CEERS: Diversity of Lyα Emitters during the Epoch of Reionization

We analyze rest-frame ultraviolet to optical spectra of three z ≃ 7.47–7.75 galaxies whose Ly α emission lines were previously detected with Keck/MOSFIRE observations, using the JWST/NIRSpec observations from the Cosmic Evolution Early Release Science survey. From NIRSpec data, we confirm the systemic redshifts of these Ly α emitters, and emission-line ratio diagnostics indicate these galaxies were highly ionized and metal-poor. We investigate Ly α line properties, including the line flux, velocity offset, and spatial extent. For the one galaxy where we have both NIRSpec and MOSFIRE measurements, we find a significant offset in their flux measurements (∼1.3–5× greater in MOSFIRE) and a marginal difference in the velocity shifts. The simplest interpretation is that the Ly α emission is extended and not entirely encompassed by the NIRSpec slit. The cross-dispersion profiles in NIRSpec reveal that Ly α in one galaxy is significantly more extended than the nonresonant emission lines. We also compute the expected sizes of ionized bubbles that can be generated by the Ly α sources and discuss viable scenarios for the creation of sizable ionized bubbles (>1 physical Mpc). The source with the highest-ionization condition is possibly capable of ionizing its own bubble, while the other two do not appear to be capable of ionizing such a large region, but require additional sources of ionizing photons. Therefore, the fact that we detect Ly α from these galaxies suggests diverse scenarios for the escape of Ly α during the epoch of reionization. High-spectral-resolution spectra with JWST/NIRSpec will be extremely useful for constraining the physics of patchy reionization.