The epoch of reionization in the Rh = ct universe

Fulvio Melia, Marco Fatuzzo

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


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 τ ~ 0.066 ± 0.012 through the EoR. In the context of Γ cold dark matter, 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 fion ~ 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-RobertsonWalker cosmology known as the Rh = ct universe, and determine the value of fion required with this different rate of expansion. We find that Rh =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 ≲ Ωb ≲ 0.037. This model can also fit the EoR data with fion ~ 0.05, but only if the Lyman continuum photon production is highly efficient and Ωb ~ 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 Rh = ct when complete structure formation models become available.

Original languageEnglish (US)
Pages (from-to)3422-3431
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Jan 9 2016


  • Cosmological parameters
  • Cosmology: observations
  • Cosmology: theory
  • Early universe
  • Galaxies: general
  • Quasars: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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