Starbursting [O iii] emitters and quiescent [C ii] emitters in the reionization era

Abstract

ABSTRACT Recent observations have successfully detected [O iii] $88.3\, {\rm \mu m}$ and [C ii] $157.6\, {\rm \mu m}$ lines from galaxies in the early Universe with the Atacama Large Millimeter Array. Combining cosmological hydrodynamic simulations and radiative transfer calculations, we present relations between the metal line emission and galaxy evolution at z = 6–15. We find that galaxies during their starburst phases have high [O iii] luminosity of ${\sim}10^{42}~\rm erg~s^{-1}$. Once supernova feedback quenches star formation, [O iii] luminosities rapidly decrease and continue to be zero for ${\sim}100\, {\rm Myr}$. The slope of the relation between $\log {(\rm SFR/\rm M_{\odot }~ yr^{-1})}$ and $\log {(L_{\rm [O\, \small {III}]}/\mathrm{L}_{\odot })}$ at z = 6–9 is 1.03, and 1.43 for $\log {(L_{\rm [C\, \small {II}]}/\mathrm{L}_{\odot })}$. As gas metallicity increases from sub-solar to solar metallicity by metal enrichment from star formation and feedback, the line luminosity ratio $L_{\rm [O\, \small {III}]} / L_{\rm [C\, \small {II}]}$ decreases from ∼10 to ∼1 because the O/C abundance ratio decreases due to carbon-rich winds from AGB stars and the mass ratio of H ii to H i regions decreases due to rapid recombination. Therefore, we suggest that the combination of [O iii] and [C ii] lines is a good probe to investigate the relative distribution of ionized and neutral gas in high-z galaxies. In addition, we show that deep [C ii] observations with a sensitivity of ∼10−2 mJy arcsec−2 can probe the extended neutral gas discs of high-z galaxies.