First Light And Reionisation Epoch Simulations (FLARES) - III. The properties of massive dusty galaxies at cosmic dawn

Using the First Light And Reionisation Epoch Simulations (FLARES), we explore the dust-driven properties of massive high-redshift galaxies at z ∈ [5, 10]. By post-processing, the galaxy sample using the radiative transfer code SKIRT we obtain the full spectral energy distribution. We explore the resultant luminosity functions, IRX-β relations as well as the luminosity-weighted dust temperatures in the Epoch of Reionisation (EoR). We find that most of our results are in agreement with the current set of observations, but underpredict the number densities of bright IR galaxies, which are extremely biased towards the most overdense regions. We see that the FLARES IRX-β relation (for 5 ≤ z ≤ 8) pre-dominantly follows the local starburst relation. The IRX shows an increase with stellar mass, plateauing at the high-mass end (~10¹⁰ M_⊙) and shows no evolution in the median normalisation with redshift. We also look at the dependence of the peak dust temperature (T_peak) on various galaxy properties including the stellar mass, IR luminosity, and sSFR, finding the correlation to be strongest with sSFR. The luminosity-weighted dust temperatures increase towards higher redshifts, with the slope of the T_peak-redshift relation showing a higher slope than the lower redshift relations obtained from previous observational and theoretical works. The results from FLARES, which are able to provide a better statistical sample of high-redshift galaxies compared to other simulations, provides a distinct vantage point for the high-redshift Universe.