Detection of OH and wide H i absorption toward B0218+357 |
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| Authors: | N Kanekar J N Chengalur A G de Bruyn D Narasimha |
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| Institution: | Institute of Astronomy, Madingley Road, Cambridge CB3 0HA;SISSA, via Beirut, 2-4, 34014 Trieste, Italy |
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| Abstract: | Large-scale polarization of the cosmic microwave background measured by the WMAP satellite requires a mean optical depth to Thomson scattering, τe～ 0.17 . The reionization of the Universe must therefore have begun at relatively high redshift. We have studied the reionization process using supercomputer simulations of a large and representative region of a universe which has cosmological parameters consistent with the WMAP results ( Ωm= 0.3, ΩΛ= 0.7, h = 0.7, Ωb= 0.04, n = 1 and σ8= 0.9 ). Our simulations follow both the radiative transfer of ionizing photons and the formation and evolution of the galaxy population which produces them. A previously published model with ionizing photon production as expected for zero-metallicity stars distributed according to a standard stellar initial mass function (IMF) (1061 photons per unit solar mass of formed stars) and with a moderate photon escape fraction from galaxies (5 per cent), produces τe= 0.104 , which is within 1.0 to 1.5σ of the 'best' WMAP value. Values of up to 0.16 can be produced by taking larger escape fractions or a top-heavy IMF. The data do not require a separate populations of 'miniquasars' or of stars forming in objects with total masses below 109 M⊙ . Reconciling such early reionization with the observed Gunn–Peterson troughs in z > 6 quasars may be challenging. Possible resolutions of this problem are discussed. |
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| Keywords: | radiation mechanisms: non-thermal galaxies: active galaxies: jets quasars: individual: 3C 9 X-rays: galaxies |
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