Pisces I (dwarf galaxy)

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Pisces I Dwarf Galaxy[1]
Observation data (J2000 epoch)
Constellation Pisces
Right ascension ~23h 40m 00s[2]
Declination ~ −0.3°[2]
Distance 260 kly (80 kpc)[3]
Type dSph?
Apparent size (V) ~1°[2]
Other designations
Pisces I,[1] Psc I,[4] PGC 3792,[5] LEDA 3792[4]
See also: Galaxy, List of galaxies

Pisces I (Psc I) or Pisces Overdensity is a clump of stars in the Milky Way's halo, which may be a disrupted dwarf spheroidal galaxy.[1] It is situated in the Pisces constellation and was discovered in 2009 by analysis of distribution of RR Lyrae stars in the data obtained by the Sloan Digital Sky Survey's data.[3] The galaxy is located at the distance of about 80 kpc from the Sun and moves towards it with a speed of about 75 km/s.[2]

Pisces I is one of the faintest satellites of the Milky Way.[1] Its mass is estimated to be at least 105 Solar masses.[3] However it has a large size of about several degrees (around 1  kpc) and may be in a transitional phase between a gravitationally bound galaxy and completely unbound system.[2] Pisces I is located near the plane, where the Magellanic Clouds lie. There may exist a connection between the Magellanic stream and this galaxy.[3]


  1. ^ a b c d Belokurov, V.; et al. (2010), "Big fish, small fish: Two New Ultra-Faint Satellites of the Milky Way", The Astrophysical Journal Letters, 712: L103–106, Bibcode:2010ApJ...712L.103B, arXiv:1002.0504Freely accessible, doi:10.1088/2041-8205/712/1/L103. 
  2. ^ a b c d e Kollmeier, Juna A.; et al. (2009), "Spectroscopic Confirmation of the Pisces Overdensity", The Astrophysical Journal Letters, 705 (2): L158–L162, Bibcode:2009ApJ...705L.158K, arXiv:0908.1381Freely accessible, doi:10.1088/0004-637X/705/2/L158. 
  3. ^ a b c d Watkins, L. L.; et al. (2009), "Substructure revealed by RR Lyraes in SDSS Stripe 82", Monthly Notices of the Royal Astronomical Society, 398 (4): 1757–70, Bibcode:2009MNRAS.398.1757W, arXiv:0906.0498Freely accessible, doi:10.1111/j.1365-2966.2009.15242.x. 
  4. ^ a b "NAME Pisces I -- Galaxy". SIMBAD. 
  5. ^ "Object No. 1 - Pisces I". NASA/IPAC Extragalactic Database.