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We have investigated the effects of a bar and an asymmetric spiral structure on the neutral hydrogen distribution and kinematics in the strongly barred spiral galaxy NGC 7479. The strongest 21‐cm line emission at 1‐kpc resolution comes from the western spiral arm which appears to be slightly inclined to the plane of the main disc. In contrast, the area within the radius of the bar is devoid of 21‐cm line emission. The radio continuum emission at 21 cm follows the bar dust lanes, but beyond 3 kpc from the nucleus the radio continuum emission has a peculiar morphology, unlike that of optical and near‐infrared images. We did not detect any low surface brightness gas‐rich companions in the near neighbourhood of NGC 7479. This leads us to propose that the strong western spiral arm was created in a recent minor merger.

The possible formation and evolution of dwarf irregular galaxies from material derived from perturbed evolved galaxies is addressed via an H 1 study of a likely example, the peculiar system NGC 5291. This 1427 Astron.

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