Nebular abundances in galaxies: Beware of biases

TL;DR

This paper highlights potential biases in nebular abundance measurements in galaxies using strong line methods, emphasizing the importance of considering structural differences to avoid inaccurate metallicity comparisons.

Contribution

It warns against biases in nebular abundance estimates from strong line methods when galaxy properties differ from calibration samples.

Findings

Strong line methods can be significantly biased by galaxy structural differences.

Calibration samples may not be representative of all galaxy types.

Caution is needed when comparing metallicities across diverse galaxy samples.

Abstract

The derivation of nebular abundances in galaxies using strong line methods is simple and quick. Various indices have been designed and calibrated for this purpose, and they are widely used. However, abundances derived with such methods may be significantly biased, if the objects under study have different structural properties (hardness of the ionizing radiation field, morphology of the nebulae) than those used to calibrate the methods. Special caution is required when comparing the metallicities of different samples, like, for example, blue compact galaxies and other emission line dwarf galaxies, or samples at different redshifts.