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

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$\ddot{I}ƒ$ mean scatter in the MZR to be 0.05 dex. The 1$\ddot{I}ƒ$ 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$\ddot{I}ƒ$ 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.

26 Pages, 20 Figures, 5 tables. Accepted for publication in ApJ