The Interstellar Medium Conditions of a Strong Ly <i>α</i> Emitter at <i>z</i> = 8.279 from JWST: A Robust Lyman Continuum Leaker Candidate at the Epoch of Reionization

Abstract Making use of JWST NIRSpec and NIRCam data, we conduct a detailed analysis of GN- z 8-LAE, a strong Ly α emitter at z = 8.279. We investigate the interstellar medium (ISM) conditions that enable the Ly α detection in this source at the Epoch of Reionization (EoR) and scrutinize GN- z 8-LAE as an early reionizer. In agreement with previous results, we find that GN- z 8-LAE is a young galaxy (age ∼10 Myr) with a lower stellar mass ( M ⋆ ∼ 10 7.66 M ⊙ ) than most Ly α emitters (LAEs) at similar redshifts. The derived stellar-mass and star formation rate surface densities are Σ M ⋆ ∼ 355 M ⊙ pc - 2 and Σ SFR ∼ 88 M ⊙ yr −1 kpc 2 , respectively. Our spectral analysis indicates that: the Ly α line peak has a small velocity offset Δ v = 133 ± 72 km s −1 with respect to the galaxy systemic redshift; C iv ]/C iii ] ≈ 3.3; and the ISM is characterized by a hard ionization field, although no signatures of active galactic nuclei are present. Moreover, we report the presence of N iii ] λ 1750 emission, implying supersolar N abundance, which makes GN- z 8-LAE one of the first strong Ly α and nitrogen emitters at the EoR. Based on all these properties, we apply a wide range of methods to constrain the Lyman continuum escape fraction ( f esc LyC ) of GN- z 8-LAE and report f esc LyC > 14 % in all cases. Therefore, we conclude that GN- z 8-LAE is a robust candidate for a Lyman continuum leaker at the EoR that is being caught at the moment of efficiently reionizing its surrounding medium.