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  • Author(s): Guo, Y
  • Koo, DC
  • Lu, Y
  • Forbes, JC
  • Rafelski, M
  • Trump, JR
  • Amorín, R
  • Barro, G
  • Davé, R
  • Faber, SM
  • Hathi, NP
  • Yesuf, H
  • Cooper, MC
  • Dekel, A
  • Guhathakurta, P
  • Kirby, EN
  • Koekemoer, AM
  • Pérez-González, PG
  • Lin, L
  • Newman, JA
  • Primack, JR
  • Rosario, DJ
  • Willmer, CNA
  • Yan, R
  • et al.

We present the stellar mass (M )gas-phase metallicity relation (MZR) and its scatter at intermediate redshifts (0.5 ≤ z ≤ 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 ≳ 24 AB) sample are representative of normal starforming galaxies. For masses below 10 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 10 M < M < 10 M : 12 + log (O/H) = (5.83 ± 0.19) +(0.30 ± 0.02) log (M /M ). At 10 M < M < 10 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 10 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 (δ ? ) or the scatter of the M -M relation (δ ) 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 δ and δ remain unchanged from z = 0.7 to z = 0. ∗ ∗ o o o ∗ o o ∗ o o Ṁ ∗ halo SHMR ∗ Ṁ SHMR 9 8 ∗ 11 9 10.5 9 o

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