Abundance gradients in M31 - Comparison of results from supernova remnants and H II regions

Abstract

Eleven H II region spectra and those of six previously reported supernova remnants (SNRs) in M31 are obtained, along with the abundances of the H II regions. It is found that both N and O abundances decrease by a factor of approximately four, from the innermost regions studied, at about 4 kpc, to the outer regions, at about 23 kpc. These gradients are similar to those of other intermediate and late-type spiral galaxies, and the mean N and S abundances are similar to those of the Orion Nebula. The mean oxygen abundance, however, is found to be higher by a factor of two, accounting for the low excitation of the M31 H II regions. While a comparison of SNR and H II region abundance gradients shows agreement for nitrogen, contradictory results are found for oxygen which may be due to problems with the shock models.