Talk Title: The growth of the earliest supermassive black holes and their contribution to reionization
Abstract: Recent data on cosmic microwave background anisotropies(by WMAP) and on the spectra of high-redshift quasars (by the SDSS) together imply that the reionization history of the universe is extended and complex. I will discuss currently available observational constraints, and the extent to which accreting black holes (BHs) can help explain these data. I will show new evidence that the intergalactic medium contains a significant amount of neutral hydrogen at z~6 and is experiencing rapid ionization. However, I will argue that quasars are unlikely to drive the observed evolution of the neutral fraction without over-producing the present-day soft X-ray background. On the other hand, the seeds of the z~6 quasar BHs likely appeared at much earlier epochs (z~20), and produced hard ionizing radiation by accretion. These early BHs are promising candidates to account for the high redshift (z~15) ionization implied by the WMAP data.
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