M81 Group

A member of the M81 Group, Messier 81 (also known as NGC 3031 or Bode's Galaxy)
Observation data (Epoch J2000)
Constellation(s)	Ursa Major/Camelopardalis
Number of galaxies	34[1]
Brightest member	M81[1]
Other designations
NGC 3031 Group
See also: Galaxy groups and clusters, List of galaxy clusters
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The M81 Group is a group of galaxies in the constellation Ursa Major that includes the well-known galaxies Messier 81 and Messier 82, as well as several other galaxies with high apparent brightnesses.^[1] The approximate center of the group is located at a distance of 3.6 Mpc, making it one of the nearest groups to the Local Group.^[1] The group is estimated to have a total mass of (1.03 ± 0.17)×10¹²M_☉.^[2] The M81 Group, the Local Group, and other nearby groups all lie within the Virgo Supercluster (i.e. the Local Supercluster).^[3]

Members

The table below lists galaxies that have been identified as associated with the M81 Group by I. D. Karachentsev.^[1]

Members of the M81 Group

Name	Type[4]	R.A. (J2000)[4]	Dec. (J2000)[4]	Redshift (km/s)[4]	Apparent Magnitude[4]
Arp's Loop		09h 57m 32.6s	+69° 17′ 00″	99	16.1
DDO 78	Im	10h 26m 27.4s	+67° 39′ 16″	55 ± 10	15.8
F8D1	dE	09h 44m 47.1s	+67° 26′ 19″		13.9
FM1	dSph	09h 45m 10.0s	+68° 45′ 54″		17.5
HIJASS J1021+6842		10h 21m 00.0s	+68° 42′ 00″	46	20
HS 117	I	10h 21m 25.2s	+71° 06′ 51″	-37	16.5
Holmberg I	IAB(s)m	09h 40m 32.3s	+71° 10′ 56″	139 ± 0	13.0
Holmberg II	Im	08h 19m 05.0s	+70° 43′ 12″	142 ± 1	11.1
Holmberg IX	Im	09h 57m 32.0s	+69° 02′ 45″	46 ± 6	14.3
IC 2574	SAB(s)m	10h 28m 23.5s	+68° 24′ 44″	57 ± 2	13.2
IKN		10h 08m 05.9s	+68° 23′ 57″		17.0
KKH 57	dSph	10h 00m 16.0s	+63° 11′ 06″		18.5
Messier 81	SA(s)ab	09h 55m 33.2s	+69° 03′ 55″	-34 ± 4	7.9
Messier 81 Dwarf A	I	08h 23m 56.0s	+71° 01′ 45″	113 ± 0	16.5
Messier 82	I0	09h 55m 52s	+69° 40′ 47″	203 ± 4	9.3
NGC 2366	IB(s)m	07h 28m 54.7s	+69° 12′ 57″	80 ± 1	11.4
NGC 2403	SAB(s)cd	07h 36m 51.4s	+65° 36′ 09″	131 ± 3	8.9
NGC 2976	SAc pec	09h 47m 15.5s	+67° 54′ 59″	3 ± 5	10.8
NGC 3077	I0 pec	10h 03m 19.1s	+68° 44′ 02″	14 ± 4	10.6
NGC 4236	SB(s)dm	12h 16m 42s	+69° 27′ 45″	0 ± 4	10.1
PGC 28529	Im	09h 53m 48.5s	+68° 58′ 08″	-40	17.1
PGC 28731	dE	09h 57m 03.1s	+68° 35′ 31″	-135 ± 30	15.6
PGC 29231	dE	10h 04m 41.1s	+68° 15′ 22″		16.7
PGC 31286	dSph	10h 34m 29.8s	+66° 00′ 30″		16.7
PGC 32667	Im	10h 52m 57.1s	+69° 32′ 58″	116 ± 1	14.9
UGC 4459	Im	08h 34m 07.2s	+66° 10′ 54″	20 ± 0	14.5
UGC 4483		08h 37m 03.0s	+69° 46′ 31″	156 ± 0	15.1
UGC 5428	Im	10h 05m 06.4s	+66° 33′ 32″	-129 ± 0	18
UGC 5442	Im	10h 07m 01.9s	+67° 49′ 39″	-18 ± 14	18
UGC 5692	13.5	10h 30m 35.0s	+70° 37′ 07.2″	56 ± 3	13.5
UGC 6456	Pec	11h 27m 59.9s	+78° 59′ 39″	-103 ± 0	14.5
UGC 7242	Scd	12h 14m 08.4s	+66° 05′ 41″	68 ± 2	14.6
UGC 8201	Im	13h 06m 24.9s	+67° 42′ 25″	31 ± 0	12.8
UGCA 133	Im	07h 34m 11.4s	+66° 53′ 10″		15.6

Note that the object names used in the above table differ from the names used by Karachentsev. NGC, IC, UGC, and PGC numbers have been used in many cases to allow for easier referencing.

Interactions within the group

Messier 81, Messier 82, and NGC 3077 are all strongly interacting with each other.^[5] The gravitational interactions have stripped some hydrogen gas away from all three galaxies, leading to the formation of filamentary gas structures within the group.^[5] Moreover, the interactions have also caused some interstellar gas to fall into the centers of Messier 82 and NGC 3077, which has led to strong starburst activity (or the formation of many stars) within the centers of these two galaxies.^[5]

External links

• M81 Group @ SEDS
• M81 Group from An Atlas of The Universe

References

1. ^ ^{a b c d e} I. D. Karachentsev (2005). "The Local Group and Other Neighboring Galaxy Groups". Astronomical Journal 129 (1): 178–188. arXiv:astro-ph/0410065. Bibcode 2005AJ....129..178K. doi:10.1086/426368. 
2. ^ Karachentsev, I. D.; Kashibadze, O. G. (2006). "Masses of the local group and of the M81 group estimated from distortions in the local velocity field". Astrophysics 49 (1): 3–18. Bibcode 2006Ap.....49....3K. doi:10.1007/s10511-006-0002-6. 
3. ^ R. B. Tully (1982). "The Local Supercluster". Astrophysical Journal 257: 389–422. Bibcode 1982ApJ...257..389T. doi:10.1086/159999. 
4. ^ ^{a b c d e} "NASA/IPAC Extragalactic Database". Results for various galaxies. http://nedwww.ipac.caltech.edu/. Retrieved 2007-02-09. 
5. ^ ^{a b c} M. S. Yun, P. T. P. Ho, K. Y. Lo (1994). "A high-resolution image of atomic hydrogen in the M81 group of galaxies". Nature 372 (6506): 530–532. Bibcode 1994Natur.372..530Y. doi:10.1038/372530a0. PMID 7990925.