2016ApJ...822..103G

We present the stellar mass ( {M}_{*} )-gas-phase metallicity relation (MZR) and its scatter at intermediate redshifts ( 0.5\leqslant z\leqslant 0.7 ) for 1381 field galaxies collected from deep spectroscopic surveys. The star formation rate (SFR) and color at a given {M}_{*} of this magnitude-limited ( R\lesssim 24 AB) sample are representative of normal star-forming galaxies. For masses below 10⁹ {M}_☉ , our sample of 237 galaxies is ∼10 times larger than those in previous studies beyond the local universe. This huge gain in sample size enables superior constraints on the MZR and its scatter in the low-mass regime. We find a power-law MZR at 10⁸ {M}_☉ \lt {10}^{11} {M}_☉ : 12+log(O/H)=(5.83±0.19) +(0.30±0.02)log({M}_{*}/{M}☉) . At 10⁹ {M}_☉ \lt {10}^{10.5} {M}_☉ , our MZR shows agreement with others measured at similar redshifts in the literature. Our power-law slope is, however, shallower than the extrapolation of the MZRs of others to masses below 10⁹ {M}_☉ . The SFR dependence of the MZR in our sample is weaker than that found for local galaxies (known as the fundamental metallicity relation). Compared to a variety of theoretical models, the slope of our MZR for low-mass galaxies agrees well with predictions incorporating supernova energy-driven winds. Being robust against currently uncertain metallicity calibrations, the scatter of the MZR serves as a powerful diagnostic of the stochastic history of gas accretion, gas recycling, and star formation of low-mass galaxies. Our major result is that the scatter of our MZR increases as {M}_{*} decreases. Our result implies that either the scatter of the baryonic accretion rate ( σ_{dot}M ) or the scatter of the {M}_{*} - {M}_halo relation ( σ_SHMR ) increases as {M}_{*} decreases. Moreover, our measure of scatter at z=0.7 appears consistent with that found for local galaxies. This lack of redshift evolution constrains models of galaxy evolution to have both σ_{dot}M and σ_SHMR remain unchanged from z=0.7 to z=0.