N/O in spiral discs: A new algorithm for abundance determinations

Abstract

We obtain nitrogen abundances in the H II regions of selected spiral galaxies by using a new algorithm developed from grids of photoionization models. The new method requires only the observation of optical [N II], [O II] and [O III] lines. We show the self-consistency of the new method, and also the agreement with more detailed modelling of individual H II regions. Gradients in [N/O] against effective radius and [O/H] are presented for a well-observed subset of galaxies from the Vila-Costas & Edmunds sample.