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/
Sky Maps Per Frequency Band
HEALPix, nested, res 9 (Nside=512)
0.23°- 0.93° (frequency dependent)
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 have been supplied through LAMBDA. Full five year maps were produced by performing a weighted, pixel-by-pixel, mean of the five single year maps; the N_Obs measurement was used to weight this mean. For the Stokes I maps, the mean temperature outside of the temperature analysis/KQ85 mask was subtracted from each single year map before the five year weighted mean was calculated. The zero point of each five year Stokes I map has been set using a Galactic csc |b| model. The N_Obs measurements were added together to produce the final N_Obs measurement. In addition, the full five year Stokes I maps have been smoothed to 1° resolution and are supplied as a separate data product.
WMAP maps are stored in FITS binary table extensions. The maps are stored in the first extension in a file; the number of columns in 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. The number of columns depends upon which maps are included; these columns may be:
The column names for I, Q, U, and N_Obs maps 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 Q_POLARISATION and U_POLARISATION exist in files containing polarization maps; the names were selected to be compatible with existing HEALPix software. The SPUR_SIGNAL columns exists only in polarization map files that contain an 'S' map.
The WMAP skymaps used the HEALPix nested pixel ordering scheme in Galactic coordinates. For the convenience of users who do not have HEALPix software installed, we provide a series of FITS sky map files that give the sky coordinates of each pixel center for various resolutions.
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 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 Jarosik, et.al., 2007 and in Hinshaw, et.al., 2008 for more details. There are two forms of this matrix, depending upon whether or not the bandpass mismatch term (S map) has been included in the file.
If the S map is supplied then the columns of this extension are:
The covariance matrix for a pixel may then be constructed by assembling the row elements into a 3x3 symmetric matrix with the form:
If, on the other hand, the S map is not supplied then the columns of this extension are:
The covariance matrix of a pixel may be constructed by assembling the row elements into a 2x2 symmetric matrix with the form: