Ursa Major II Dwarf

From the Science Archives, the open-project database of science information
Jump to navigation Jump to search
Ursa Major II Dwarf Galaxy[1]
Observation data (J2000 epoch)
ConstellationUrsa Major
Right ascension08h 51m 30.0s[1]
Declination+63° 07′ 48″[1]
Distance98 ± 16 kly (30 ± 5 kpc)[2]
Apparent magnitude (V)14.3 ± 0.5[2]
Characteristics
TypedSph[2]
Apparent size (V)32 ± 2′[3]
Other designations
UMa II galaxy, Ursa Major II Dwarf[1]
See also: Galaxy, List of galaxies

Ursa Major II Dwarf (UMa II dSph) is a dwarf spheroidal galaxy situated in the Ursa Major constellation and discovered in 2006 in the data obtained by the Sloan Digital Sky Survey.[2] The galaxy is located approximately 30 kpc from the Sun and moves towards the Sun with the velocity of about 116 km/s.[4] 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 140 pc.[3]

Ursa Major II is one of the smallest and faintest satellites[note 1] of the Milky Way—its integrated luminosity is about 4000 times that of the Sun (absolute visible magnitude of about −4.2),[2] which is much lower than the luminosity of the majority of globular clusters. Uma II is even less luminous than some stars, like Canopus in the Milky Way. It is comparable in luminosity to Bellatrix in Orion. However, its mass is about 5 million solar masses, which means that galaxy's mass to light ratio is around 2000.[4] This may be an overestimate as the galaxy has somewhat irregular shape and may be in process of tidal disruption.[2]

The stellar population of Uma II consists mainly of old stars formed at least 10 billion years ago.[2] The metallicity of these old stars is also very low at [Fe/H] ≈ −2.44 ± 0.06, which means that they contain 300 times less heavy elements than the Sun.[5] The stars of Uma II were probably among the first stars to form in the Universe. Currently there is no star formation in Uma II. The measurements have so far failed to detect any neutral hydrogen in it—the upper limit is only 562 solar masses.[6]

See also[edit]

Notes[edit]


Add your comment
The Science Archives welcomes all comments. If you do not want to be anonymous, register or log in. It is free.


As a reminder, article comments are only for discussions on how to improve the article. Please direct other comments to a user's talk page. Please be formal and do not use excessive uppercase. Please be advised you may receive an automatic block if you break the article comments policy. For information regarding what is acceptable/not acceptable in article comments, please message Icons-flag-ru.png Joey (talk), Natalia (talk), Icons-flag-fr.png ynoss (talk), or Icons-flag-ca.png Daniel (older account/talk).


References[edit]

  1. 1.0 1.1 1.2 1.3 Lua error in Module:Citation/CS1 at line 379: attempt to call method 'match' (a nil value).
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Zucker, D. B.; Belokurov, V.; Evans, N. W.; Kleyna, J. T.; Irwin, M. J.; Wilkinson, M. I.; Fellhauer, M.; Bramich, D. M. et al. (2006). "A Curious Milky Way Satellite in Ursa Major". The Astrophysical Journal 650: L41. arXiv:astro-ph/0606633. Bibcode 2006ApJ...650L..41Z. doi:10.1086/508628.
  3. 3.0 3.1 3.2 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. arXiv:0805.2945. Bibcode 2008ApJ...684.1075M. doi:10.1086/590336.
  4. 4.0 4.1 Simon, J. D.; Geha, M. (2007). "The Kinematics of the Ultra‐faint Milky Way Satellites: Solving the Missing Satellite Problem". The Astrophysical Journal 670: 313. arXiv:0706.0516. Bibcode 2007ApJ...670..313S. doi:10.1086/521816.
  5. 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.
  6. 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.
<comments />
As a reminder, article comments are only for discussions on how to improve the article. Please direct other comments to a user's talk page. Please be formal and do not use excessive uppercase. Please be advised you may receive an automatic block if you break the article comments policy. For information regarding what is acceptable/not acceptable in article comments, please message Icons-flag-ru.png Joey (talk), Natalia (talk), Icons-flag-fr.png ynoss (talk), or Icons-flag-ca.png Daniel (older account/talk).