Are There Enough Ionizing Photons to Reionize the Universe by z=6?

Abstract

An estimate for the number of ionizing photons per baryon as a function of redshift is computed based on the plausible extrapolation of the observed galaxy UV luminosity function and the latest results on the properties of the escape fraction of ionizing radiation. It is found that, if the escape fraction for low mass galaxies (Mtot<10^{11}Msun) is assumed to be negligibly small, as indicated by numerical simulations, then there are not enough ionizing photons to reionize the universe by z=6 for the cosmology favored by the WMAP 3rd year results, while the WMAP 1st year cosmology is marginally consistent with the reionization requirement. The escape fraction as a function of galaxy mass would have to be constant to within a factor of two for the whole mass range of galaxies for reionization to be possible within the WMAP 3rd year cosmology.

submitted to ApJ. Comments and objections are welcome

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• A downturn in intergalactic CIV as redshift 6 is approached
• Reopening the window on charged dark matter
• Relative Role of Stars and Quasars in Cosmic Reionization
• The UDF05 Follow-up of the HUDF: II. Constraints on Reionization from z-dropout Galaxies
• A Common Origin for Globular Clusters and Ultra-faint Dwarfs in Simulations of the First Galaxies
• The Effect of Galactic Properties on the Escape Fraction of Ionizing Photons
• On the minimum mass of reionization sources
• The Predicament of Absorption-Dominated Reionization: Increased Demands on Ionizing Sources
• Impact of Dark Matter Annihilation on the High-Redshift Intergalactic Medium
• A Magellan IMACS Spectroscopic Search for Lyman-Alpha Emitting Galaxies at Redshift 5.7
• The Escape Fraction of Ionizing Photons During the Epoch of Reionization: observability with the Square Kilometre Array
• The Impact of Unresolved Turbulence on the Escape Fraction of Lyman Continuum Photons
• Non-parametric Reconstruction of Photon Escape Fraction from Reionization
• Redshifted 21cm Observations of High Redshift Quasar Proximity Zones