Effect of Foregrounds on the CMBR Multipole Alignment

TL;DR

This paper investigates how foreground removal techniques impact the observed alignment of the CMBR quadrupole and octopole, concluding that foreground cleaning causes random shifts that do not artificially create alignments.

Contribution

It provides a detailed analysis of foreground effects on multipole alignment using symmetry-based eigenvector methods and simulated data, clarifying the impact of cleaning procedures.

Findings

Foreground shifts are small and random in direction.

Foreground cleaning does not artificially induce multipole alignment.

Results are consistent across different simulation and analysis methods.

Abstract

We analyze the effect of foregrounds on the observed alignment of CMBR quadrupole and octopole. The alignment between these multipoles is studied by using a symmetry based approach which assigns a principal eigenvector (PEV) or an axis with each multipole. We determine the significance of alignment between these multipoles by using the Internal Linear Combination (ILC) 5 and 7 year map s and also the maps obtained by using the Internal Power Spectrum Estimation (IPSE) procedure. The effect of foreground cleaning is studied in detail within the framework of the IPSE method both analytically and numerically. By using simulated CMBR data, we study how the PEVs of the pure simulated CMB map differ from those of the final cleaned map. We find that, in general, the shift in the PEVs is relatively small and in random directions. Due to the random nature of the shift we conclude that it can only lead to misalignment rather than alignment of multipoles. We also directly estimate the significance of alignment by using simulated cleaned maps. We find that the results in this case are identical to those obtained by simple analytic estimate or by using simulated pure CMB maps.