List of Andromeda's satellite galaxies

Great Andromeda Nebula 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 14 dwarf galaxies: the brightest and largest is M32, which can be seen with a backyard telescope. The second brightest and closest one to M32 is M110. The other galaxies are fainter, and were mostly discovered only starting from the 1970s.

On January 11, 2006, it was announced that Andromeda's faint companion galaxies lie on or close to a single plane running through Andromeda'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 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 IV ^*	dIm?	22-24	00^h 42^m 32.798^s	+40° 34′ 16.27″		+16.6		1972	previously believed to be a satellite of Andromeda, but disproven in 2014.
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 is a companion galaxy of the Andromeda Galaxy.

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

Interacting with Andromeda

Andromeda Galaxy (M31) in Infrared, with the hole arc at bottom right.

New images from NASA's Spitzer Space Telescope shed light on the Andromeda Galaxy's violent past. The images show that one of Andromeda's satellite galaxies, M32, blasted through one of Andromeda's spiral arms a few million years ago. Infrared pictures of Andromeda's two spiral arms demonstrate that they and the prominent star-forming ring are separate structures. The images also show a hole where the rings seem to split into arcs. This hole is where astronomers believe M32 punched through Andromeda's galactic disk.

See also

• Milky Way's satellite galaxies
• 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