Canes Venatici II (dwarf galaxy)

Canes Venatici II Dwarf Galaxy[1]
Observation data (J2000 epoch)
Constellation	Canes Venatici
Right ascension	12^h 57^m 10^s[1]
Declination	+34° 19′ 15″[1]
Distance	490+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
Type	dSph[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 the data obtained by Sloan Digital Sky Survey.^[2] The galaxy is located at the 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 the 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 galaxy's mass to light ratio is around 340. A high mass to light ratio implies that CVn II is dominated by the 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. The measurement 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. "SIMBAD Astronomical Database". Results for CVN II Dwarf Galaxy. Retrieved 2010-02-06.
2. Belokurov, V.; Zucker, D. B.; Evans, N. W.; Kleyna, J. T.; Koposov, S.; Hodgkin, S. T.; Irwin, M. J.; Gilmore, G.; Wilkinson, M. I.; Fellhauer, M.; Bramich, D. M.; Hewett, P. C.; Vidrih, S.; De Jong, J. T. A.; Smith, J. A.; Rix, H. ‐W.; Bell, E. F.; Wyse, R. F. G.; Newberg, H. J.; Mayeur, P. A.; Yanny, B.; Rockosi, C. M.; Gnedin, O. Y.; Schneider, D. P.; Beers, T. C.; Barentine, J. C.; Brewington, H.; Brinkmann, J.; Harvanek, M.; Kleinman, S. J. (2007). "Cats and Dogs, Hair and a Hero: A Quintet of New Milky Way Companions". The Astrophysical Journal. 654 (2): 897. arXiv:astro-ph/0608448. Bibcode:2007ApJ...654..897B. doi:10.1086/509718.
3. Greco, Claudia; Dall’Ora, Massimo; Clementini, Gisella; et al. (2008). "On the Newly Discovered Canes Venatici II dSph Galaxy". The Astrophysical Journal. 675 (2): L73–L76. arXiv:0712.2241. Bibcode:2008ApJ...675L..73G. doi:10.1086/533585.
4. 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. arXiv:0805.2945. Bibcode:2008ApJ...684.1075M. doi:10.1086/590336.
5. Sakamoto, T.; Hasegawa, T. (2006). "Discovery of a Faint Old Stellar System at 150 kpc". The Astrophysical Journal. 653 (1): L29–L32. arXiv:astro-ph/0610858. Bibcode:2006ApJ...653L..29S. doi:10.1086/510332.
6. Simon, J. D.; Geha, M. (2007). "The Kinematics of the Ultra‐faint Milky Way Satellites: Solving the Missing Satellite Problem". The Astrophysical Journal. 670: 313. arXiv:0706.0516. Bibcode:2007ApJ...670..313S. doi:10.1086/521816.
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: L43. arXiv:0807.1925. Bibcode:2008ApJ...685L..43K. doi:10.1086/592432.
8. Grcevich, J.; Putman, M. E. (2009). "H I in Local Group Dwarf Galaxies and Stripping by the Galactic Halo". The Astrophysical Journal. 696: 385. arXiv:0901.4975. Bibcode:2009ApJ...696..385G. doi:10.1088/0004-637X/696/1/385.