This survey of dwarf galaxies in the M 81 group area revealed:
1) a detection rate of 49%, most of which are background galaxies relative to the M 81 group, and
2) no new HI rich dwarfs in the M 81 group. With the detection limit in mind, this result is unexpected. HI-observations of the Centaurus and Sculptor groups (Côté 1995) yielded 9 new HI rich dwarf members around those groups with a detection limit of about 107 solar masses.
While it is true that the velocity range covered by local neutral hydrogen prohibits detection of faint galaxies within this range, we would still expect at least a dozen or so dwarf galaxies to be detectable in the M 81 group if it had a luminosity function similar to that of the Centaurus and Sculptor groups. The undetected galaxies might be either low surface brightness galaxies in the background or dwarf ellipticals in the M 81 group itself.
In their study on dwarf galaxies Binggeli et al. (1990) concluded that "dwarf galaxies obey a morphology-density relation like the giants", and "dEs prefer strongly dense environments on all scales". Hence the different dwarf population of the Centaurus and Sculptor groups on one side and the M 81 group on the other side might just be documenting the large variety in the population of groups.
Acknowledgements
We are grateful to Wal Sargent for making available the catalog of M 81 group dwarf galaxy candidates prior to publication. This research has been supported, in part, by a NASA LTSARP grant (No.\ NAGW-3189) to EDS.