The M81 Group

The M81 group is another famous group of galaxies mainly because it contains the famous M81/M82 pair of galaxies discovered in 1784. NGC 2403 is another prominant spiral galaxy on the right side of the group. M82 is a famous example of a starburst galaxy - there is a lot of star formation occuring in this galaxy.

The M81 Group

Below - three galaxies in the right side of the M81 group. NGC 2366 (left) is an irregular galaxy where a lot of recent star formation has occured. The brightest part of this galaxy is known as NGC 2363 - it is a huge HII region (emission nebula) where a lot of bright blue stars have formed. NGC 2403 (centre) is the second largest galaxy in the M81 group. Holmberg II (right) is one of nine low-surface-brightness galaxies listed by Erik Holmberg in the 1950's, three of which are associated with the M81 group.

NGC 2366 NGC 2403 Holmberg II
NGC 2366 NGC 2403 Holmberg II

The Galaxies of the M81 Group

This is a list of the main galaxies in the M81 group. The three main galaxies in this group are M81, NGC 2403 and NGC 4236.

  1             2        3      4     5      6    7     8     9
Name           Equatorial      Blue  Type  Size Size   RV   Other
               Coordinates     Mag          (')  kly  km/s  Names
               RA       Dec
UGC 3794     07 22.9  +77 48   17.8  SBm    1.0    5    ? 
NGC 2366     07 28.9  +69 12   11.9  Irr    8.1   30   134
UGCA 133     07 34.2  +66 53   15.9  E      3.0   10    ?   DDO 44
NGC 2403     07 36.8  +65 36    8.9  SBc   21.9   75   181
Holmberg II  08 19.1  +70 43   11.1  Irr    7.9   30   207  UGC 4305
M81dwA       08 23.2  +71 02   16.5  Irr    1.8    5   163  PGC 23521
UGC 4459     08 34.2  +66 11   15.0  Irr    1.5    5    95  DDO 53
UGC 4483     08 37.1  +69 47   15.5  Irr    1.1    5   217
UGC 4945     08 55.9  +72 01   17?   E      1.3    5   700  UGCA 158
Holmberg I   09 40.5  +71 11   13.2  Irr    3.6   15   208  UGC 5139
NGC 2976     09 47.3  +67 55   10.9  Sc     5.9   20    94
M81          09 55.6  +69 04    7.9  Sab   26.9   95    50  NGC 3031
M82          09 55.8  +69 41    9.2  Irr   11.2   40   296  NGC 3034
Holmberg IX  09 57.7  +69 03   14.4  Irr    2.5   10   134  UGC 5336
NGC 3077     10 03.4  +68 44   10.6  Irr    5.4   20   102
UGC 5428     10 05.1  +66 33   16.0  E      0.9    5   -22  DDO 71
UGC 5423     10 05.5  +70 22   15.9  Irr    0.9    5   424  M81dwB
UGC 5442     10 07.1  +67 49   15.4  E      1.8    5    78
DDO 78       10 26.5  +67 40   15.8  E      2.0    5    ?   PGC 30664
IC 2574      10 28.4  +68 25   10.8  SBm   13.2   45   142
UGC 5692     10 30.6  +70 37   13.5  Sm     3.2   10   262  DDO 82
UGCA 220     10 49.3  +64 43   16.9  Irr    1.7    5    ? 
UGC 5918     10 49.6  +65 32   15.1  Irr    2.4   10   452  DDO 87
UGC 6456     11 28.0  +78 59   15.9  Irr    1.4    5   -61
NGC 3738     11 35.8  +54 31   12.1  Irr    2.5   10   406
NGC 4236     12 16.8  +69 28   10.1  SBd   21.9   75    87
NGC 4605     12 40.0  +61 37   10.9  SBc    5.8   20   272
UGC 8201     13 06.5  +67 42   12.9  Irr    3.5   10   121  DDO 165
NGC 5204     13 29.6  +58 26   11.7  Sm     5.0   15   329
Column 1: The usual name of the galaxy.
Column 2: The Right Ascension for epoch 2000.
Column 3: The Declination for epoch 2000.
Column 4: The blue apparent magnitude of the galaxy.
Column 5: The galaxy type: E=Elliptical, S0=Lenticular, Sa,Sb,Sc,Sd=Spiral,
          SBa,SBb,SBc,SBd=Barred Spiral, Sm,SBm,Irr=Irregular.
Column 6: The angular diameter of the galaxy (arcminutes).
Column 7: The diameter of the galaxy (thousands of light years).
Column 8: The recessional velocity (km/s) of the galaxy relative to
          the cosmic microwave background.
Column 9: Other names of the galaxy.

References:
Karachentsev I, Dolphin A, Geisler D, Grebel E, Guhathakurta P, Hodge P, Karachentseva V,
        Sarajedini A, Seitzer P, Sharina M, (2002), The M 81 group of galaxies: New 
        distances, kinematics and structure. Astron and Astrophys, 383, 125.
van Driel W, Kraan-Korteweg R, Binggeli B, Huchtmeier W, (1998), An HI line search for
        optically identified dwarf galaxy candidates in the M 81 group. Astron and
        Astrophys Supp, 127, 397.
Schmidt K, Priebe A, Boller T, (1993), Nearby Galaxies. Astron Nachr, 314, 371.
The HyperLeda Database, (2003).

Below - three more M81 group galaxies. M82 (left) is a very famous example of a starburst galaxy - it contains a lot of young, bright stars probably because a close encounter with its more massive neighbour M81 has triggered a lot of new star formation. IC 2574 (centre) by contrast is a much dimmer galaxy even though it is approximately the same size as M82. NGC 4236 (right) is a large galaxy in the left side of the M81 group.

M82 IC 2574 NGC 4236
M82 IC 2574 NGC 4236

Shown below is M81. This galaxy is the dominant galaxy in the group and it is similar in size to the Milky Way. This galaxy is one of the brightest galaxies in the sky, and although it is too faint to see with the naked eye, it is an easy galaxy to find with binoculars if you know where to look.

M81
M81

Below - three bright dwarf galaxies in the M81 group. NGC 2976 (left) is a small spiral galaxy approximately two million light years behind M81. NGC 3077 (centre) is much closer to M81 - they are separated by about 140 thousand light years. NGC 4605 (right) is a small spiral galaxy on the left edge of the group.

NGC 2976 NGC 3077 NGC 4605
NGC 2976 NGC 3077 NGC 4605

Properties of the M81 Group
Equatorial Coordinates RA=10h00m Dec=+68
Galactic Coordinates l=145 b=+40
Supergalactic Coordinates L=40 B=0
Distance to the centre of the group 12 million light years
Number of large galaxies 7
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