Connecting the escape fraction of Lyman-alpha and Lyman-continuum photons in star-forming galaxies at z ≃ 4-5

Abstract

We present a study of the connection between the escape fraction of Lyman-alpha () and Lyman-continuum (LyC) photons within a sample of N = 152 star-forming galaxies selected from the VANDELS survey at 3.85 ≤ zspec ≤ 4.95 (〈zspec) = 4.36). By combining measurements of H equivalent width derived from broad-band photometry with measurements of Ly equivalent width from the VANDELS spectra, we individually estimate for our full sample. In agreement with previous studies, we find a positive correlation between and, with increasing from at Å to at Å. For the first time at z ≃ 4-5, we investigate the relationship between and using estimates derived using the equivalent widths of low-ionization, far-ultraviolet absorption lines in composite VANDELS spectra. Our results indicate that rises monotonically with, following a relation of the form. Based on composite spectra of sub-samples with approximately constant Wλ(Lyα), but widely different, we demonstrate that the -correlation is not driven by a secondary correlation between and Wλ(Lyα). The observed - correlation is in good qualitative agreement with theoretical predictions and provides further evidence that estimates of within the Epoch of Reionization should be based on proxies sensitive to neutral gas density/geometry and dust attenuation.