Origin of elevated [O iii]/[C ii] ratios in early galaxies

Determine which interstellar-medium properties primarily produce the elevated [O iii]88 μm/[C ii] ratios observed in many galaxies at redshift greater than six, including the roles of ionisation parameter, metallicity, oxygen-to-carbon abundance, and neutral-gas covering fraction.

Background

The [O iii]88 μm/[C ii] ratio varies substantially among high-redshift galaxies and is often much higher than in typical local star-forming galaxies. REBELS-25 has an unusually low ratio for its redshift, which the authors associate with its relatively evolved and metal-rich interstellar medium.

The paper notes that several physical mechanisms could produce elevated ratios, including higher ionisation parameters, lower metallicities, enhanced O/C abundances, and reduced neutral-gas covering fractions. Their relative importance remains unresolved.