Small galaxy groups are very important objects for investigation because as a rule they contain a few interacting/merging galaxies. Therefore it is the unique laboratories for investigations of galaxy/group evolution, the role of environmental influence on galaxy properties like star formation rates, colours, luminosities, galaxy formation and dynamic etc. In general terms, small galaxy groups differ on two types: compact (virialized with interacting/merging members) and loose (non -virialized, members of these groups are located far from each other than in compact ones).
The most known catalogs of such groups are:
- Arp’s catalog of pecular galaxies (1966)
- Vorontsov-Veliaminov catalogs of Interacting galaxies (1959-2001)
- Hickson compact galaxy groups (1982)
- Double galaxies by Karachentsev (1987)
- Catalogs of galaxy triplets: Northern (Karachentseva, Karachensev & Shcherbanovsky, 1979) and Southern (Karachentseva & Karachentsev, 2000)
Starting from year 2000, many catalogs of pairs, triplets and small galaxy groups in different redshift ranges were published due to apperance of large extragalactic data bases and surveys like NED,HYPERLEDA, SDSS etc.