2021MNRAS.500..558M

We report the discovery of a double-peaked Lyman α profile in a galaxy at z = 6.803, A370p_z1, in the parallel Frontier Field of Abell 370. The velocity separation between the blue and red peaks of the Lyman α profile (Δv=101_–19⁺³⁸ (±48) km s^–1) suggests an extremely high escape fraction of ionizing photons > 59(51) per cent (2σ). The spectral energy distribution indicates a young (50 Myr), star-forming (12±6 M_☉yr^–1) galaxy with an IRAC excess implying strong [O III] + H β emission. On the basis of the high escape fraction measured, we demonstrate that A370p_z1 was solely capable of creating an ionized bubble sufficiently large to account for the blue component of its Lyman α profile. We discuss whether A370p_z1 may be representative of a larger population of luminous z ≃ 7 double-peaked Lyman α emitting sources with high escape fractions that self-ionized their surroundings without contributions from associated ultraviolet-fainter sources.