The Lyman Continuum Escape Survey: Connecting Time-Dependent [OIII] and
  [OII] Line Emission with Lyman Continuum Escape Fraction in Simulations of
  Galaxy Formation
  Escaping Lyman continuum photons from galaxies likely reionized the
intergalactic medium at redshifts $z\gtrsim6$. 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 $z\sim2-3$ 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
[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 between $f_{esc}$ and O$_{32}$. Like the observations, we
find that the largest $f_{esc}$ values occur at elevated O$_{32}\sim3-10$ and
that the combination of high $f_{esc}$ and low O$_{32}$ is extremely rare.
While high $f_{esc}$ 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 ($\sim$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 O$_{32}$, high $f_{esc}$ 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 large $f_{esc}$ tends to occur when
O$_{32}$ is large, but large O$_{32}$ does not necessarily imply efficient
Lyman continuum escape.
