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Published March 1, 2023 | Published
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BICEP/Keck. XVI. Characterizing Dust Polarization through Correlations with Neutral Hydrogen


We characterize Galactic dust filaments by correlating BICEP/Keck and Planck data with polarization templates based on neutral hydrogen (H 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, H i 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 H i emission into distinct velocity components and detect dust polarization correlated with the local Galactic H i but not with the H i associated with Magellanic Stream i. We present a robust, multifrequency detection of polarized dust emission correlated with the filamentary H i morphology template down to 95 GHz. For assessing its utility for foreground cleaning, we report that the Hi morphology template correlates in B 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 be β = 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 H i. Finally, we explore the morphological parameter space in the H i-based filamentary model.

Additional Information

© 2023. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. We thank the anonymous referee for a thoughtful review. This work was supported by the National Science Foundation under grant No. AST-2106607. The BICEP/Keck projects have been made possible through a series of grants from the National Science Foundation including 0742818, 0742592, 1044978, 1110087, 1145172, 1145143, 1145248, 1639040, 1638957, 1638978, and 1638970, and by the Keck Foundation. We thank the staff of the U.S. Antarctic Program and in particular the South Pole Station and the heroic winter-overs without whose help this research would not have been possible. We also thank all those who have contributed past efforts to the BICEP/Keck series of experiments. This publication utilizes data from Planck, an ESA science mission funded by ESA Member States, NASA, and Canada. This work makes use of data from the H i4PI Survey, which is constructed from the Effelsberg–Bonn H i Survey (EBHIS), made with the 100 m radio telescope of the MPIfR at Effelsberg/Germany, and the Galactic All-Sky Survey (GASS), observed with the Parkes Radio Telescope, part of the Australia Telescope National Facility, which is funded by the Australian Government for operation as a National Facility managed by CSIRO. EBHIS was funded by the Deutsche Forschungsgemein-schaft (DFG) under the grants KE757/7-1 to 7–3. The computations in this paper were run on the Sherlock cluster, supported by the Stanford Research Computing Center at Stanford University, and on the Odyssey/Cannon cluster, supported by the FAS Science Division Research Computing Group at Harvard University. Software: astropy (Astropy Collaboration et al. 2013, 2018), Healpix 22 (Górski et al. 2005), healpy (Zonca et al. 2019), matplotlib (Hunter 2007), numpy (Oliphant 2015), cobaya (Torrado & Lewis 2019, 2021), GetDist (Lewis 2019).

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August 22, 2023
August 22, 2023