Sensitivity-improved Polarization Maps at 40 GHz with CLASS and WMAP Data

Improved polarization measurements at frequencies below 70 GHz with degree-level angular resolution are crucial for advancing our understanding of the Galactic synchrotron radiation and the potential polarized anomalous microwave emission and ultimately benefiting the detection of primordial B modes. In this study, we present sensitivity-improved 40 GHz polarization maps obtained by combining the CLASS 40 GHz and Wilkinson Microwave Anisotropy Probe (WMAP) Q -band data through a weighted average in the harmonic domain. The decision to include WMAP Q -band data stems from similarities in the bandpasses. Leveraging the accurate large-scale measurements from the WMAP Q band and the high-sensitivity information from the CLASS 40 GHz band at intermediate scales, the noise level at ℓ ∈ [30, 100] is reduced by a factor of 2–3 in the map space. A pixel domain analysis of the polarized synchrotron spectral index ( β s ) using the WMAP K band and the combined maps (mean and 16th/84th percentiles across the β s map: − 3.08 − 0.20 + 0.20 ) reveals a stronger preference for spatial variation (probability to exceed for a uniform β s hypothesis smaller than 0.001) than the results obtained using WMAP K and Ka bands ( − 3.08 − 0.14 + 0.14 ). The cross-power spectra of the combined maps follow the same trend as other low-frequency data, and validation through simulations indicates negligible bias introduced by the combination method (subpercent level in the power spectra). The products of this work are publicly available on LAMBDA ( https://lambda.gsfc.nasa.gov/product/class/class_prod_table.html ).