The interstellar medium conditions of a strong Lya emitter at z = 8.279 revealed by JWST: a robust LyC leaker candidate at the Epoch of Reionization

TL;DR

This study uses JWST data to analyze a high-redshift galaxy, GN-z8-LAE, revealing its interstellar medium conditions and strong Lyman continuum leakage, making it a promising candidate for contributing to cosmic reionization.

Contribution

It provides detailed ISM properties and LyC escape fraction estimates for a z=8.279 galaxy, highlighting its role in reionization and identifying it as a robust LyC leaker candidate.

Findings

GN-z8-LAE is a young, low-mass galaxy with high star formation surface density.

The galaxy shows a small Lya velocity offset and a hard ionization field without AGN signatures.

It has a high Lyman continuum escape fraction (>14%), indicating efficient reionization contribution.

Abstract

Making use of JWST NIRSpec and NIRCam data, we conduct a detailed analysis of the spectroscopic and photometric properties of GN-z8-LAE, a strong Lya emitter at z=8.279. Our goal is to investigate the interstellar medium (ISM) physical conditions that enable the Lya detection in this source at the Epoch of Reionization (EoR) and scrutinize GN-z8-LAE as an early reionizer. In broad agreement with previous results, we find that GN-z8-LAE is a young galaxy (age ~ 10 Myr) with a low stellar mass (M* ~ 10^7.66 Msun), significantly lower than those of most Lya emitters known at similarly high redshifts. The derived stellar mass and star formation rate surface densities are 355 Msun/pc^2 and 88 Msun/yr/kpc^2, respectively. Our spectral analysis indicates that: the Lya line peak has a small velocity offset 133+-72 km/s with respect to the galaxy systemic redshift; CIV] / CIII] ~ 3.3; the ISM is characterized by a hard ionization field, although no signature of AGN is present. Moreover, we report the presence of NIII]1750 emission with super-solar N abundance, which makes GN-z8-LAE one of the first known cases of a simultaneous strong Lya and nitrogen emitter at the EoR. Based on all these properties, we apply a wide range of methods to constrain the absolute Lyman continuum escape fraction of GN-z8-LAE, and find that it is >14% in all cases. Therefore, we conclude that GN-z8-LAE is a robust candidate for a Lyman continuum (LyC) leaker at the EoR which is being caught at the moment of efficiently reionizing its surrounding medium.