Boötes II (dwarf galaxy)
| Bootes II Dwarf Galaxy[1] | |
|---|---|
| Observation data (J2000 epoch) | |
| Constellation | Boötes |
| Right ascension | 13h 58m 00s[1] |
| Declination | +12° 51′ 00″[1] |
| Distance | 136 ± 7 kly (42 ± 2 kpc)[2][3] |
| Type | dSph[4] |
| Apparent dimensions (V) | 8.0+2.2 −2.8′[2] |
| Apparent magnitude (V) | 15.8 ± 0.5[4] |
| Other designations | |
| Boo II,[2] PGC 4713552 | |
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 galaxy—Boötes 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
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<references />, or <references group="..." />| Location |
Milky Way → Milky Way subgroup → Local Group → Virgo Supercluster → Laniakea Supercluster → Observable universe → Universe
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| Galactic core | |||||||||
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| Satellite galaxies |
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