Affiliation: Department of Physics and Astronomy, Univ. of Florence

Contribution: Oral

Title: Accurate Metallicity Determination in Ionized Gas through Advanced Photoionization Modelling with HOMERUN

Abstract: Powerful observational facilities such as JWST, EUCLID, ALMA, and VLT are providing a wealth of new data to uncover the processes behind the formation of the first stars, galaxies, and supermassive black holes. These advancements enable us to study the intricate relationship between star formation and AGN activity. However, the tools used to interpret this data have not evolved at the same pace. A critical aspect of understanding galaxy formation lies in accurately determining the metallicity of ionized gas, as it provides essential clues through the mass-metallicity and fundamental metallicity relations. The traditional Te-method, which estimates gas densities and temperatures from forbidden line ratios, has been a cornerstone for decades. However, its reliance on simplified assumptions due to past computational constraints necessitates more precise methods in light of todays advanced spectroscopic measurements. I will present HOMERUN, an innovative approach to photoionization modelling that achieves an unprecedented accuracy of 10% in reproducing observed line ratios across a wide range of ionization stages. Our method involves a weighted combination of multiple single-cloud photoionization models, with the novelty lying in the computation of weights dictated by observations. This approach significantly enhances the precision of metallicity determinations in ionized gas compared to existing models. The results from applying these models to various samples of HII regions, star-forming galaxies, and AGN will be discussed. These findings address discrepancies in metallicities between HI regions and stars in our Galaxy, estimate the average physical conditions of ionized gas in galaxies, and demonstrate how the Te-method can severely underestimate gas abundances. This advanced photoionization modelling technique promises to refine our understanding of galaxy formation and evolution, in line with the latest observational achievements.

This contribution can be found here (pdf).