THE Lyα–LyC CONNECTION: EVIDENCE FOR AN ENHANCED CONTRIBUTION OF UV-FAINT GALAXIES TO COSMIC REIONIZATION

Abstract

ABSTRACT The escape of ionizing Lyman continuum (LyC) photons requires the existence of low- N H i sightlines, which also promote escape of Ly α . We use a suite of 2500 Ly α Monte-Carlo radiative transfer simulations through models of dusty, clumpy interstellar (“multiphase”) media from Gronke & Dijkstra, and compare the escape fractions of Ly α ( ) and LyC radiation ( ). We find that and are correlated: galaxies with a low consistently have a low , while galaxies with a high exhibit a large dispersion in . We argue that there is increasing observational evidence that Ly α escapes more easily from UV-faint galaxies. The correlation between and 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 is closely connected to the observed Ly α spectral line shape. Specifically, LyC-emitting galaxies typically having narrower, more symmetric line profiles. This prediction is qualitatively similar to that for “shell models.”