Dust attenuation, dust emission, and dust temperature in galaxies at
  z>=5: a view from the FIRE-2 simulations
  We present a suite of 34 high-resolution cosmological zoom-in simulations
consisting of thousands of halos up to M_halo~10^12 M_sun (M_star~10^10.5
M_sun) at z>=5 from the Feedback in Realistic Environments project. We
post-process our simulations with a three-dimensional Monte Carlo dust
radiative transfer code to study dust extinction, dust emission, and dust
temperature within these simulated z>=5 galaxies. Our sample forms a tight
correlation between infrared excess (IRX=F_IR/F_UV) and ultraviolet
(UV)-continuum slope (beta_UV), despite the patchy, clumpy dust geometry shown
in our simulations. We find that the IRX-beta_UV relation is mainly determined
by the shape of the extinction curve and is independent of its normalization
(set by the dust-to-gas ratio). The bolometric IR luminosity (L_IR) correlates
with the intrinsic UV luminosity and the star formation rate (SFR) averaged
over the past 10 Myr. We predict that at a given L_IR, the peak wavelength of
the dust spectral energy distributions for z>=5 galaxies is smaller by a factor
of 2 (due to higher dust temperatures on average) than at z=0. The higher dust
temperatures are driven by higher specific SFRs and SFR surface densities with
increasing redshift. We derive the galaxy UV luminosity functions (LFs) at
z=5-10 from our simulations and confirm that a heavy attenuation is required to
reproduce the observed bright-end UVLFs. We also predict the IRLFs and UV
luminosity densities at z=5-10. We discuss the implications of our results on
current and future observations probing dust attenuation and emission in z>=5
galaxies.
