Dusty galaxies in the Epoch of Reionization: simulations

The recent discovery of dusty galaxies well into the Epoch of Reionization (redshift z>6) poses challenging questions about the properties of the interstellar medium in these pristine systems. By combining state-of-the-art hydrodynamic and dust radiative transfer simulations, we address these questions focusing on the recently discovered dusty galaxy A2744YD4 (z=8. 38, Laporte et al. 2017}). We show that we can reproduce the observed spectral energy distribution (SED) only using different physical values with respect to the inferred ones by Laporte et al (2017), i. e. a star formation rate of SFR = 78\; M_ yr^-1, a factor 4 higher than deduced from simple Spectral Energy Distribution fitting. In this case we find: (a) dust attenuation (corresponding to V=1. 4) is consistent with a Milky Way extinction curve; (b) the dust-to-metal ratio is low, fd 0. 08, implying that early dust formation is rather inefficient; (c) the luminosity-weighted dust temperature is high, Td=91 23\, K, as a result of the intense (100 MW) interstellar radiation field; (d) due to the high Td, the ALMA Band 7 detection can be explained by a limited dust mass, Md=1. 6 10⁶ M_. Finally, the high dust temperatures might solve the puzzling low infrared excess recently deduced for high-z galaxies from the IRX- relation.