The Epoch of Reionization in the R_h=ct Universe
  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.
