Two-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 -cold dark matter ( CDM) 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 two-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 are in good agreement ( 30 per cent probability) with a CDM model when the WMAP data are considered as a particular realization drawn from a set of realistic CDM simulations with the corresponding covariance. This is also true for the higher-order moments, shown here up to sixth 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-fitting model for the low-order multipoles based on the two-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 K 2 ). The errors increase by about a factor of 5 if we assume the CDM model. If we exclude the Galactic plane |b| < 30 from our analysis, we recover very similar values within the errors (i.e. 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.