WMAP DR1 Internal Linear Combination (ILC) Map Description
The data made available through this page has been updated. The most recent version of this data may be accessed through https://lambda.gsfc.nasa.gov/product/wmap/current/
HEALPix, nested, res 9 (Nside=512)
The Internal Linear Combination (ILC) map is formed from a weighted linear combination of the 5 Smoothed I Maps in which the weights are chosen to maintain the CMB anisotropy signal while minimizing the Galactic foreground contribution. The weights are determined by minimizing the variance of the measured temperatures with the additional constraint that sum of the weights is equal to 1. To account for the spatial variation of the spectral indices of the various foreground components across the sky and in particular in the Galactic plane, the sky is divided into 12 regions: 11 regions within the inner Galactic plane and 1 covering the outer Galactic plane and high Galactic latitudes. The weights are calculated for each of the 12 regions and the final ILC map is generated using the obtained coefficients after smoothing the region boundaries with a 1.5 deg kernel. Pixel temperatures are given in mK (thermodynamic).
In addition to the ILC map, we provide a FITS-format map of the 12 weighted regions in the HEALPix projection, numbered from 0-11. For each pixel in the map, the N_OBS field is given the value of the region to which it belongs. The weights for each region are documented in the header.
The ILC map is useful for visual presentation of the CMB anisotropy signature and for foreground studies. However, because of the complicated noise properties of this map, it should NOT be used for CMB studies.
More details can be found in: