List of Andromeda's satellite galaxies

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The Andromeda Galaxy with M110 at upper left and M32 to the right of the core Pic iroberts1.jpg
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 35 dwarf galaxies [1] : 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.

Contents

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 [2] Apparent magnitude Mass-to-light ratio 3D distance to M31 (kly)Year
discovered		Notes
M32 dE22.4800h 42m 41.877s+40° 51′ 54.71″+8.11749
M110 dE62.6900h 40m 22.054s+41° 41′ 08.04″−16.5+8.51773
NGC 185 dE52.0100h 38m 57.523s+48° 20′ 14.86″+10.11787
NGC 147 dE52.200h 33m 12.131s+48° 30′ 32.82″+10.51829
Andromeda I dSph 2.4300h 45m 39.264s+38° 02′ 35.17″−11.8+13.631 ± 6 [2] 1970
Andromeda II***dSph2.1301h 16m 28.136s+33° 25′ 50.36″−12.6+13.513 ± 3 [2] 1970
Andromeda III dSph2.4400h 35m 31.777s+36° 30′ 04.19″−10.2+15.019 ± 12 [2] 1970
Andromeda V dSph2.5201h 10m 16.952s+47° 37′ 40.12″−9.6+15.978 ± 50 [3] 1998
Pegasus Dwarf Spheroidal
(Andromeda VI)		dSph2.5523h 51m 46.516s+24° 34′ 55.69″−11.5+14.212 ± 5 [3] 1998
Cassiopeia Dwarf
(Andromeda VII)		dSph2.4923h 26m 33.321s+50° 40′ 49.98″−13.3+12.97.1 ± 2.8 [2] 1998
Andromeda VIII dSph2.700h 42m 06s+40° 37′ 00″+9.12003Tidally disrupting; identification unclear
Andromeda IX dSph2.500h 52m 52.493s+43° 11′ 55.66″−8.3+16.2127.22004
Andromeda X dSph2.901h 06m 34.740s+44° 48′ 23.31″−8.1+16.163 ± 40 [2] 332.72005
Andromeda XI [4] dSph00h 46m 20s+33° 48′ 05″−7.32006
Andromeda XII [4] dSph00h 47m 27s+33° 22′ 29″−6.42006
Andromeda XIII [4] (Pisces III)dSph00h 51m 49.555s+33° 00′ 31.40″−6.92006
Andromeda XIV [5] (Pisces IV)dSph00h 41m 35.219s+29° 41′ 45.87″−8.3102 ± 71 [2] 2007
Andromeda XV [5] dSph01h 14m 18.7s+38° 07′ 02.9″−9.42007
Andromeda XVI [5] (Pisces V)dSph2.143 [6] 00h 59m 29.843s+32° 22′ 27.96″−9.2580.62007
Andromeda XVII [5] dSph00h 37m 07s+44° 19′ 20″−8.5313.12008
Andromeda XVIII [5] dSph/Sm00h 02m 15.184s+45° 05′ 19.78″515.32008
Andromeda XIX [5] dSph00h 19m 32.1s+35° 02′ 37.1″−9.32008
Andromeda XX [5] dSph00h 07m 30.530s+35° 07′ 45.94″−6.3512.12008
Andromeda XXI [5] dSph23h 54m 47.7s+42° 28′ 15″−9.9472.92009
Andromeda XXII [5] dSph00h 27m 40s+28° 05′ 25″−7.09102009
Andromeda XXIII [5] dIrr01h 29m 21.944s+38° 43′ 05.97″427.32011
Andromeda XXIV [5] 01h 18m 30s+46° 21′ 58″401.22011
Andromeda XXV [5] 00h 30m 08.9s+46° 51′ 07″319.62011
Andromeda XXVI [5] 00h 23m 45.6s+47° 54′ 58″489.22011
Andromeda XXVII [5] 00h 37m 27.1s+45° 23′ 13″2011Tidally disrupted [7]
Andromeda XXVIII [8] dSph22h 32m 41.449s+31° 12′ 59.10″−8.8 [9] 2011
Andromeda XXIX [8] dIrr23h 58m 55.440s+30° 45′ 22.09″6362011
Andromeda XXX (Cassiopeia II) [10] dSph?00h 36m 34.9s+49° 38′ 48″
Andromeda XXXI (Lacerta I) [10] dSph?22h 58m 16.3s+41° 17′ 28″2013
Andromeda XXXII (Cassiopeia III) [10] dSph?2.74 [11] 00h 35m 59.4s+51° 33′ 35″508 [11] 2013
Andromeda XXXIII (Perseus I) [10] dSph?2.41 [11] 03h 01m 23.6s+40° 59′ 18″1,140 [11] 2013
Tidal Stream Northwest
(Tidal Stream E and F) [12] 		00h 20m 00s+46° 00′ 00″2009
Tidal Stream Southwest [12] 00h 30m 00s+37° 30′ 00″2009
Pegasus V galaxy (Peg V, Andromeda XXXIV)d682 kpc (2.22 Mly)23h 18m 27.8s±0.1+33° 21′ 32″±3−6.38002022 [13] [14] [15]
Andromeda XXXV [16] 3.0200h 26m 38.6s+40° 06′ 29.3″-5.25202025
Triangulum Galaxy*
(M33)		SA(s)cd2.5901h 33m 50.883s+30° 39′ 36.54″+6.27750 [17] 1654?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. [18] However, the name Pisces II was later used for a different galaxy that is a satellite of the Milky Way, [19] so it is not used here.

See also

References

  1. ↑ "NASA's Hubble Provides Bird's-Eye View of Andromeda Galaxy's Ecosystem - NASA Science". 2025-02-27. Retrieved 2025-03-18.
  2. 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.
  3. 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.
  4. 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.
  5. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Discovery of the Local Group Galaxies
  6. ↑ 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.
  7. ↑ 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 .
  8. 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)
  9. ↑ Fu, Sal Wanying; Weisz, Daniel R.; Starkenburg, Else; Martin, Nicolas; Collins, Michelle L. M.; Savino, Alessandro; Boylan-Kolchin, Michael; Côté, Patrick; Dolphin, Andrew E.; Longeard, Nicolas; Mateo, Mario L.; Mercado, Francisco J.; Sandford, Nathan R.; Skillman, Evan D. (2024). "Stellar Metallicities and Gradients in the Faint M31 Satellites Andromeda XVI and Andromeda XXVIII". The Astrophysical Journal. 975 (1): 2. arXiv: 2407.04698 . Bibcode:2024ApJ...975....2F. doi: 10.3847/1538-4357/ad76a2 .
  10. 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.
  11. 1 2 3 4 Rhode, Katherine L.; Smith, Nicholas J.; Crnojevic, Denija; Sand, David J.; Lambert, Ryan A.; Vesperini, Enrico; Smith, Madison V.; Janowiecki, Steven; Salzer, John J.; Karunakaran, Ananthan; Spekkens, Kristine (2023). "Exploring the Structures and Substructures of the Andromeda Satellite Dwarf Galaxies Cassiopeia III, Perseus I, and Lacerta I". The Astronomical Journal. 166 (5): 180. arXiv: 2309.01045 . Bibcode:2023AJ....166..180R. doi: 10.3847/1538-3881/acf859 .
  12. 1 2 New tidal streams found in Andromeda reveal history of galactic mergers
  13. ↑ "Pegasus V: New Ultra-Faint Dwarf Galaxy Spotted in Outskirts of Andromeda". Sci-News. 1 July 2022.
  14. ↑ University of Surrey (30 June 2022). "New fossil galaxy discovery could answer important questions about the history of the universe". EurkAlert!. AAAS.
  15. ↑ 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 .
  16. ↑ Arias, Jose Marco; Bell, Eric F.; Gozman, Katya; Jang, In Sung; Stockton, Saxon; Gnedin, Oleg Y.; D’Souza, Richard; Monachesi, Antonela; Bailin, Jeremy; Nidever, David; de Jong, Roelof S. (2025-03-11). "Andromeda XXXV: The Faintest Dwarf Satellite of the Andromeda Galaxy". The Astrophysical Journal Letters. 982 (1): L3. Bibcode:2025ApJ...982L...3A. doi: 10.3847/2041-8213/adb433 . ISSN   2041-8205.
  17. ↑ "Messier Object 33". www.messier.seds.org. Retrieved 2021-05-21.
  18. ↑ 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.
  19. ↑ 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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