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An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not produced by stars. Such excess non-stellar emission has been observed in the radio, microwave, infrared, optical, ultra-violet, X-ray and gamma ray wavebands. A galaxy hosting an AGN is called an "active galaxy". The non-stellar radiation from an AGN is theorized to result from the accretion of matter by a supermassive black hole at the center of its host galaxy.
Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, their host galaxies are clearly detectable.
Stephan's Quintet is a visual grouping of five galaxies of which four form the first compact galaxy group ever discovered. The group, visible in the constellation Pegasus, was discovered by Édouard Stephan in 1877 at the Marseille Observatory. The group is the most studied of all the compact galaxy groups. The brightest member of the visual grouping is NGC 7320, which has extensive H II regions, identified as red blobs, where active star formation is occurring.
Carl Keenan Seyfert was an American astronomer. He is best known for his 1943 research paper on high-excitation line emission from the centers of some spiral galaxies, which are named Seyfert galaxies after him. Seyfert's Sextet, a group of galaxies, is also named after him.
The Sombrero Galaxy is a peculiar galaxy of unclear classification in the constellation borders of Virgo and Corvus, being about 9.55 megaparsecs from the Milky Way galaxy. It is a member of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the Virgo Supercluster. It has a diameter of approximately 15 kiloparsecs, three-tenths the size of the Milky Way.
The Haleakalā Observatory, also known as the Haleakalā High Altitude Observatory Site, is Hawaii's first astronomical research observatory. It is located on the island of Maui and is owned by the Institute for Astronomy of the University of Hawaiʻi, which operates some of the facilities on the site and leases portions to other organizations. Tenants include the Air Force Research Laboratory (AFRL) and the Las Cumbres Observatory Global Telescope Network (LCOGTN). At over 3,050 meters (10,010 ft) in altitude, the summit of Haleakalā is above one third of the Earths's troposphere and has excellent astronomical seeing conditions.
NGC 3227 is an intermediate spiral galaxy that is interacting with the dwarf elliptical galaxy NGC 3226. The two galaxies are one of several examples of a spiral with a dwarf elliptical companion that are listed in the Atlas of Peculiar Galaxies. Both galaxies may be found in the constellation Leo. It is a member of the NGC 3227 Group of galaxies, which is a member of the Leo II Groups, a series of galaxies and galaxy clusters strung out from the right edge of the Virgo Supercluster.
NGC 5548 is a Type I Seyfert galaxy with a bright, active nucleus. This activity is caused by matter flowing onto a 65 million solar mass (M☉) supermassive black hole at the core. Morphologically, this is an unbarred lenticular galaxy with tightly-wound spiral arms, while shell and tidal tail features suggest that it has undergone a cosmologically-recent merger or interaction event. NGC 5548 is approximately 245 million light years away and appears in the constellation Boötes. The apparent visual magnitude of NGC 5548 is approximately 13.3 in the V band.
NGC 5033 is an inclined spiral galaxy located in the constellation Canes Venatici. Distance estimates vary from between 38 and 60 million light years from the Milky Way. The galaxy has a very bright nucleus and a relatively faint disk. Significant warping is visible in the southern half of the disk. The galaxy's relatively large angular size and relatively high surface brightness make it an object that can be viewed and imaged by amateur astronomers. The galaxy's location relatively near Earth and its active galactic nucleus make it a commonly studied object for professional astronomers.
NGC 5005, also known as Caldwell 29, is an inclined spiral galaxy in the constellation Canes Venatici. The galaxy has a relatively bright nucleus and a bright disk that contains multiple dust lanes. The galaxy's high surface brightness makes it an object that is visible to amateur astronomers using large amateur telescopes.
A low-ionization nuclear emission-line region (LINER) is a type of galactic nucleus that is defined by its spectral line emission. The spectra typically include line emission from weakly ionized or neutral atoms, such as O, O+, N+, and S+. Conversely, the spectral line emission from strongly ionized atoms, such as O++, Ne++, and He+, is relatively weak. The class of galactic nuclei was first identified by Timothy Heckman in the third of a series of papers on the spectra of galactic nuclei that were published in 1980.
NGC 4051 is an intermediate spiral galaxy in the constellation of Ursa Major. It was discovered on 6 February 1788 by John Herschel.
NGC 4030 is a grand design spiral galaxy located about 64 million light years away in the constellation Virgo. It is a member of the NGC 4030 Group of galaxies, which is a member of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the Virgo Supercluster. With an apparent visual magnitude of 10.6, it is visible with a small telescope as a 3 arc minute wide feature about 4.75° to the southeast of the star Beta Virginis. It is inclined by an angle of 47.1° to the line of sight from the Earth and is receding at a velocity of 1,465 km/s.
NGC 5643 is an intermediate spiral galaxy in the constellation Lupus. Based on the tip of the red-giant branch distance indicator, it is located at a distance of about 40 million light-years. NGC 5643 has an active galactic nucleus and is a type II Seyfert galaxy.
NGC 2623/Arp 243 is an interacting galaxy located in the constellation Cancer. NGC 2623 is the result of two spiral galaxies that have merged. Scientists believe that this situation is similar to what will occur to the Milky Way, which contains the Solar System, and the neighboring galaxy, the Andromeda Galaxy in four billion years. Studying this galaxy and its properties have provided scientists with a better idea of the coming collision of the Milky Way and the Andromeda. Due to NGC 2623 being in the late stage of merging, the compression of the gas within the galaxy has led to a large amount of star formation, and to its unique structure of a bright core with two extending tidal tails.
NGC 7469 is an intermediate spiral galaxy in the constellation of Pegasus. NGC 7469 is located about 200 million light-years away from Earth, which means, given its apparent dimensions, that NGC 7469 is approximately 90,000 light-years across. It was discovered by William Herschel on November 12, 1784.
NGC 3367 is a barred spiral galaxy located in the constellation Leo. It is located at a distance of about 120 million light years from Earth, which, given its apparent dimensions, means that NGC 3367 is about 85,000 light years across. It was discovered by William Herschel on March 19, 1784.
NGC 1386 is a spiral galaxy located in the constellation Eridanus. It is located at a distance of circa 53 million light years from Earth, which, given its apparent dimensions, means that NGC 1386 is about 50,000 light years across. It is a Seyfert galaxy, the only one in Fornax Cluster.
NGC 2273 is a barred spiral galaxy located in the constellation Lynx. It is located at a distance of circa 95 million light years from Earth, which, given its apparent dimensions, means that NGC 2273 is about 100,000 light years across. It was discovered by Nils Dunér on September 15, 1867.
NGC 931 is a spiral galaxy located in the constellation Triangulum. It is located at a distance of circa 200 million light-years from Earth, which, given its apparent dimensions, means that NGC 931 is about 200,000 light years across. It was discovered by Heinrich d'Arrest on September 26, 1865. It is classified as a Seyfert galaxy.
References
- 1 2 3 "Haleakalā High Altitude Observatory Site Management Plan" (PDF). University of Hawai‘i Institute for Astronomy. 2010-06-08. Retrieved 2012-04-26.
- ↑ Yoshii, Y.; Kobayashi, Y.; Minezaki, T. (2003). "The MAGNUM (Multicolor Active Galactic NUclei Monitoring) Project". American Astronomical Society Meeting Abstracts #202. 35: 752. Bibcode:2003AAS...202.3803Y.
- ↑ "UH Institute for Astronomy Press Release".
- ↑ "Hawaii Telescopes Record Cosmic Explosion - Space News - redOrbit". www.redorbit.com. Archived from the original on 2011-05-22.
- ↑ "Honolulu Star-Bulletin Hawaii News".
- ↑ http://www.journals.uchicago.edu/doi/abs/10.1086/499326 The Astrophysical Journal, 639:46–63, 2006 March 1 "Reverberation Measurements of the Inner Radius of the Dust Torus in Nearby Seyfert 1 Galaxies"
- ↑ Kobayashi, Y.; Yoshii, Y.; Minezaki, T. (2004-10-01). "MAGNUM project: four years of operation of the fully automated observatory". Astronomische Nachrichten. 325 (6–8): 537–539. Bibcode:2004AN....325..537K. doi:10.1002/asna.200410275. ISSN 1521-3994.