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Session 51 - Star Formation & Chemical Evolution of Galaxies.
Display session, Tuesday, January 16
North Banquet Hall, Convention Center
The formation and evolution of dwarf irregular galaxies from tidally removed material in interacting systems are discussed via a case study of the peculiar system NGC 5291. This system contains an S0 galaxy interacting with a disturbed companion known as the Seashell. The pair is located in the western outskirts of the IC 4329 cluster. Initial observations indicated a complex of star-formation knots extending roughly 4' north and 4' south of the galaxy, and a large HI extent apparently offset to the west. High resolution atomic hydrogen observations taken with the VLA are presented here and confirm that the HI is offset, but also reveal that it forms an incomplete ring, or tail, to the west. NGC 5291 shows a high velocity gradient in HI; the Seashell was not detected and is presumably stripped of gas by the interaction. Several of the optical knots coincide with large concentrations (10 EXP 9 solar masses) of HI. Each of the knots is compared to a set of criteria designed to determine if these objects are bound against their own internal kinetic energy and are tidally stable relative to the host galaxies. A large star-forming knot located in the north part of the ring is shown to meet the established criteria, is self-gravitating, and possesses a stellar component. It is suggested that this object is a genuinely young dwarf irregular galaxy that has evolved from the interaction and that this entire complex contains several proto or young dwarf irregular galaxies in various stages of development.
