Lyman-$\alpha$ Emitting Galaxies (LAEs) at Cosmic Dawn: Implications and Predictions

TL;DR

This paper predicts the properties of high-redshift Lyman-alpha emitting galaxies under two reionization scenarios, suggesting future observations can distinguish which scenario accurately describes cosmic reionization.

Contribution

It introduces detailed predictions for LAE properties in two reionization models, aiding future observational tests to determine the correct cosmic reionization history.

Findings

High-z LAE luminosity functions differ significantly between scenarios.

Current observations favor the double reionization scenario.

Predictions will be testable with upcoming JWST data.

Abstract

The detection of Lyman-$\alpha$ emitting galaxies (LAEs) puts severe constraints on the reionization history. In this Paper we derive the properties of very high-$z$ LAEs predicted in the only two reionization scenarios shown in a previous Paper to be consistent with current data on 15 independent evolving global (or averaged) cosmic properties regarding luminous objects and the intergalactic medium and the optical depth to electron scattering of ionized hydrogen to CMB photons: one with a monotonic behavior, which is completed by $z=6$, as commonly considered, and another one with a non-monotonic behavior with two full ionization events at $z=6$ and $z=10$. We find that the Ly$\alpha$ luminosity functions of very high-$z$ LAEs are very distinct in those two scenarios. Thus, comparing these predictions to the observations that will soon be available thanks to new instruments such as the James Webb Space Telescope, it should be possible to unveil the right reionization scenario. In the meantime, we can compare the predicted redshift distribution and UV (or Lyman-$\alpha$) luminosities of very high-$z$ LAEs to those of the few objects already observed at $z>7.5$. By doing that we find that such data are in tension with the single reionization scenario, while they are fully compatible with the double reionization scenario.