We present the Atacama Large Millimeter/submillimeter Array ( ALMA ) detection of the [ O iii ] 88 \micron line and rest-frame 90 \micron 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 \micron flux density of 137 \pm 26 \mu Jy corresponds to a de-lensed total infrared ( IR ) luminosity of L _ { \mathrm { IR } } = ( 1.7 \pm 0.3 ) \times 10 ^ { 11 } L _ { \sun } if assuming a dust temperature of T _ { \mathrm { dust } } = 50 K and an emissivity index of \beta = 1.5 , yielding a large dust mass of 4 \times 10 ^ { 6 } M _ { \sun } .
The ultraviolet-to-far IR spectral energy distribution modeling where the [ O iii ] emissivity model is incorporated suggests the presence of a young ( \tau _ { \mathrm { age } } \approx 4 Myr ) , star-forming ( SFR \approx 60 ~ { } M _ { \sun } yr ^ { -1 } ) , moderately metal-polluted ( Z \approx 0.2 Z _ { \odot } ) stellar component with a mass of M _ { \mathrm { 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 _ { \mathrm { age } } \approx 4 Myr , suggesting a pre-existing evolved stellar component with M _ { \mathrm { star } } \sim 3 \times 10 ^ { 9 } ~ { } M _ { \sun } and \tau _ { \mathrm { age } } \sim 0.3 Gyr as the origin of the dust mass .