Bootes II dwarf galaxy

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Galaxie
Bootes II Dwarf Galaxy
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Constellation Bear keeper
Position
equinox :  J2000.0 , epoch : J2000.0
Right ascension 13 h 58 m 00 s
declination 12 ° 51 '00 ″
Appearance
Morphological type dSph  
Brightness  (visual) 15.8 ± 0.5 mag
Angular expansion (8.0 + 2.2 - 2.8) ′
Physical data
Affiliation Local group  
distance (136,000 ± 7,000) ly /
(42,000 ± 2,000) pc
Metallicity [Fe / H] −1.8
history
Catalog names
Boo II

Bootes II (also Boo II for short ) is a spheroidal dwarf galaxy (dSph) in the constellation of the Bear Catcher . It was in the year 2007 in photographs of the screening of the Sloan Digital Sky Survey discovered. The galaxy is about 42 k pc from our solar system and is moving at 120 km / s towards the sun . As a spheroidal dwarf galaxy, it has an approximately round shape with a half-light radius of only 51 pc (other sources even mention 36 pc).

properties

Luminosity

Bootes II is one of the smallest and faintest satellite galaxies in our Milky Way (only Segue 2 and Willman 1 are fainter). With M V = -2.7 m, the integral luminosity is only 1000 times as strong as that of the sun, so the luminosity is below that of the majority of globular clusters . However, the mass of the dwarf galaxy is significantly more significant due to the high mass-luminosity ratio of more than 100, which suggests a high density of dark matter .

Metallicity

The star population of Bootes II consists mainly of older stars that formed 10 to 12 billion years ago. The metallicity of these old stars is low with [Fe / H] = −1.8 . They have 80 times less heavy elements than our sun. At the moment no star formation can be determined in Bootes II . Also up to now no neutral hydrogen gas could be measured in the dwarf galaxy (upper limit for this is only 86 M ☉ ).

Affiliation

Boat II is 1.5 ° (corresponding to 1.6 CCP) away from the boat I . However, it is unlikely that the two galaxies are physically coupled, as they move in opposite directions in relation to the Milky Way and do so at the high relative speed of 200 km / s. However, it seems more likely that Bootes II is part of the Sagittarius Current and therefore more of a satellite galaxy or even a globular cluster of the Sagittarius dwarf galaxy that was withdrawn 4–7 billion years ago .

additional

Web links

Commons : Bear Guardian Constellation  - Collection of images, videos and audio files

Individual evidence

  1. ↑ a b SIMBAD Astronomical Database. In: Results for Bootes II. Retrieved February 13, 2010 .
  2. ↑ a b c d e f S.M. Walsh, Jerjen, H .; Willman, B .: A Pair of Boötes: A New Milky Way Satellite . In: The Astrophysical Journal . 662, No. 2, 2007, pp. L83-L86. arxiv : 0705.1378 . bibcode : 2007ApJ ... 662L..83W . doi : 10.1086 / 519684 .
  3. ↑ a b c d e f N.F. Martin, De Jong, JTA; Rix, HW: A Comprehensive Maximum Likelihood Analysis of the Structural Properties of Faint Milky Way Satellites . In: The Astrophysical Journal . 684, No. 2, 2008, p. 1075. doi : 10.1086 / 590336 .
  4. ↑ a b c d S.M. Walsh, Willman, B .; Sand, D. et al. : Boötes II ReBoöted: An MMT / MegaCam Study of an Ultrafaint Milky Way Satellite . In: The Astrophysical Journal . 688, No. 1, 2008, pp. 245-253. arxiv : 0712.3054 . bibcode : 2008ApJ ... 688..245W . doi : 10.1086 / 592076 .
  5. ↑ a b c d e Andreas Koch, Wilkinson, Mark I .; Kleyna, Jan T. et al. : A Spectroscopic Confirmation of the Bootes II Dwarf Spheroidal . In: The Astrophysical Journal . 690, No. 1, 2009, pp. 453-462. arxiv : 0809.0700 . bibcode : 2009ApJ ... 690..453K . doi : 10.1088 / 0004-637X / 690/1/453 .
  6. ↑ J. Grcevich, Putman, ME: HI in Local Group Dwarf Galaxies and stripping by the Galactic halo . In: The Astrophysical Journalvolume = 696 . 2009, p. 385. doi : 10.1088 / 0004-637X / 696/1/385 .