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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.
Circinus is a small, faint constellation in the southern sky, first defined in 1756 by the French astronomer Nicolas-Louis de Lacaille. Its name is Latin for compass, referring to the drafting tool used for drawing circles. Its brightest star is Alpha Circini, with an apparent magnitude of 3.19. Slightly variable, it is the brightest rapidly oscillating Ap star in the night sky. AX Circini is a Cepheid variable visible with the unaided eye, and BX Circini is a faint star thought to have been formed from the merger of two white dwarfs. Two sun-like stars have planetary systems: HD 134060 has two small planets, and HD 129445 has a Jupiter-like planet. Supernova SN 185 appeared in Circinus in 185 AD and was recorded by Chinese observers. Two novae have been observed more recently, in the 20th century.
Messier 106 is an intermediate spiral galaxy in the constellation Canes Venatici. It was discovered by Pierre Méchain in 1781. M106 is at a distance of about 22 to 25 million light-years away from Earth. M106 contains an active nucleus classified as a Type 2 Seyfert, and the presence of a central supermassive black hole has been demonstrated from radio-wavelength observations of the rotation of a disk of molecular gas orbiting within the inner light-year around the black hole. NGC 4217 is a possible companion galaxy of Messier 106.
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 514 is a low-luminosity, intermediate spiral galaxy in the equatorial constellation of Pisces, located at a distance of approximately 83 million light-years from the Milky Way. It was discovered on 16 October 1784 by astronomer William Herschel. The general form of the galaxy is specified by its morphological classification of SAB(rs)c, which indicates it has a weak bar system at the core (SAB), an incomplete ring formation around the bar (rs), and somewhat loosely-wound spiral arms (c). This galaxy has an H II nucleus with an extended region that displays weak emission lines in the optical range, but not in the near infrared. The suspected supermassive black hole at the core has an estimated mass of 3.2×106 M☉.
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 4151 is an intermediate spiral Seyfert galaxy with weak inner ring structure located 15.8 megaparsecs from Earth in the constellation Canes Venatici. The galaxy was first mentioned by William Herschel on March 17, 1787; it was one of the six Seyfert galaxies described in the paper which defined the term. It is one of the nearest galaxies to Earth to contain an actively growing supermassive black hole. The black hole would have a mass on the order of 2.5 million to 30 million solar masses. It was speculated that the nucleus may host a binary black hole, with about 40 million and about 10 million solar masses respectively, orbiting with a 15.8-year period. This is, however, still a matter of active debate.
NGC 7314 is a spiral galaxy located in the southern constellation of Piscis Austrinus. It was discovered by English astronomer John Herschel on July 29, 1834. This is a nearby Seyfert (active) galaxy, located at a distance of approximately 54.6 megalight-years from the Milky Way. Since it appears to have detached spiral arm segments, it was listed in Halton Arp's Atlas of Peculiar Galaxies.
NGC 4051 is an intermediate spiral galaxy in the constellation of Ursa Major. It was discovered on 6 February 1788 by John Herschel.
NGC 3783 is a barred spiral galaxy located about 135 million light years away in the constellation Centaurus. It is inclined by an angle of 23° to the line of sight from the Earth along a position angle of about 163°. The morphological classification of SBa indicates a bar structure across the center (B) and tightly-wound spiral arms (a). Although not shown by this classification, observers note the galaxy has a luminous inner ring surrounding the bar structure. The bright compact nucleus is active and categorized as a Seyfert 1 type. This nucleus is a strong source of X-ray emission and undergoes variations in emission across the electromagnetic spectrum.
NGC 6814 is an intermediate spiral galaxy in constellation Aquila. It is located at a distance of about 75 million light years from Earth, which, given its apparent dimensions, means that NGC 6814 is about 85,000 light years across. NGC 6814 has an extremely bright nucleus and is a type 1.5 Seyfert galaxy. The galaxy is also a highly variable source of X-ray radiation. The ultraviolet and optical emission also varies, although more smoothly, with time lag of two days. The cause of the lag and the smoothing of light curves is considered to be the reprocessing of the X-rays in the accretion disk. The cause of the active galactic nucleus is suspected to be a supermassive black hole with a mass about 18 million times that of the Sun. Many regions of ionised gas are studded along the dusty spiral arms.
NGC 2992 is a Seyfert galaxy located 103 million light years distant in the equatorial constellation of Hydra. It was discovered in 1785 by Anglo-German astronomer William Herschel.
LEDA 83677 is a lenticular galaxy located about 290 million light-years away in the constellation Coma Berenices. It is a member of the Coma cluster of galaxies. LEDA 83677 is also classified as a type 1 Seyfert galaxy. The core of the galaxy is emitting high-energy X-rays and ultraviolet light, probably caused by a massive black hole lurking in the core.
NGC 1019 is a barred spiral galaxy approximately 316 million light-years away from Earth in the constellation of Cetus. It was discovered by French astronomer Édouard Stephan on December 1, 1880 with the 31" reflecting telescope at the Marseille Observatory.
NGC 985 is a ring galaxy in the constellation of Cetus. It is located about 550 million light years away from Earth, which means, given its apparent dimensions, that NGC 985 is approximately 160,000 light years across. It was discovered by Francis Leavenworth in 1886. It is a type 1 Seyfert galaxy.
NGC 3393 is a barred spiral galaxy located in the constellation Hydra. It is located at a distance of circa 180 million light-years from Earth, which, given its apparent dimensions, means that NGC 3393 is about 140,000 light-years across. It was discovered by John Herschel on March 24, 1835. It is a Type II Seyfert galaxy. The galaxy is known to host two supermassive black holes, which are the nearest known pair of supermassive black holes to Earth.
NGC 4589 is an elliptical galaxy located in the Draco constellation. It is at a distance of about 108 million light-years away from the Earth. It is known by its designations PGC 42139 or UGC 7797.
NGC 676 is a lenticular Seyfert 2 galaxy about 18.7 Mly away in the constellation Pisces. It can be seen near the star α Piscium. Located close to the celestial equator, it is visible from both hemispheres. BD +04 0244, a star with a visual magnitude of 10.44, is superposed 5.1 arc seconds south-southwest of the nucleus. It is one of the 621 galaxies described in Marat Arakelian's catalog of high-surface-brightness galaxies.
NGC 7679 is a lenticular galaxy with a peculiar morphology in the constellation Pisces. It is located at a distance of circa 200 million light years from Earth, which, given its apparent dimensions, means that NGC 7679 is about 60,000 light years across. It was discovered by Heinrich d'Arrest on September 23, 1864. The total infrared luminosity is 1011.05 L☉, and thus it is categorised as a luminous infrared galaxy. NGC 7679 is both a starburst galaxy and a Seyfert galaxy.
NGC 2617 is a Seyfert galaxy in the equatorial constellation of Hydra. It was discovered on February 12, 1885, by French astronomer Édouard Stephan. In 1888, Danish astronomer J. L. E. Dreyer described it as "extremely faint, very small, 2 very faint stars involved". It is located at an estimated distance of 202 million light years. In the infrared, the galaxy has an angular size of 0.693 by 0.652 arcminutes.
References
- 1 2 3 4 Staff (20 January 2020). "2MASX J13251937-3824524 - Seyfert 1 Galaxy". SIMBAD . Retrieved 20 January 2020.
- 1 2 Staff (2 August 2008). "Finding the constellation which contains given sky coordinates". DJM.cc. Retrieved 20 January 2020.
- 1 2 3 Drake, Nadia (20 January 2020). "Astronomers just got a deep peek at a black hole - Using a technique akin to echolocation, scientists were able to map the region around a distant black hole's event horizon in unprecedented detail". National Geographic Society . Retrieved 20 January 2020.
- ↑ "Search specification: IRAS 13224-3809". HyperLeda. Université Claude Bernard Lyon 1. Retrieved 23 February 2021.
- 1 2 Alston, William N.; et al. (20 January 2020). "A dynamic black hole corona in an active galaxy through X-ray reverberation mapping". Nature Astronomy . 4 (6): 597–602. arXiv: 2001.06454 . doi:10.1038/s41550-019-1002-x. hdl:1721.1/129519. S2CID 210713866 . Retrieved 20 January 2020.
- ↑ University of Southampton (20 January 2020). "Echoes of light help scientists map the behaviour of a black hole". Technology.org. Retrieved 20 January 2020.
