Similar star formation rate and metallicity evolution timescales drive the fundamental metallicity relation

TL;DR

This study uses hydrodynamical simulations to analyze the timescales of galaxy SFR and metallicity evolution, revealing their anti-correlated behavior and its role in driving the fundamental metallicity relation (FMR).

Contribution

It demonstrates that similar evolution timescales and anti-correlation between SFR and metallicity are essential for the existence of the FMR, providing a new perspective on galaxy evolution models.

Findings

SFR and metallicity evolve over similar timescales in simulations.

Anti-correlation between SFR and metallicity drives the FMR.

Burstiness in SFR may weaken the FMR in certain models.

Abstract

The fundamental metallicity relation (FMR) is a postulated correlation between galaxy stellar mass, star formation rate (SFR), and gas-phase metallicity. At its core, this relation posits that offsets from the mass-metallicity relation (MZR) at a fixed stellar mass are correlated with galactic SFR. In this Letter, we quantify the timescale with which galactic SFRs and metallicities evolve using hydrodynamical simulations. We find that Illustris and IllustrisTNG predict that galaxy offsets from the star formation main sequence and MZR evolve over similar timescales, are often anti-correlated in their evolution, evolve with the halo dynamical time, and produce a pronounced FMR. In fact, for a FMR to exist, the metallicity and SFR must evolve in an anti-correlated sense which requires that they evolve with similar time variability. In contrast to Illustris and IllustrisTNG, we speculate that the SFR and metallicity evolution tracks may become decoupled in galaxy formation models dominated by globally-bursty SFR histories, which could weaken the FMR residual correlation strength. This opens the possibility of discriminating between bursty and non-bursty feedback models based on the strength and persistence of the FMR -- especially at high redshift.