DISCOVERY OF NUMEROUS DWARF GALAXIES IN THE 2 NEAREST GROUPS OF GALAXIES

We report the discovery of a large population of dwarf irregular galax ies in the two nearest groups of galaxies outside the Local Group, the Sculptor and the Centaurus A groups (2.5 and 3.5 Mpc), Total areas of approximately 940 and 910 square degrees in these groups were scanned visually on the SRC J films to find dwarf candidates. Redshifts were obtained by an H I survey carried out at Parkes, with detection limits of 4x10(6) M-. and 7.8x10(6) M-., and 33 dwarf galaxies were successf ully detected in the groups. A follow-up optical survey (H alpha spect roscopy) detected a few more, and confirmed most of the H I redshifts. A total of 16 and 20 dwarf galaxies are found in Sculptor and Centaur us A, of which 6 are newly identified objects, and 5 more have newly d etermined redshifts, In both groups the dwarf members show a wider spa tial and velocity distribution than the brighter members. From their r adial velocities and projected distances we estimate the crossing time s of the groups, which confirm that they are not yet virialised. (C) 1 997 American Astronomical Society.