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 haloes up to M_(halo) ∼ 10^(12) M_⊙ (⁠M_∗ ∼ 10^(10.5) M_⊙⁠) 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 attenuation, 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 (βUV), despite the patchy, clumpy dust geometry shown in our simulations. We find that the IRX–βUV relation is mainly determined by the shape of the attenuation law 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 (UVLFs) 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 IR luminosity functions (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.