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 (1.03 ± 0.17). The M81 Group, the Local Group, and other nearby groups all lie within the Virgo Supercluster (i.e. the Local Supercluster).

Members

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

+Members of the M81 Group Name Type R.A. (J2000) Dec. (J2000) Redshift (km/s) Apparent Magnitude Arp's Loop 99 16.1 DDO 78 Im 55 ± 10 15.8 F8D1 dE 13.9 FM1 dSph 17.5 HIJASS J1021+6842 46 20 HS 117 I −37 16.5 Holmberg I IAB(s)m 139 ± 0 13.0 Holmberg II Im 142 ± 1 11.1 Holmberg IX Im 46 ± 6 14.3 IC 2574 SAB(s)m 57 ± 2 13.2 IKN (galaxy) 17.0 KKH 57 dSph 18.5 Messier 81 SA(s)ab −34 ± 4 6.9 Messier 81 Dwarf A I 113 ± 0 16.5 Messier 82 I0 203 ± 4 9.3 NGC 2366 IB(s)m 80 ± 1 11.4 NGC 2403 SAB(s)cd 131 ± 3 8.9 NGC 2976 SAc pec 3 ± 5 10.8 NGC 3077 I0 pec 14 ± 4 10.6 NGC 4236 SB(s)dm 0 ± 4 10.1 PGC 28529 Im −40 17.1 PGC 28731 dE −135 ± 30 15.6 PGC 29231 dE 16.7 PGC 31286 dSph 16.7 PGC 32667 Im 116 ± 1 14.9 UGC 4459 Im 20 ± 0 14.5 UGC 4483 156 ± 0 15.1 UGC 5428 Im −129 ± 0 18 UGC 5442 Im −18 ± 14 18 UGC 5692 Sm 56 ± 3 13.5 UGC 6456 Pec −103 ± 0 14.5 UGC 7242 Scd 68 ± 2 14.6 UGC 8201 Im 31 ± 0 12.8 UGCA 133 dSph 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. 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 (or the formation of many stars) 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.

Gallery

M81 Group

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