Recent observations have successfully detected UV-bright and infrared-bright galaxies in the epoch of reionization .
However , the origin of their radiative properties has not been understood yet .
Combining cosmological hydrodynamic simulations and radiative transfer calculations , we present predictions of multi-wavelength radiative properties of the first galaxies at z \sim 6 - 15 .
Using zoom-in initial conditions , we investigate three massive galaxies and their satellites in different environment and halo masses : M _ { h } = 2.4 \times 10 ^ { 10 } { M _ { \odot } } ( Halo-10 ) , 1.6 \times 10 ^ { 11 } { M _ { \odot } } ( Halo-11 ) and 0.7 \times 10 ^ { 12 } { M _ { \odot } } ( Halo-12 ) at z = 6 .
We find that most of gas and dust are ejected from star-forming regions by supernova feedback , which allows UV photons to escape .
We show that the peak of the spectral energy distribution ( SED ) rapidly changes between UV and infrared wavelengths on a time-scale of \sim 100 Myrs due to intermittent star formation and feedback , and the escape fraction of UV photons fluctuates in the range of 0.2 - 0.8 at z < 10 with a time-averaged value of 0.3 .
When dusty gas covers the star-forming regions , the galaxies become bright in the observed-frame sub-millimeter wavelengths .
We predict the detectability of high- z galaxies with the Atacama Large Millimeter Array ( ALMA ) .
For a sensitivity limit of 0.1 { mJy } at 850 { \mu m } , the detection probability of galaxies in halos M _ { h } \gtrsim 10 ^ { 11 } { M _ { \odot } } at z \lesssim 7 exceeds fifty per cent .
We argue that supernova feedback can produce the observed diversity of SEDs for high- z galaxies .