Hide-and-Seek with the Fundamental Metallicity Relation

TL;DR

This study examines the fundamental metallicity relation in star-forming galaxies using a new metallicity indicator, finding that the previously observed anti-correlation with star formation rate disappears with this method, but the relation may still exist.

Contribution

It demonstrates that the anti-correlation in the FMR is sensitive to the metallicity calibration method used, challenging previous interpretations.

Findings

Anti-correlation between metallicity and SFR disappears with new indicator

Metallicity sensitive to emission line ratio [NII]/[SII]

FMR may still exist despite previous null results

Abstract

We use $\sim$83,000 star-forming galaxies at $0.04<z<0.3$ from the Sloan Digital Sky Survey to study the so-called fundamental metallicity relation (FMR) and report on the disappearance of its anti-correlation between metallicity and star formation rate (SFR) when using the new metallicity indicator recently proposed by Dopita et al. In this calibration, metallicity is primarily sensitive to the emission line ratio [NII]$\lambda$6584 / [SII]$\lambda\lambda$6717, 6731 that is insensitive to dilution by pristine infalling gas that may drive the FMR anti-correlation with SFR. Therefore, we conclude that the apparent disappearance of the FMR (using this new metallicity indicator) does not rule out its existence.