The LyA-LyC Connection: Evidence for an Enhanced Contribution of
  UV-faint Galaxies to Cosmic Reionization
  The escape of ionizing Lyman Continuum (LyC) photons requires the existence
of low-N_HI sightlines, which also promote escape of Lyman-Alpha (Lya). We use
a suite of 2500 Lya Monte-Carlo radiative transfer simulations through models
of dusty, clumpy interstellar (`multiphase') media from Gronke & Dijkstra
(2016), and compare the escape fractions of Lya [f_esc(Lya)] and LyC radiation
[f_esc(LyC)]. We find that f_esc(LyC) and f_esc(Lya) are correlated: galaxies
with a low f_esc(Lya) consistently have a low f_esc(LyC), while galaxies with a
high f_esc(Lya) exhibit a large dispersion in f_esc(LyC). We argue that there
is increasing observational evidence that Lya escapes more easily from UV-faint
galaxies. The correlation between f_esc(LyC) and f_esc(Lya) then implies that
UV-faint galaxies contribute more to the ionizing background than implied by
the faint-end slope of the UV-luminosity function. In multiphase gases, the
ionizing escape fraction is most strongly affected by the cloud covering
factor, f_cl, which implies that f_esc(LyC) is closely connected to the
observed Lya spectral line shape. Specifically, LyC emitting galaxies typically
having narrower, more symmetric line profiles. This prediction is qualitatively
similar to that for `shell models'.
