2020ApJ...902L..39B

Escaping Lyman continuum photons from galaxies likely reionized the intergalactic medium at redshifts z >= 6. However, the Lyman continuum is not directly observable at these redshifts and secondary indicators of Lyman continuum escape must be used to estimate the budget of ionizing photons. Observationally, at redshifts z ∼ 2-3 where the Lyman continuum is observationally accessible, surveys have established that many objects that show appreciable Lyman continuum escape fractions f_esc also show enhanced [O III]/[O II] (O₃₂) emission line ratios. Here, we use radiative transfer analyses of cosmological zoom-in simulations of galaxy formation to study the physical connection between f_esc and O₃₂. Like the observations, we find that the largest f_esc values occur at elevated O₃₂ ∼ 3-10 and that the combination of high f_esc and low O₃₂ is extremely rare. While high f_esc and O₃₂ often are observable concurrently, the timescales of the physical origin for the processes are very different. Large O₃₂ values fluctuate on short (∼1 Myr) timescales during the Wolf-Rayet-powered phase after the formation of star clusters, while channels of low absorption are established over tens of megayears by collections of supernovae. We find that while there is no direct causal relation between f_esc and O₃₂, high f_esc most often occurs after continuous input from star formation-related feedback events that have corresponding excursions to large O₃₂ emission. These calculations are in agreement with interpretations of observations that large f_esc tends to occur when O₃₂ is large, but large O₃₂ does not necessarily imply efficient Lyman continuum escape.