Uncorrelated universe: Statistical anisotropy and the vanishing angular correlation function in WMAP years 1–3

Abstract

The large-angle (low-l) correlations of the cosmic microwave background (CMB) as reported by the Wilkinson Microwave Anisotropy Probe (WMAP) after their first year of observations exhibited statistically significant anomalies compared to the predictions of the standard inflationary big-bang model. We suggested then that these implied the presence of a solar system foreground, a systematic correlated with solar system geometry, or both. We reexamine these anomalies for the data from the first three years of WMAP's operation. We show that, despite the identification by the WMAP team of a systematic correlated with the equinoxes and the ecliptic, the anomalies in the first-year internal linear combination (ILC) map persist in the three-year ILC map, in all-but-one case at similar statistical significance. The three-year ILC quadrupole and octopole therefore remain inconsistent with statistical isotropy - they are correlated with each other (99.6% C.L.), and there are statistically significant correlations with local geometry, especially that of the solar system. The angular two-point correlation function at scales > 60 deg in the regions outside the (kp0) galactic cut, where it is most reliably determined, is approximately zero in all wavebands and is even more discrepant with the best-fit Lambda CDM inflationary model than in the first-year data - 99.97% C.L. for the new ILC map. The full-sky ILC map, on the other hand, has a nonvanishing angular two-point correlation function, apparently driven by the region inside the cut, but which does not agree better with Lambda CDM. The role of the newly-identified low-l systematics is more puzzling than reassuring.