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

TL;DR

This study derives oxygen abundances in nearby galaxies using SDSS spectra, proposing a new method to estimate metallicity when key lines are outside the observed range, and analyzes the radial distribution of oxygen in NGC 4490.

Contribution

It introduces a novel approach to determine oxygen abundance using the Te method with the ff relation for SDSS spectra lacking [OII]3727 data, and provides the first radial abundance profile for NGC 4490.

Findings

Reliable (O/H)_ff abundances using the two-dimensional t_2 - t_3 relation.

Oxygen abundances in 29 galaxies range narrowly between 8.2 and 8.4.

First radial oxygen abundance distribution measured in NGC 4490.

Abstract

We have derived the oxygen abundance for a sample of nearby galaxies in the Data Release 5 of the Sloan Digital Sky Survey (SDSS) which possess at least two independent spectra of one or several HII regions with a detected [OIII]4363 auroral line. Since, for nearby galaxies, the [OII]3727 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 ff relation. (O/H)_7325 abundances have also been determined, based on the [OII]7320,7330 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 t_2 - t_3 relations. It was found that the (O/H)_ff abundances derived with the parametric two-dimensional t_2 - t_3 relation are most reliable. Oxygen abundances have been determined in 29 nearby galaxies, based on 84 individual abundance determinations in HII 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.