Abstract
Abridged We present the results of MMT and Keck spectroscopy for a large
sample of $0.1złeq1$ emission-line galaxies selected from our narrow-band
imaging in the Subaru Deep Field. In total, we have measured the weak
OIII$łambda$4363 line for 164 galaxies (66 with at least 3$\sigma$
detections, and 98 with significant upper limits). The strength of this nebular
emission line is set by the electron temperature ($T_e$) for the ionized gas in
these galaxies. Since the gas temperature is regulated by the metal content, an
inverse relationship exists between gas-phase oxygen abundance and
OIII$łambda$4363 line strength. Our $T_e$-based metallicity study is the
first to span $\approx$8 Gyr of cosmic time and $\approx$3 dex in stellar mass
for low-mass galaxies, $(M_star/M_sun)\approx6.0-9.0$. Combined with
extensive multi-wavelength photometry, we investigate the evolution of the
stellar mass--gas metallicity relation, and its dependence on dust-corrected
star formation rate. The latter is obtained from high signal-to-noise Balmer
emission-line measurements. Our mass-metallicity relation is consistent with
Andrews & Martini at $złeq0.3$, and evolves toward lower abundances at a given
stellar mass, $\propto(1+z)^-2.32^+0.53_-0.35$. We find that galaxies
with lower metallicities have higher star formation rates at a given stellar
mass and redshift, although the scatter is large ($\approx$0.3 dex) and the
trend is weaker than seen in local studies. We also compare our
mass--metallicity relation against predictions from high-resolution galaxy
formation simulations and find good agreement with models that adopt energy and
momentum stellar feedback. In addition, we have identified 16 extremely
metal-poor galaxies with abundances less than a tenth of solar; our most
metal-poor galaxy at $z\approx0.85$ has an oxygen abundance that is similar to
I Zw 18.
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