Witnessing the reionization history using Cosmic Microwave Background observation from Planck

Dhiraj Kumar Hazra, George F. Smoot

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)


We constrain the history of reionization using the data from Planck 2015 Cosmic Microwave Background (CMB) temperature and polarization anisotropy observations. We also use prior constraints on the reionization history at redshifts ∼7-8 obtained from Lyman-α emission observations. Using the free electron fractions at different redshifts as free parameters, we construct the complete reionization history using polynomials. Our construction provides an extremely flexible framework to search for the history of reionization as a function of redshifts. We present a conservative and an optimistic constraint on reionization that are categorized by the flexibilities of the models and datasets used to constrain them, and we report that CMB data marginally favors extended reionization histories. In both the cases, we find the mean values of optical depth to be larger (≈0.09 and 0.1) than what we find in standard steplike reionization histories (0.079 ± 0.017). At the same time we also find that the maximum free electron fraction allowed by the data for redshifts more than 15 is ∼0.25 at 95.4% confidence limit in the case of optimistic constraint.

Original languageEnglish
Article number028
JournalJournal of Cosmology and Astroparticle Physics
Issue number11
Publication statusPublished - Nov 20 2017
Externally publishedYes


  • cosmological parameters from CMBR
  • intergalactic media
  • Lyman alpha forest
  • reionization

ASJC Scopus subject areas

  • Astronomy and Astrophysics

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