Abstract

Context. The epoch of reionization is a landmark in structure formation and galaxy evolution. How it happened is still not clear, especially regarding which population of objects was responsible for contributing the bulk of ionizing photons to this process. Doubly peaked Lyman-alpha profiles in this epoch are of particular interest since they hold information about the escape of ionizing radiation and the environment surrounding the source.Aims. We wish to understand the escape mechanisms of ionizing radiation in Ly alpha emitters during this time and the origin of a doubly peaked Lyman-alpha profile. We also wish to estimate the size of a potential ionized bubble.Methods. Using radiative transfer models, we fit the line profile of a bright Ly alpha emitter at z similar to 6.9 using various gas geometries. The line modeling reveals significant radiation escape from this system.Results. The studied source shows significant escape (fesc(Ly alpha) similar to 0.8, as predicted by the best fitting radiative transfer model) and appears to inhabit an ionized bubble of radius Rb approximate to 0.8-0.3+0.5 pMpc(tage/108)1/3 R b approximate to 0 . 8 - 0.3 + 0.5 pMpc t age 10 8 1 3 $ R_{b}\approx 0.8<^>{+0.5}_{-0.3}\,\mathrm{pMpc}\left(\frac{t_{\mathrm{age}}}{10<^>{8}}\right)<^>{\frac{1}{3}} $ . Radiative transfer modeling predicts the line to be completely redward of the systemic redshift. We suggest the line morphology is produced by inflows, by multiple components emitting Ly alpha, or by an absorbing component in the red wing.Conclusions. We propose that CDFS-1's profile has two red peaks produced by winds within the system. Its high fesc(Ly alpha) and the low-velocity offset from the systemic redshift suggest that the source is an active ionizing agent. Future observations will reveal whether a peak is present blueward of the systemic redshift or if multiple components produce the profile.