Sextans B

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Sextans B
Sextans B.jpg
Observation data (J2000 epoch)
Constellation Sextans
Right ascension 10h 00m 00.1s [1]
Declination +05° 19′ 56″ [1]
Redshift 300 ± 0 km/s [1]
Distance 4.44 ± 0.23 Mly (1.36 ± 0.07 Mpc) [2] [3]
Apparent magnitude  (V)11.9 [1]
Characteristics
Type ImIV–V [1]
Apparent size  (V)5.1′ × 3.5′ [1]
Other designations
UGC 5373, [1] PGC 28913, [1] DDO 70, [1] Sex B [1]

Sextans B (also known as UGC 5373 and DDO 70) 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. [4] It is a type Ir IV–V galaxy according to the galaxy morphological classification scheme. [5] Sextans B may also be gravitationally associated with the galaxies NGC 3109 and the Antlia Dwarf. [6]

Sextans B has a uniform stellar population, [7] but the interstellar medium in it may be inhomogeneous. [8] 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. [7] Star formation in the galaxy seems to have proceeded in distinct periods of low intensity, separated by shorter periods of no activity. [7] The existence of Cepheid variables in the galaxy implies that Sextans B contains at least some young stars. [5] The metallicity of Sextans B is very low, with a value of approximately Z = 0.001. [7] Sextans B is receding from the Milky Way with a speed of approximately 300 kilometres per second (190 mi/s), [8] and probably lies just outside the edge of the Local Group, so as its neighbour Sextans A. [9]

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. [10] It also contains a massive globular cluster. [11]

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The Local Group is the galaxy group that includes the Milky Way. 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">Pegasus Dwarf Spheroidal Galaxy</span> Dwarf spheroidal galaxy in the constellation Pegasus

The Pegasus Dwarf Spheroidal is a dwarf spheroidal galaxy about 2.7 million light-years away in the constellation Pegasus. The Pegasus Dwarf is a member of the Local Group and a satellite galaxy of the Andromeda Galaxy (M31).

<span class="mw-page-title-main">Pegasus Dwarf Irregular Galaxy</span> Dwarf irregular galaxy in the constellation of Pegasus

The Pegasus Dwarf Irregular Galaxy is a dwarf irregular galaxy in the direction of the constellation Pegasus. It was discovered by A. G. Wilson in the 1950s. The Pegasus Dwarf is a companion of the Andromeda Galaxy in the Local Group.

<span class="mw-page-title-main">Sculptor Galaxy</span> Intermediate spiral galaxy in the constellation Sculptor

The Sculptor Galaxy is an intermediate spiral galaxy in the constellation Sculptor. The Sculptor Galaxy is a starburst galaxy, which means that it is currently undergoing a period of intense star formation.

<span class="mw-page-title-main">NGC 185</span> Galaxy in the constellation Cassiopeia

NGC 185 is a dwarf spheroidal galaxy located 2.08 million light-years from Earth, appearing in the constellation Cassiopeia. It is a member of the Local Group, and is a satellite of the Andromeda Galaxy (M31). NGC 185 was discovered by William Herschel on November 30, 1787, and he cataloged it "H II.707". John Herschel observed the object again in 1833 when he cataloged it as "h 35", and then in 1864 when he cataloged it as "GC 90" within his General Catalogue of Nebulae and Clusters. NGC 185 was first photographed between 1898 and 1900 by James Edward Keeler with the Crossley Reflector of Lick Observatory. Unlike most dwarf elliptical galaxies, NGC 185 contains young stellar clusters, and star formation proceeded at a low rate until the recent past. NGC 185 has an active galactic nucleus (AGN) and is usually classified as a type 2 Seyfert galaxy, though its status as a Seyfert is questioned. It is possibly the closest Seyfert galaxy to Earth, and is the only known Seyfert in the Local Group.

<span class="mw-page-title-main">Andromeda I</span> Dwarf galaxy in the constellation Andromeda

Andromeda I is a dwarf spheroidal galaxy (dSph) about 2.40 million light-years away in the constellation Andromeda. Andromeda I is part of the local group of galaxies and a satellite galaxy of the Andromeda Galaxy (M31). It is roughly 3.5 degrees south and slightly east of M31. As of 2005, it is the closest known dSph companion to M31 at an estimated projected distance of ~40 kpc or ~150,000 light-years.

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

The Sculptor Dwarf Galaxy is a dwarf spheroidal galaxy that is a satellite of the Milky Way. The galaxy lies within the constellation Sculptor. It was discovered in 1937 by American astronomer Harlow Shapley using the 24-inch Bruce refractor at Boyden Observatory. The galaxy is located about 290,000 light-years away from the Solar System. The Sculptor Dwarf contains only 4 percent of the carbon and other heavy elements in our own galaxy, the Milky Way, making it similar to primitive galaxies seen at the edge of the universe.

<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 4.34 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">Sagittarius Dwarf Irregular Galaxy</span> Dwarf galaxy in the constellation of Sagittarius

The Sagittarius Dwarf Irregular Galaxy (SagDIG) is a dwarf galaxy in the constellation of Sagittarius. It lies about 3.4 million light-years away. It was discovered by Cesarsky et al. on a photographic plate taken for the ESO (B) Atlas on 13 June 1977 using the ESO 1 meter Schmidt telescope.

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

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<span class="mw-page-title-main">Ursa Minor Dwarf</span> Dwarf spheroidal galaxy

The Ursa Minor Dwarf is a dwarf spheroidal galaxy, discovered by A.G. Wilson of the Lowell Observatory, in the United States, during the Palomar Sky Survey in 1955. It appears in the Ursa Minor constellation, and is a satellite galaxy of the Milky Way. The galaxy consists mainly of older stars and seems to house little to no ongoing star formation. Its centre is around 225,000 light years distant from Earth.

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

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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">IC 1613</span> Irregular dwarf galaxy in the constellation Cetus

IC 1613 is an irregular dwarf galaxy, visible in the constellation Cetus near the star 26 Ceti. It was discovered in 1906 by Max Wolf, and is approaching Earth at 234 km/s.

<span class="mw-page-title-main">Leo II (dwarf galaxy)</span> Dwarf Spheroidal galaxy in the constellation Leo

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<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 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-Sextans Group</span> Small galaxy group in the constellations of Hydra, Sextans, Antlia and Leo

The Antlia-Sextans Group is a small grouping of galaxies in the constellations Hydra, Sextans, Antlia and Leo. 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 group, and thus the nearest group to the Local Group. It is, on average, approximately 4.3 million light-years away from the Milky Way.

References

  1. 1 2 3 4 5 6 7 8 9 10 "NASA/IPAC Extragalactic Database". Results for Sex B. Retrieved 2006-12-13.
  2. ↑ I. D. Karachentsev; V. E. Karachentseva; W. K. Hutchmeier; D. I. Makarov (2004). "A Catalog of Neighboring Galaxies". Astronomical Journal. 127 (4): 2031–2068. Bibcode:2004AJ....127.2031K. doi: 10.1086/382905 .
  3. ↑ Karachentsev, I. D.; Kashibadze, O. G. (2006). "Masses of the local group and of the M81 group estimated from distortions in the local velocity field". Astrophysics. 49 (1): 3–18. Bibcode:2006Ap.....49....3K. doi:10.1007/s10511-006-0002-6. S2CID   120973010.
  4. ↑ Sandage, Allan; Carlson, George (July 1985). "The brightest stars in nearby galaxies. V – Cepheids and the brightest stars in the dwarf galaxy Sextans B compared with those in Sextans A". Astronomical Journal . 90: 1019–1026. Bibcode:1985AJ.....90.1019S. doi: 10.1086/113809 .
  5. 1 2 van den bergh, Sidney (2000). The galaxies of the Local Group. University of Cambridge. p. 265. ISBN   978-0-521-65181-3.
  6. ↑ van den Bergh, Sidney (1999). "Stellar Content of Local Group Galaxies – An Introduction". The Stellar Content of Local Group Galaxies. 192: 3. Bibcode:1999IAUS..192....3V.
  7. 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.
  8. 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.
  9. ↑ Alloin, Danielle M.; Gieren, Wolfgang (2000). Stellar candles for the extragalactic distance scale. University of Cambridge. p. 265. ISBN   978-3-540-20128-1.
  10. ↑ 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.
  11. ↑ 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.


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