QUIJOTE scientific results – XII. Characterization of the polarized synchrotron emission at the power spectrum level in the QUIJOTE-MFI wide survey

We present an analysis of the polarized synchrotron emission at the power-spectrum level in the multipole range 30 ≤ ℓ < 130, using the recent QUIJOTE-MFI wide survey (10–20 GHz) in combination with Planck and WMAP data. The EE and BB power spectra are well described by a simple power-law model, with no evidence for the need of additional parameters. The best-fit slopes are αEE = −3.24 ± 0.12 and αEE = −3.81 ± 0.34 for |b| > 20○, hinting toward a steepening of the BB spectrum relative to EE at the ∼1.6σ level. The synchrotron frequency spectral indices are found to be β ₛEE = -3.26 ± 0.05 and β ₛBB = -3.25 ± 0.10 for the same cut, in agreement with earlier real-space analyses. We find no evidence for spatial variations of βs across different Galactic latitude cuts, within current uncertainties. The synchrotron BB/EE power ratio is approximately 0.2 over the considered multipole range, lower than typical values for thermal dust, and consistent with previous measurements. We also measure a dust-synchrotron spatial correlation in the range 0.1–0.25 over 30 ≤ ℓ < 130. Using these results, we estimate the level of synchrotron contamination in future CMB B-mode measurements, finding an average power in the considered sky masks equivalent to r ≃ 0.003 at 90 GHz and r ≃ 0.0002 at 150 GHz for the relevant angular scales.