Detection of the Far-infrared [O III] and Dust Emission in a Galaxy at
  Redshift 8.312: Early Metal Enrichment in the Heart of the Reionization Era
  We present the Atacama Large Millimeter/submillimeter Array (ALMA) detection
of the [O III] 88 $\mu$m line and rest-frame 90 $\mu$m dust continuum emission
in a Y-dropout Lyman break galaxy (LBG), MACS0416_Y1, lying behind the Frontier
Field cluster MACS J0416.1-2403. This [O III] detection confirms the LBG with a
spectroscopic redshift of $z = 8.3118 \pm 0.0003$, making this object one of
the furthest galaxies ever identified spectroscopically. The observed 850
$\mu$m flux density of $137 \pm 26$ $\mu$Jy corresponds to a de-lensed total
infrared (IR) luminosity of $L_{\rm IR} = (1.7 \pm 0.3) \times 10^{11}
L_{\odot}$ if assuming a dust temperature of $T_{\rm dust} = 50$ K and an
emissivity index of $\beta = 1.5$, yielding a large dust mass of $4 \times 10^6
M_{\odot}$. The ultraviolet-to-far IR spectral energy distribution modeling
where the [O III] emissivity model is incorporated suggests the presence of a
young ($\tau_{\rm age} \approx 4$ Myr), star-forming (SFR $\approx 60
M_{\odot}$ yr$^{-1}$), moderately metal-polluted ($Z \approx 0.2 Z_{\odot}$)
stellar component with a mass of $M_{\rm star} = 3 \times 10^8 M_{\odot}$. An
analytic dust mass evolution model with a single episode of star-formation does
not reproduce the metallicity and dust mass in $\tau_{\rm age} \approx 4$ Myr,
suggesting a pre-existing evolved stellar component with $M_{\rm star} \sim 3
\times 10^9 M_{\odot}$ and $\tau_{\rm age} \sim 0.3$ Gyr as the origin of the
dust mass.
