Professor, Department of Astronomy and Astrophysics
University of Chicago

Group Contact CV SnapShots
CMB Introduction '96   Intermediate '01   Polarization Intro '01   Cosmic Symphony '04   Polarization Primer '97   Review '02   Power Animations   Lensing   Power Prehistory   Legacy Material '96   PhD Thesis '95 Baryon Acoustic Oscillations Cosmic Shear Clusters
Transfer Function WMAP Likelihood Reionization PPF for CAMB Halo Mass Conversion Cluster Abundance
Cosmology I [legacy 321] Cosmology II [321] Current Topics [282] Galaxies and Universe [242] Radiative Processes [305] Research Preparation [307] GR Perturbation Theory [408] CMB [448] Cosmic Acceleration [449]

Doppler Effect

Naively, velocity fields of order $v \sim 10^{-3}$ (see e.g. [Strauss & Willick, 1995] for a review) and optical depths of a few percent would imply a Doppler effect that rivals the acoustic peaks themselves. That this is not the case is the joint consequence of the cancellation described in §4.2.1 and the fact that the acoustic peaks are not ``Doppler peaks'' (see §3.8). Since the Doppler effect comes from the peculiar velocity along the line of sight, it retains no contributions from linear modes with wavevectors perpendicular to the line of sight. But as we have seen, these are the only modes that survive cancellation (see Plate 3 and [Kaiser, 1984]). Consequently, the Doppler effect from reionization is strongly suppressed and is entirely negligible below $\ell \sim 10^2$ unless the optical depth in the reionization epoch approaches unity (see Plate 5b).