Bridging Optical and Far-Infrared Emission-Line Diagrams of Galaxies from Local to the Epoch of Reionization: Characteristic High [O III] 88 $\mathrm{\mu m}$/SFR at $z > 6$

Understand

We present photoionization modeling of galaxy populations at $z\sim0$, $2$, and $> 6$ to bridge optical and far-infrared (FIR) emission-line diagrams.

• We collect galaxies with measurements of optical and/or FIR ([O III] 88 $\mathrm{\mu m}$ and [C II] 158 $\mathrm{\mu m}$) emission line fluxes and plot them on the [O III]$\lambda5007/\mathrm{H\beta}$--[N II]$\lambda6585/\mathrm{H\alpha}$ (BPT) and L([O III]88)/SFR--L([C II]158)/SFR diagrams, where SFR is the star-formation rate and L([O III]88) and L([C II]158) are the FIR line luminosities.
• We aim to explain the galaxy distributions on the two diagrams with photoionization models that employ three nebular parameters: the ionization parameter $U$, hydrogen density $n_\text{H}$, and gaseous metallicity $Z_\text{gas}$.
• Our models successfully reproduce the nebular parameters of local galaxies, and then predict the distributions of the $z\sim0$, $2$, and $> 6$ galaxies on the diagrams.