The distribution and physical properties of high-redshift [OIII]
  emitters in a cosmological hydrodynamics simulation
  Recent observations with the Atacama Large Millimeter/submillimeter Array
(ALMA) detected far-infrared emission lines such as the [OIII] 88 \mu m line
from galaxies at $z \sim 7 - 9$. Far-infrared lines can be used to probe the
structure and kinematics of such high-redshift galaxies as well as to
accurately determine their spectroscopic redshifts. We use a cosmological
simulation of galaxy formation to study the physical properties of [OIII] 88
\mu m emitters. In a comoving volume of 50 $h^{-1}$ Mpc on a side, we locate 34
galaxies with stellar masses greater than $10^8\ {\rm M_\odot}$ at $z = 9$, and
more than 270 such galaxies at $z = 7$. We calculate the [OIII] 88 \mu m
luminosities ($L_{\rm OIII}$) by combining a physical model of HII regions with
emission line calculations using the photoionization code CLOUDY. We show that
the resulting $L_{\rm OIII}$, for a given star formation rate, is slightly
higher than predicted from the empirical relation for local galaxies, and is
consistent with recent observations of galaxies at redshifts 7 - 9. Bright
[OIII] emitters with $L_{\rm OIII} > 10^8 {\rm L_\odot}$ have stellar masses
greater than $10^9\ {\rm M_\odot}$, star formation rates higher than $3\ {\rm
M_\odot\ yr}^{-1}$, and the typical metallicity is $\sim 0.1\ {\rm Z_\odot}$.
The galaxies are hosted by dark matter halos with masses greater than
$10^{10.5}\ {\rm M_\odot}$. Massive galaxies show characteristic structure
where the [OIII] emitting gas largely overlaps with young stars, but the
emission peak is separated from the main stellar population, suggesting the
stochastic and localized nature of star formation in the first galaxies. We
propose to use the [OIII] 5007 \AA\ line, to be detected by James Webb Space
Telescope (JWST), to study the properties of galaxies whose [OIII] 88 \mu m
line emission has been already detected with ALMA.
