Antlia Dwarf

The Antlia Dwarf is a dwarf spheroidal/irregular galaxy. It lies about 1.3 Mpc (4.3 million light-years) 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.[3][7]

Not to be confused with Antlia II.

Antlia Dwarf
Antlia Dwarf by Hubble Space Telescope
Observation data (J2000 epoch)
ConstellationAntlia
Right ascension10h 04m 03.9s[1]
Declination−27° 19′ 55″[1]
Redshift362 ± 0 km/s[1]
Distance1.32 ± 0.06[2] Mpc
1.33 ± 0.10[3] Mpc
1.31 ± 0.03[4] Mpc
1.29 ± 0.02[5] Mpc
1.25[6] Mpc
Group or clusterAntlia-Sextans Group
Apparent magnitude (V)15.67 ± 0.02[2]
Characteristics
TypedE3.5[1] dSph,[3] dSph/Irr
Mass3 × 107 M☉
Apparent size (V)2′.0 × 1′.5[1]
Other designations
Antlia Dwarf Galaxy,[1] PGC 29194[1]

Discovery

The Antlia Dwarf was first cataloged in 1985 by H. Corwin, Gérard de Vaucouleurs, and A. de Vaucouleurs. Later in 1985 and 1987, it was noted as a possible nearby dwarf galaxy by two groups of astronomers.[3] It was finally confirmed as a dwarf galaxy in 1997 by Alan Whiting, Mike Irwin and George Hau during a survey of the northern sky. They for the first time resolved it into stars and determined the distance to it—1.15 Mpc (the modern distance estimate is slightly larger).[8] The same year, Antonio Aparicio, Julianne Dalcanton, Carme Gallart and David Martinez-Delgado studied for the first time its stellar content and measured its mass, luminosity and metallicity.[2]

In 1999, the Antlia Dwarf was identified by Sidney van den Bergh as the fourth member of the Antlia-Sextans Group—the group of galaxies closest to the Local Group.[3]

Properties

The Antlia Dwarf is classified alternatively as a dwarf elliptical galaxy of type dE3.5,[8][9] or either as a dwarf spheroidal galaxy (dSph) or as a transitional galaxy from spheroidal to irregular types (dSph/Irr).[3] The last classification is due to a substantial star formation in this galaxy in the last 0.1 billion years.[2]

Antlia Dwarf comprises two components: a core and an old halo.[2] Its half-light radius is about 0.25 kpc.[8] The metallicity is very low, at about <[Fe/H]>=−1.6 to −1.9 meaning that Antlia Dwarf contains 40–80 times less heavy elements than the Sun.[2][10] The galaxy has a well-defined and easily observed red giant branch, which makes measuring its distance relatively easy.[9] The total luminosity of Antlia Dwarf is approximately 1 million times that of the Sun (the visible absolute magnitude is MV=−10.3).[2]

The stellar mass of Antlia Dwarf is estimated to be about 2–4×106 solar masses, while its total mass (within the visible radius) is approximately 4 × 107 solar masses.[2] The galaxy contains stars of all ages but is dominated by old stars with the age of more than 10 billion year. There seems to have been a major episode of star formation in the Antlia Dwarf around 100 million years ago.[4][9] However, the young stars are confined to the central core of the galaxy.[10]

Antlia Dwarf is unusual among dwarf spheroidal galaxies in that it contains large amounts (as much as 7 ×105 solar masses) of neutral atomic hydrogen.[11][12] However it does not have significant H II regions and does not actively form stars at the present moment.[9]

Location and interactions

The Antlia Dwarf is located about 1.31 megaparsecs (4.3×10^6 ly) away, in the constellation Antlia.[9] Its distance from the barycenter of the Local Group is about 1.7 Mpc. At this distance, it is situated well outside the Local Group and is a member of a separate group of dwarf galaxies called Antlia-Sextans Group.[3] The Antlia Dwarf is separated from the small spiral/irregular galaxy NGC 3109 by only 1.18 degrees on the sky, which corresponds to a physical separation of 29 kiloparsecs (95×10^3 ly) to 180 kiloparsecs (590×10^3 ly) depending on their radial separation.[2][3]

The Antlia Dwarf and NGC 3109 may be actually physically bound if the distance between them is not very large.[3][8] However their velocity relative to each other—43 km/s[3] makes it questionable whether they are in fact a bound system, especially if the distance between them is closer to the upper limit—180 kpc.[2][9] If they are gravitationally bound, their total mass may be as high as 78 billion solar masses.[4]

Observations have also demonstrated that NGC 3109 has a warp in its gaseous disk that is traveling at the same velocity as the gas in the Antlia Dwarf, indicating that the two galaxies had a close encounter about one billion years ago.[12]

References
  1. "NASA/IPAC Extragalactic Database". Results for Antlia Dwarf. Retrieved 30 November 2006.
  2. Aparicio, Antonio; Dalcanton, J. J.; Gallart, C.; Martinez-Delgado, D. (October 1997). "The Nature of the Antlia Galaxy: A New Dwarf Irregular in the Outskirts of the Local Group". The Astronomical Journal. 114 (4): 1447–1457. Bibcode:1997AJ....114.1447A. doi:10.1086/118575.
  3. Van Den Bergh, S. (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. S2CID 119338768.
  4. Piersimoni, A. M.; Piersimoni, A. M.; Bono, G.; Castellani, M.; Marconi, G.; Cassisi, S.; Buonanno, R.; Nonino, M. (December 1999). "A new investigation on the Antlia Dwarf Galaxy". Astronomy & Astrophysics. 352: L63–L68. arXiv:astro-ph/9909198. Bibcode:1999A&A...352L..63P.
  5. Dalcanton, J. J.; Williams, B. F.; Seth, A. C.; Dolphin, A.; Holtzman, J.; Rosema, K.; Skillman, E. D.; Cole, A.; Girardi, L. O.; Gogarten, S. M.; Karachentsev, I. D.; Olsen, K.; Weisz, D.; Christensen, C.; Freeman, K.; Gilbert, K.; Gallart, C.; Harris, J.; Hodge, P.; De Jong, R. S.; Karachentseva, V.; Mateo, M.; Stetson, P. B.; Tavarez, M.; Zaritsky, D.; Governato, F.; Quinn, T. (2009). "The Acs Nearby Galaxy Survey Treasury". The Astrophysical Journal Supplement Series. 183 (1): 67–108. arXiv:0905.3737. Bibcode:2009ApJS..183...67D. doi:10.1088/0067-0049/183/1/67. S2CID 5032304.
  6. Tully, R. B.; Rizzi, L.; Dolphin, A. E.; Karachentsev, I. D.; Karachentseva, V. E.; Makarov, D. I.; Makarova, L.; Sakai, S.; Shaya, E. J. (2006). "Associations of Dwarf Galaxies". The Astronomical Journal. 132 (2): 729–748. arXiv:astro-ph/0603380. Bibcode:2006AJ....132..729T. doi:10.1086/505466. S2CID 119505770.
  7. Grebel, Eva K.; Gallagher, John S., III; Harbeck, Daniel (April 2003). "The Progenitors of Dwarf Spheroidal Galaxies". The Astronomical Journal. 125 (4): 1926–1939. arXiv:astro-ph/0301025. Bibcode:2003AJ....125.1926G. doi:10.1086/368363. S2CID 18496644.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  8. Whiting, Alan B.; Irwin, M. J.; Hau, George K. T. (September 1997). "A new galaxy in the Local Group: The Antlia Dwarf Galaxy". The Astronomical Journal. 114 (3): 996–1001. arXiv:astro-ph/9706173. Bibcode:1997AJ....114..996W. doi:10.1086/118530. S2CID 8218571.
  9. Pimbblet, K. A.; Couch, W. J. (2011). "Antlia Dwarf Galaxy: Distance, quantitative morphology and recent formation history via statistical field correction". Monthly Notices of the Royal Astronomical Society. 419 (2): 1153. arXiv:1109.1142. Bibcode:2012MNRAS.419.1153P. doi:10.1111/j.1365-2966.2011.19769.x. S2CID 106400803.
  10. Sarajedini, Ata; Claver, C. F.; Ostheimer, James C. Jnr.; Ostheimer, James C. (December 1997). "The properties of the Antlia Dwarf Galaxy". The Astronomical Journal. 114 (6): 2505–2513. Bibcode:1997AJ....114.2505S. doi:10.1086/118663.
  11. van den Bergh, Sidney (2000). The galaxies of the Local Group. University of Cambridge. p. 266. ISBN 0-521-65181-6.
  12. Barnes, D. G.; W. J. G. de Blok (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.
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