Ursa Major II dwarf galaxy

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Galaxy
Ursa Major II dwarf galaxy
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AladinLite
Constellation Big Bear
Position
equinoxJ2000.0 , epoch : J2000.0
Right ascension 08 h 5 m 30.0 s
declination 63 ° 07 ′ 48 ″
Appearance
Morphological type dSph  
Brightness  (visual) (14.3 ± 0.5) mag
Angular expansion (32 ± 2) ′
Physical data
Affiliation Local group  
Radial velocity 116 km / s  
distance (98,000 ± 16,000) ly /
(30,000 ± 5,000) pc
history
Discovery date 2006
Catalog names

Ursa Major II (also briefly UMa II ) is a spheroidal dwarf galaxy (dSph) in the constellation of the Great Bear and in 2006, after analyzing the recordings of the screening of the Sloan Digital Sky Survey discovered.

properties

The galaxy is approximately 30 k pc away from our solar system and is moving towards it at a speed of about 116 km / s . Due to its spheroidal property, it has an approximately elliptical aspect ratio of 2: 1 with a half-light radius of only about 140 pc . UMa II is thus one of the smallest and faintest satellites of our Milky Way (only Com , Segue 1 , Segue 2 , Bootes II and Willman 1 are fainter).
The integral of the brightness is approximately equal to the dwarf galaxy 4000 times the sun , representing an absolute magnitude of -4.2 M corresponds. This is significantly less than the luminosity of most globular clusters . UMa II itself is fainter than some single stars such as Canopus in the constellation Kiel of the ship . It is comparable in luminosity to Bellatrix in the constellation Orion .

On the other hand, the galaxy has a mass of 5 million solar masses, which equates to a mass-luminosity ratio of about 2000, which would make the galaxy an extremely strongly dominated object by dark matter . However, this could also turn out to be a misjudgment if the dwarf galaxy is no longer in virial equilibrium. The fact that it is already disturbed by the tidal forces acting on it can be seen in its rudimentary irregularity.

The star population of UMA II is composed mainly of ancient stars that were formed at least 10 billion years ago. The metallicity of this population turns out to be extremely low in metal with [Fe / H] ≈ −2.44 ± 0.06. The sun has about 300 times as many heavy elements . The stars of this galaxy are among the very first stars to be formed in the cosmos . Currently, no more stars are forming in the Ursa Majoris II dwarf galaxy , and no neutral hydrogen gas could be detected in the galaxy. The upper limit of detection is currently only 562 solar masses.

additional

Individual evidence

  1. SIMBAD Astronomical Database . In: Results for Ursa Major II . Retrieved November 19, 2011.
  2. a b c d e f g h i sugar, DB; Belokurov, V .; Evans, NW; Kleyna, JT; Irwin, MJ; Wilkinson, MI; Fellhauer, M .; Bramich, DM et al .: A Curious Milky Way Satellite in Ursa Major . In: Astrophysical Journal . 650: L41, 2006. doi : 10.1086 / 508628 .
  3. a b c Martin, NF; De Jong, JTA; Rix, HW: A Comprehensive Maximum Likelihood Analysis of the Structural Properties of Faint Milky Way Satellites . In: The Astrophysical Journal . 684 (2): 1075, 2008. doi : 10.1086 / 590336 .
  4. a b Simon, JD; Geha, M .: The Kinematics of the Ultra ‐ faint Milky Way Satellites: Solving the Missing Satellite Problem . In: The Astrophysical Journal . 670: 313, 2007. doi : 10.1086 / 521816 .
  5. Kirby, EN; Simon, JD; Geha, M .; Guhathakurta, P .; Frebel, A .: Uncovering Extremely Metal-Poor Stars in the Milky Way's Ultrafaint Dwarf Spheroidal Satellite Galaxies . In: The Astrophysical Journal . 685: L43, 2008. doi : 10.1086 / 592432 .
  6. Grcevich, J .; Putman, ME: HI in Local Group Dwarf Galaxies and Stripping by the Galactic Halo . In: The Astrophysical Journal . 696: 385, 2009. doi : 10.1088 / 0004-637X / 696/1/385 .

Web links

Commons : Greater Bear constellation  - Collection of images, videos and audio files