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. 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. The group is estimated to have a total mass of.
The M81 Group, the Local Group, and other nearby groups all lie within the Virgo Supercluster.

Members

The table below lists galaxies that have been identified as associated with the M81 Group by I. D. Karachentsev.
NameTypeR.A. Dec. Redshift Apparent Magnitude
Arp's Loop9916.1
DDO 78Im55 ± 1015.8
F8D1dE13.9
FM1dSph17.5
HIJASS J1021+68424620
HS 117I-3716.5
Holmberg IIABm139 ± 013.0
Holmberg IIIm142 ± 111.1
Holmberg IXIm46 ± 614.3
IC 2574SABm57 ± 213.2
IKN17.0
KKH 57dSph18.5
Messier 81SAab-34 ± 46.9
Messier 81 Dwarf AI113 ± 016.5
Messier 82I0203 ± 49.3
NGC 2366IBm80 ± 111.4
NGC 2403SABcd131 ± 38.9
NGC 2976SAc pec3 ± 510.8
NGC 3077I0 pec14 ± 410.6
NGC 4236SBdm0 ± 410.1
PGC 28529Im-4017.1
PGC 28731dE-135 ± 3015.6
PGC 29231dE16.7
PGC 31286dSph16.7
PGC 32667Im116 ± 114.9
UGC 4459Im20 ± 014.5
UGC 4483156 ± 015.1
UGC 5428Im-129 ± 018
UGC 5442Im-18 ± 1418
UGC 569213.556 ± 313.5
UGC 6456Pec-103 ± 014.5
UGC 7242Scd68 ± 214.6
UGC 8201Im31 ± 012.8
UGCA 133Im15.6

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. Observations of the 21-centimeter hydrogen line indicate how the galaxies are connected.
The gravitational interactions have stripped some hydrogen gas away from all three galaxies, leading to the formation of filamentary gas structures within the group. Bridges of neutral hydrogen have been shown to connect M81 with M82 and NGC 3077. 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 within the centers of these two galaxies. Computer simulations of tidal interactions have been used to show how the current structure of the group could have been created.

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