Dust opacity and its effect on determining the properties of high-redshift galaxies

Dust has been identified as a prime tracer of metals in galaxies, and its infrared (IR) emission is a useful proxy for the star formation rate. It has been suggested that the dust mass is also a good tracer of the gas mass in galaxies. Determining the dust mass in high-redshift submillimeter (submm) galaxies will therefore allow a comparison between their star formation rate and their gas content, the main driver of their star formation rate and efficiency. However, determining the dust mass in galaxies is a formidable challenge since galaxies can be optically thick at infrared wavelengths. A significant fraction of the dust emission is then self-absorbed, distorting the shape of the emerging spectrum. Typical attempts to fit such spectra with that of template galaxy spectra or spectra calculated for optically-thin environments will yield inaccurate results. We will present our preliminary analysis of the dust mass in SPT0311-58 E, a hyperluminous submm galaxy at z = 6.9, when the universe was a mere 800 Myr old. We find that about 1.3e9 Msun of dust could be "hidden" in the galaxy, about 2-3 times higher than previous estimates that do not include the effect of dust self-absorption.