The Oxygen Abundance of Nearby Galaxies from Sloan Digital Sky Survey Spectra

Abstract

We have derived the oxygen abundance for a sample of nearby galaxies in Data Release 5 of the Sloan Digital Sky Survey (SDSS) that possess at least two independent spectra of one or several H II regions with a detected [O III] λ4363 auroral line. Since, for nearby galaxies, the [O II] λ3727 nebular line is out of the observed wavelength range, we propose a method to derive (O/H)ff abundances using the classic Te method coupled with the flux-flux (ff) relation. (O/H)7325 abundances have also been determined, based on the [O II] λλ7320, 7330 line intensities and using a small modification of the standard Te method. The (O/H)ff and (O/H)7325 abundances have been derived with both the one- and two-dimensional t2-t3 relations. It was found that the (O/H)ff abundances derived with the parametric two-dimensional t2-t3 relation are the most reliable. Oxygen abundances have been determined in 29 nearby galaxies on the basis of 84 individual abundance determinations in H II regions. Because of our selection methods, the metallicity of our galaxies lies in the narrow range 8.2 12 + log(O/H) 8.4. The radial distribution of oxygen abundances in the disk of the spiral galaxy NGC 4490 is determined for the first time.