paper

Dust in the reionization era: ALMA observations of a =8.38 Galaxy

arXiv:1703.02039 · doi:10.3847/2041-8213/aa62aa

Abstract

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 . Deep X-SHOOTER spectra confirms the high redshift identity of A2744_YD4 via the detection of Lyman emission at a redshift =8.38. The association with the ALMA detection is confirmed by the presence of [OIII] 88m emission at the same redshift. Although both emission features are only significant at the 4 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 () indicates A2744_YD4 has a stellar mass of 210 M, a star formation rate of M/yr and a dust mass of 610 M. We discuss the implications of the formation of such a dust mass only 200 Myr after the onset of cosmic reionisation.

Accepted for publication in ApJL

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