'LAMBDA - WMAP 'Foreground Cleaned' I Maps (Q, V and W Differencing Assemblies) 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/

Coordinate System:
Projection Type:
0.23° - 0.5° (frequency dependent)
HEALPix, nested, res 9 (Nside=512)
Download Links:

These files contain the 'foreground-cleaned' sky maps used in the generation of the WMAP first-year CMB power spectrum. The Galactic foreground signal, consisting of synchrotron, free-free, and dust emission, was removed using the 3-band, 5-parameter template fitting method described in Bennett et al (2003). Note that since the templates were fit only with data outside of the Kp2 mask, the foreground removal is not applicable to regions near the Galactic plane, where the spectrum of the Galactic emission is different. The advantage of this technique over the MEM-based Galaxy modeling method is that the well-specified noise properties of the original maps are preserved.

WARNING: prior to fitting, the template sky maps were convolved to the WMAP beam response using a harmonic space algorithm with a cutoff in l-space of l_max=1024. This results in some ringing around bright sources, particularly the LMC at high latitudes. If regions around bright sources are not masked, (especially the LMC at high latitudes) one may find false excess power in these regions. We recommend that one of the standard sky cuts supplied with the first year WMAP data be employed when analyzing these maps. We have found no evidence for excess power when such a cut is employed. Note that the power spectrum released with the first-year data was based on the "Kp2" cut and is not affected by these artifacts.

The data provided in each map consist of two fields for each pixel:

  • the thermodynamic temperature, in mK, and
  • the effective number of observations, N_obs.

Pixel noise can be evaluated from N_obs via sigma = sigma_0/sqrt(N_obs), where sigma_0 for each differencing assembly is listed in the following table:

Differencing Assembly Q1 Q2 V1 V2 W1 W2 W3 W4
sigma_0 (mK) 2.26677 2.15567 3.28789 2.93683 5.85196 6.53276 6.88032 6.72537

More details can be found in:

"First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations:
Foreground Emission," Bennett, et al., 2003

"First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations:
The Angular Power Spectrum," Hinshaw, et al., 2003

WMAP Explanatory Supplement

Release Notes:

Initial release of the foreground-cleaned maps.

Documentation updated to include a warning about harmonic ringing in the templates around bright sources. The sky maps are unchanged.

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. Andrew F. Ptak
LAMBDA Director: Dr. Thomas M. Essinger-Hileman
NASA Official: Dr. Thomas M. Essinger-Hileman
Web Curator: Mr. Michael R. Greason