Deriving the abundance distribution of HII galaxies using sulphur as tracer: Exploring the high-metallicity end

TL;DR

This study uses sulphur as a tracer to extend the metallicity range of HII galaxy abundance distributions, providing a more comprehensive understanding of their chemical composition.

Contribution

It introduces a new empirical calibration based on the S23 parameter that extends metallicity measurements up to solar levels in HII galaxies.

Findings

Sulphur-based abundances reach at least solar metallicity.

The S23 calibration provides a reliable method within the spectral range 6000-9500 A.

Sulphur and oxygen abundance distributions are similar when temperature-sensitive lines are detected.

Abstract

The main objective of this work is to derive the distribution of the the metal content of HII galaxies using sulphur as an abundance tracer. This increases the metallicity range that can safely be reached. We selected a sample of emission-line galaxies that we extracted from the SDSS-DR16. These objects have a redshift of z less than 0.04 so that the [SIII] 9069 A emission line and H beta equivalent widths that are higher than 10 A in emission were included, and they are compact in appearance. We used the so-called direct method for objects with the electron-temperature-sensitive [SIII] 6312 A emission line, and an empirical method based on the S23 parameter. The last provided an abundance calibration that monotonically increased up to at least the solar value, and can be applied based on the spectral range from 6000 to 9500 A alone. We show that the bias that is introduced when the [OIII] 4363 A line is required restricts the sample to objects with an [OIII] electron temperature higher than 10,000K, and their temperature distribution is then rather narrow. For objects with determinations of te [SIII], the distribution is flatter and wider, which fits a more realistic scenario better. For the objects in the sample that required the detection of the [OIII] 4363 A line and [SIII] 6312 A, the distribution abundances as traced directly by oxygen and sulphur appear to be very similar to each other. However, when the restriction for weak temperature-sensitive lines is relaxed, the abundance distribution is wider . In summary, the abundance distributions traced by sulphur can reach reliable abundances up to the solar value at least and provide a more complete picture of the metallicity distribution of HII galaxies.