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Published December 20, 2016 | Published + Submitted
Journal Article Open

BICEP2 / Keck Array VIII: Measurement of gravitational lensing from large-scale B-mode polarization


We present measurements of polarization lensing using the 150 GHz maps, which include all data taken by the BICEP2 and Keck Array Cosmic Microwave Background polarization experiments up to and including the 2014 observing season (BK14). Despite their modest angular resolution (~0º.5), the excellent sensitivity (~3μK-arcmin) of these maps makes it possible to directly reconstruct the lensing potential using only information at larger angular scales (ℓ ⩾ 700). From the auto-spectrum of the reconstructed potential, we measure an amplitude of the spectrum to be A_L^(øø) = 1.15 ± 0.36 (Planck ΛCDM prediction corresponds to A_L^(øø) = 1) and reject the no-lensing hypothesis at 5.8σ, which is the highest significance achieved to date using an EB lensing estimator. Taking the cross-spectrum of the reconstructed potential with the Planck 2015 lensing map yields A_L^(øø) = 1.13 ± 0.20. These direct measurements of A_L^(øø) are consistent with the ΛCDM cosmology and with that derived from the previously reported BK14 B-mode auto-spectrum (A_L^(BB) = 1.20 ± 0.17). We perform a series of null tests and consistency checks to show that these results are robust against systematics and are insensitive to analysis choices. These results unambiguously demonstrate that the B modes previously reported by BICEP/Keck at intermediate angular scales (150 ≾ ℓ ≾ 350) are dominated by gravitational lensing. The good agreement between the lensing amplitudes obtained from the lensing reconstruction and B-mode spectrum starts to place constraints on any alternative cosmological sources of B modes at these angular scales.

Additional Information

© 2016 American Astronomical Society. Received 2016 June 3. Accepted 2016 August 22. Published 2016 December 19. The Keck Array project has been made possible through support from the National Science Foundation under Grants ANT-1145172 (Harvard), ANT-1145143 (Minnesota), and ANT-1145248 (Stanford), and from the Keck Foundation (Caltech). The development of antenna-coupled detector technology was supported by the JPL Research and Technology Development Fund and grant Nos. 06-ARPA206-0040 and 10-SAT10-0017 from the NASA APRA and SAT programs. The development and testing of focal planes were supported by the Gordon and Betty Moore Foundation at Caltech. Readout electronics were supported by a Canada Foundation for Innovation grant to UBC. The computations in this paper were run on the Odyssey cluster supported by the FAS Science Division Research Computing Group at Harvard University. The analysis effort at Stanford and SLAC is partially supported by the U.S. Department of Energy Office of Science. We thank the staff of the U.S. Antarctic Program and in particular the South Pole Station without whose help this research would not have been possible. Special thanks go to our heroic winter-overs Robert Schwarz and Steffen Richter. We thank all those who have contributed past efforts to the BICEP-Keck Array series of experiments, including the BICEP1 team. T.N. acknowledges support from Japan Society for the Promotion of Science Postdoctoral Fellowships for Research Abroad.

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Submitted - 1606.01968v2.pdf

Published - Ade_2016_ApJ_833_228.pdf


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August 22, 2023
August 22, 2023