A Global ILC Approach in Pixel Space over Large Angular Scales of the
  Sky using CMB Covariance Matrix
  We propose a new internal linear combination (ILC) method in the pixel space,
applicable on large angular scales of the sky, to estimate a foreground
minimized Cosmic Microwave Background (CMB) temperature anisotropy map by
incorporating prior knowledge about the theoretical CMB covariance matrix.
Usual ILC method in pixel space, on the contrary, does not use any information
about the underlying CMB covariance matrix. The new approach complements the
usual pixel space ILC technique specifically at low multipole region, using
global information available from theoretical CMB covariance matrix as well as
from the data. Since we apply our method over the large scale on the sky
containing low multipoles we perform foreground minimization globally. We apply
our methods on low resolution Planck and WMAP foreground contaminated CMB maps
and validate the methodology by performing detailed Monte-Carlo simulations.
Our cleaned CMB map and its power spectrum have significantly less error than
those obtained following usual ILC technique at low resolution that does not
use CMB covariance information. Another very important advantage of our method
is that the cleaned power spectrum does not have any negative bias at the low
multipoles because of effective suppression of CMB-foreground chance
correlations on large angular scales of the sky. Our cleaned CMB map and its
power spectrum match well with those estimated by other research groups.
