2-point anisotropies in WMAP and the Cosmic Quadrupole

Large-scale modes in the temperature anisotropy power spectrum C l measured by the Wilkinson Microwave Anisotropy Probe (WMAP), seem to have lower amplitudes ( C 2 , C 3 and C 4 ) than that expected in the so called concordance ΛCDM model. In particular, the quadrupole C 2 is reported to have a smaller value than allowed by cosmic variance. This has been interpreted as a possible indication of new physics. In this paper we re-analyse the WMAP data using the 2-point angular correlation and its higher-order moments. This method, which requires a full covariance analysis, is more direct and provides better sampling of the largest modes than the standard harmonic decomposition. We show that the WMAP data is in good agreement ( ≃ 30% probability) with a ΛCDM model when the WMAP data is considered as a particular realization drawn from a set of realistic ΛCDM simulations with the corresponding covariance. This is also true for the higher-order moments, shown here up to 6th order, which are consistent with the Gaussian hypothesis. The sky mask plays a major role in assessing the significance of these agreements. We recover the best fit model for the low-order multipoles based on the 2-point correlation with different assumptions for the covariance. Assuming that the observations are a fair sample of the true model, we find C 2 = 123 ± 233, C 3 = 217 ± 241 and C 4 = 212 ± 162 (in µK 2 ). The errors increase by about a factor of 5 if we assume the ΛCDM model. If we exclude the Galactic plane | b | < 30 from our analysis, we recover very similar values within the errors (ie C 2 = 172 , C 3 = 89 , C 4 = 129). This indicates that the Galactic plane is not responsible for the lack of large-scale power in the WMAP data.