Wilkinson Microwave Anisotropy Probe

The data made available through this page has been updated. The most recent version of this data may be accessed through /product/map/current/

Product Name
Foreground Reduced Low Resolution Sky Maps
Coord. System
Projection Type
HEALPix, nested, res 4 (Nside=16)
0.23°- 0.93° (frequency dependent)


These low resolution maps were created by degrading the foreground reduced res 9 single year individual D/A polarization maps to res 4 using the QQ, QU, and UU covariance matrices, omitting pixel-to-pixel covariance.

The inverse covariance matrices were corrected using the standard polarization mask to ignore covariance with pixels within the cut. These matrices were also corrected for the effects of compression and foreground cleaning by increasing the noise per observation by a few percent; the noise per observation has been applied to the matrices.

Rows and columns that correspond to pixels in the polarization mask are zero, so that the matrices are singular as supplied. To make them non-singular, the row and the column corresponding to each zero element of the diagonal need to be deleted.

A small effect due to transmission imbalance between the A side and the B side of the instrument has been projected out of the inverse variance matrices as described in Section 3.5.1 of Jarosik et al. (2007).

WMAP maps are stored in FITS binary table extensions. The maps are stored in the first extension in a file; the format of this table depends upon whether polarization maps have been included in the file. Some files also contain the polarization covariance matrices for the maps; if supplied these matrices are stored in a second binary table extension.

As previously stated, the first FITS extension contains the maps. These maps are in a nested HEALPix format, with each row representing a single pixel. There are either four or two columns depending upon whether or not polarization maps are included; these columns are:

TEMPERATURE The Stokes I, or temperature, measurement in mK (thermodynamic).
Q_POLARISATION The Stokes Q polarization measurement in mK (thermodynamic).
U_POLARISATION The Stokes U polarization measurement in mK (thermodynamic).
N_OBS The effective number of observations.

The column names were selected to be compatible with existing HEALPix software. The TEMPERATURE and N_OBS columns are the only columns that exist in files that do not contain polarization maps.

The EE fit in the parameter likelihood computation required only the Q and U components of the Q and V maps. Therefore these are the only maps that were produced for this deliverable category. Since the Stokes I and N_Obs maps were not produced in this form, these fields have been zero'ed out in the map files available through LAMBDA.

Additional Information

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A service of the HEASARC and of the Astrophysics Science Division at NASA/GSFC
Goddard Space Flight Center, National Aeronautics and Space Administration
HEASARC Director: Dr. Alan P. Smale
LAMBDA Director: Dr. Eric R. Switzer
NASA Official: Dr. Eric R. Switzer
Web Curator: Mr. Michael R. Greason