Limits on Polarized Dust Spectral Index Variations for CMB Foreground Analysis

Abstract Using Planck polarization data, we search for and constrain spatial variations of the polarized dust foreground cosmic microwave background (CMB) observations, specifically in its spectral index, β d . Failure to account such will cause errors cleaning that propagate into on cosmological parameter recovery from cleaned CMB map. It is unclear how robust prior studies data constrained are due challenges with noise modeling, residual systematics, priors. To clarify constraints variation, employ two pixel space analyses at >3.°7 scales ≈60% sky high Galactic latitudes. A template fitting method, which measures over three regions ≈20% sky, does not find significant deviations a uniform = 1.55, consistent determinations. An additional analysis these regions, based multifrequency fits model per pixel, puts limits σ β d , Gaussian variation The support up 0.45 highest latitudes, 0.30 midlatitudes, 0.15 low We also demonstrate care must be taken when interpreting current constraints, maps, simulations. Due systematics signal-to-noise ratios forecasts ongoing future missions should include possibility large values as estimated this paper, data.