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

We present a study of the connection between the escape fraction of Lyman-alpha (Lyα) 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. By combining measurements of Hα equivalent width (Wλ(Hα)) derived from broad-band photometry with Lyα equivalent width (Wλ(Lyα)) measurements from VANDELS spectra, we individually estimate fLyαesc for our full sample. In agreement with previous studies, we find a positive correlation between Wλ(Lyα) and fLyαesc, increasing from fLyαesc≃0.04 at Wλ(Lyα)=10Å to fLyαesc≃0.1 at Wλ(Lyα)=25Å. For the first time at z∼4−5, we investigate the relationship between fLyαesc and fLyCesc using fLyCesc estimates derived using the equivalent widths of low-ionization, FUV absorption lines in composite VANDELS spectra. Our results indicate that fLyCesc rises monotonically with fLyαesc, following the relation fLyCesc≃0.15+0.06−0.04fLyαesc. Based on composite spectra of sub-samples with roughly constant Wλ(Lyα), but very different fLyαesc, we show that the fLyCesc−fLyαesc correlation is not driven by a secondary correlation between fLyαescand Wλ(Lyα). The fLyCesc−fLyαesc correlation is in good qualitative agreement with theoretical predictions and provides further evidence that estimates of fLyCesc within the Epoch of Reionization should be based on proxies sensitive to neutral gas density/geometry and dust attenuation.