Professor, Department of Astronomy and Astrophysics
University of Chicago

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Scattering Secondaries

From the observations both of the lack of of a Gunn-Peterson trough [Gunn & Peterson, 1965] in quasar spectra and its preliminary detection [Becker et al, 2001], we know that hydrogen was reionized at $z_{\rm ri}\mathrel{\hbox to 0pt{\lower 3pt\hbox{$\mathchar''218$}\hss}
\raise 2.0pt\hbox{$\mathchar''13E$}}6$. This is thought to occur through the ionizing radiation of the first generation of massive stars (see e.g. [Loeb & Barkana, 2001] for a review). The consequent recoupling of CMB photons to the baryons causes a few percent of them to be rescattered. Linearly, rescattering induces three changes to the photon distribution: suppression of primordial anisotropy, generation of large angle polarization, and a large angle Doppler effect. The latter two are suppressed on small scales by the cancellation highlighted in §4.2.1. Non-linear effects can counter this suppression; these are the subject of active research and are outlined in §4.3.4.

Plate 5b: Secondary anisotropies: (b) Scattering secondaries: rescattering suppression, Doppler, modulated Doppler (density and ionization), and SZ effects.