Boötes II (dwarf galaxy)

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Bootes II Dwarf Galaxy[1]
Observation data (J2000 epoch)
ConstellationBoötes
Right ascension13h 58m 00s[1]
Declination+12° 51′ 00″[1]
Distance136 ± 7 kly (42 ± 2 kpc)[2][3]
Apparent magnitude (V)15.8 ± 0.5[4]
Characteristics
TypedSph[4]
Apparent size (V)8.0+2.2
−2.8
[2]
Other designations
Boo II,[2] PGC 4713552
See also: Galaxy, List of galaxies

Bootes II or Boo II is a dwarf spheroidal galaxy situated in the Bootes constellation and discovered in 2007 in the data obtained by Sloan Digital Sky Survey.[4] The galaxy is located at the distance of about 42 kpc from the Sun and moves towards the Sun with the speed of 120 km/s.[4][5] It is classified as a dwarf spheroidal galaxy (dSph) meaning that it has an approximately round shape with the half-light radius of about 51 pc.[2][note 1]

Bootes II is one of the smallest and faintest satellites[note 2] of the Milky Way—its integrated luminosity is about 1,000 times that of the Sun (absolute visible magnitude of about −2.7), which is much lower than the luminosity of the majority of globular clusters.[2] However the mass of the galaxy is substantial corresponding to the mass to light ratio of more than 100.[3]

The stellar population of Bootes II consists mainly of moderately old stars formed 10–12 billion years ago.[5] The metallicity of these old stars is low at [Fe/H]=−1.8, which means that they contain 80 times less heavy elements than the Sun.[3][5] Currently there is no star formation in Bootes II. The measurements have so far failed to detect any neutral hydrogen in it—the upper limit is only 86 solar masses.[6]

Bootes II is located only 1.5 degrees (~1.6 kpc) away from another dwarf galaxyBoötes I,[4] although they are unlikely to be physically associated because they move in opposite directions relative to the Milky Way. Their relative velocity—about 200 km/s is too high. It is more likely associated with the Sagittarius Stream and, therefore, with the Sagittarius Dwarf Elliptical Galaxy (SagDEG). Bootes II may be either a satellite galaxy of SagDEG or one of its star clusters torn from the main galaxy 4–7 billion years ago.[5]

Notes[edit]

  1. Other sources give the half-light radius of about 36 pc.[3]
  2. Only Segue 1, Segue 2 and Willman 1 are fainter.[2]


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References[edit]

  1. 1.0 1.1 1.2 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 Martin, Nicolas F.; de Jong, Jelte T. A.; Rix, Hans-Walter (September 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.
  3. 3.0 3.1 3.2 3.3 Walsh, S.M.Expression error: Unrecognized word "etal". (2008). "Boötes II ReBoöted: An MMT/MegaCam Study of an Ultrafaint Milky Way Satellite". The Astrophysical Journal 688 (1): 245–253. arXiv:0712.3054. Bibcode 2008ApJ...688..245W. doi:10.1086/592076.
  4. 4.0 4.1 4.2 4.3 4.4 Walsh, S.M.; Jerjen, H.; Willman, B. (June 2007). "A Pair of Boötes: A New Milky Way Satellite". The Astrophysical Journal 662 (2): L83–L86. arXiv:0705.1378. Bibcode 2007ApJ...662L..83W. doi:10.1086/519684.
  5. 5.0 5.1 5.2 5.3 Koch, AndreasExpression error: Unrecognized word "etal". (January 2009). "A Spectroscopic Confirmation of the Bootes II Dwarf Spheroidal". The Astrophysical Journal 690 (1): 453–462. arXiv:0809.0700. Bibcode 2009ApJ...690..453K. doi:10.1088/0004-637X/690/1/453.
  6. Grcevich, Jana; Putman, Mary E. (May 2009). "H I in Local Group Dwarf Galaxies and Stripping by the Galactic Halo". The Astrophysical Journal 696 (1): 385. arXiv:0901.4975. Bibcode 2009ApJ...696..385G. doi:10.1088/0004-637X/696/1/385.
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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).