THE GAS PHASE MASS METALLICITY RELATION FOR DWARF GALAXIES: DEPENDENCE ON STAR FORMATION RATE AND HI GAS MASS

Using a sample of dwarf galaxies observed using the VIMOS IFU on the Very Large Telescope, we investigate the mass–metallicity relation (MZR) as a function of star formation rate (FMR_SFR) as well as HI-gas mass (FMR_HI). We combine our IFU data with a subsample of galaxies from the ALFALFA HI survey crossmatched to the Sloan Digital Sky Survey (SDSS) to study the FMR_SFR and FMR_HI across the stellar mass range 10^6.6–10^8.8 M_⊙, with metallicities as low as 12 + log(O/H) = 7.67. We find the 1σ mean scatter in the MZR to be 0.05 dex. The 1σ mean scatter in the FMR_SFR (0.02 dex) is significantly lower than that of the MZR. The FMR_SFR is not consistent between the IFU observed galaxies and the ALFALFA/SDSS galaxies for SFRs lower than 10^−2.4 M_⊙ 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_HI. We also find that the FMR_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_SFR) and HI-gas mass (FML_HI). We find that the FML_HI relation is consistent between the IFU observed dwarf galaxy sample and the larger ALFALFA/SDSS sample. However, the 1σ scatter for the FML_HI relation is not improved over the FMR_HI scenario. This leads us to conclude that the FMR_HI is the best candidate for a physically motivated fundamental metallicity relation