The Archival Discovery of a Strong Lyα and [C ii] Emitter at z = 7.677

Abstract

Abstract We report the archival discovery of Lyα emission from the bright ultraviolet galaxy Y002 at z = 7.677, spectroscopically confirmed by its ionized carbon [C ii] 158 μm emission line. The Lyα line is spatially associated with the rest-frame UV stellar emission (M UV ∼ −22, 2× brighter than M UV ⋆ ), and it appears offset from the peak of the extended [C ii] emission at the current ∼1″ spatial resolution. We derive an estimate of the unobscured SFRUV = (22 ± 1) M ⊙ yr−1 and set an upper limit of SFRIR < 15 M ⊙ yr−1 from the far-infrared (FIR) wavelength range, which globally places Y002 on the SFR(UV+IR)–L [C II] correlation observed at lower redshifts. In terms of velocity, the peak of the Lyα emission is redshifted by Δv Lyα ∼ 500 km s−1 from the systemic redshift set by [C ii] and a high-velocity tail extends up to ∼1000 km s−1. The velocity offset is up to ∼3.5× higher than the average estimate for similarly UV-bright emitters at z ∼ 6–7, which might suggest that we are witnessing the merging of two clumps. A combination of strong outflows and the possible presence of an extended ionized bubble surrounding Y002 would likely facilitate the escape of copious Lyα light, as indicated by the large equivalent width EW0(Lyα) = 24 − 6 + 5 Å. Assuming that [C ii] traces the neutral hydrogen, we estimate a H i gas fraction of M H I/M ⋆ ≳ 8 for Y002 as a system and speculate that patches of high H i column densities could contribute to explaining the observed spatial offsets between Lyα- and [C ii]-emitting regions. The low dust content, implied by the nondetection of the FIR continuum emission at rest frame ∼160 μm, would be sufficient to absorb any potential Lyα photons produced within the [C ii] clump as a result of large H i column densities.