The Gas Phase Mass Metallicity Relation for Dwarf Galaxies: Dependence on Star Formation Rate and HI Gas Mass

TL;DR

This study investigates how the gas-phase mass-metallicity relation in dwarf galaxies depends on star formation rate and HI gas mass, revealing that HI mass provides a more consistent and physically motivated relation than star formation rate.

Contribution

The paper introduces the FMR$_{ ext{HI}}$ as a new, more stable fundamental metallicity relation based on HI gas mass, outperforming the SFR-based relation in dwarf galaxies.

Findings

FMR$_{ ext{HI}}$ has the lowest scatter among studied relations.

FMR$_{ ext{SFR}}$ shows inconsistencies at low SFRs.

FMR$_{ ext{HI}}$ is consistent across different galaxy samples.

Abstract

Using a sample of dwarf galaxies observed using the VIMOS IFU on the VLT, we investigate the mass-metallicity relation (MZR) as a function of star formation rate (FMR$_{\text{SFR}}$) as well as HI-gas mass (FMR$_{\text{HI}}$). We combine our IFU data with a subsample of galaxies from the ALFALFA HI survey crossmatched to the Sloan Digital Sky Survey to study the FMR$_{\text{SFR}}$ and FMR$_{\text{HI}}$ across the stellar mass range 10$^{6.6}$ to 10$^{8.8}$ M$_\odot$, with metallicities as low as 12+log(O/H) = 7.67. We find the 1$\sigma$ mean scatter in the MZR to be 0.05 dex. The 1$\sigma$ mean scatter in the FMR$_{\text{SFR}}$ (0.02 dex) is significantly lower than that of the MZR. The FMR$_{\text{SFR}}$ is not consistent between the IFU observed galaxies and the ALFALFA/SDSS galaxies for SFRs lower than 10$^{-2.4}$ M$_\odot$ yr$^{-1}$, however this could be the result of limitations of our measurements in that regime. The lowest mean scatter (0.01 dex) is found in the FMR$_{\text{HI}}$. We also find that the FMR$_{\text{HI}}$ is consistent between the IFU observed dwarf galaxies and the ALFALFA/SDSS crossmatched sample. We introduce the fundamental metallicity luminosity counterpart to the FMR, again characterized in terms of SFR (FML$_{\text{SFR}}$) and HI-gas mass (FML$_{\text{HI}}$). We find that the FML$_{\text{HI}}$ relation is consistent between the IFU observed dwarf galaxy sample and the larger ALFALFA/SDSS sample. However the 1$\sigma$ scatter for the FML$_{\text{HI}}$ relation is not improved over the FMR$_{\text{HI}}$ scenario. This leads us to conclude that the FMR$_{\text{HI}}$ is the best candidate for a physically motivated fundamental metallicity relation.