The M81 Group

The M81 Group is situated at a distance of 3.6Mpc, which combined with its high galactic latitude makes it relatively accessible to observers. It is also the richest and most compact of all groups within 10Mpc. It is composed of the 19#19 10#10 magnitude Sb galaxy M81 itself (also classified as a LINER, or Seyfert galaxy), the amorphous galaxies M82 and NGC3077, the Sd galaxy NGC2976 and the Sm galaxy IC2574. In addition to these giant galaxies, there are about 40 dwarf galaxy systems belonging to the group. Modern wide-field CCD searches have recently uncovered a few additional low surface brightness systems in the group. HI searches for new members have been undertaken, but there have been no discovery of new candidates sufficiently gas rich to be detected. There has also been a high rate of non-detections in the radio searches, indicating a very low HI content in numerous known dwarf galaxies, or possible confusion with galactic high velocity clouds. Most members of the M81 group are presently in a phase of strong interacting with each other, due to the common HI envelope the galaxies are apparently embedded in.

The region of the sky towards the M81 Group is characterized by relatively patchy extinction (see Fig -b), so many objects of very low surface brightness, of uncertain type, might be either faint dwarf galaxies or galactic cirrus.

Figure: Distribution on the plane of the sky of all 40 members and possible members of the M81 group. The morphological type of the galaxies is indicated. Uncertain group members are put in parentheses. The scale bar of 0.5 Mpc is based on a distance of 4 Mpc.

20#20

Figure: (a) - 40 min. R image of UGCA 220 (lower right). (b) - IRAS 100 micron image of the M81 region. The positions of the objects UGCA 220, DDO 87, BKK 4, BK 7N, BKK 6, BKK 7, BKK 8, BKK 9, BK 8N and BKK 11 are shown as crosses. Note the apparent association of these objects with a large-scale IRAS cirrus feature slightly to the east (left). The positions of M81, M82, NGC 2976 as well as NGC 3077 are also indicated.

21#21

In total, photometry has been carried out for 25 galaxies in and around the group.