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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mo>Σ</mml:mo> <mml:msup> <mml:mi>M</mml:mi> <mml:mo>⋆</mml:mo> </mml:msup> </mml:msub> <mml:mo>∼</mml:mo> <mml:mn>355</mml:mn> <mml:mspace width="0.25em"/> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> <mml:mspace width="0.25em"/> <mml:msup> <mml:mi>pc</mml:mi> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> 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 ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi>f</mml:mi> <mml:mi>esc</mml:mi> <mml:mi>LyC</mml:mi> </mml:msubsup> </mml:math> ) of GN- z 8-LAE and report <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi>f</mml:mi> <mml:mi>esc</mml:mi> <mml:mi>LyC</mml:mi> </mml:msubsup> <mml:mo>&gt;</mml:mo> <mml:mn>14</mml:mn> <mml:mo>%</mml:mo> </mml:math> 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.