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 Sky Maps Per Frequency Band
Coord. System
Projection Type
HEALPix, nested, res 9 (Nside=512)
0.23°- 0.93° (frequency dependent)


The foreground reduced skymaps were produced by removing a foreground model from the 'unreduced' maps using the Foreground Template Model discussed in Hinshaw, et.al., 2006 and Page, et.al, 2006; see those papers for details. Briefly, synchrotron, free-free, and dust emission templates were modeled and then subtracted from the single year 'unreduced' maps. The goal was to produce a set of maps with the foreground removed while retaining WMAP's noise characteristics.

Because the K and Ka maps were used to produce the foreground models, only Q, V, and W band foreground reduced maps were created and delivered to LAMBDA.

As with the 'unreduced' maps, full three year maps were produced by performing a weighted, pixel-by-pixel, mean of the three single year maps; the N_Obs measurement was used to weight this mean. The N_Obs measurements were added together to produce the final, three year, N_Obs measurement.

This same weighted mean method was then used to combine three year maps of the same frequency band into a single map for each frequency. Two maps were combined to produce the Q and V band maps; four maps were combined to produce the W band map.

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.

Additional Information

Release Notes

  • 03 April 2006 - The FREQ keyword value in the primary FITS header was modified to contain the correct value. No change was made to the data, and the file version number was not incremented.

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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