Boötes II

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Boötes II Dwarf Galaxy[1]
Observation data (J2000 epoch)
ConstellationBoötes
Right ascension13h 58m 00s[1]
Declination+12° 51′ 00″[1]
Heliocentric radial velocity−126 km/s[2]
Distance136 ± 7 kly (42 ± 2 kpc)[3][4]
Apparent magnitude (V)15.8 ± 0.5[5]
Characteristics
TypedSph[5]
Apparent size (V)8.0+2.2
−2.8′[3]
Other designations
Boo II,[3] PGC 4713552

Boötes II or Boo II is a dwarf spheroidal galaxy situated in the constellation Boötes and discovered in 2007 in the data obtained by Sloan Digital Sky Survey.[5] The galaxy is located at the distance of about 42 kpc from the Sun and moves towards the Sun with the speed of 126 km/s.[2] 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.[3][note 1]

Boötes 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.[3] However the mass of the galaxy is substantial corresponding to the mass to light ratio of more than 100.[4]

The stellar population of Boötes II consists mainly of moderately old stars formed 10–12 billion years ago.[6] The metallicity of these old stars is low at [Fe/H]=−2.3, which means that they contain 200 times less heavy elements than the Sun.[2] Currently there is no star formation in Boötes II. The measurements have so far failed to detect any neutral hydrogen in it—the upper limit is only 86 solar masses.[7]

Boötes II is located only 1.5 degrees (~1.6 kpc) away from another dwarf galaxy—Boötes I,[5] 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). Boötes 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.[6]

Notes

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  1. ^ Other sources give the half-light radius of about 36 pc.[4]
  2. ^ Only Segue 1, Segue 2 and Willman 1 are fainter.[3]

References

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  2. ^ a b c Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  3. ^ a b c d e f Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  4. ^ a b c Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  5. ^ a b c d Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  6. ^ a b Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  7. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).


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