Andromeda XVIII
Galaxy in constellation Andromeda
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Andromeda XVIII, discovered in 2008, is a dwarf spheroidal galaxy (has no rings, low luminosity, much dark matter, little gas or dust), which is a satellite of the Andromeda Galaxy (M31). It is one of the 14 known dwarf galaxies orbiting M31. It is relatively isolated, being about 1.8 million light-years (579 kpc) away. However, for an isolated dwarf galaxy it is also unusually quiescent. This suggests that Andromeda XVIII is a backsplash galaxy, a galaxy that once had a close orbital encounter with a more massive galaxy which stripped it of much of its star-forming matter. However, alternative hypotheses are also possible for Andromeda XVIII.[2]
| Andromeda XVIII | |
|---|---|
DSS image of Andromeda XVIII | |
| Observation data (J2000 epoch) | |
| Constellation | Andromeda |
| Right ascension | 00h 02m 14.5s[1] |
| Declination | +45° 05′ 20″[1] |
| Heliocentric radial velocity | −337.2 km/s[2] |
| Distance | 4,420 ± 290 kly (1,355 ± 88 kpc) |
| Group or cluster | Local Group |
| Apparent magnitude (V) | 15.50 ± 0.24[3] |
| Absolute magnitude (V) | −10.41 ± 0.28[3] |
| Characteristics | |
| Type | dSph[1] |
| Mass | 4.2×106 ± 0.3×106[3] M☉ |
| Half-light radius (physical) | 325 ± 24[4] |
| Other designations | |
| PGC 5056918[5] | |
It was announced in 2010 that the orbiting galaxies lie close to a plane running through M31's center.[citation needed]
