The Mass-Metallicity and the Fundamental Metallicity Relation revisited on a fully Te-based abundance scale for galaxies

TL;DR

This study revisits the relationships between stellar mass, metallicity, and star formation rate in local galaxies using a fully Te-based metallicity scale, providing refined parametrizations and a new fundamental metallicity relation.

Contribution

It introduces a new functional form for the mass-metallicity relation and a parametrization of the FMR incorporating SFR dependence on the turnover mass, all on a consistent Te abundance scale.

Findings

The MZR slope and saturation metallicity agree with previous Te-based studies.

The metallicity scatter reduces significantly for highly star-forming galaxies.

The new FMR has a residual scatter of 0.054 dex, serving as a benchmark for future studies.

Abstract

The relationships between stellar mass, gas-phase metallicity and star formation rate (i.e. the Mass-Metallicity, MZR, and the Fundamental Metallcity Relation, FMR) in the local Universe are revisited by fully anchoring the metallicity determination for SDSS galaxies on the Te abundance scale defined exploiting the strong-line metallicity calibrations presented in Curti et al. (2017). Self-consistent metallicity measurements allow a more unbiased assessment of the scaling relations involving M, Z and SFR, which provide powerful constraints for the chemical evolution models. We parametrise the MZR with a new functional form which allows us to better characterise the turnover mass. The slope and saturation metallicity are in good agreement with previous determinations of the MZR based on the Te method, while showing significantly lower normalisation compared to those based on photoionisation models. The Z- SFR dependence at fixed stellar mass is also investigated, being particularly evident for highly star forming galaxies, where the scatter in metallicity is reduced up to a factor of ~30%. A new parametrisation of the FMR is given by explicitly introducing the SFR-dependence of the turnover mass into the MZR. The residual scatter in metallicity for the global galaxy population around the new FMR is 0.054 dex. The new FMR presented in this work represents a useful local benchmark to compare theoretical predictions and observational studies (of both local and high-redshift galaxies) whose metallicity measurements are tied to the abundance scale defined by the Te method, hence allowing to properly assess its evolution with cosmic time.