Chlorine abundances in star-forming regions of the local Universe

¹ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
² Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
³ Instituto de Astronomía, Universidad Nacional Autónoma de México, Ap. 70-264, 04510 CDMX, Mexico
⁴ Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK
⁵ Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE-CONAHCyT), Luis E. Erro 1, 72840, Tonantzintla, Puebla, Mexico
⁶ Isaac Newton Group of Telescopes, Apto 321, 38700 Santa Cruz de La Palma, Canary Islands, Spain

^★ Corresponding author: maialen.orte@iac.es

Received: 29 January 2025
Accepted: 21 March 2025

Abstract

Aims. We aim to study the behaviour of Cl abundance and its ratios with respect to O, S, and Ar abundances in a sample of more than 200 spectra of Galactic and extragalactic H II regions and star-forming galaxies (SFGs) of the local Universe.

Methods. We used the DEep Spectra of Ionised REgions Database (DESIRED) Extended project (DESIRED-E) that comprises more than 2000 spectra of H II regions and SFGs with direct determinations of electron temperature (T_e). From this database, we selected spectra for which it is possible to determine the Cl²⁺ abundance and whose line ratios meet certain observational criteria. We calculated the physical conditions and Cl, O, S, and Ar abundances in a homogeneous manner for all the spectra. We compared them with results of photoionisation models to carry out an analysis of which is the most appropriate T_e indicator for the nebular volume where Cl²⁺ lies, proposing a scheme that improves the determination of the Cl²⁺ abundance. We compared the Cl/O ratios obtained using two different ionisation correction factor (ICF) schemes. We also compared the nebular Cl/O distribution with stellar determinations.

Results. Our analysis indicates that one of the tested ICF schemes provides a better match to the observed Cl/O ratio distributions. We find that the log(Cl/O) versus 12+log(O/H) and log(Cl/Ar) versus 12+log(Ar/H) distributions are not correlated in the whole metallicity range covered by our objects indicating a lockstep evolution of those elements. In contrast, the log(Cl/S) versus 12+log(S/H) distribution shows a weak correlation with a slight negative slope.