An Improved Diffuse Foreground Subtraction by ILC method: CMB Map and
  Angular Power Spectrum using Planck and WMAP Observations
  We report an improved technique for diffuse foreground minimization from
Cosmic Microwave Background (CMB) maps using a new multi-phase iterative
internal-linear-combination (ILC) approach in harmonic space. The new procedure
consists of two phases. In phase 1, a diffuse foreground cleaned map is
obtained by performing a usual ILC operation in the harmonic space in a single
iteration over the desired portion of the sky. In phase 2, we obtain the final
foreground cleaned map using an iterative ILC approach also in the harmonic
space, however, now, during each iteration of foreground minimization, some of
the regions of the sky that are not being cleaned in the current iteration, are
replaced by the corresponding cleaned portions of the phase 1 cleaned map. The
new ILC method nullifies a foreground leakage signal that is otherwise
inevitably present in the old and usual harmonic space iterative ILC method.
The new method is flexible to handle input frequency maps, irrespective of
whether or not they initially have the same instrumental and pixel resolution,
by bringing them to a common and maximum possible beam and pixel resolution at
the beginning of the analysis. This dramatically reduces data redundancy and
hence memory usage and computational cost. During the ILC weight calculation it
avoids any need to deconvolve partial sky spherical harmonic coefficients by
the beam and pixel window functions, which in strict mathematical sense, is not
well-defined for azimuthally symmetric window functions. Using WMAP 9-year and
Planck-2015 published frequency maps we obtain a pair of foreground cleaned CMB
maps and CMB angular power spectrum. Our power spectrum match well with
Planck-2015 results, with some difference. Finally, we show that the weights
for ILC foreground minimization have an intrinsic characteristic that it tends
to produce a statistically isotropic CMB map as well.
