The Lyman Continuum Escape Survey: Connecting Time-dependent [O III] and [O II] Line Emission with Lyman Continuum Escape Fraction in Simulations of Galaxy Formation

Abstract

Escaping Lyman continuum photons from galaxies likely reionized the intergalactic medium at redshiftsz greater than or similar to 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 redshiftsz similar to 2-3 where the Lyman continuum is observationally accessible, surveys have established that many objects that show appreciable Lyman continuum escape fractionsf(esc)also show enhanced [Oiii]/[Oii] (O-32) emission line ratios. Here, we use radiative transfer analyses of cosmological zoom-in simulations of galaxy formation to study the physical connection betweenf(esc)and O-32. Like the observations, we find that the largestf(esc)values occur at elevated O-32 similar to 3-10 and that the combination of highf(esc)and low O(32)is extremely rare. While highf(esc)and O(32)often are observable concurrently, the timescales of the physical origin for the processes are very different. Large O(32)values fluctuate on short (similar to 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 betweenf(esc)and O-32, highf(esc)most often occurs after continuous input from star formation-related feedback events that have corresponding excursions to large O(32)emission. These calculations are in agreement with interpretations of observations that largef(esc)tends to occur when O(32)is large, but large O(32)does not necessarily imply efficient Lyman continuum escape.