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

Abstract We present the Atacama Large Millimeter/submillimeter Array detection of the O iii 88 μ m line and rest-frame 90 μ m dust continuum emission in a Y -dropout Lyman break galaxy (LBG), MACS0416Y1 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 ± 0. 0003, making this object one of the farthest galaxies ever identified spectroscopically. The observed 850 μ m flux density of 137 ± 26 μ Jy corresponds to a de-lensed total infrared (IR) luminosity of if assuming a dust temperature of T dust = 50 K and an emissivity index of β = 1. 5, yielding a large dust mass of. The ultraviolet-to-far-IR spectral energy distribution modeling where the O iii emissivity model is incorporated suggests the presence of a young (τ age ≈ 4 Myr), star-forming (yr −1), moderately metal-polluted (Z ≈ 0. 2 Z ⊙) stellar component with a mass of M star = 3 × 10 8 M ⊙. An analytic dust mass evolution model with a single episode of star formation does not reproduce the metallicity and dust mass in τ age ≈ 4 Myr, suggesting a pre-existing evolved stellar component with M star ∼ 3 × 10 9 M ☉ and τ age ∼ 0. 3 Gyr as the origin of the dust mass.