THE SPECTRAL EVOLUTION OF THE FIRST GALAXIES. II. SPECTRAL SIGNATURES OF LYMAN CONTINUUM LEAKAGE FROM GALAXIES IN THE REIONIZATION EPOCH

Abstract

The fraction of ionizing photons (fesc) that escape from z>6 galaxies is an\nimportant parameter when assessing the role of these objects in the\nreionization of the Universe, but the opacity of the intergalactic medium\nprecludes a direct measurement of fesc for individual galaxies at these epochs.\nWe argue, that since fesc regulates the impact of nebular emission on the\nspectra of galaxies, it should nonetheless be possible to indirectly probe fesc\nwell into the reionization epoch. As a first step, we demonstrate that by\ncombining measurements of the rest-frame UV slope beta with the equivalent\nwidth of the Hb emission line, galaxies with very high Lyman continuum escape\nfractions (fesc>0.5) should be identifiable up to z~9 through spectroscopy with\nthe upcoming James Webb Space Telescope (JWST). By targeting strongly lensed\ngalaxies behind low-redshift galaxy clusters, JWST spectra of sufficiently good\nquality can be obtained for M(1500)<-16.0 galaxies at z~7 and for M(1500)<-17.5\ngalaxies at z~9. Dust-obscured star formation may complicate the analysis, but\nsupporting observations with ALMA or the planned SPICA mission may provide\nuseful constraints on the dust properties of these galaxies.\n