We present the stellar mass (M*)–gas-phase metallicity relation (MZR) and its scatter at intermediate redshifts (0.5 ≤ z ≤ 0.7) for 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 ≲ 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 at M < M* < 1011 M: 12 + log(O/H) = (5.83 ± 0.19) + (0.30 ± 0.02) log(M*/M). At 109 M < M* < 1010.5 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 ) or the scatter of the M*Mhalo 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 and σ SHMR remain unchanged from z = 0.7 to z = 0.

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Published in The Astrophysical Journal, v. 822, no. 2, 103, p. 1-18.

© 2016. The American Astronomical Society. All rights reserved.

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Several authors from UCSC acknowledge support from NSF grant AST-0808133. Support for Program HST-GO-12060 and HST-AR-13891 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS 5-26555. M.R. also acknowledges support from an appointment to the NASA Postdoctoral Program at Goddard Space Flight Center. J.F. is supported by HST-AR-13909. J.R.T. acknowledges support from NASA through Hubble Fellowship grant #51330 awarded by the Space Telescope Science Institute. A.D. is supported by ISF grant 24/12, by the I-CORE Program of the PBC ISF grant 1829/12, and by NSF grant AST-1405962. P.G.P.G. acknowledges support from Spanish MINECO grant AYA2012-31277.