ABUNDANCES IN SPIRAL GALAXIES - EVIDENCE FOR PRIMARY NITROGEN-PRODUCTION

We present the results of nitrogen and oxygen abundance measurements f or 185 H II regions spanning a range of radii in 13 spiral galaxies. A s expected, the nitrogen-to-oxygen ratio increases linearly with the o xygen abundance for high-metallicity H II regions, indicating that nit rogen is predominantly a secondary element. However, the nitrogen-to-o xygen ratio plateaus for oxygen abundances less than 1/3 solar [12 + l og(O/H) < 8.45], as is also seen in low-metallicity dwarf galaxies. Th is result suggests that the observed trend in dwarf galaxies is not du e to the outflow of enriched material in a shallow gravitational poten tial. While the effects of the infall of pristine material and delayed nitrogen delivery are still unconstrained, nitrogen does appear to ha ve both a primary and a secondary component at low metallicities in al l types of galaxies.