2024A&A...689A.353D

Context. Observations of cosmic microwave background (CMB) polarization, essential for probing a potential phase of inflation in the early Universe, suffer from contamination by polarized emission from the Galactic interstellar medium.
Aims. This work combines existing observations from the WMAP and Planck space missions to make a low-noise map of polarized synchrotron emission that can be used to clean forthcoming CMB observations.
Methods. We combine DR5 K, Ka and Q WMAP maps with PR4 30 and 44 GHz Planck LFI maps, using weights that near-optimally combine the observations as a function of sky direction, angular scale, and polarization orientation.
Results. We publish well-characterized maps of synchrotron Q and U Stokes parameters at ν = 30 GHz and an angular resolution of 1 degree. A statistical description of uncertainties is provided with Monte-Carlo simulations of additive and multiplicative errors.
Conclusions. Our maps are the most sensitive full-sky maps of synchrotron polarization to date, and are made available to the scientific community on a dedicated website.