Does the Fundamental Metallicity Relation Evolve with Redshift? II: The Evolution in Normalisation of the Mass-Metallicity Relation

TL;DR

This study investigates whether the Fundamental Metallicity Relation (FMR) evolves with redshift by comparing predictions from cosmological simulations to observational data, revealing that the FMR's normalization changes over time and varies across models.

Contribution

It introduces the concepts of static and dynamic FMRs and demonstrates their applicability across different cosmological simulations, highlighting the importance of baryon cycle implementation.

Findings

Static FMRs in SIMBA do not predict evolution well.

Dynamic FMRs in Illustris, IllustrisTNG, and EAGLE better match observed trends.

Simulations show offsets from the FMR at high redshift, indicating evolving baryon cycles.

Abstract

The metal content of galaxies is a direct probe of the baryon cycle. A hallmark example is the relationship between a galaxy's stellar mass, star formation rate (SFR), and gas-phase metallicity: the Fundamental Metallicity Relation (FMR). While low-redshift ($z\lesssim4$) observational studies suggest that the FMR is redshift-invariant, recent high-$z$ JWST data indicate deviations from the FMR established at low-$z$. In this study, we utilize the FMR to predict the evolution of the normalisation of the mass-metallicity relation (MZR) using the cosmological simulations Illustris, IllustrisTNG, EAGLE, and SIMBA. Our findings demonstrate that a $z = 0$ calibrated FMR struggles to predict the evolution in the MZR of each simulation. To quantify the divergence of the predictions, we introduce the concepts of a ``static'' FMR, where the role of the SFR in setting the normalization of the MZR does not change with redshift, and a ``dynamic'' FMR, where the role of SFR evolves over time. We find static FMRs in SIMBA and dynamic FMRs in Illustris, IllustrisTNG and EAGLE. We suggest that the differences between these models likely points to the subtle differences in the implementation of the baryon cycle. Moreover, we echo recent JWST results at $z > 4$ by finding significant offsets from the FMR in IllustrisTNG and EAGLE, suggesting that the observed FMR may have a similar dynamic trend as these simulations. Overall, our findings imply that the current FMR framework neglects important time variations of these simulations' baryon cycles.