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We report on the detection of the [CII] 157.7 $\mu$m emission from the Lymanbreak galaxy (LBG) MACS0416_Y1 at z = 8.3113, by using the Atacama LargeMillimeter/submillimeter Array (ALMA). The luminosity ratio of [OIII] 88 $\mu$m(from previous campaigns) to [CII] is 9.31 $\pm$ 2.6, indicative of hardinterstellar radiation fields and/or a low covering fraction ofphoto-dissociation regions. The emission of [CII] is cospatial to the 850$\mu$m dust emission (90 $\mu$m rest-frame, from previous campaigns), howeverthe peak [CII] emission does not agree with the peak [OIII] emission,suggesting that the lines originate from different conditions in theinterstellar medium. We fail to detect continuum emission at 1.5 mm (160 $\mu$mrest-frame) down to 18 $\mu$Jy (3$\sigma$). This nondetection places a stronglimit on the dust spectrum, considering the 137 $\pm$ 26 $\mu$Jy continuumemission at 850 $\mu$m. This suggests an unusually warm dust component (T $>$80 K, 90% confidence limit), and/or a steep dust-emissivity index ($\beta_{\rmdust}$ $>$ 2), compared to galaxy-wide dust emission found at lower redshifts(typically T $\sim$ 30 - 50 K, $\beta_{\rm dust}$ $\sim$ 1 - 2). If suchtemperatures are common, this would reduce the required dust mass and relax thedust production problem at the highest redshifts. We therefore warn against theuse of only single-wavelength information to derive physical properties,recommend a more thorough examination of dust temperatures in the earlyUniverse, and stress the need for instrumentation that probes the peak of warmdust in the Epoch of Reionization.

ALMA uncovers the [CII] emission and warm dust continuum in a z = 8.31 Lyman break galaxy