Lyman-alpha emission at the end of reionization: Line strengths and profiles from MMT and JWST observations at z ∼ 5–6

Aims. With JWST, it is now possible to use Lyman-Alpha (Ly alpha) emission from galaxies beyond z > 8 to trace neutral hydrogen in the intergalactic medium (IGM) as the Universe became reionized. However, observed Ly alpha emission lines are known to be affected by scattering by neutral hydrogen in the IGM and the interstellar and circumgalactic medium (CGM), necessitating "baseline" models of Ly alpha properties in the ionized IGM to disentangle their impacts. In this work, we characterize Ly alpha properties at the end of of the epoch of reionization (EoR) at z similar to 5 - 6, providing a baseline that can be applied to z > 6 observations. Methods. We targeted GOODS-N with MMT/Binospec, obtaining R similar to 4360 rest-frame UV spectra of 236 galaxies at z similar to 5 - 6, selected primarily from HST/CANDELS, finding 62 Ly alpha detections. We used JWST observations from JADES and FRESCO for a subset of our sources to characterize Ly alpha properties as a function of the UV continuum and H alpha emission. We present the first statistical measurements of the Ly alpha FWHM distribution at z similar to 5 - 6, along with empirical baseline models for the Ly alpha equivalent width (EWLy alpha) and escape fraction (f(esc)(Ly alpha)) that are conditional on the UV magnitude and slope. Results. We found our EW(Ly alpha )and f(esc)(Ly alpha )models strongly depend on UV magnitude, inferring that 45 +/- 5% and < 62 +/- 8% of M-UV= -19.5 galaxies have EWLy alpha > 25 & Aring; and f(esc)(Ly alpha)> 0.2, respectively. We also found a mean FWHM(Ly alpha )of 245 km s(-1 )and median Ly alpha velocity offset of 258 km s(-1), both displaying a correlation with increasing UV luminosity. Our median observed Ly alpha line profile is broader and has higher velocity offset compared to pre-JWST models based on z similar to 2 lines, which might reflect both resonant scattering by residual neutral hydrogen in the IGM at z similar to 5 - 6 and increasing ISM and CGM densities. Our median line profile thus predicts higher Ly alpha transmission in a fully neutral IGM, providing insights into recent detections of Ly alpha at z > 10.