List of Andromeda's satellite galaxies

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 only starting from the 1970s.

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

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.

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]	Magnitude	Mass-to-light ratio	Year discovered	Notes
M32	dE2	2.48	00^h 42^m 41.877^s	+40° 51′ 54.71″		+9.2		1749
M110	dE6	2.69	00^h 40^m 22.054^s	+41° 41′ 08.04″		+9.4		1773
NGC 185	dE5	2.01	00^h 38^m 57.523^s	+48° 20′ 14.86″		+11		1787
NGC 147	dE5	2.2	00^h 33^m 12.131^s	+48° 30′ 32.82″		+12		1829
Andromeda I	dSph	2.43	00^h 45^m 39.264^s	+38° 02′ 35.17″	-11.8	+13.2	31 ± 6[1]	1970
Andromeda II	dSph	2.13	01^h 16^m 28.136^s	+33° 25′ 50.36″	-12.6	+13	13 ± 3[1]	1970
Andromeda III	dSph	2.44	00^h 35^m 31.777^s	+36° 30′ 04.19″	-10.2	+10.3	19 ± 12[1]	1970
Andromeda V	dSph	2.52	01^h 10^m 16.952^s	+47° 37′ 40.12″	-9.6	+15.4	78 ± 50[2]	1998
Pegasus Dwarf Spheroidal (Andromeda VI)	dSph	2.55	23^h 51^m 46.516^s	+24° 34′ 55.69″	-11.5	+14.5	12 ± 5[2]	1998
Cassiopeia Dwarf (Andromeda VII)	dSph	2.49	23^h 26^m 33.321^s	+50° 40′ 49.98″	-13.3	+12.9	7.1 ± 2.8[1]	1998
Andromeda VIII	dSph	2.7	00^h 42^m 06^s	+40° 37′ 00″		+9.1		2003
Andromeda IX	dSph	2.5	00^h 52^m 52.493^s	+43° 11′ 55.66″	-8.3	+16.2		2004
Andromeda X	dSph	2.9	01^h 06^m 34.740^s	+44° 48′ 23.31″	-8.1	+16.2	63 ± 40[1]	2005
Andromeda XI[3]	dSph		00^h 46^m 20^s	+33° 48′ 05″	-7.3			2006
Andromeda XII[3]	dSph		00^h 47^m 27^s	+33° 22′ 29″	-6.4			2006
Andromeda XIII[3]	dSph		00^h 51^m 49.555^s	+33° 00′ 31.40″	-6.9			2006
Andromeda XIV[4]	dSph		00^h 41^m 35.219^s	+29° 41′ 45.87″	-8.3		102 ± 71[1]	2007
Andromeda XV[4]	dSph		01^h 14^m 18.7^s	+38° 07′ 02.9″	-9.4			2007
Andromeda XVI[4]	dSph		00^h 59^m 29.843^s	+32° 22′ 27.96″	-9.2			2007
Andromeda XVII[4]	dSph		00^h 37^m 07^s	+44° 19′ 20″	-8.5			2008
Andromeda XVIII[4]	dSph/Sm		00^h 02^m 15.184^s	+45° 05′ 19.78″				2008
Andromeda XIX[4]	dSph		00^h 19^m 32.1^s	+35° 02′ 37.1″	-9.3			2008
Andromeda XX[4]	dSph		00^h 07^m 30.530^s	+35° 07′ 45.94″	-6.3			2008
Andromeda XXI[4]	dSph		23^h 54^m 47.7^s	+42° 28′ 15″	-9.9			2009
Andromeda XXII[4]	dSph		00^h 27^m 40^s	+28° 05′ 25″	-7.0			2009
Andromeda XXIII[4]	dIrr		01^h 29^m 21.944^s	+38° 43′ 05.97″				2011
Andromeda XXIV[4]			01^h 18^m 30^s	+46° 21′ 58″				2011
Andromeda XXV[4]			00^h 30^m 08.9^s	+46° 51′ 07″				2011
Andromeda XXVI[4]			00^h 23^m 45.6^s	+47° 54′ 58″				2011
Andromeda XXVII[4]			00^h 37^m 27.1^s	+45° 23′ 13″				2011
Andromeda XXVIII[5]	dSph		22^h 32^m 41.449^s	+31° 12′ 59.10″				2011
Andromeda XXIX[5]	dIrr		23^h 58^m 55.440^s	+30° 45′ 22.09″				2011
Tidal Stream Northwest (Tidal Stream E and F)[6]			00^h 20^m 00^s	+46° 00′ 00″				2009
Tidal Stream Southwest[6]			00^h 30^m 00^s	+37° 30′ 00″				2009
Triangulum Galaxy* (M33)	SA(s)cd	2.59	01^h 33^m 50.883^s	+30° 39′ 36.54″		+6.27		1654?	Exact distance and relation to Andromeda uncertain

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

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

See also

• Satellite galaxies of the Milky Way
• List of nearest galaxies
• Local Group

References

1. The SPLASH Survey: Internal Kinematics, Chemical Abundances, and Masses of the Andromeda I, II, III, VII, X, and XIV Dwarf Spheroidal Galaxies, Kalirai, J. S. et al., 2010
2. The scatter about the 'Universal' dwarf spheroidal mass profile: a kinematic study of the M31 satellites And V and And VI, Collins, M.L.M. et al., 2011.
3. Discovery and analysis of three faint dwarf galaxies and a globular cluster in the outer halo of the Andromeda galaxy, N. F. Martin et.al, 2006.
4. Discovery of the Local Group Galaxies
5. 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)
6. New tidal streams found in Andromeda reveal history of galactic mergers

External links

• Andromeda's thin sheet of satellites - Dark matter filiments or galaxtic cannibalism?
• Strange Setup: Andromeda's Satellite Galaxies All Lined Up