Foreground: Synchrotron Spectral Index in Brightness Temperature

A linear combination method is used to produce WMAP 23 GHz and Planck LFI 30 GHz temperature maps ("ADR maps") for which the Anomalous Microwave Emission (spinning dust) and CMB signal have been significantly mitigated. In conjunction with the Haslam 408 MHz and WHAM H-α surveys, these two ADR maps are used to produce an estimate of the synchrotron spectral index in brightness temperature over nearly the entire sky. Results for some sky regions are more uncertain than for others however, and a mask is provided to indicate the "analysis region" where the results are believed to be largely unbiased.

Released files include:

1. The ADR maps at 23 and 30 GHz and accompanying instrumental uncertainties.
2. The mask defining the analysis region.
3. The synchrotron spectral index map and statistical uncertainties. In general, systematic uncertainties per pixel of very roughly Δβ = 0.05 should also be anticipated (note this is a simplification, see paper for details).

More details can be found in:

• Using Two-frequency Dust Spectral Matching to Separate Galactic Synchrotron and Free–Free Temperature Foregrounds from the Cosmic Microwave Background, Weiland et al. (2025)