Microwave Sky and the Local Rees–Sciama Effect

The microwave sky shows unexpected features at the largest angular scales, among them the alignments of the dipole, quadrupole and octopole. Motivated by recent X-ray cluster studies, we investigate the possibility that local structures at the 100 hMpc scale could be responsible for such correlations. These structures give rise to a local Rees–Sciama contribution to the microwave sky that may amount to ∆T/T ∼ 10 at the largest angular scales. We model local structures by a spherical overdensity (Lemâıtre–Tolman–Bondi model) and assume that the Local Group is falling toward the centre. We superimpose the local Rees–Sciama effect on a statistically isotropic, gaussian sky. As expected, we find alignments among low multipoles, but a closer look reveals that they do not agree with the type of correlations revealed by the data.