Wilkinson Microwave Anisotropy Probe DR2
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/
Sky Maps Per Frequency Band
0.23°- 0.93° (frequency dependent)
HEALPix, nested, res 9 (Nside=512)
Iterative algorithms are used to create skymaps from the calibrated differential time-ordered WMAP data for each of the ten differencing assemblies. Each pixel in a map represents a sky temperature for the bandpass appropriate to the differencing assembly. The CMB dipole has been removed from the Stokes I maps.
Maps for each year of WMAP data [currently the first, second, and third] were produced using the iterative method described above and have been supplied through LAMBDA. 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 zero point of each three year Stokes I map has been set using a Galactic csc|b| model. 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
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.
Pixel noise in units of mK can be evaluated from N_obs with the expression
σ = σ0 / sqrt(N_Obs)
Some files that contain polarization maps contain a second FITS extension
containing the #nxn# polarization noise covariance matrices for the pixels in the
maps of the first FITS extension. These matrices are used in the map-making
process and characterize the noise properties of the polarization maps. See
section 3.4 of Jarosik, et.al., 2006 in
the set of three year WMAP papers for more details. The columns of this extension are:
The covariance matrix of a pixel may be constructed by assembling the row elements into a 3x3 or 2x2 symmetric matrix with the form:
The size of the matrix depends upon whether or not the spurious signal component is included.