Antlia-Sextans Group

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NGC 3109, largest and dominant member, optical image from Pan-STARRS Optical Galaxy Survey NGC 3109 PanS.jpg
NGC 3109, largest and dominant member, optical image from Pan-STARRS Optical Galaxy Survey

The Antlia-Sextans Group is a small Galaxy group in the constellations Hydra, Sextans, Antlia and Leo. It is, on average, approximately 4.3 million light-years away from the Milky Way. It is generally considered to be at the very edge of the Local Group and thus part of it. However, other researchers indicate it is an independent Galaxy group, unlikely to be gravitationally bound to the Local Group due to probably lying outside the Local Group's Zero-velocity surface, and thus the nearest Galaxy group to the Local Group rather than a subgroup within the Local Group. [1] Nonetheless—this possible independence may disappear as the Milky Way continues coalescing with Andromeda due to the increased mass, and density thereof, plausibly widening the radius of the Zero-velocity surface of the Local Group.

Contents

Members

The Antlia-Sextans Group consists of the galaxies NGC 3109, Sextans A, Sextans B, Antlia Dwarf, Leo P and Antlia B. Leo A might also belong to the group, but this is considered unlikely.

NGC 3109

NGC 3109 is the largest and dominant member of this group, with a diameter of 41,700 light-years, almost half the diameter of the Milky Way. [2] It was the first discovered member of the group, discovered in 1835. It is also second closest to Earth, at a distance of 4.348 million light-years away. It was thought to be an irregular galaxy, but is now theorized to possibly be a barred spiral. It seems to be a galaxy with no central core. Based on spectroscopy of blue supergiants in NGC 3109, it is known that the galaxy has a low metallicity, similar to that to the Small Magellanic Cloud. [3] It is one of the most metal-poor galaxies in the Local group, if it is included. [4] NGC 3109 seems to contain an unusually large number of planetary nebulae for its luminosity. [5] It also contains a substantial amount of dark matter. [6]

From measurements of the neutral atomic hydrogen in the galaxy, it has been found that the disk of NGC 3109 is warped. [7]

Antlia Dwarf

Antlia Dwarf, by Hubble Space Telescope Antlia Dwarf PGC 29194 Hubble WikiSky.jpg
Antlia Dwarf, by Hubble Space Telescope

Antlia Dwarf is the smallest and closest galaxy in the group, only 2,610 light-years in diameter at a distance of 4.305 million light-years. [8] The gas in the Antlia Dwarf galaxy has the same radial velocity as a warp in the disk of NGC 3109, indicating that the two galaxies had a close encounter approximately one billion years ago. [7]

Sextans A

Square-shaped Sextans A, with bright star clusters and bright Milky Way's foreground star Sextans dwarf.jpg
Square-shaped Sextans A, with bright star clusters and bright Milky Way's foreground star

Sextans A is 7,990 light-years in diameter, and square-shaped, and contains numerous star clusters, located at the distance of about 4.658 million light-years away. [9] Sextans A has a peculiar square shape. Massive short-lived stars exploded in supernovae that caused more star formation, triggering yet more supernovae, ultimately resulting in an expanding shell. Young blue stars now highlight areas and shell edges high in current star formation, which from the perspective of observers on Earth appears roughly square. [10] The 10.4m telescope Gran Telescopio Canarias recently observed the OB-type stars that power the giant HII regions. [11] Sextans A have formed a pair with the most remote galaxy in the group, Sextans B.

Sextans B

Sextans B, by Hubble Space Telescope Sextans B Hubble WikiSky.jpg
Sextans B, by Hubble Space Telescope

Sextans B is the second largest galaxy in the group, with a diameter of 8,900 light-years. [12] Sextans B is the most distant from Earth in the group, at 5.101 million light-years away. [12] Sextans B has a uniform stellar population, [13] but the interstellar medium in it may be inhomogeneous. [14] Its mass is estimated to be about 2 × 108 times the mass of the Sun, of which 5.5 × 107 is in the form of atomic hydrogen. [13] Star formation in the galaxy seems to have proceeded in distinct periods of low intensity, separated by shorter periods of no activity. [13] The existence of Cepheid variables in the galaxy implies that Sextans B contains at least some young stars. [15] The metallicity of Sextans B is rather low, with a value of approximately Z = 0.001. [13] Sextans B is receding from the Milky Way with a speed of approximately 300 kilometres per second (190 mi/s), [14] and probably lies just outside the edge of the Local Group, so as its neighbour Sextans A. [16]

Five planetary nebulae have been identified in Sextans B, which is one of the smallest galaxies where planetary nebulae have been observed. These appear point-like and can be identified by their spectral emission lines. [17] It also contains a massive globular cluster. [18]

Leo P

Leo P (AGC 208583 [19] ) is a small irregular galaxy discovered in 2013. It is only 0.4 Mpc from the Sextans B, so it is considered as a member of this grouping. It is the most distant member of all, with a distance of 5.3 million light years.

Antlia B

Antlia B is recently discovered small galaxy. It is known to be a satellite of NGC 3109 situated at the distance of 1.35±0.06 pc and is similar to the Antlia Dwarf in many ways. Antlia B is transitioning from an irregular galaxy to a dwarf spheroidal. It contains mainly metal poor old stars, although a small number of young blue stars (<1 Gyr) is present. The galaxy possesses a substantial (~300,000 solar masses) amount of neutral hydrogen but no outgoing star formation. [20] [21]

Members of the Antlia-Sextans Group [22]
Name Type [23] R.A. (J2000) [23] Dec. (J2000) [23] Redshift (km/s) [23] Apparent Magnitude [23]
NGC 3109 SB(s)m10h 03m 06.9s−26° 09′ 34″+403 ± 110.4
Sextans A IBm10h 11m 00.8s−04° 41′ 34″+324 ± 211.9
Sextans B ImIV–V10h 00m 00.1s+05° 19′ 56″+300 ± 011.9
Antlia Dwarf dSph/Irr10h 04m 03.9s−27° 19′ 55″+362 ± 015.67 ± 0.02
Leo P Irr10h 21m 45.1s+18° 05' 17"N/A16.9
Antlia BdTrans9h 48m 56s−25° 59' 24"+37616.0 ± 0.6

See also

Related Research Articles

<span class="mw-page-title-main">Galaxy</span> Large gravitationally bound system of stars and interstellar matter

A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. The word is derived from the Greek galaxias (γαλαξίας), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. Galaxies, averaging an estimated 100 million stars, range in size from dwarfs with less than a thousand stars, to the largest galaxies known – supergiants with one hundred trillion stars, each orbiting its galaxy's center of mass. Most of the mass in a typical galaxy is in the form of dark matter, with only a few percent of that mass visible in the form of stars and nebulae. Supermassive black holes are a common feature at the centres of galaxies.

<span class="mw-page-title-main">Local Group</span> Group of galaxies that includes the Milky Way

The Local Group is the galaxy group that includes the Milky Way, where Earth is located. It has a total diameter of roughly 3 megaparsecs (10 million light-years; 9×1019 kilometres), and a total mass of the order of 2×1012 solar masses (4×1042 kg). It consists of two collections of galaxies in a "dumbbell" shape; the Milky Way and its satellites form one lobe, and the Andromeda Galaxy and its satellites constitute the other. The two collections are separated by about 800 kiloparsecs (3×10^6 ly; 2×1019 km) and are moving toward one another with a velocity of 123 km/s. The group itself is a part of the larger Virgo Supercluster, which may be a part of the Laniakea Supercluster. The exact number of galaxies in the Local Group is unknown as some are occluded by the Milky Way; however, at least 80 members are known, most of which are dwarf galaxies.

<span class="mw-page-title-main">Triangulum Galaxy</span> Spiral galaxy in the constellation Triangulum

The Triangulum Galaxy is a spiral galaxy 2.73 million light-years (ly) from Earth in the constellation Triangulum. It is catalogued as Messier 33 or NGC (New General Catalogue) 598. With the D25 isophotal diameter of 18.74 kiloparsecs (61,100 light-years), the Triangulum Galaxy is the third-largest member of the Local Group of galaxies, behind the Andromeda Galaxy and the Milky Way.

<span class="mw-page-title-main">Sombrero Galaxy</span> Galaxy in the constellation Virgo

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 an isophotal diameter of approximately 29.09 to 32.32 kiloparsecs, making it slightly bigger in size than the Milky Way.

<span class="mw-page-title-main">Sextans A</span> Dwarf irregular galaxy in the constellation Sextans

Sextans A is a small dwarf irregular galaxy. It spans about 5000 light-years across, and is located at 4.3 million light-years away, in the outskirts of the Local Group of galaxies, which includes the Milky Way galaxy, and to which Sextans A may or may not belong.

<span class="mw-page-title-main">NGC 3109</span> Galaxy in the constellation Hydra

NGC 3109 is a small barred Magellanic type spiral or irregular galaxy around 4.35 Mly away in the direction of the constellation of Hydra. NGC 3109 is believed to be tidally interacting with the dwarf elliptical galaxy Antlia Dwarf. It was discovered by John Herschel on March 24, 1835 while he was in what is now South Africa.

<span class="mw-page-title-main">NGC 6822</span> Galaxy in the constellation Sagittarius

NGC 6822 is a barred irregular galaxy approximately 1.6 million light-years away in the constellation Sagittarius. Part of the Local Group of galaxies, it was discovered by E. E. Barnard in 1884, with a six-inch refractor telescope. It is the closest non-satellite galaxy to the Milky Way, but lies just outside its virial radius. It is similar in structure and composition to the Small Magellanic Cloud. It is about 7,000 light-years in diameter.

The Sextans Dwarf Spheroidal is a dwarf spheroidal galaxy that was discovered in 1990 by Mike Irwin as the 8th satellite of the Milky Way, located in the constellation of Sextans. It is also an elliptical galaxy, and displays a redshift because it is receding from the Sun at 224 km/s. The distance to the galaxy is 320,000 light-years and the diameter is 8,400 light-years along its major axis.

<span class="mw-page-title-main">NGC 2683</span> Galaxy in the constellation Lynx

NGC 2683 is a field spiral galaxy in the northern constellation of Lynx. It was nicknamed the "UFO Galaxy" by the Astronaut Memorial Planetarium and Observatory. It was discovered by the astronomer William Herschel on February 5, 1788.

<span class="mw-page-title-main">NGC 1427</span> Galaxy in the constellation Fornax

NGC 1427 is a low-luminosity elliptical galaxy located approximately 71 million light-years away from Earth. It was discovered by John Frederick William Herschel on November 28, 1837. It is a member of the Fornax Cluster. The galaxy has a stellar mass of 7.9 × 1010M☉, and a total mass of 9.4 × 1010M☉. However, the mass of the dark matter halo surrounding the galaxy is around 4.3 × 1012M☉.

<span class="mw-page-title-main">Sextans B</span> Dwarf irregular galaxy in the constellation Sextans

Sextans B is an irregular galaxy that may be part of the Local Group, or lie just beyond it. Sextans B is 4.44 million light-years away from Earth and thus is one of the most distant members of the Local Group, if it is indeed a member. It forms a pair with its neighbouring galaxy Sextans A. It is a type Ir IV–V galaxy according to the galaxy morphological classification scheme. Sextans B may also be gravitationally associated with the galaxies NGC 3109 and the Antlia Dwarf.

<span class="mw-page-title-main">Antlia Dwarf</span> Galaxy in the constellation Antlia

The Antlia Dwarf is a dwarf spheroidal/irregular galaxy. It lies about 1.3 Mpc from Earth in the constellation Antlia. It is the fourth and faintest member of the nearby Antlia-Sextans Group of galaxies. The galaxy contains stars of all ages, contains significant amounts of gas, and has experienced recent star formation. The Antlia Dwarf is believed to be tidally interacting with the small barred spiral galaxy NGC 3109.

<span class="mw-page-title-main">NGC 247</span> Galaxy in the constellation Cetus

NGC 247 is an intermediate spiral galaxy about 11.1 Mly away in the constellation Cetus. This distance was confirmed in late February 2011. Previous measurements showed that the galaxy was about 12.2 Mly away, but this was proved to be wrong. NGC 247 is a member of the Sculptor Group, and is 70 000 light years in diameter.

<span class="mw-page-title-main">NGC 4605</span> Galaxy in the constellation Ursa Major

NGC 4605 is a dwarf barred spiral galaxy in the constellation Ursa Major, located at a distance of 18.1 ± 0.3 megalight-years from the Milky Way. Physically it is similar in size and in B-band absolute magnitude to the Large Magellanic Cloud. It is a member of the M81 Galaxy Group, along with Messier 81 and Messier 101.

<span class="mw-page-title-main">NGC 4449</span> Galaxy in the constellation Canes Venatici

NGC 4449, also known as Caldwell 21, is an irregular Magellanic type galaxy in the constellation Canes Venatici, being located about 13 million light-years away. It is part of the M94 Group or Canes Venatici I Group that is relatively close to the Local Group hosting our Milky Way galaxy.

<span class="mw-page-title-main">Antlia Cluster</span> Galaxy cluster in the constellation Antlia

The Antlia Cluster is a cluster of galaxies located in the Hydra–Centaurus Supercluster. The Antlia Cluster is the third-nearest to the Local Group after the Virgo Cluster and Fornax Cluster. Antlia's distance from Earth is 40.5 megaparsecs to 40.9 Mpc (133.4 Mly) and can be viewed from Earth in the constellation Antlia. The Antlia Cluster should not be confused with the Antlia Dwarf galaxy.

<span class="mw-page-title-main">NGC 24</span> Galaxy in the constellation Sculptor

NGC 24 is a spiral galaxy in the southern constellation of Sculptor, about 23.8 megalight-years distant from the Milky Way. It was discovered by British astronomer William Herschel in 1785, and measures some 40,000 light-years across. The general shape of this galaxy is specified by its morphological classification of SA(s)c, which indicates it is an unbarred spiral with no ring-like structure and moderate to loosely-wound spiral arms. This galaxy is positioned in the vicinity of the Sculptor Group, but is actually a background object that is more than three times as distant. It may form a pair with another background galaxy, NGC 45.

<span class="mw-page-title-main">NGC 4660</span> Galaxy in the constellation Virgo

NGC 4660 is an elliptical galaxy located about 63 million light-years away in the constellation Virgo. The galaxy was discovered by astronomer William Herschel on March 15, 1784 and is a member of the Virgo Cluster.

<span class="mw-page-title-main">NGC 3311</span> Galaxy in the constellation Hydra

NGC 3311 is a super-giant elliptical galaxy located about 190 million light-years away in the constellation Hydra. The galaxy was discovered by astronomer John Herschel on March 30, 1835. NGC 3311 is the brightest member of the Hydra Cluster and forms a pair with NGC 3309 which along with NGC 3311, dominate the central region of the Hydra Cluster.

References

  1. ↑ van den Bergh, Sidney (June 1999). "The Nearest Group of Galaxies". The Astrophysical Journal. 517 (2): L97–L99. arXiv: astro-ph/9904425 . Bibcode:1999ApJ...517L..97V. doi:10.1086/312044.
  2. ↑ "Detailed Information for Object NGC 3109". NASA/IPAC Extragalactic Database . Retrieved September 13, 2023.
  3. ↑ Evans, Chris; et al. (2006). "The ARAUCARIA Project – First Observations of Blue Supergiants in NGC 3109" (PDF). The Messenger. 126: 5. Bibcode:2006Msngr.126....5E . Retrieved 2010-09-24.
  4. ↑ Pena, M. "An interesting comparison between PNE and H II regions in NGC 3109 and NGC 6822" (PDF). Revista Mexicana de Astronomía y Astrofísica. 35: 74–75. Retrieved 2010-09-24.
  5. ↑ Richer, Michael G.; Marshall L. McCall (1992). "Planetary nebulae and H II regions in NGC 3109". The Astronomical Journal . 103: 54–59. Bibcode:1992AJ....103...54R. doi: 10.1086/116040 .
  6. ↑ Jobin, Marc; Carignan, Claude (1990). "The dark side of NGC 3109". The Astronomical Journal . 100 (3): 648–662. Bibcode:1990AJ....100..648J. doi: 10.1086/115548 .
  7. 1 2 Barnes, D. G.; de Blok, W. J. G. (August 2001). "On the Neutral Gas Content and Environment of NGC 3109 and the Antlia Dwarf Galaxy". The Astronomical Journal . 122 (2): 825. arXiv: astro-ph/0107474 . Bibcode:2001AJ....122..825B. doi:10.1086/321170. S2CID   15734118.
  8. ↑ "Detailed Information for Object Antlia Dwarf". NASA/IPAC Extragalactic Database . Retrieved September 13, 2023.
  9. ↑ "Detailed Information for Object Sextans A". NASA/IPAC Extragalactic Database . Retrieved September 13, 2023.
  10. ↑ Nemiroff, R.; Bonnell, J., eds. (November 3, 1998). "Sextans A: A Seemingly Square Galaxy". Astronomy Picture of the Day . NASA.
  11. ↑ Camacho, I.; Garcia, M.; Herrero, A.; Simón-Díaz, S. (2016). "OB stars at the lowest Local Group metallicity". Astronomy & Astrophysics. 585: A82. arXiv: 1510.05408 . Bibcode:2016A&A...585A..82C. doi:10.1051/0004-6361/201425533. ISSN   0004-6361. S2CID   119162797.
  12. 1 2 "Detailed Information for Object Sextans B". NASA/IPAC Extragalactic Database . Retrieved September 13, 2023.
  13. 1 2 3 4 Tosi, M; Greggio, L.; Marconi, G.; Focardi, P. (September 1991). "Star formation in dwarf irregular galaxies – Sextans B". Astronomical Journal . 102: 951–974. Bibcode:1991AJ....102..951T. doi:10.1086/115925.
  14. 1 2 Kniazev, Alexei Y.; Grebel, Eva K.; Pustilnik, Simon A.; Pramskij, Alexander G.; Zucker, Daniel B. (October 2005). "Spectrophotometry of Sextans A and B: Chemical Abundances of H II Regions and Planetary Nebulae". Astronomical Journal . 130 (4): 1558–1573. arXiv: astro-ph/0502562 . Bibcode:2005AJ....130.1558K. doi:10.1086/432931. S2CID   14176608.
  15. ↑ van den bergh, Sidney (2000). The galaxies of the Local Group. University of Cambridge. p. 265. ISBN   978-0-521-65181-3.
  16. ↑ Alloin, Danielle M.; Gieren, Wolfgang (2000). Stellar candles for the extragalactic distance scale. University of Cambridge. p. 265. ISBN   978-3-540-20128-1.
  17. ↑ Magrini, L.; Corradi, R. L. M.; Walton, N. A.; Zijlstra, A. A.; Pollacco, D. L.; Walsh, J. R.; Perinotto, M.; Lennon, D. J.; Greimel, R. (2002). "The Local Group Census: Planetary nebulae in Sextans B". Astronomy & Astrophysics . 386 (3): 869–873. arXiv: astro-ph/0202516 . Bibcode:2002A&A...386..869M. doi:10.1051/0004-6361:20020296. S2CID   16954005.
  18. ↑ Sharina, M.E.; Puzia, T. H.; Krylatyh, A. S. (September 2009). "A globular cluster in the dwarf galaxy Sextans B". Astrophysical Bulletin . 62 (3): 209–216. arXiv: 0704.3908 . Bibcode:2007AstBu..62..209S. doi:10.1134/S1990341307030029. S2CID   119588326.
  19. ↑ "Galassia Leo P".
  20. ↑ Hargis, J. R.; Albers, S.; Crnojević, D.; Sand, D. J.; Weisz, D. R.; Carlin, J. L.; Spekkens, K.; Willman, B.; Peter, A. H. G.; Grillmair, C. J.; Dolphin, A. E. (1 January 2020). "Hubble Space Telescope Imaging of Antlia B: Star Formation History and a New Tip of the Red Giant Branch Distance". The Astrophysical Journal. 888 (1): 31. Bibcode:2020ApJ...888...31H. doi: 10.3847/1538-4357/ab58d2 .
  21. ↑ Sand, D. J.; Spekkens, K.; Crnojević, D.; Hargis, J. R.; Willman, B.; Strader, J.; Grillmair, C. J. (9 October 2015). "Antlia B: A Faint Dwarf Galaxy Member of the NGC 3109 Association". The Astrophysical Journal. 812 (1): L13. arXiv: 1508.01800 . Bibcode:2015ApJ...812L..13S. doi:10.1088/2041-8205/812/1/L13.
  22. ↑ McQuinn, Kristen B. W.; Skillman, Evan D.; Dolphin, Andrew; Cannon, John M.; Salzer, John J.; Rhode, Katherine L.; Adams, Elizabeth A. K.; Berg, Danielle; Giovanelli, Riccardo; Girardi, Léo; Haynes, Martha P. (2015-10-20). "Leo P: An Unquenched Very Low-Mass Galaxy". The Astrophysical Journal. 812 (2): 158. arXiv: 1506.05495 . Bibcode:2015ApJ...812..158M. doi:10.1088/0004-637X/812/2/158. ISSN   0004-637X. S2CID   116977635.
  23. 1 2 3 4 5 "NASA/IPAC Extragalactic Database". Results for various galaxies. Retrieved 2006-10-15.
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