Andromeda XVIII explained

Andromeda XVIII
Epoch:	J2000
Constellation Name:	Andromeda
Ra:	^[1]
H Radial V:	-337.2 km/s
Group Cluster:	Local Group
Type:	dSph
Appmag V:	15.50 ± 0.24^[2]
Absmag V:	−10.41 ± 0.28
Mass:	±
Half Light Radius Pc:	325 ± 24^[3]
Names:	PGC 5056918^[4]

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.^[5]

It was announced in 2010 that the orbiting galaxies lie close to a plane running through M31's center.

See also

• List of Andromeda's satellite galaxies

Notes and References

1. 10.1086/591313. A Trio of New Local Group Galaxies with Extreme Properties. The Astrophysical Journal. 688. 2. 1009. 2008. McConnachie. Alan W. Huxor. Avon. Martin. Nicolas F. Irwin. Mike J. Chapman. Scott C. Fahlman. Gregory. Ferguson. Annette M. N. Ibata. Rodrigo A. Lewis. Geraint F. Richer. Harvey. Tanvir. Nial R. 0806.3988. 2008ApJ...688.1009M. 16950090.
2. 10.1093/mnras/stw2502. Star formation history of And XVIII: a dwarf spheroidal galaxy in isolation. Monthly Notices of the Royal Astronomical Society. 464. 2. 2281. 2017. Makarova. L. N. Makarov. D. I. Karachentsev. I. D. Tully. R. B. Rizzi. L. free . 1609.09706. 2017MNRAS.464.2281M. 119275751.
3. 10.1088/0004-637X/768/2/172. A Kinematic Study of the Andromeda Dwarf Spheroidal System. The Astrophysical Journal. 768. 2. 172. 2013. Collins. Michelle L. M. Chapman. Scott C. Rich. R. Michael. Ibata. Rodrigo A. Martin. Nicolas F. Irwin. Michael J. Bate. Nicholas F. Lewis. Geraint F. Peñarrubia. Jorge. Arimoto. Nobuo. Casey. Caitlin M. Ferguson. Annette M. N. Koch. Andreas. McConnachie. Alan W. Tanvir. Nial. 1302.6590. 2013ApJ...768..172C. 67749084.
4. NAME Andromeda XVIII. 19 September 2017.
5. 10.3847/1538-4357/ad55f0. free . Kinematics and Metallicity of the Dwarf Spheroidal Galaxy Andromeda XVIII . 2024 . Kvasova . Kateryna A. . Kirby . Evan N. . Beaton . Rachael L. . The Astrophysical Journal . 972 . 2 . 180 . 2404.11804 . 2024ApJ...972..180K .