A long time ago in an LAE far, far away: A signpost of early reionisation or a nascent AGN at z = 13?

The JADES survey recently reported the discovery of JADES-GS-z13-1-LA at, the highest redshift Ly emitter (LAE) ever observed. This observation suggests that either the intergalactic medium (IGM) surrounding JADES-GS-z13-1-LA is highly ionised, or the galaxy's intrinsic Ly emission properties are extreme. We use radiative transfer simulations of reionisation that capture the distribution of ionised gas in the IGM to investigate the implications of JADES-GS-z13-1-LA for reionisation. We find that if JADES-GS-z13-1-LA is a typical star forming galaxy (SFG) with properties characteristic of LAEs at, its detection suggests that the universe is 5% ionised by. We also investigate the possibility that the extreme properties of JADES-GS-z13-1-LA are driven by an AGN. Using a simple analysis based on the fact that AGN are expected to produce more ionising photons than SFGs, we estimate that the probability that JADES-GS-z13-1-LA hosts an AGN is 71%, 42%, and 15% if the IGM is, and ionised, respectively. We also highlight other features in the spectrum of JADES-GS-z13-1-LA that may be indicative of AGN activity, including strong Ly damping wing absorption extending to Å, and a possible CII* emission line. Our findings strongly motivate dedicated follow-up observations of JADES-GS-z13-1-LA to determine whether it hosts an AGN.