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.