Abundance determination in HII regions from spectra without the [OII]3727+3729 line

TL;DR

This paper introduces an empirical calibration method to determine oxygen and nitrogen abundances in HII regions using strong emission lines, especially when the [OII]3727+3729 line is unavailable, enabling analysis of spectra from various sources.

Contribution

The paper presents a novel NS calibration that estimates abundances without relying on the [OII] line, expanding the applicability of spectral analysis in HII regions.

Findings

Reliable abundance estimates across all metallicities

Applicable to SDSS spectra lacking the [OII] line

Effective for nearby galaxy HII regions

Abstract

We suggest an empirical calibration for determination of oxygen and nitrogen abundances and electron temperature in HII regions where the [OII]3727+3729 line (R_2) is not available. The calibration is based on the strong emission lines of OIII, NII, and SII (NS calibration) and derived using the spectra of HII regions with measured electron temperatures as calibration datapoints. The NS calibration makes it possible to derive abundances for HII regions in nearby galaxies from the SDSS spectra where R_2 line is out of the measured wavelength range, but can also be used for the oxygen and nitrogen abundances determinations in any HII region independently whether the nebular oxygen line [OII]3727+3729 is available or not. The NS calibration provides reliable oxygen and nitrogen abundances for HII regions over the whole range of metallicities.