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Constraints On First-Light Ionizing Sources From Optical Depth Of The Cosmic Microwave Background, J Shull, Aparna Venkatesan

Physics and Astronomy

We examine the constraints on high-redshift star formation, ultraviolet and X-ray preionization, and the epoch of reionization at redshift z_r, inferred from the recent WMAP-5 measurement, τ_e = 0.084 ± 0.016, of the electron- scattering optical depth of the cosmic microwave background (CMB). Half of this scattering can be accounted for by the optical depth, τ_e = 0.04-0.05, of a fully ionized intergalactic medium (IGM) at z ≤ z_GP ≈ 6-7, consistent with Gunn-Peterson absorption in neutral hydrogen. The required additional optical depth, Δτ_e = 0.03 ± 0.02 atz > z_GP, …