mpc)|||
|NGC 2903||SBbc||Leo||09h 32m 10.1s||+21° 30′ 03″||30.6 Mly (9.4 Mpc)|||
|NGC 3115||S0||Sextans||10h 05m 14.0s||−7° 43′ 07″||31.6 Mly (9.7 Mpc)|||
|NGC 3621||SA(s)d||Hydra||11h 18m 16.5s||–32° 48′ 51″||21.7 Mly (6.7 Mpc)|||
|NGC 4136||SABc||Coma Berenices||12h 09m 17.7s||+29° 55′ 39″||40.9 Mly (12.5 Mpc)|||
|NGC 4605||SB(s)c||Ursa Major||12h 39m 59.4s||+61° 36′ 33″||15.3 Mly (4.7 Mpc)|||
|NGC 5068||SAB(rs)cd||Virgo||13h 18m 54.8s||−21° 02′ 21″||19.8 Mly (6.1 Mpc)|||
|30 kly (9.2 kpc)||Draco||17h 49m 26.514s||+70° 08′ 39.63″||18.5 Mly (5.7 Mpc)||Also called the "Lost-In-Space galaxy" due to its location next to the Local Void.|||
In astronomy, the 2dF Galaxy Redshift Survey (Two-degree-Field Galaxy Redshift Survey), 2dF or 2dFGRS is a redshift survey conducted by the Anglo-Australian Observatory (AAO) with the 3.9m Anglo-Australian Telescope between 1997 and 11 April 2002. The data from this survey were made public on 30 June 2003. The survey determined the large-scale structure in two large slices of the Universe to a depth of around 2.5 billion light years (redshift ~ 0.2). It was the world's largest redshift survey between 1998 (overtaking Las Campanas Redshift Survey) and 2003 (overtaken by the Sloan Digital Sky Survey). Matthew Colless, Richard Ellis, Steve Maddox and John Peacock were in charge of the project. Team members Shaun Cole and John Peacock were awarded a share of the 2014 Shaw Prize in astronomy for results from the 2dFGRS.6dF Galaxy Survey
The 6dF Galaxy Survey (Six-degree Field Galaxy Survey), 6dF or 6dFGS is a redshift survey conducted by the Anglo-Australian Observatory (AAO) with the 1.2m UK Schmidt Telescope between 2001 and 2009. The data from this survey were made public on 31 March, 2009. The survey has mapped the nearby universe over nearly half the sky. Its 136,304 spectra have yielded 110,256 new extragalactic redshifts and a new catalog of 125,071 galaxies. For a subsample of 6dF a peculiar velocity survey is measuring mass distribution and bulk motions of the local Universe. As of July 2009, it is the third largest redshift survey next to the Sloan Digital Sky Survey (SDSS) and the 2dF Galaxy Redshift Survey (2dFGRS).Butcher–Oemler Effect
The Butcher–Oemler Effect is a scientific hypothesis suggesting the cores of galaxy clusters at intermediate redshift (z ~ 0.3) contain a larger fraction of blue galaxies than do the cores of low redshift clusters. The claim was first put forward by Harvey Butcher and Augustus Oemler in a 1978 Astrophysical Journal paper.The original Butcher–Oemler paper presents photometry of two clusters of galaxies, Cl 0024+1654 at z = 0.39 and 3C 295 at z = 0.46. These clusters are not atypical in their morphology or richness. They are both rich and centrally concentrated, rather like the nearby Coma Cluster. The surprising conclusion is that in the cores of these distant clusters more blue galaxies are observed than are observed in the cores of nearby clusters of similar richness and morphology.
Cluster galaxy "blueness" may, under certain circumstances, be used as an indicator of ongoing star formation. Astronomers have identified three spectral classes in which a significant set of blue galaxy cluster members may be categorized. The first is objects undergoing vigorous star formation with very blue colors and spectra showing emission-filled H-delta lines. Secondly, post-starburst galaxies are also observed. These are cluster members showing similarly blue colors as starburst galaxies only with moderate to strong H-delta absorption. Third are cluster members showing broad and/or high excitation line spectra, often found in active galactic nuclei. The Butcher–Oemler observations suggest at intermediate redshift a higher rate of star formation may be observed in a fraction of the galaxies in the cores of rich clusters than in the cores of rich clusters at low redshift.
The 1978 Butcher–Oemler paper sparked considerable debate. The ensuing series of Butcher–Oemler papers spans six years concluding with The Evolution of Galaxies in Clusters. V. A Study of Populations since z ~ 0.5. This paper presents photometry of 33 clusters of galaxies with redshifts varying from 0.003, the Virgo Cluster, to 0.54, the cluster Cl 0016+16. This study bolsters the conclusion put forward in their original 1978 paper, that there has been "strong, recent evolution of galaxies in clusters".
The Butcher–Oemler conclusion generated numerous investigations of the cores of rich clusters at intermediate redshift (0.3 ≤ z ≤ 0.9): Couch and Newell (1984), like Butcher and Oemler, acquired broadband photometry of such environments. Couch et al. (1983), Ellis et al. (1985), MacLaren, Ellis and Couch (1988), Aragon-Salamanca, Ellis and Sharples (1991) and Aragon-Salamanca et al. (1993) imaged clusters with redshifts between 0.5 ≤ z ≤ 0.9 in both optical and infrared bands. Spectroscopic observations were conducted by Dressler and Gunn (1982), Lavery and Henry (1985) and Couch and Sharples (1987). Studies of the morphologies of the galaxies in the cores of these clusters were undertaken using the Hubble Space Telescope by Couch et al. (1994) and Dressler et al. (1994). The outcome of these investigations is that the Butcher–Oemler effect is widespread in rich clusters at z > 0.2 and is due to vigorous episodes of star formation in a subset of the cluster members.
The effect does appear to be confined to rich clusters, at least as rich or richer than the Virgo cluster. Allington-Smith et al. (1993) observed galaxies in small groups out to a redshift of 0.5 and found no relation between the fraction of blue members and group richness; groups of all richnesses were observed to have similar high fractions of blue galaxies. Colless et al. (1990, 1993) have confirmed that better than 95% of blue field galaxies brighter than bJ = 22.5 are at redshifts less than z = 0.5, verifying at the 90% confidence level models predicting no luminosity evolution of the field galaxy population since z = 1. Using the Hubble Space Telescope, Dressler et al. (1994) observed the cluster CL 0930+4713 at 0.41 and Couch et al. (1994) observed AC 114 at z = 0.31 and Abell 370 at z = 0.37. These authors independently arrived at the conclusion that every observation of a merger between cluster members, both of which showed blue colors, had the spectroscopic signature of a starburst or post-starburst object. It is plausible therefore, that the Butcher–Oemler effect may be partially the result of galaxy–galaxy mergers.Coma Filament
Coma Filament is a galaxy filament. The filament contains the Coma Supercluster of galaxies and forms a part of the CfA2 Great Wall.Experimental physics
Experimental physics is the category of disciplines and sub-disciplines in the field of physics that are concerned with the observation of physical phenomena and experiments. Methods vary from discipline to discipline, from simple experiments and observations, such as the Cavendish experiment, to more complicated ones, such as the Large Hadron Collider.Galaxy
A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. The word galaxy is derived from the Greek galaxias (γαλαξίας), literally "milky", a reference to the Milky Way. Galaxies range in size from dwarfs with just a few hundred million (108) stars to giants with one hundred trillion (1014) stars, each orbiting its galaxy's center of mass.
Galaxies are categorized according to their visual morphology as elliptical, spiral, or irregular. Many galaxies are thought to have supermassive black holes at their centers. The Milky Way's central black hole, known as Sagittarius A*, has a mass four million times greater than the Sun. As of March 2016, GN-z11 is the oldest and most distant observed galaxy with a comoving distance of 32 billion light-years from Earth, and observed as it existed just 400 million years after the Big Bang.
Research released in 2016 revised the number of galaxies in the observable universe from a previous estimate of 200 billion (2×1011) to a suggested 2 trillion (2×1012) or more, containing more stars than all the grains of sand on planet Earth. Most of the galaxies are 1,000 to 100,000 parsecs in diameter (approximately 3000 to 300,000 light years) and separated by distances on the order of millions of parsecs (or megaparsecs). For comparison, the Milky Way has a diameter of at least 30,000 parsecs (100,000 LY) and is separated from the Andromeda Galaxy, its nearest large neighbor, by 780,000 parsecs (2.5 million LY).
The space between galaxies is filled with a tenuous gas (the intergalactic medium) having an average density of less than one atom per cubic meter. The majority of galaxies are gravitationally organized into groups, clusters, and superclusters. The Milky Way is part of the Local Group, which is dominated by it and the Andromeda Galaxy and is part of the Virgo Supercluster. At the largest scale, these associations are generally arranged into sheets and filaments surrounded by immense voids. The largest structure of galaxies yet recognised is a cluster of superclusters that has been named Laniakea, which contains the Virgo supercluster.Great Observatories Origins Deep Survey
The Great Observatories Origins Deep Survey, or GOODS, is an astronomical survey combining deep observations from three of NASA's Great Observatories: the Hubble Space Telescope, the Spitzer Space Telescope, and the Chandra X-ray Observatory, along with data from other space-based telescopes, such as XMM Newton, and some of the world's most powerful ground-based telescopes.
GOODS is intended to enable astronomers to study the formation and evolution of galaxies in the distant, early universe.
The Great Observatories Origins Deep Survey consists of optical and near-infrared imaging taken with the Advanced Camera for Surveys on the Hubble Space Telescope, the Very Large Telescope and the 4-m telescope at Kitt Peak National Observatory; infrared data from the Spitzer Space Telescope. These are added to pre-existing x-ray data from the Chandra X-ray Observatory and ESAs XMM-Newton, two fields of 10' by 16'; one centered on the Hubble Deep Field North (12h 36m 55s, +62° 14m 15s) and the other on the Chandra Deep Field South (3h 32m 30s, -27° 48m 20s).
The two GOODS fields are the most data-rich areas of the sky in terms of depth and wavelength coverage.Irregular galaxy
An irregular galaxy is a galaxy that does not have a distinct regular shape, unlike a spiral or an elliptical galaxy. Irregular galaxies do not fall into any of the regular classes of the Hubble sequence, and they are often chaotic in appearance, with neither a nuclear bulge nor any trace of spiral arm structure.Collectively they are thought to make up about a quarter of all galaxies. Some irregular galaxies were once spiral or elliptical galaxies but were deformed by an uneven external gravitational force. Irregular galaxies may contain abundant amounts of gas and dust. This is not necessarily true for dwarf irregulars.Irregular galaxies are commonly small, about one tenth the mass of the Milky Way galaxy. Due to their small sizes, they are prone to environmental effects like crashing with large galaxies and intergalactic clouds.List of galaxies
The following is a list of notable galaxies.
There are about 51 galaxies in the Local Group (see list of nearest galaxies for a complete list), on the order of 100,000 in our Local Supercluster and an estimated number of about one to two trillion in all of the observable universe.
The discovery of the nature of galaxies as distinct from other nebulae (interstellar clouds) was made in the 1920s. The first attempts at systematic catalogues of galaxies were made in the 1960s, with the Catalogue of Galaxies and Clusters of Galaxies listing 29,418 galaxies and galaxy clusters, and with the Morphological Catalogue of Galaxies, a putatively complete list of galaxies with photographic magnitude above 15, listing 30,642. In the 1980s, the Lyons Groups of Galaxies listed 485 galaxy groups with 3,933 member galaxies. Galaxy Zoo is a project aiming at a more comprehensive list: launched in July 2007, it has classified over one million galaxy images from The Sloan Digital Sky Survey, The Hubble Space Telescope and the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey.There is no universal naming convention for galaxies, as they are mostly catalogued before it is established whether the object is or isn't a galaxy. Mostly they are identified by their celestial coordinates together with the name of the observing project (HUDF, SDSS, 3C, CFHQS, NGC/IC, etc.)Lynx–Ursa Major Filament
Lynx–Ursa Major Filament (LUM Filament) is a galaxy filament.The filament is connected to and separate from the Lynx–Ursa Major Supercluster.NGC 1313
NGC 1313 (also known as the Topsy Turvy Galaxy) is a field galaxy and a barred spiral galaxy discovered by the Scottish astronomer James Dunlop on 27 September 1826. It has a diameter of about 50,000 light-years, or about half the size of the Milky Way.NGC 1313 lies within the Virgo Supercluster.NGC 404
NGC 404 is a field galaxy located about 10 million light years away in the constellation Andromeda. It was discovered by William Herschel in 1784, and is visible through small telescopes. NGC 404 lies just beyond the Local Group and does not appear gravitationally bound to it. It is located within 7 arc-minutes of second magnitude star Mirach, making it a difficult target to observe or photograph and granting it the nickname "Mirach's Ghost".NGC 4555
NGC 4555 is a solitary elliptical galaxy about 40,000 parsecs (125,000 light-years) across, and about 310 million light years distant. Observations by the Chandra X-ray Observatory have shown it to be surrounded by a halo of hot gas about 120,000 parsecs across. The hot gas has a temperature of around 10,000,000 kelvins. The galaxy is one of the few elliptical galaxies proven to have significant amounts of dark matter. Large amounts of dark matter are necessary to prevent the gas from escaping the galaxy; the visible mass clearly is not large enough to hold such an extensive gas halo. The dark matter halo is estimated to have 10 times the mass of the stars in the galaxy.
NGC 4555 is important because of its isolation. Most elliptical galaxies are found in the cores of groups and clusters of galaxies, and almost all those for which dark matter estimates are available are located in the centres of these larger systems. In these circumstances it impossible to know whether the dark matter is associated with the galaxy or the surrounding cluster. NGC 4555, as a field galaxy is not part of any group or cluster, and therefore provides strong evidence that dark matter can be associated with individual ellipticals.
Despite being isolated, NGC 4555 is part of the Coma Supercluster.NGC 7424
NGC 7424 is a barred spiral galaxy located 37.5 million light-years away in the southern constellation Grus (the Crane). Its size (about 100,000 light-years) makes it similar to our own galaxy, the Milky Way.
It is called a "grand design" galaxy because of its well defined spiral arms. One supernova and two ultraluminous X-ray sources have been discovered in NGC 7424.Perseus–Pegasus Filament
Perseus–Pegasus Filament is a galaxy filament containing the Perseus-Pisces Supercluster and stretching for roughly a billion light years (or over 300/h Mpc). Currently, it is considered to be one of the largest known structures in the universe. This filament is adjacent to the Pisces–Cetus Supercluster Complex.Ursa Major Filament
Ursa Major Filament is a galaxy filament. The filament is connected to the CfA Homunculus, a portion of the filament forms a portion of the "leg" of the Homunculus.Virgo Supercluster
The Virgo Supercluster (Virgo SC) or the Local Supercluster (LSC or LS) is a mass concentration of galaxies containing the Virgo Cluster and 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). The Virgo SC 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 Virgo Supercluster is only a lobe of an even greater supercluster, Laniakea, a larger, competing referent of Local Supercluster centered on the Great Attractor.Void (astronomy)
Cosmic voids are vast spaces between filaments (the largest-scale structures in the universe), which contain very few or no galaxies. Voids typically have a diameter of 10 to 100 megaparsecs; particularly large voids, defined by the absence of rich superclusters, are sometimes called supervoids. They have less than one tenth of the average density of matter abundance that is considered typical for the observable universe. They were first discovered in 1978 in a pioneering study by Stephen Gregory and Laird A. Thompson at the Kitt Peak National Observatory.Voids are believed to have been formed by baryon acoustic oscillations in the Big Bang, collapses of mass followed by implosions of the compressed baryonic matter. Starting from initially small anisotropies from quantum fluctuations in the early universe, the anisotropies grew larger in scale over time. Regions of higher density collapsed more rapidly under gravity, eventually resulting in the large-scale, foam-like structure or "cosmic web" of voids and galaxy filaments seen today. Voids located in high-density environments are smaller than voids situated in low-density spaces of the universe.Voids appear to correlate with the observed temperature of the cosmic microwave background (CMB) because of the Sachs–Wolfe effect. Colder regions correlate with voids and hotter regions correlate with filaments because of gravitational redshifting. As the Sachs–Wolfe effect is only significant if the universe is dominated by radiation or dark energy, the existence of voids is significant in providing physical evidence for dark energy.