The Andromeda Galaxy with M110 at upper left and M32 to the right of the core

The Andromeda Galaxy (M31) has satellite galaxies just like the Milky Way. Orbiting M31 are at least 13 dwarf galaxies: the brightest and largest is M110, which can be seen with a basic telescope. The second-brightest and closest one to M31 is M32. The other galaxies are fainter, and were mostly discovered starting from the 1970s.

On January 11, 2006, it was announced that Andromeda Galaxy's faint companion galaxies lie on or close to a single plane running through the Andromeda Galaxy's center. This unexpected distribution is not obviously understood in the context of current models for galaxy formation. The plane of satellite galaxies points toward a nearby group of galaxies (M81 Group), possibly tracing the large-scale distribution of dark matter.

It is unknown whether the Triangulum Galaxy is a satellite of Andromeda.

Table of known satellites

Andromeda Galaxy's satellites are listed here by discovery (orbital distance is not known). Andromeda IV is not included in the list, as it was discovered to be roughly 10 times further than Andromeda from the Milky Way in 2014, and therefore a completely unrelated galaxy.

Andromeda Galaxy's satellites
Name Type Distance from Sun
(million ly)		 Right Ascension** Declination** Absolute Magnitude[1] Apparent magnitude Mass-to-light ratio 3D distance to M31 (kly) Year
discovered		 Notes
M32 dE2 2.48 00h 42m 41.877s +40° 51′ 54.71″ +8.1 1749
M110 dE6 2.69 00h 40m 22.054s +41° 41′ 08.04″ −16.5 +8.5 1773
NGC 185 dE5 2.01 00h 38m 57.523s +48° 20′ 14.86″ +10.1 1787
NGC 147 dE5 2.2 00h 33m 12.131s +48° 30′ 32.82″ +10.5 1829
Andromeda I dSph 2.43 00h 45m 39.264s +38° 02′ 35.17″ −11.8 +13.6 31 ± 6[1] 1970
Andromeda II*** dSph 2.13 01h 16m 28.136s +33° 25′ 50.36″ −12.6 +13.5 13 ± 3[1] 1970
Andromeda III dSph 2.44 00h 35m 31.777s +36° 30′ 04.19″ −10.2 +15.0 19 ± 12[1] 1970
Andromeda V dSph 2.52 01h 10m 16.952s +47° 37′ 40.12″ −9.6 +15.9 78 ± 50[2] 1998
Pegasus Dwarf Spheroidal
(Andromeda VI)		 dSph 2.55 23h 51m 46.516s +24° 34′ 55.69″ −11.5 +14.2 12 ± 5[2] 1998
Cassiopeia Dwarf
(Andromeda VII)		 dSph 2.49 23h 26m 33.321s +50° 40′ 49.98″ −13.3 +12.9 7.1 ± 2.8[1] 1998
Andromeda VIII dSph 2.7 00h 42m 06s +40° 37′ 00″ +9.1 2003 Tidally disrupting; identification unclear
Andromeda IX dSph 2.5 00h 52m 52.493s +43° 11′ 55.66″ −8.3 +16.2 127.2 2004
Andromeda X dSph 2.9 01h 06m 34.740s +44° 48′ 23.31″ −8.1 +16.1 63 ± 40[1] 332.7 2005
Andromeda XI[3] dSph 00h 46m 20s +33° 48′ 05″ −7.3 2006
Andromeda XII[3] dSph 00h 47m 27s +33° 22′ 29″ −6.4 2006
Andromeda XIII[3] (Pisces III) dSph 00h 51m 49.555s +33° 00′ 31.40″ −6.9 2006
Andromeda XIV[4] (Pisces IV) dSph 00h 41m 35.219s +29° 41′ 45.87″ −8.3 102 ± 71[1] 2007
Andromeda XV[4] dSph 01h 14m 18.7s +38° 07′ 02.9″ −9.4 2007
Andromeda XVI[4] (Pisces V) dSph 2.143[5] 00h 59m 29.843s +32° 22′ 27.96″ −9.2 580.6 2007
Andromeda XVII[4] dSph 00h 37m 07s +44° 19′ 20″ −8.5 313.1 2008
Andromeda XVIII[4] dSph/Sm 00h 02m 15.184s +45° 05′ 19.78″ 515.3 2008
Andromeda XIX[4] dSph 00h 19m 32.1s +35° 02′ 37.1″ −9.3 2008
Andromeda XX[4] dSph 00h 07m 30.530s +35° 07′ 45.94″ −6.3 512.1 2008
Andromeda XXI[4] dSph 23h 54m 47.7s +42° 28′ 15″ −9.9 472.9 2009
Andromeda XXII[4] dSph 00h 27m 40s +28° 05′ 25″ −7.0 910 2009
Andromeda XXIII[4] dIrr 01h 29m 21.944s +38° 43′ 05.97″ 427.3 2011
Andromeda XXIV[4] 01h 18m 30s +46° 21′ 58″ 401.2 2011
Andromeda XXV[4] 00h 30m 08.9s +46° 51′ 07″ 319.6 2011
Andromeda XXVI[4] 00h 23m 45.6s +47° 54′ 58″ 489.2 2011
Andromeda XXVII[4] 00h 37m 27.1s +45° 23′ 13″ 2011 Tidally disrupted[6]
Andromeda XXVIII[7] dSph 22h 32m 41.449s +31° 12′ 59.10″ 2011
Andromeda XXIX[7] dIrr 23h 58m 55.440s +30° 45′ 22.09″ 636 2011
Andromeda XXX (Cassiopeia II)[8] dSph? 00h 36m 34.9s +49° 38′ 48″
Andromeda XXXI (Lacerta I)[8] dSph? 22h 58m 16.3s +41° 17′ 28″ 2013
Andromeda XXXII (Cassiopeia III)[8] dSph? 00h 35m 59.4s +51° 33′ 35″ 2013
Andromeda XXXIII (Perseus I)[8] dSph? 03h 01m 23.6s +40° 59′ 18″ 2013
Tidal Stream Northwest
(Tidal Stream E and F)[9]		 00h 20m 00s +46° 00′ 00″ 2009
Tidal Stream Southwest[9] 00h 30m 00s +37° 30′ 00″ 2009
Pegasus V galaxy (Peg V) d 682 kpc (2.22 Mly) 23h 18m 27.8s±0.1 +33° 21′ 32″±3 −6.3 245 kpc (800 kly) 2022 [10][11][12]
Triangulum Galaxy*
(M33)		 SA(s)cd 2.59 01h 33m 50.883s +30° 39′ 36.54″ +6.27 1654? It is around 750000 light years from Andromeda.[13] Its relation to Andromeda is uncertain.

* It is uncertain whether it is a companion galaxy of the Andromeda Galaxy.

** RA/DEC values marked in Italics are rough estimates.

*** Martin et al. (2009) gave aliases to several satellite galaxies of the Andromeda Galaxy that are located in Pisces.[14] However, the name Pisces II was later used for a different galaxy that is a satellite of the Milky Way,[15] so it is not used here.

See also

References

  1. 1 2 3 4 5 6 7 Kalirai, Jason S.; Beaton, Rachael L.; Geha, Marla C.; Gilbert, Karoline M.; Guhathakurta, Puragra; Kirby, Evan N.; Majewski, Steven R.; Ostheimer, James C.; Patterson, Richard J.; Wolf, Joe (2010). "The SPLASH Survey: Internal Kinematics, Chemical Abundances, and Masses of the Andromeda I, II, III, VII, X, and XIV Dwarf Spheroidal Galaxies". The Astrophysical Journal. 711 (2): 671–692. arXiv:0911.1998. Bibcode:2010ApJ...711..671K. doi:10.1088/0004-637X/711/2/671. S2CID 43188686.
  2. 1 2 Collins, M. L. M.; Chapman, S. C.; Rich, R. M.; Irwin, M. J.; Peñarrubia, J.; Ibata, R. A.; Arimoto, N.; Brooks, A. M.; Ferguson, A. M. N.; Lewis, G. F.; McConnachie, A. W.; Venn, K. (2011). "The scatter about the 'Universal' dwarf spheroidal mass profile: A kinematic study of the M31 satellites and V and VI". Monthly Notices of the Royal Astronomical Society. 417 (2): 1170. arXiv:1103.2121. Bibcode:2011MNRAS.417.1170C. doi:10.1111/j.1365-2966.2011.19342.x. S2CID 6345715.
  3. 1 2 3 Martin, N. F.; Ibata, R. A.; Irwin, M. J.; Chapman, S.; Lewis, G. F.; Ferguson, A. M. N.; Tanvir, N.; McConnachie, A. W. (2006). "Discovery and analysis of three faint dwarf galaxies and a globular cluster in the outer halo of the Andromeda galaxy". Monthly Notices of the Royal Astronomical Society. 371 (4): 1983–1991. arXiv:astro-ph/0607472. Bibcode:2006MNRAS.371.1983M. doi:10.1111/j.1365-2966.2006.10823.x. S2CID 20171599.
  4. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Discovery of the Local Group Galaxies
  5. ↑ Monelli, Matteo; Martínez-Vázquez, Clara E.; Bernard, Edouard J.; Gallart, Carme; Skillman, Evan D.; Weisz, Daniel R.; Dolphin, Andrew E.; Hidalgo, Sebastian L.; Cole, Andrew A.; Martin, Nicolas F.; Aparicio, Antonio; Cassisi, Santi; Boylan-Kolchin, Michael; Mayer, Lucio; McConnachie, Alan; McQuinn, Kristen B. W.; Navarro, Julio F. (2016). "The Islands Project. I. Andromeda Xvi, an Extremely Low Mass Galaxy Not Quenched by Reionization". The Astrophysical Journal. 819 (2): 147. arXiv:1603.00625. Bibcode:2016ApJ...819..147M. doi:10.3847/0004-637X/819/2/147. S2CID 32263075.
  6. ↑ Preston, Janet; Collins, Michelle L. M.; Ibata, Rodrigo A.; Tollerud, Erik J.; Rich, R. Michael; Bonaca, Ana; McConnachie, Alan W.; Mackey, Dougal; Lewis, Geraint F.; Martin, Nicolas F.; Peñarrubia, Jorge; Chapman, Scott C.; Delorme, Maxime (2019). "A dwarf disrupting - Andromeda XXVII and the North West Stream". Monthly Notices of the Royal Astronomical Society. 490 (2): 2905–2917. arXiv:1909.09661. Bibcode:2019MNRAS.490.2905P. doi:10.1093/mnras/stz2529.
  7. 1 2 Moore, Nicole Casal (7 Nov 2011), "Newly found dwarf galaxies could help reveal the nature of dark matter", News Service, University of Michigan, retrieved 10 Dec 2011 (reprinted in R&D Magazine)
  8. 1 2 3 4 McConnachie, Alan W. (2012). "The observed properties of dwarf galaxies in and around the Local Group". The Astronomical Journal. 144 (1): 4. arXiv:1204.1562. Bibcode:2012AJ....144....4M. doi:10.1088/0004-6256/144/1/4. S2CID 118515618.
  9. 1 2 New tidal streams found in Andromeda reveal history of galactic mergers
  10. ↑ "Pegasus V: New Ultra-Faint Dwarf Galaxy Spotted in Outskirts of Andromeda". Sci-News. 1 July 2022.
  11. ↑ University of Surrey (30 June 2022). "New fossil galaxy discovery could answer important questions about the history of the universe". EurkAlert!. AAAS.
  12. ↑ Collins, Michelle L. M.; Charles, Emily J. E.; Martínez-Delgado, David; Monelli, Matteo; Karim, Noushin; Donatiello, Giuseppe; Tollerud, Erik J.; Boschin, Walter (2022). "Pegasus V/Andromeda XXXIV–a newly discovered ultrafaint dwarf galaxy on the outskirts of Andromeda". Monthly Notices of the Royal Astronomical Society: Letters. 515 (1): L72–L77. arXiv:2204.09068. Bibcode:2022MNRAS.515L..72C. doi:10.1093/mnrasl/slac063.
  13. ↑ "Messier Object 33". www.messier.seds.org. Retrieved 2021-05-21.
  14. ↑ Martin, Nicolas F.; McConnachie, Alan W.; Irwin, Mike; Widrow, Lawrence M.; Ferguson, Annette M. N.; Ibata, Rodrigo A.; Dubinski, John; Babul, Arif; et al. (1 November 2009). "PAndAS' CUBS: Discovery of Two New Dwarf Galaxies in the Surroundings of the Andromeda and Triangulum Galaxies". The Astrophysical Journal. 705 (1): 758–765. arXiv:0909.0399. Bibcode:2009ApJ...705..758M. doi:10.1088/0004-637X/705/1/758. S2CID 15277245.
  15. ↑ Belokurov, V.; Walker, M. G.; Evans, N. W.; Gilmore, G.; Irwin, M. J.; Just, D.; Koposov, S.; Mateo, M.; Olszewski, E.; Watkins, L.; Wyrzykowski, L. (2010). "Big Fish, Little Fish: Two New Ultra-Faint Satellites of the Milky Way". The Astrophysical Journal. 712 (1): L103–L106. arXiv:1002.0504. Bibcode:2010ApJ...712L.103B. doi:10.1088/2041-8205/712/1/L103. S2CID 29195107.
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