Sextans B

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Sextans B
Sextans B.jpg
Sextans B, imaged by the 4-meter Telescope at Kitt Peak National Observatory
Observation data (J2000 epoch)
Constellation Sextans
Right ascension 10h 00m 00.1s [1]
Declination +05° 19′ 56″ [1]
Redshift 301 ± 1 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]
Size~8,900  ly (2.73  kpc) (estimated) [1]
Apparent size  (V)5.1′ × 3.5′ [1]
Other designations
DDO 70, UGC 5373, MCG +01-26-005, PGC 28913, CGCG 036-012

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. The earliest known reference to this galaxy is from a 1954 paper by Edison Pettit in The Astrophysical Journal, where it was listed as "Wilson Dwarf". [4]

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. [5] It is a type Ir IV–V galaxy according to the galaxy morphological classification scheme. [6] Sextans B may also be gravitationally associated with the galaxies NGC 3109 and the Antlia Dwarf. [7]

Sextans B has a uniform stellar population, [8] but the interstellar medium in it may be inhomogeneous. [9] 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. [8] Star formation in the galaxy seems to have proceeded in distinct periods of low intensity, separated by shorter periods of no activity. [8] The existence of Cepheid variables in the galaxy implies that Sextans B contains at least some young stars. [6] The metallicity of Sextans B is very low, with a value of approximately Z = 0.001. [8] Sextans B is receding from the Milky Way with a speed of approximately 300 kilometres per second (190 mi/s), [9] and probably lies just outside the edge of the Local Group, so as its neighbour Sextans A. [10]

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. [11] It also contains a massive globular cluster. [12]

Although no supernovae have been observed in Sextans B, the galaxy is close enough for classical novae to be detected. The first confirmed nova in this galaxy was discovered by ATLAS at magnitude 18.553 on 10 November 2024, and designated AT 2024aawe. [13]

Related Research Articles

<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">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">Messier 32</span> Dwarf elliptical galaxy in the constellation Andromeda

Messier 32 is a dwarf "early-type" galaxy about 2,650,000 light-years (810,000 pc) from the Solar System, appearing in the constellation Andromeda. M32 is a satellite galaxy of the Andromeda Galaxy (M31) and was discovered by Guillaume Le Gentil in 1749.

<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">Dwarf spheroidal galaxy</span> Low-luminosity galaxy of old stars & little dust

A dwarf spheroidal galaxy (dSph) is a term in astronomy applied to small, low-luminosity galaxies with very little dust and an older stellar population. They are found in the Local Group as companions to the Milky Way and as systems that are companions to the Andromeda Galaxy (M31). While similar to dwarf elliptical galaxies in appearance and properties such as little to no gas or dust or recent star formation, they are approximately spheroidal in shape and generally have lower luminosity.

<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 4.35 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">Phoenix Dwarf</span> Galaxy in the constellation of Phoenix

The Phoenix Dwarf is a dwarf irregular galaxy discovered in 1976 by Hans-Emil Schuster and Richard Martin West and mistaken for a globular cluster. It is currently 1.44 Mly away from Earth. Its name comes from the fact that it is part of the Phoenix constellation.

<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.

<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">NGC 5253</span> Irregular galaxy in the M83 group of galaxies

NGC 5253 is an irregular galaxy in the constellation Centaurus. It was discovered by William Herschel on 15 March 1787.

<span class="mw-page-title-main">Palomar 12</span> Globular cluster in the constellation Capricornus

Palomar 12 is a globular cluster in the constellation Capricornus, and is a member of the Palomar Globular Clusters group.

<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">Maffei 1</span> Galaxy in the constellation Cassiopeia

Maffei 1 is a massive elliptical galaxy in the constellation Cassiopeia. Once believed to be a member of the Local Group of galaxies, it is now known to belong to a separate group, the IC 342/Maffei Group. It was named after Paolo Maffei, who discovered it and the neighboring Maffei 2 in 1967 via their infrared emissions.

<span class="mw-page-title-main">NGC 6441</span> Globular cluster in Scorpius

NGC 6441, sometimes also known as the Silver Nugget Cluster, is a globular cluster in the southern constellation of Scorpius. It was discovered by the Scottish astronomer James Dunlop on May 13, 1826, who described it as "a small, well-defined rather bright nebula, about 20″ in diameter". The cluster is located 5 arc minutes east-northeast of the star G Scorpii, and is some 43,000 light-years from the Sun.

<span class="mw-page-title-main">Antlia-Sextans Group</span> Galaxy group in the constellations of Hydra, Sextans, Antlia and Leo

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. 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.

References

  1. 1 2 3 4 5 6 7 "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. ↑ Pettit, Edison (1954). "Magnitudes and Color Indices of Extragalactic Nebulae Determined Photoelectrically". The Astrophysical Journal. 120: 413. Bibcode:1954ApJ...120..413P. doi:10.1086/145932.
  5. ↑ 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 .
  6. 1 2 van den bergh, Sidney (2000). The galaxies of the Local Group. University of Cambridge. p. 265. ISBN   978-0-521-65181-3.
  7. ↑ 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.
  8. 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.
  9. 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.
  10. ↑ Alloin, Danielle M.; Gieren, Wolfgang (2000). Stellar candles for the extragalactic distance scale. University of Cambridge. p. 265. ISBN   978-3-540-20128-1.
  11. ↑ 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.
  12. ↑ 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.
  13. ↑ "AT 2024aawe". Transient Name Server. IAU . Retrieved 12 November 2024.


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