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

Abstract

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).