We present the results of nitrogen and oxygen abundance measurements for 185 \ion H2 regions spanning a range of radius in 13 spiral galaxies .
As expected , the nitrogen–to–oxygen ratio increases linearly with the oxygen abundance for high metallicity \ion H2 regions , indicating that nitrogen is predominately a secondary element .
However , the nitrogen–to–oxygen ratio plateaus for oxygen abundances less than 1/3 solar ( 12+log ( O/H ) < 8.45 ) , as is also seen in low metallicity dwarf galaxies .
This result suggests that the observed trend in dwarf galaxies is not due to outflow of enriched material in a shallow gravitational potential .
While the effects of infall of pristine material and delayed nitrogen delivery are still unconstrained , nitrogen does appear to have both a primary and secondary component at low metallicities in all types of galaxies .