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For other dwarf galaxies labelled Pisces, see Pisces (disambiguation).

Pisces II (Psc II)[6][A] is an ultra-faint dwarf-spheroidal galaxy and satellite of the Milky Way, located in the Pisces constellation 180 kpc (587,081 light years) from Earth.[1] Discovered in 2009 by public analysis of Data Release 7 (DR7) of the Sloan Digital Sky Survey,[1] it is classified as a dwarf spheroidal galaxy (dSph) and is one of the smallest and faintest satellite galaxies of the Milky Way.[2][7]

Structure

Pisces is a small irregular galaxy, with a moderately-aged and older stellar population of metal-poor stars, consisting primarily of stars formed about 10 billion years ago.[1][8] The metallicity of these old stars is low, at −2.3 < [Fe/H] < −1.7, which means that the ratio of their mass that consists of heavy metals[B] is less than that of the Sun.[1] Its luminosity is about 10,000 times that of the Sun (absolute magnitude of about −5), which corresponds to the luminosity of an average globular cluster.[6][8]

Potential past interactions

In 2016, follow-up work on Pisces II and Pegasus III[8] highlighted that both lie relatively close to each other (within approximately 43 kiloparsecs), and share similar radial velocities in the Milky Way’s rest frame.[2][8] This suggests that these two satellite galaxies may actually be associated with one another, potentially having interacted in the past; however, further spectroscopic measurements are needed to confirm this.[2][7]

See Also

Notes

  1. ^ a b Andromeda II was also given the alias Pisces II by Martin et al. (2009), who also proposed aliases for several other satellite galaxies of the Andromeda Galaxy[5] However, that name was later used by a different group unaware of these names, for this object.
  2. ^ In astronomy and physical cosmology, unlike other physical sciences, “heavy metals” refers to all elements except hydrogen and helium.

References

  1. ^ a b c d e f g h Belokurov, V.; Walker, M. G.; Evans, N. W.; Gilmore, G.; Irwin, M. J.; Just, D.; Koposov, S.; Mateo, M.; Olszewski, E.; Watkins, L.; Wyrzykowski, L. (2010). “Big Fish, Little Fish: Two New Ultra-Faint Satellites of the Milky Way”. The Astrophysical Journal. 712 (1): L103–L106. arXiv:1002.0504. Bibcode:2010ApJ…712L.103B. doi:10.1088/2041-8205/712/1/L103. S2CID 29195107.
  2. ^ a b c d e Richstein, Hannah; Patel, Ekta; Kallivayalil, Nitya; Simon, Joshua D.; Zivick, Paul; Tollerud, Erik; Fritz, Tobias; Warfield, Jack T.; Besla, Gurtina; Van Der Marel, Roeland P.; Wetzel, Andrew; Choi, Yumi; Deason, Alis; Geha, Marla; Guhathakurta, Puragra; Jeon, Myoungwon; Kirby, Evan N.; Libralato, Mattia; Sacchi, Elena; Sohn, Sangmo Tony (2022). “Structural Parameters and Possible Association of the Ultra-faint Dwarfs Pegasus III and Pisces II from Deep Hubble Space Telescope Photometry”. The Astrophysical Journal. 933 (2): 217. arXiv:2204.01917. Bibcode:2022ApJ…933..217R. doi:10.3847/1538-4357/ac7226. S2CID 247957904.
  3. ^ “Object No. 1 – PISCES II”. NASA/IPAC Extragalactic Database.
  4. ^ “NAME Pisces II — Galaxy”. SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 24 March 2018.
  5. ^ Martin, Nicolas F.; McConnachie, Alan W.; Irwin, Mike; Widrow, Lawrence M.; Ferguson, Annette M. N.; Ibata, Rodrigo A.; Dubinski, John; Babul, Arif; et al. (1 November 2009). “PAndAS’ CUBS: Discovery of Two New Dwarf Galaxies in the Surroundings of the Andromeda and Triangulum Galaxies”. The Astrophysical Journal. 705 (1): 758–765. arXiv:0909.0399. Bibcode:2009ApJ…705..758M. doi:10.1088/0004-637X/705/1/758. S2CID 15277245.
  6. ^ a b “Dwarf Galaxies in Pisces – NASA Science”. 2016-08-11. Retrieved 2026-04-21.
  7. ^ a b Kim, Dongwon; Jerjen, Helmut; Geha, Marla; Chiti, Anirudh; Milone, Antonino P.; Mackey, Dougal; da Costa, Gary; Frebel, Anna; Conn, Blair (2016). “Portrait of a Dark Horse: A Photometric and Spectroscopic Study of the Ultra-Faint Milky Way Satellite Pegasus III”. The Astrophysical Journal. 833 (1): 16. arXiv:1608.04934. Bibcode:2016ApJ…833…16K. doi:10.3847/0004-637X/833/1/16. S2CID 73677994.
  8. ^ a b c d Garofalo, Alessia; Tantalo, Maria; Cusano, Felice; Clementini, Gisella; Calura, Francesco; Muraveva, Tatiana; Paris, Diego; Speziali, Roberto (2021-07-01). “Born in a Pair (?): Pisces II and Pegasus III*”. The Astrophysical Journal. 916 (1): 10. arXiv:2105.11488. Bibcode:2021ApJ…916…10G. doi:10.3847/1538-4357/ac0253. ISSN 0004-637X.

Further reading