We report on the detailed analysis of a gravitationally-lensed Y-band dropout , A2744_YD4 , selected from deep Hubble Space Telescope imaging in the Frontier Field cluster Abell 2744 .
Band 7 observations with the Atacama Large Millimeter Array ( ALMA ) indicate the proximate detection of a significant 1mm continuum flux suggesting the presence of dust for a star-forming galaxy with a photometric redshift of z \simeq 8 .
Deep X-SHOOTER spectra confirms the high redshift identity of A2744_YD4 via the detection of Lyman \alpha emission at a redshift z =8.38 .
The association with the ALMA detection is confirmed by the presence of [ OIII ] 88 \mu m emission at the same redshift .
Although both emission features are only significant at the 4 \sigma level , we argue their joint detection and the positional coincidence with a high redshift dropout in the HST images confirms the physical association .
Analysis of the available photometric data and the modest gravitational magnification ( \mu \simeq 2 ) indicates A2744_YD4 has a stellar mass of \sim 2 \times 10 ^ { 9 } M _ { \odot } , a star formation rate of \sim 20 M _ { \odot } /yr and a dust mass of \sim 6 \times 10 ^ { 6 } M _ { \odot } .
We discuss the implications of the formation of such a dust mass only \simeq 200 Myr after the onset of cosmic reionisation .