Observations of the mass and light distribution of NGC 5963, an unusual low surface brightness spiral

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While the inner region of NGC 5963 appears to be a vigorous and nearly normal spiral of late type, the spiral is surrounded by a low surface brightness disk in which low surface brightness H II regions define a roughly spiral pattern. The rotation curve and optical surface photometry presented are used to derive the radial dependence of the local mass-to-light ratio, which in the inner, high surface brightness regions is about two, and 18 in the outer regions. In addition to this lack of coupling between mass and light distributions, it is found that the star-forming history of the inner and outer regions is very different. The observed N II forbidden line/H-alpha ratio, which is high in the inner disk and drops significantly just outside this region, suggests that star formation, gas depletion and element production have proceeded more rapidly in the inner than in the outer regions of this galaxy.