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Foreground Data

Foreground Overview

Plot of Anisotropy vs. Frequency Plot of Anisotropy vs. Frequency Plot of Anisotropy vs. Frequency

The Milky Way emits microwave radiation that can interfere with observations of the CMB anisotropy. Fortunately there is a local minimum in the Galactic emission near 70 or 80 GHz where the CMB signal is relatively bright compared to the Galactic signal. The figures above show recent determinations of the rms anisotropy as a function of frequency for the CMB and for sources of foreground emission: synchrotron, free-free, spinning dust, and thermal dust emission. The first two figures show results for temperature anisotropy, from Bennett et al. 2013 (left) and from Planck 2015 Results X. The third figure shows results for polarization anisotropy from Planck 2015 Results X. Polarization anisotropy for free-free emission and spinning dust emission is negligible. In each figure, the lower and upper curves for each foreground component show the anisotropy for two sky cuts, retaining 69% and 75% of the sky respectively for the first figure, 81% and 93% of the sky for the second figure, and 73% and 93% of the sky for the third figure. The figure from Bennett et al. 2013 is available on our foreground image page.The other figures are available from the Planck Picture Gallery and are credited to ESA and the Planck Collaboration.

One frequently used technique for removing Galactic foregrounds is to use existing Galactic maps as foreground emission templates and scale assuming a frequency dependence. Such templates are available in the Data Products section, generally as maps stored in nested HEALPix pixelization.

Models of the foreground emission also exist, either resulting from studies at specific frequencies (e.g., see the foreground data product listings for WMAP and COBE/DMR), or presented as generalized software for a variety of applications (e.g., WOMBAT foreground tools).

In addition to maps of diffuse emission, the Products section provides links to a number of Point Source catalogs. Pixels contaminated by bright resolved sources can be masked; residual contamination from unresolved sources may be estimated or modeled.

The following external links also address foreground removal and/or modelling:

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