The Epoch of Reionization in the R_h=ct Universe

TL;DR

This paper explores how the epoch of reionization can be explained within the R_h=ct universe, showing it can match observations with reasonable baryon density and ionizing photon efficiency, offering an alternative to LCDM.

Contribution

It demonstrates that the R_h=ct cosmology can account for EoR properties and fits observational data with plausible parameters, providing a new perspective on cosmic reionization.

Findings

R_h=ct explains EoR properties well within certain baryon density ranges.

The model fits data with an ionizing photon escape fraction of about 0.05.

Reionization can be modeled effectively in R_h=ct with high star-formation efficiency.

Abstract

The measured properties of the epoch of reionization (EoR) show that reionization probably began around z ~ 12-15 and ended by z=6. In addition, a careful analysis of the fluctuations in the cosmic microwave background indicate a scattering optical depth tau ~ 0.066+/-0.012 through the EoR. In the context of LCDM, galaxies at intermediate redshifts and dwarf galaxies at higher redshifts now appear to be the principal sources of UV ionizing radiation, but only for an inferred (ionizing) escape fraction f_ion ~ 0.2, which is in tension with other observations that suggest a value as small as ~ 0.05. In this paper, we examine how reionization might have progressed in the alternative Friedmann-Robertson Walker cosmology known as the R_h=ct Universe, and determine the value of f_ion required with this different rate of expansion. We find that R_h=ct accounts quite well for the currently known properties of the EoR, as long as its fractional baryon density falls within the reasonable range 0.026 < Omega_b < 0.037. This model can also fit the EoR data with f_ion ~ 0.05, but only if the Lyman continuum photon production is highly efficient and Omega_b ~ 0.037. These results are still preliminary, however, given their reliance on a particular form of the star-formation rate density, which is still uncertain at very high redshifts. It will also be helpful to reconsider the EoR in R_h=ct when complete structure formation models become available.