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Andromeda XVIII
DSS image of Andromeda XVIII
Observation data (J2000 epoch)
Constellation	Andromeda
Right ascension	00 02 14.5
Declination	+45° 05′ 20″
Heliocentric radial velocity	−337.2 km/s
Distance	4,420 ± 290 kly (1,355 ± 88 kpc)
Group or cluster	Local Group
Apparent magnitude (V)	15.50 ± 0.24
Absolute magnitude (V)	−10.41 ± 0.28
Characteristics
Type	dSph
Mass	4.2×10 ± 0.3×10 M☉
Half-light radius (physical)	325 ± 24
Other designations
PGC 5056918

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.

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

References

1. ^ 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 (2008). "A Trio of New Local Group Galaxies with Extreme Properties". The Astrophysical Journal. 688 (2): 1009. arXiv:0806.3988. Bibcode:2008ApJ...688.1009M. doi:10.1086/591313. S2CID 16950090.
2. ^ Kvasova, Kateryna A.; Kirby, Evan N.; Beaton, Rachael L. (2024). "Kinematics and Metallicity of the Dwarf Spheroidal Galaxy Andromeda XVIII". The Astrophysical Journal. 972 (2): 180. arXiv:2404.11804. Bibcode:2024ApJ...972..180K. doi:10.3847/1538-4357/ad55f0.
3. ^ Makarova, L. N; Makarov, D. I; Karachentsev, I. D; Tully, R. B; Rizzi, L (2017). "Star formation history of And XVIII: a dwarf spheroidal galaxy in isolation". Monthly Notices of the Royal Astronomical Society. 464 (2): 2281. arXiv:1609.09706. Bibcode:2017MNRAS.464.2281M. doi:10.1093/mnras/stw2502. S2CID 119275751.
4. 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 (2013). "A Kinematic Study of the Andromeda Dwarf Spheroidal System". The Astrophysical Journal. 768 (2): 172. arXiv:1302.6590. Bibcode:2013ApJ...768..172C. doi:10.1088/0004-637X/768/2/172. S2CID 67749084.
5. "NAME Andromeda XVIII". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 19 September 2017.

v t e Andromeda Galaxy
Location	Andromeda Galaxy → Andromeda subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Local Hole → Observable universe → Universe Each  → may be read as "within" or "part of".
Satellite galaxies	M32 M110 NGC 185 NGC 147 Andromeda I Andromeda II Andromeda III Andromeda IV* Andromeda V Andromeda VI Andromeda VII Andromeda VIII Andromeda IX Andromeda X Andromeda XI Andromeda XII Andromeda XIII Andromeda XIV Andromeda XV Andromeda XVI Andromeda XVII Andromeda XVIII Andromeda XIX Andromeda XX Andromeda XXI Andromeda XXII Andromeda XXIII Andromeda XXIV Andromeda XXV Andromeda XXVI Andromeda XXVII Andromeda XXVIII Andromeda XXIX Triangulum subgroup* *It is uncertain whether these are companion galaxies of the Andromeda Galaxy
Catalogued stars	AE Andromedae AF Andromedae M31-RV
Other	Andromeda–Milky Way collision S Andromedae Mayall II M32p NGC 206 3XMM J004232.1+411314
Category

v t e Constellation of Andromeda
Adhil Andromeda in Chinese astronomy List of Andromeda's satellite galaxies List of stars in Andromeda
Stars	Bayer α (Alpheratz) β (Mirach) γ (Almach) δ ε ζ η θ ι κ λ μ ν ξ (Adhil) ο π ρ σ τ υ (Titawin) φ χ ψ ω A b c υ Per (Nembus) Flamsteed 2 3 4 5 6 7 8 9 10 11 12 13 14 (Veritate) 15 18 22 23 26 28 32 36 39 41 44 45 47 55 56 58 59 63 64 65 66 6 Per Variable R T U W Z RT RV RX SU SW TU TW WZ XZ AB AC AD AE AF AR BM BX CC CG CN DS DX EG ET EU FF GO GP GQ GX GR GY HH HN IW KK KX KZ LL LN LP LQ OP OS OU PX PY QR QV QX V385 V428 V439 V455 V529 V807 HR 1 40 56 78 104 122 134 178 275 282 283 289 379 410 483 687 746 748 8884 8925 8950 8962 8973 9011 9074 9075 9105 HD 16175 (Buna) 222155 Other 3XMM J004232.1+411314 ADS 48 HAT-P-6 (Sterrennacht) HAT-P-16 HAT-P-19 HAT-P-28 M31-RV KELT-1 NGC 44 NGC 82 NGC 84 NGC 91 NGC 162 NGC 464 Qatar-3 Qatar-4 Qatar-5 PA-99-N2 WASP-1 WISE 0146+4234 WISE J0005+3737 WISE J004945.61+215120.0
Exoplanets 14 Andromedae b κ Andromedae b υ Andromedae b c d Gliese 15 Ab c HD 13931 b HD 16175 b HAT-P-6b HAT-P-32b WASP-1b WASP-33b Qatar-4b Qatar-5b
Star clusters	NGC 206 272 752 956 7686 Other Mayall II RBC EXT8
Nebulae	NGC 7662
Galaxies	Messier 32 110 NGC 5 11 13 19 20 21 27 39 43 48 49 51 67 68 69 70 71 72 74 76 79 80 81 83 85 86 90 93 94 96 97 108 109 112 140 149 160 169 181 183 184 214 218 226 228 229 233 243 252 258 260 262 280 304 317 389 393 404 425 431 477 512 513 523 528 529 531 536 542 561 605 620 668 679 687 700 703 704 705 708 709 710 712 714 717 721 732 753 759 801 812 834 891 906 910 911 912 913 920 937 980 995 996 999 1000 7640 7836 Numbered I II III IV V VIII IX X XI XVIII XIX XXI Other 3C 66A 3C 66B Andromeda Galaxy Arp 273 Donatiello I UGC 1840
Galaxy clusters Abell 262 NGC 68 group
Astronomical events GRB 101225A SN 1885A (S)
Category

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