M81 Group

The M81 Group is a galaxy group in the constellations Ursa Major and Camelopardalis that includes the 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]

M81 Group
Observation data (Epoch J2000)
Constellation(s)	Ursa Major/Camelopardalis
Brightest member	M81[1] (pictured)
Number of galaxies	34[1]
Other designations
NGC 3031 Group

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[citation needed]		09h 57m 32.6s	+69° 17′ 00″	99	16.1
DDO 78[citation needed]	Im	10h 26m 27.4s	+67° 39′ 16″	55 ± 10	15.8
F8D1[citation needed]	dE	09h 44m 47.1s	+67° 26′ 19″		13.9
FM1[citation needed]	dSph	09h 45m 10.0s	+68° 45′ 54″		17.5
HIJASS J1021+6842[citation needed]		10h 21m 00.0s	+68° 42′ 00″	46	20
HS 117[citation needed]	I	10h 21m 25.2s	+71° 06′ 51″	-37	16.5
Holmberg I[citation needed]	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	6.9
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	Sm	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	dSph	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] Observations of the 21-centimeter hydrogen line indicate how the galaxies are connected.^[6] 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] Bridges of neutral hydrogen have been shown to connect M81 with M82 and NGC 3077.^[6][7] 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] Computer simulations of tidal interactions have been used to show how the current structure of the group could have been created.^[8]

Gallery

• 
  Galaxy UGC 8201 is a dwarf irregular galaxy member of the M81 galaxy group.^[9]
• 
  Amateur picture Messier 81 + 82 and NGC 3077 all of the M81 group, 33 frames stacked of 1 minute each.
• 
  The spiral galaxies Messier 81 and 82 and the dwarf galaxy Holmberg IX from GALEX
• 
  Close up view of Messier 81 from GALEX
• 
  The spiral galaxy Messier 81 from Spitzer Space Telescope
• 
  The spiral galaxy Messier 81 from Spitzer Space Telescope
• 
  Starburst galaxy Messier 82 from Hubble Space Telescope
• 
  NGC 2403 in mid-infrared view, combining the 3.6, 5.8 and 8.0 μm bands of the Spitzer Space Telescope
• 
  NGC 2403 in Mid-infrared view, combining the 3.6, 8.0 and 24 μm bands of the Spitzer Space Telescope
• 
  NGC 2403 from Hubble Space Telescope
• 
  NGC 2403 from Hubble Space Telescope illustrated
• 
  Supernova SN2004DJ in the spiral galaxy NGC 2403
• 
  Supernova 2004dj in NGC 2403
• 
  NGC 4236 from GALEX
• 
  NGC 2366 from Hubble Space Telescope
• 
  Galaxy NGC 2976 from Spitzer Space Telescope in infrared
• 
  Galaxy NGC 2976 from an amateur Astronomer
• 
  Galaxy NGC 4605 from GALEX
• 
  NGC 2363 from Hubble Space Telescope
• 
  NGC 2537 from GALEX
• 
  Holmberg II from Spitzer Space Telescope in infrared
• 
  UGC 5423 / M81 dwarf B from Spitzer Space Telescope in infrared
• 
  NGC 3077 from 2MASS
• 
  IC 2574

See also

• UGC 5497