Extended HI emission associated with the low-surface-brightness companions of the SO galaxy NGC 4026

An HI survey has been made of the SO galaxy NGC 4026 and its nearby low-surface-brightness companions. Although the SO galaxy was not detected in HI, filamentary neutral hydrogen was found in its near vicinity associated with the companion galaxies UGC 6956 and 6922. In particular an HI filament was observed extending 50 to 60 kpc from UGC 6956 and curving in an arc to the south of NGC 4026. A bridge of gas was also seen connecting UGC 6956 to 6922. A third galaxy, UGC 6917 was found to have a disturbed velocity field. The distribution and kinematics of the gas strongly suggests that tidal interactions are taking place in this system. It is likely that the SO galaxy dominates the gravitational potential of the group and is tidally stripping gas from its nearest companion UGC 6956. The outcome of this interaction may be the formation of an HI ring around NGC 4026 on a time-scale of 107 to 108 yr. It is suggested that the tidal capture of gas from small companion galaxies like UGC 6956 could provide a mechanism for the origin of outer HI rings in other SO galaxies. (author)