Infrared properties of z = 7 galaxies from cosmological simulations

Three-dimensional panchromatic dust radiative transfer calculations are performed on a set of 198 galaxies of stellar masses in the range of 5 × 10⁸ to 3 × 10¹⁰ M from a cosmological hydrodynamic simulation (resolved at 29 h ^-1 pc) at z 7. In a companion paper, the stellar mass and UV luminosity functions and the UV-optical and FUV-NUV colors are shown to be in good agreement with observations if a Small Magellanic Cloud type dust extinction curve is adopted. Here, we make useful predictions, self-consistently, of the infrared properties of these z 7 simulated galaxies that can be confronted with upcoming ALMA data. Our findings are as follows. (1) The effective radius in the rest-frame MIPS70 μm band is in the range of 80-400 pc proper for z = 7 galaxies with L FIR = 10^11.3-10 ¹² L . (2) The median of the peak wavelength of the far-infrared (FIR) spectral energy distribution is in the range of 45-60 μm, depending on the dust-to-metal ratio. (3) For star formation rate in the range of 3-100 M yr^-1, the median FIR to bolometric luminosity ratio is 60%-90%. (4) The FIR luminosity function displays a power law in the high end with a slope of -3.1 ± 0.4 instead of the usual exponential decline.