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 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 WMAP Q band and the high-sensitivity information from 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 WMAP K band and the combined maps (mean and 16/84th percentile across the β_s map: -3.08_-0.20^+0.20) reveals a stronger preference for spatial variation (PTE 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 (sub-percent level in the power spectra). The products of this work are publicly available on 𝙻𝙰𝙼𝙱𝙳𝙰.