  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
color 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 ($4 \times 10^{11}~{\rm M_{\odot}}$ at $M_{\rm UV} = -21$). The dust
attenuation and UV slope $\beta$ 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 dependency on the mass. We also find an
increasing star formation history with a time-scale of $\sim100$ Myr in the
high-$z$ galaxies. An average metallicity weighted by the Lyman continuum
luminosity reaches up to $>0.1$ Solar even at $z \sim 10$, suggesting a rapid
metal enrichment. We also expect $\geq 0.1$ mJy at 350 GHz of the dust thermal
emission from the galaxies with $H_{160} \leq 27$, which can be detectable with
the Atacama Large Milimetre-submilimetre Array. The galaxies selected by the
UDF12 survey contribute to only $52--12\%$ of the cosmic SFR density from $z
\sim 7$ to $z \sim 10$, respectively. The James Webb Space Telescope will push
the detection fraction up to $77--72\%$.
