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 A2744_YD4 ($z=8.38$,
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
$\mathrm{SFR} = 78\;\rm M_\odot \rm yr^{-1}$, a factor $\approx 4$ higher than
deduced from simple Spectral Energy Distribution fitting. In this case we find:
(a) dust attenuation (corresponding to $\tau_V=1.4$) is consistent with a Milky
Way extinction curve; (b) the dust-to-metal ratio is low, $f_\mathrm{d} \sim
0.08$, implying that early dust formation is rather inefficient; (c) the
luminosity-weighted dust temperature is high, $T_d=91\pm 23\, \rm K$, as a
result of the intense ($\approx 100\times$ MW) interstellar radiation field;
(d) due to the high $T_d$, the ALMA Band 7 detection can be explained by a
limited dust mass, $M_d=1.6\times 10^6 $M$_\odot$. Finally, the high dust
temperatures might solve the puzzling low infrared excess recently deduced for
high-$z$ galaxies from the IRX-$\beta$ relation.
