HII-CHI-mistry for active galactic nuclei: optical sulphur abundances without empirical ionisation correction factors
Abstract
> The determination of sulphur abundances in active galactic nuclei (AGN) is uncertain because ionisation correction factors (ICFs) are commonly calibrated for HII regions. We extend the HII-CHI-mistry methodology to derive total S/H in AGN from optical emission lines through comparison with photoionisation models. Tests against Seyfert galaxies with direct-method ionic abundances favour models with alpha_ox=-1.2 and a 98% free-electron stopping criterion. While O/H agrees with previous determinations, HCm yields systematically larger S/H than direct-method analyses using classical ICFs, suggesting that these prescriptions underestimate higher sulphur ionisation stages in AGN. Applied to MaNGA Seyfert and LINER-like regions, the method reveals a common positive S/O-metallicity relation. Seyferts show slightly larger median S/O than star-forming regions at high O/H, while LINERs occupy an intermediate position. These differences become weaker when S/H rather than O/H is used as the metallicity tracer, although Seyferts still tend to populate the upper envelope. Sulphur may therefore provide a robust tracer of gas-phase metallicity, while the differences between Seyferts and LINERs may reflect differences in their ionisation conditions and ionising SEDs.
Versions
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BibTeX
@misc{perezmontero2026hiichimistry,
title = {{HII-CHI-mistry for active galactic nuclei: optical sulphur abundances without empirical ionisation correction factors}},
author = {E. Pérez-Montero and O. L. Dors Jr. and I. A. Zinchenko and B. Pérez-D\'ıaz and J. M. V\'ılchez},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2608.25919},
eprint = {2608.25919},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.25919},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - HII-CHI-mistry for active galactic nuclei: optical sulphur abundances without empirical ionisation correction factors
AU - E. Pérez-Montero
AU - O. L. Dors Jr.
AU - I. A. Zinchenko
AU - B. Pérez-D\'ıaz
AU - J. M. V\'ılchez
PY - 2026
DA - 2026/10/27
PB - arXiv
DO - 10.48550/arxiv.2608.25919
UR - https://arxiv.org/abs/2608.25919
AB - > The determination of sulphur abundances in active galactic nuclei (AGN) is uncertain because ionisation correction factors (ICFs) are commonly calibrated for HII regions. We extend the HII-CHI-mistry methodology to derive total S/H in AGN from optical emission lines through comparison with photoionisation models. Tests against Seyfert galaxies with direct-method ionic abundances favour models with alpha_ox=-1.2 and a 98% free-electron stopping criterion. While O/H agrees with previous determinations, HCm yields systematically larger S/H than direct-method analyses using classical ICFs, suggesting that these prescriptions underestimate higher sulphur ionisation stages in AGN. Applied to MaNGA Seyfert and LINER-like regions, the method reveals a common positive S/O-metallicity relation. Seyferts show slightly larger median S/O than star-forming regions at high O/H, while LINERs occupy an intermediate position. These differences become weaker when S/H rather than O/H is used as the metallicity tracer, although Seyferts still tend to populate the upper envelope. Sulphur may therefore provide a robust tracer of gas-phase metallicity, while the differences between Seyferts and LINERs may reflect differences in their ionisation conditions and ionising SEDs.
ER -