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 Ṁ) 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 Ṁ and σ SHMR remain unchanged from z = 0.7 to z = 0.
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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.
Guo, Yicheng; Koo, David C.; Lu, Yu; Forbes, John C.; Rafelski, Marc; Trump, Jonathan R.; Amorín, Ricardo; Barro, Guillermo; Davé, Romeel; Faber, S. M.; Hathi, Nimish P.; Yesuf, Hassen; Cooper, Michael C.; Dekel, Avishai; Guhathakurta, Puragra; Kirby, Evan N.; Koekemoer, Anton M.; Pérez-González, Pablo G.; Lin, Lihwai; Newman, Jeffery A.; Primack, Joel R.; Rosario, David J.; Willmer, Christopher N. A.; and Yan, Renbin, "Stellar Mass–Gas-Phase Metallicity Relation at 0.5 ≤ z ≤ 0.7: A Power Law with Increasing Scatter Toward the Low-Mass Regime" (2016). Physics and Astronomy Faculty Publications. 418.