Characterizing Lyman alpha emission from high-redshift galaxies

The Lyman α (Lyα) line from high-redshift galaxies is a powerful probe of the epoch of reionization (EoR). Neutral hydrogen in the intergalactic medium (IGM) can significantly attenuate the emergent Lyα line, even in the damping wing of the cross section. However, interpreting this damping wing imprint relies on prior knowledge of the spectrum that escapes from the galaxy and its environs into the IGM. This emergent spectrum is highly sensitive to the composition and geometry of the interstellar and circumgalactic media and therefore exhibits a large galaxy-to-galaxy scatter. Characterizing this scatter is further complicated by nontrivial selection effects introduced by observational surveys. Here we build a flexible, empirical model for the emergent Lyα spectra. Our model characterizes the emergent Lyα luminosity, the velocity offset of the Lyα line with respect to the systemic redshift, and the Hα luminosity using multivariate probability distributions conditioned on the UV magnitude. We constrained these distributions using observations of z NIRCam, and we forward-modeled the observational selection functions together with the galaxy parameters. Our model yields Lyα equivalent-width distributions that better match independent Subaru observations than previous empirical models. The extended distributions of Lyα equivalent widths and velocity offsets that we obtain could facilitate Lyα transmission during the early stages of the EoR. We also illustrate how our model can identify GN-z11-like outliers, which may originating from merging systems. We provide fitting functions and make our model publicly available. galaxies with VLT MUSE and JWST