Polarized Synchrotron Foreground Assessment for CMB Experiments

Polarized Galactic synchrotron emission is an undesirable foreground for cosmic microwave background (CMB) experiments observing at frequencies $< 150$ GHz. We perform a combined analysis of observational data 1.4, 2.3, 23, 30 and 33 GHz to quantify the spatial variation polarized spectral index, $\beta^{pol}$, on $\sim3.5^\circ$ scales. compare results from different combinations address limitations inconsistencies present in these public data, form composite map $\beta^{pol}$. Data quality masking leaves 44% sky coverage (73% $|b|> 45^\circ$). Generally $-3.2 < \beta^{pol} \lesssim -3$ inner plane spurs, but Fan Region outer Galaxy has flatter index. find clear index steepening with increasing latitude south $\Delta \beta^{pol}=0.4$, smaller $0.25$ north. Near pole $\beta^{pol} \approx -3.4$. Longitudinal variations \sim 0.1$ about latitudinal mean are also detected. Within BICEP2/Keck survey footprint, we consistency constant value, = -3.25 \pm 0.04$ (statistical) $\pm 0.02$ (systematic). compute frequency which thermal dust contribute equally total foreground. The among datasets encountered this work make value additional independent surveys multiple frequencies, especially between $10-20$ GHz, provided have sufficient sensitivity control instrumental systematic errors.