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

## TL;DR

This paper reports the detection of dust and gas in a galaxy at redshift 8.38, providing insights into early galaxy formation and dust production shortly after reionization.

## Contribution

First detection of dust and [OIII] emission in a galaxy at z=8.38, confirming early dust formation within 200 million years of reionization.

## Key findings

- Detection of 1mm continuum flux indicating dust presence
- Confirmation of high redshift via Lyman alpha and [OIII] emission
- Estimated stellar mass, star formation rate, and dust mass of the galaxy

## 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 $z\simeq8$. 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 ($\mu\simeq2$) indicates A2744_YD4 has a stellar mass of $\sim$ 2$\times$10$^9$ M$_{\odot}$, a star formation rate of $\sim20$ 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.