We characterize Galactic dust filaments by correlating BICEP/Keck and Planck data with polarization templates based on neutral hydrogen (H
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Abstract i ) observations. Dust polarization is important for both our understanding of astrophysical processes in the interstellar medium (ISM) and the search for primordial gravitational waves in the cosmic microwave background (CMB). In the diffuse ISM, Hi is strongly correlated with the dust and partly organized into filaments that are aligned with the local magnetic field. We analyze the deep BICEP/Keck data at 95, 150, and 220 GHz, over the low-column-density region of sky where BICEP/Keck has set the best limits on primordial gravitational waves. We separate the Hi emission into distinct velocity components and detect dust polarization correlated with the local Galactic Hi but not with the Hi associated with Magellanic Streami . We present a robust, multifrequency detection of polarized dust emission correlated with the filamentary Hi morphology template down to 95 GHz. For assessing its utility for foreground cleaning, we report that the Hi morphology template correlates inB modes at a ∼10%–65% level over the multipole range 20 <ℓ < 200 with the BICEP/Keck maps, which contain contributions from dust, CMB, and noise components. We measure the spectral index of the filamentary dust component spectral energy distribution to beβ = 1.54 ± 0.13. We find no evidence for decorrelation in this region between the filaments and the rest of the dust field or from the inclusion of dust associated with the intermediate velocity Hi . Finally, we explore the morphological parameter space in the Hi -based filamentary model. -
Abstract We report on the design and performance of the B
icep3 instrument and its first three-year data set collected from 2016 to 2018. Bicep3 is a 52 cm aperture refracting telescope designed to observe the polarization of the cosmic microwave background (CMB) on degree angular scales at 95 GHz. It started science observation at the South Pole in 2016 with 2400 antenna-coupled transition-edge sensor bolometers. The receiver first demonstrated new technologies such as large-diameter alumina optics, Zotefoam infrared filters, and flux-activated SQUIDs, allowing ∼10× higher optical throughput compared to theKeck design. Bicep3 achieved instrument noise equivalent temperatures of 9.2, 6.8, and 7.1 and reached StokesQ andU map depths of 5.9, 4.4, and 4.4μ K arcmin in 2016, 2017, and 2018, respectively. The combined three-year data set achieved a polarization map depth of 2.8μ K arcmin over an effective area of 585 square degrees, which is the deepest CMB polarization map made to date at 95 GHz.