Astronomy:Canes Venatici II

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Short description: Galaxy in constellation Canes Venatici
Canes Venatici II Dwarf Galaxy[1]
Observation data (J2000 epoch)
ConstellationCanes Venatici
Right ascension 12h 57m 10s[1]
Declination+34° 19′ 15″[1]
Distance490+49
−43 kly (150+15
−13 kpc)[2]
522+16
−13 kly (160+4
−5 kpc)[3]
Apparent magnitude (V)15.1±0.5[2]
Characteristics
TypedSph[2]
Apparent size (V)3.2′+0.6′
−0.4′[4]
Other designations
CVn II[1][note 1], PGC 4713558

Canes Venatici II or CVn II is a dwarf spheroidal galaxy situated in the Canes Venatici constellation and discovered in 2006 in data obtained by the Sloan Digital Sky Survey.[2] The galaxy is located at a distance of about 150 kpc from the Sun and moves towards the Sun with the velocity of about 130 km/s.[2][6] It is classified as a dwarf spheroidal galaxy (dSph) meaning that it has an elliptical (ratio of axes ~ 2:1) shape with a half-light radius of about 74+14
−10 pc.[4]

CVn II is one of the smallest and faintest satellites of the Milky Way—its integrated luminosity is about 8,000 times that of the Sun (absolute visible magnitude of about −4.9), which is much lower than the luminosity of a typical globular cluster.[4] However, its mass is about 2.5 million solar masses, which means that its mass to light ratio is around 340. A high mass to light ratio implies that CVn II is dominated by dark matter.[6]

The stellar population of CVn II consists mainly of old stars formed more than 12 billion years ago.[3] The metallicity of these old stars is also very low at [Fe/H] ≈ −2.19±0.58, which means that they contain 150 times less heavy elements than the Sun.[7] The stars of CVn II were probably among the first stars to form in the Universe. Currently there is no star formation in CVn II. Measurements have so far failed to detect neutral hydrogen in it—the upper limit is 14000 solar masses.[8]

Notes

  1. ↑ The galaxy was also independently discovered by T. Sakamoto and T. Hasegawa as SDSS J1257+3419.[5]

References

  1. ↑ 1.0 1.1 1.2 1.3 "NAME CVn II dSph". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=NAME+CVn+II+dSph. 
  2. ↑ 2.0 2.1 2.2 2.3 2.4 Belokurov, V.; Zucker, D. B.; Evans, N. W.; Kleyna, J. T.; Koposov, S.; Hodgkin, S. T.; Irwin, M. J.; Gilmore, G. et al. (2007). "Cats and Dogs, Hair and a Hero: A Quintet of New Milky Way Companions". The Astrophysical Journal 654 (2): 897–906. doi:10.1086/509718. Bibcode: 2007ApJ...654..897B. 
  3. ↑ 3.0 3.1 Greco, Claudia et al. (2008). "On the Newly Discovered Canes Venatici II dSph Galaxy". The Astrophysical Journal 675 (2): L73–L76. doi:10.1086/533585. Bibcode: 2008ApJ...675L..73G. 
  4. ↑ 4.0 4.1 4.2 Martin, N. F.; De Jong, J. T. A.; Rix, H. W. (2008). "A Comprehensive Maximum Likelihood Analysis of the Structural Properties of Faint Milky Way Satellites". The Astrophysical Journal 684 (2): 1075–1092. doi:10.1086/590336. Bibcode: 2008ApJ...684.1075M. 
  5. ↑ Sakamoto, T.; Hasegawa, T. (2006). "Discovery of a Faint Old Stellar System at 150 kpc". The Astrophysical Journal 653 (1): L29–L32. doi:10.1086/510332. Bibcode: 2006ApJ...653L..29S. 
  6. ↑ 6.0 6.1 Simon, J. D.; Geha, M. (2007). "The Kinematics of the Ultra‐faint Milky Way Satellites: Solving the Missing Satellite Problem". The Astrophysical Journal 670 (1): 313–331. doi:10.1086/521816. Bibcode: 2007ApJ...670..313S. 
  7. ↑ Kirby, E. N.; Simon, J. D.; Geha, M.; Guhathakurta, P.; Frebel, A. (2008). "Uncovering Extremely Metal-Poor Stars in the Milky Way's Ultrafaint Dwarf Spheroidal Satellite Galaxies". The Astrophysical Journal 685 (1): L43–L46. doi:10.1086/592432. Bibcode: 2008ApJ...685L..43K. 
  8. ↑ Grcevich, J.; Putman, M. E. (2009). "H I in Local Group Dwarf Galaxies and Stripping by the Galactic Halo". The Astrophysical Journal 696 (1): 385–395. doi:10.1088/0004-637X/696/1/385. Bibcode: 2009ApJ...696..385G. 




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