On the cosmic microwave background large-scale angular correlations

Instituto Nacional de Pesquisas Espaciais, Divisão de Astrofísica, Av. dos Astronautas 1758, 12227-010, São José dos Campos, SP – Brazil e-mail: [bernui;thyrso;alex;leonardi;ivan]@das.inpe.br

Received: 23 September 2005
Accepted: 16 January 2006

Abstract

Aims.We study the large-scale angular correlation signatures of the cosmic microwave background (CMB) temperature fluctuations from WMAP data in several spherical cap regions of the celestial sphere, outside the Kp0 or Kp2 cut-sky masks.

Methods.We applied a recently proposed method to CMB temperature maps to permit an accurate analysis of their angular correlations in the celestial sphere through the use of normalized histograms of the number of pairs of such objects with a given angular separation versus their angular separation. The method allows for a better comparison of the results from observational data with the expected CMB angular correlations of a statistically isotropic universe, computed from Monte-Carlo maps according to the WMAP best-fit ΛCDM model.

Results.We found that the already known, anomalous lack of large-scale power in full-sky CMB maps is mainly due to deficient angular correlations of a quadrupole-like signature. This result is robust with respect to frequency CMB maps and cut-sky masks. Moreover, we also confirm previous results regarding the uneven distribution in the sky of the large-scale power of WMAP data. In a bin-to-bin correlation analyses, measured by the full covariance matrix statistic, we found that the angular correlation signatures in opposite Galactic hemispheres are anomalous at a 98%–99% confidence level.