Wilkinson Microwave Anisotropy Probe DR4

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/"

DR4 Simulated Sky Maps

Coordinate System:
Projection Type:
HEALPix, nested
0.23°- 0.93° (frequency dependent)
Download Links:

Simulated sky maps result from processing a simulated differential time-ordered data (TOD) stream through the same calibration and analysis pipeline that is used for the flight data.

Simulated TOD are generated by sampling a model sky using flight-like pointings. The simulation includes:

  1. A sky model similar to the observed sky, with diffuse Galactic foregrounds and CMB, but no injection of a point source population.
  2. A realistic noise model for every channel, including white noise, 1/f noise and all inter-channel correlations that are known to exist in the radiometers.
  3. Thermal drifts in instrument gains and baselines which closely follow those occurring in flight.
  4. Smearing of the sky signal based on finite integration time per data sample.
  5. Transmission imbalance between the A- and B-side optics.
  6. Circular Gaussian beams with flight-like FWHM.
  7. Far-sidelobe beam pickup.

Once the simulated spacecraft, instrument housekeeping and instrument science packets are generated for the complete 7-year interval, they are then processed in the same manner as flight data to produce yearly simulated sky maps per differencing assembly. The foreground-cleaned simulated sky maps are generated from the raw simulated sky maps by fitting and then removing a Foreground template model, following the method described in Hinshaw, et.al., 2006 and Gold, et.al., 2009. 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.

Analogous flight data counterparts of the simulated skymaps may be found in the Full Resolution Single Year Sky Maps table of the WMAP data products page.

As with the flight data, WMAP maps of the sky are supplied in FITS files, with the maps contained within binary table extensions. The maps are stored in a nested HEALPix projection and are supplied at the WMAP's standard Res 9 (NSide=512) resolution. Stokes I (temperature), Stokes Q and U (Polarization), and bandpass mismatch (a so-called S map) maps may be supplied in a file. Also included in the maps is an Nobs map describing the number of observations used to construct each pixel. The I,Q,U,S files contain the same data as the I,Q,U files with the addition of the S map for those users that wish to account for the small covariance between Q, U, and S. A detailed description of how these files are formatted is available here.

Iterative algorithms are used to create skymaps from the calibrated differential time-ordered simulated 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.

Many of the files that contain polarization maps also contain an extension containing the polarization noise covariance matrices for the maps. See the detailed description mentioned above for formatting details.

Pixel noise in units of mK may be evaluated from Nobs with the expression σ = σ0 / sqrt(Nobs) where

σ0 For Each Differencing Assembly
K1 Ka1 Q1 Q2 V1 V2 W1 W2 W3 W4
Stokes I 1.41631 1.46171 2.26126 2.14203 3.25988 2.96328 5.84731 6.48035 6.90641 6.94788
Stokes Q,U 1.43659 1.48267 2.28570 2.16476 3.28653 2.98666 5.87943 6.51923 6.94438 7.01225

Sky Model

The sky models used to create the simulated maps are now available on LAMBDA.

The noiseless model sky used in generating the simulated time-ordered data for each differencing assembly is provided as a set of resolution 10 (Nside=1024) HEALPix nested maps in Galactic coordinates. The complete sky model description for each D/A is provided in a FITS file with three binary table extensions. The CMB temperature and polarization maps are provided in the first extension. The Galaxy model is provided in the other two extensions, with the temperature maps in the first and the polarization maps in the second. The Galaxy temperature model is computed for each channel within a D/A, allowing for a realistic frequency dependence for each channel. Polarization maps are provided in Stokes Q and U and are taken as channel independent within a D/A. Models are in thermodynamic temperature units.

Additional Information

Back To WMAP DR4: Simulated Sky Map Products

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