The Mass-Metallicity Relation in z~0.7 Dwarf Galaxies

Low-mass galaxies (with stellar mass M < 10⁹ M_*), or “dwarf” galaxies, are a useful probe of the mechanisms that affect and regulate gas properties and star formation. Because gas can more easily be heated and expelled from the shallow gravitational well of a low-mass galaxy, models suggest these galaxies may occupy more distinctive positions within common empirical relations, including the mass-metallicity relation (MZR) and star forming main sequence. We have used deep Keck/DEIMOS spectroscopy from the HALO7D survey to measure emission lines and fit redshifts for ~1400 galaxies in the CANDELS fields, including ~500 dwarf galaxies. We use the Hβ, [OIII]4959,5007, and [OII]3727,3729 emission lines to measure gas-phase metallicities for HALO7D galaxies, establishing an MZR for 0.4 < z < 1.0 galaxies down to stellar masses of 10⁸ M_*. This sample, including ~300 individual metallicity measurements for dwarf galaxies, enables an unprecedented robust measurement of the MZR and its scatter for such low-mass galaxies. We also detect the faint [NeIII]3868 and [OIII]4363 emission lines in some galaxies, allowing alternative metallicity measures for a subset of the sample. We investigate the trend and scatter of the MZR as a function of stellar mass, ionization, star formation, and other galaxy properties. We place our sample on the Fundamental Metallicity Relation (FMR) and test the relationship between metallicity scatter and the FMR.