Can one reconstruct masked CMB sky?

TL;DR

This paper investigates the effectiveness of reconstructing masked regions in CMB maps, analyzing the accuracy and limitations of such methods using real and simulated data, with implications for cosmological analysis.

Contribution

It evaluates the quality of low-resolution CMB map reconstruction methods and highlights their limitations and errors in the context of cosmological data analysis.

Findings

Reconstruction errors are significant, comparable to a fraction of the mean temperature fluctuation.

Errors vary depending on the reconstruction method and data used.

It is safer to compute the two-point correlation function on the cut-sky rather than reconstructed maps.

Abstract

The CMB maps obtained by observations always possess domains which have to be masked due to severe uncertainties with respect to the genuine CMB signal. Cosmological analyses ideally use full CMB maps in order to get e.g. the angular power spectrum. There are attempts to reconstruct the masked regions at least at low resolutions, i.e. at large angular scales, before a further analysis follows. In this paper, the quality of the reconstruction is investigated for the ILC (7yr) map as well as for 1000 CMB simulations of the LambdaCDM concordance model. The latter allows an error estimation for the reconstruction algorithm which reveals some drawbacks. The analysis points to errors of the order of a significant fraction of the mean temperature fluctuation of the CMB. The temperature 2-point correlation function C(theta) is evaluated for different reconstructed sky maps which leads to the conclusion that it is safest to compute it on the cut-sky.