Non-uniform reionization by galaxies and its effect on the cosmic microwave backgroun
Abstract
We present predictions for the reionization of the intergalactic medium (IGM) by stars in high-redshift galaxies. We calculate ionizing luminosities of galaxies, including the effects of absorption by interstellar gas and dust on the escape fraction f_esc, and follow the propagation of the ionization fronts around each galaxy in order to calculate the filling factor of ionized hydrogen in the IGM. For a Lambda CDM cosmology and a physical calculation of the escape fraction, we find that the hydrogen in the IGM will be reionized at redshift z~6 if the IGM has uniform density, and by z~2 if instead the IGM is clumped in a similar way to the dark matter. We combine our model with an N-body simulation of the distribution of dark matter in the universe to calculate the secondary temperature anisotropies induced in the cosmic microwave background (CMB). The models predict a spectrum of secondary anisotropies covering a broad range of angular scales, with fractional temperature fluctuations ~10^-6 to 10^-7 on arcminute scales. The amplitude depends strongly on the total baryon density, and less sensitively on the escape fraction f_esc. The amplitude also depends somewhat on the geometry of reionization. Measurement of these anisotropies can therefore put important constraints on the reionization process, in particular, the redshift evolution of the filling factor, and should be a primary objective of a next generation submillimeter telescope such as the Atacama Large Millimeter Array. (abridged)Keywords
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