Observational constraints of cosmic reionization

Research output: Chapter in Book/Report/Conference proceedingConference contribution


The epoch of reionization is the last unexplored phase of cosmic evolution, corresponding to a crucial era in cosmic structure formation - the formation of the first luminous objects. I review some recent constraints on the end of reionization using observations of the highest-redshift quasars and galaxies. Spectroscopic studies of Gunn-Peterson (GP) absorption, and related phenomena, suggest a qualitative change in the state of the intergalactic medium (IGM) at z ∼ 6, indicating a rapid increase in the neutral fraction of the IGM, from xHI < 10-4 at z ≤ 5.5, to xHI > 10-3, and perhaps as high as 0.3, at z ≥ 6. On the other hand, transmission spikes in the GP trough, and observations of the evolution of the Lyα galaxy luminosity function indicate xHI < 50% at z ∼ 6.5. The IGM characteristics at this epoch are consistent with the end of the overlapping stage of reionization. Current data are consistent with star-forming galaxies, in particular low-luminosity galaxies, rather than quasars and AGNs, as being the dominant sources of reionizing photons, although large uncertainties still exist in estimating the total contribution from the galaxy population at high redshift.

Original languageEnglish (US)
Title of host publicationA Century of Cosmology: Past, Present and Future
PublisherII Nuovo Cimento
Number of pages12
Publication statusPublished - 2007
EventA Century of Cosmology: Past, Present and Future - San Servolo, Venice, Italy
Duration: Aug 27 2007Aug 31 2007


OtherA Century of Cosmology: Past, Present and Future
CitySan Servolo, Venice


ASJC Scopus subject areas

  • Astronomy and Astrophysics

Cite this

Fan, X. (2007). Observational constraints of cosmic reionization. In A Century of Cosmology: Past, Present and Future (pp. 947-958). II Nuovo Cimento. https://doi.org/10.1393/ncb/i2008-10425-x