This paper addresses the reconstruction of the CMB 2point correlation function on a cut sky done in 0911.5399. (This was earlier discussed in http://cosmocoffee.info/viewtopic.php?t=1582.)
The authors write that a 10 degree smoothing applies to the maps before the reconstruction leads to an information transfer from inside the mask to outside, and it is this which makes the reconstruction accurate. They conclude that without this bleed the reconstruction algorithm does not work well enough to obtain the 2point correlation function, so it should instead be calculated on the masked sky.
[1005.5069] Can one reconstruct masked CMB sky?
Authors:  R. Aurich, S. Lustig 
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 2point 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 cutsky. 
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 Joined: March 02 2005
 Affiliation: University of Helsinki