Template fitting and the large-angle cosmic microwave background anomalies

Abstract

We investigate two possible explanations for the large-angle anomalies in the cosmic microwave background (CMB): an intrinsically anisotropic model and an inhomogeneous model. We take as an example of the former a Bianchi model (which leaves a spiral pattern in the sky) and of the latter a background model that already contains a non-linear long-wavelength plane wave (leaving a stripy pattern in the sky). We make use of an adaptation of the 'template' formalism, previously designed to detect galactic foregrounds, to recognize these patterns and produce confidence levels for their detection. The 'corrected' maps, from which these patterns have been removed, are free of anomalies, in particular their quadrupole and octopole are not planar and their intensities are not low. We stress that although the 'template' detections are not found to be statistically significant they do correct statistically significant anomalies. © 2006 RAS.