We present a demonstration of delensing the observed cosmic microwave background (CMB) B-mode polarization anisotropy. This process of reducing the gravitational-lensing-generated B-mode component will become increasingly important for improving searches for the B modes produced by primordial gravitational waves. In this work, we delens B-mode maps constructed from multi-frequency SPTpol observations of a 90 deg2 patch of sky by subtracting a B-mode template constructed from two inputs: SPTpol E-mode maps and a lensing potential map estimated from the Herschel 500 μm map of the cosmic infrared background. We find that our delensing procedure reduces the measured B-mode power spectrum by % in the multipole range 300 < ℓ < 2300; this is shown to be consistent with expectations from simulations and to be robust against systematics. The null hypothesis of no delensing is rejected at 6.9σ. Furthermore, we build and use a suite of realistic simulations to study the general properties of the delensing process and find that the delensing efficiency achieved in this work is limited primarily by the noise in the lensing potential map. We demonstrate the importance of including realistic experimental non-idealities in the delensing forecasts used to inform instrument and survey-strategy planning of upcoming lower-noise experiments, such as CMB-S4.
Bibliographical noteFunding Information:
The South Pole Telescope program is supported by the National Science Foundation through grant PLR-1248097. Partial support is also provided by the NSF Physics Frontier Center grant PHY-0114422 to the Kavli Institute of Cosmological Physics at the University of Chicago, the Kavli Foundation, and the Gordon and Betty Moore Foundation through Grant GBMF#947 to the University of Chicago. Work at Argonne National Lab is supported by UChicago Argonne, LLC, Operator of Argonne National Laboratory (Argonne). Argonne, a U.S. Department of Energy Office of Science Laboratory, is operated under Contract No. DE-AC02-06CH11357. We also acknowledge support from the Argonne Center for Nanoscale Materials. The McGill authors acknowledge funding from the Natural Sciences and Engineering Research Council of Canada, Canadian Institute for Advanced Research, and Canada Research Chairs program. This work is also supported by the U.S. Department of Energy. The CU Boulder group acknowledges support from NSF AST-0956135. BB is supported by the Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the U.S. Department of Energy. C.R. acknowledges support from a Australian Research Councils Future Fellowship (FT150100074). W.L.K.W. is grateful for support from the Croucher Foundation and hospitality of Stanford University. J.W.H. is supported by the National Science Foundation under Award No. AST-1402161. The data analysis pipeline uses the scientific python stack (Jones et al. 2001; Hunter 2007; van der Walt et al. 2011) and the HDF5 file format (The HDF Group 1997). The authors acknowledge useful discussions with Blake Sherwin and Toshiya Namikawa and use of code first written by Duncan Hanson.
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- cosmic background radiation
- cosmology: observations
- early universe