Constraints on the spectral index of polarized synchrotron emission from WMAP and Faraday-corrected S-PASS data

Abstract

We constrain the spectral index of polarized synchrotron emission, ${\beta }_s$, by correlating the recently released 2.3 GHz S-Band Polarization All Sky Survey (S-PASS) data with the 23 GHz 9-year Wilkinson Microwave Anisotropy Probe (WMAP) sky maps. We subdivide the S-PASS field, which covers the southern ecliptic hemisphere, into 95 $15^{\circ }\times 15^{\circ }$ regions and estimate the spectral index of polarized synchrotron emission within each region using a simple but robust T-T plot technique. Three different versions of the S-PASS data are considered, corresponding to: no correction for Faraday rotation; Faraday correction based on the rotation measure model presented by the S-PASS team; or Faraday correction based on a rotation measure model presented by Hutschenreuter and Enßlin. We find that the correlation between S-PASS and WMAP is strongest when applying the S-PASS model. Adopting this correction model, we find that the mean spectral index of polarized synchrotron emission gradually steepens from ${\beta }_s\approx -2.8$ at low Galactic latitudes to ${\beta }_s\approx -3.3$ at high Galactic latitudes, in good agreement with previously published results. Finally, we consider two special cases defined by the BICEP2 and SPIDER fields and obtain mean estimates of ${\beta }_{BICEP2}=-3.22\pm 0.06$ and ${\beta }_{SPIDER}=-3.21\pm 0.03$, respectively. A comparison with a similar analysis performed in the 23-33 GHz range suggests a flattening of about $\Delta {\beta }_s\sim 0.1\pm 0.2$ from low to higher frequencies, but with no statistical significance due to high uncertainties.

arXiv comment16 pages, 15 figures. Figure number 10 and 15 are new. Published in A&A

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• The Simons Observatory: Galactic Science Goals and Forecasts
• BeyondPlanck I. Global Bayesian analysis of the Planck Low Frequency Instrument data
• Tensor-to-scalar ratio forecasts for extended LiteBIRD frequency configurations
• Characterization of the polarized synchrotron emission from Planck and WMAP data
• QUIJOTE scientific results -- VIII. Diffuse polarized foregrounds from component separation with QUIJOTE-MFI
• The C-Band All-Sky Survey (C-BASS): Template Fitting of Diffuse Galactic Microwave Emission in the Northern Sky
• Polarized Synchrotron Foreground Assessment for CMB Experiments
• Morphological Analysis of the Polarized Synchrotron Emission with WMAP and Planck
• Testing for spectral index variations in polarised CMB foregrounds
• QUIJOTE scientific results -- VI. The Haze as seen by QUIJOTE
• Cosmoglobe DR1. III. First full-sky model of polarized synchrotron emission from all WMAP and Planck LFI data
• Statistical properties of Galactic synchrotron temperature and polarization maps -- a multi-frequency comparison