We have performed a large cosmological hydrodynamics simulation tailored to the deep survey with the Hubble Space Telescope made in 2012, the so-called UDF12 campaign. After making a light-cone output, we have applied the same colour-selection criteria as the UDF12 campaign to select galaxies from our simulation, and then, have examined the physical properties of them as a proxy of the real observed UDF12 galaxies at z > 7. As a result, we find that the halo mass is almost linearly proportional to the observed ultraviolet (UV) luminosity (4 × 1011M⊙ at MUV =-21). The dust attenuation and UV slope β well correlates with the observed UV luminosity, which is consistent with observations quantitatively. The star formation rate (SFR) is also linearly proportional to the stellar mass and the specific SFR shows only a weak dependence on the mass. We also find an increasing star formation history with a time-scale of ̃100 Myr in the high-z galaxies. An average metallicity weighted by the Lyman continuum luminosity reaches up to >0.1 Solar even at z ̃ 10, suggesting a rapid metal enrichment. We also expect ≥0.1 mJy at 350 GHz of the dust thermal emission from the galaxies with H160 ≤ 27, which can be detectable with the Atacama Large Millimetre-sub-millimetre Array. The galaxies selected by the UDF12 survey contribute to only 52-12 per cent of the cosmic SFR density from z ̃ 7 to z ̃ 10, respectively. The James Webb Space Telescope will push the detection fraction up to 77-72 per cent.
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