The aim of RadioForegroundsPlus is to combine the nine Planck all-sky (30-857 GHz) maps, with three unique low-frequency data sets: the QUIJOTE maps (at 11, 13, 17 and 19 GHz), the C-BASS survey (at 5 GHz) and the S-PASS data (at 2.3 GHz) to provide the best possible characterization of the physical properties of polarized emissions in the microwave domain, together with an unprecedentedly thorough description of the intensity signal. This legacy information will be essential for future ground-based, sub-orbital or space experiments.

In particular, the joint analysis of these data will allow us to achieve the following ground-breaking objectives:

1. to provide state-of-the-art legacy maps of the synchrotron, free-free and anomalous microwave emissions over extended sky coverage;
2. to characterize the spectral behaviour of synchrotron emission with high precision over the full sky, pinning down its deviations from a simple power-law;
3. to model the recovered diffuse Galactic synchrotron emission in terms of a 3D physical interpretation of the distribution of cosmic rays propagating through the magnetic field;
4. to model and characterize, or to constrain tightly, the level of a possible contribution of polarized Anomalous Microwave Emission (AME);
5. to reconstruct the regular and turbulent components of the Galactic magnetic field;
6. to provide improved catalogues of the population of radio sources observed by Planck including unique information from additional frequencies;
7. to make robust predictions about the effect of radio foregrounds on the detectability of the B-mode of polarization for future CMB experiments; and
8. to provide updated maps of thermal dust emission and to characterise its correlation with synchrotron.

RadioForegroundsPlus builds on the effort and expertise of the former RADIOFOREGROUNDS program. RadioForegroundsPlus has received funding from the European Union’s HORIZON-CL4-2023-SPACE-01 programme under grant agreement number 101135036.