The M81 group

[M81 group radio image] This group of galaxies is one of the nearest to our Local Group, being only some 12 million light-years distant, according to 1993 measurements of the Hubble Space Telescope under the direction of Wendy Freedman of the Carnegie Institution of Washington by measuring the periods of 32 Cepheid variables in M81 with the pre-repair Wide Field/Planetary Camera (WFPC I), and corrected for Hipparcos results.

The group contains two Messier objects: M81 and M82 which form an appealing interacting pair visible in the same field of view at moderate magnification. Other members include NGC 3077 and NGC 2976. As radio images such as ours have revealed, NGC 3077 is in considerable interaction with M81 and M82, plus perhaps some very small galaxies, as there is a common gaseous envelope. In our image, M81 is the spiral right and below center, M82 the not in the upper right center, and NGC 3077 is lower left; at least two dwarf galaxies appear to show up closely left of M81.

  • Radio image of M81/82/NGC 3077 (NRAO) compared to the visible light POSS image

    Further, more outlying members of the group include the irregular galaxy NGC 2366 and the fine Sc spiral NGC 2403, both lying in the constellation Camelopardalis, IC 2574, "Coddington's Nebula", which is quite irregular but shows some "faint indications of spiral structure" (Burnham), and the irregulars Holmberg I (UGC 5139) and Holmberg II (UGC 4305).

    A full list of the group, as given by R. Brent Tully in his Nearby Galaxies Catalog, is given in the table below (added to this is Holmberg IX):

    Name Name II RA(h:m) Dec(d:m)type m_v dim RV
    NGC 2366 H III.748 7:28.9 +69:13 Ir+ 10.91 7.3x3.5 252
    NGC 2403 H V.44 7:36.9 +65:36 Sc 8.39 17.8x11.0 259
    M81 dw A 8:23.9 +71:02 I? 16.5: 1.3x0.7 262
    Holm. II UGC 4305 8:18.9 +70:43 Ir+ 10.75 7.6x6.2 305
    UGC 4459 8:34.1 +66:10 Ir+ 14.38p 1.7x1.3 144
    Holm. I UGC 5139 9:40.5 +71:11 Ir+ 12.94 3.5x3.0 287
    NGC 2976 H I.285 9:47.3 +67:55 Scp 10.15 4.9x2.5 175
    M81 NGC 3031 9:55.6 +69:04 Sb 6.93 25.7x14.1 95
    M82 NGC 3034 9:55.8 +69:41 Pec 8.41 11.2x4.6 388
    Holm. IX UGC 5336 9:57.5 +69:03 Im 15.5 1.2x0.5 175
    NGC 3077 H I.286 10:03.3 +68:44 E2p 9.85 4.6x3.6 148
    M81 dw B UGC 5423 10:05.5 +70:22 Ir+ 14.94p 1.2x0.9 479
    IC 2574 10:28.4 +68:25 S+ 10.56 12.3x5.9 185

    Key: Name, Name II: Some catalog number or name for primary and secondary identification; RA/Dec: Position 2000.0; type: Hubble type; m_v: apparent visual magnitude; dim: dimension in arc minutes; RV: radial velocity (all data from the Sky Catalog 2000.0 when available).

    Hartmut Frommert (spider@seds.org)
    Christine Kronberg (smil@lrz.uni-muenchen.de)

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    Last Modification: 1 Jul 2001, 23:10 MET