Delensing the CMB with the cosmic infrared background: the impact of foregrounds
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Journal Title
Monthly Notices of the Royal Astronomical Society
ISSN
0035-8711
Publisher
Royal Astronomical Society
Type
Article
This Version
AM
Metadata
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Lizancos, A. B., Challinor, A., Sherwin, B. D., & Namikawa, T. Delensing the CMB with the cosmic infrared background: the impact of
foregrounds. Monthly Notices of the Royal Astronomical Society https://doi.org/10.17863/CAM.85676
Abstract
The most promising avenue for detecting primordial gravitational waves from
cosmic inflation is through measurements of degree-scale CMB $B$-mode
polarisation. This approach must face the challenge posed by gravitational
lensing of the CMB, which obscures the signal of interest. Fortunately, the
lensing effects can be partially removed by combining high-resolution $E$-mode
measurements with an estimate of the projected matter distribution. For
near-future experiments, the best estimate of the latter will arise from
co-adding internal reconstructions (derived from the CMB itself) with external
tracers such as the cosmic infrared background (CIB). In this work, we
characterise how foregrounds impact the delensing procedure when CIB intensity,
$I$, is used as the matter tracer. We find that higher-point functions of the
CIB and Galactic dust such as $\langle BEI \rangle_{c}$ and $\langle EIEI
\rangle_{c}$ can, in principle, bias the power spectrum of delensed $B$-modes.
To quantify these, we first estimate the dust residuals in currently-available
CIB maps and upcoming, foreground-cleaned Simons Observatory CMB data. Then,
using non-Gaussian simulations of Galactic dust -- extrapolated to the relevant
frequencies, assuming the spectral index of polarised dust emission to be fixed
at the value determined by Planck -- we show that the bias to any primordial
signal is small compared to statistical errors for ground-based experiments,
but might be significant for space-based experiments probing very large angular
scales. However, mitigation techniques based on multi-frequency cleaning appear
to be very effective. We also show, by means of an analytic model, that the
bias arising from the higher-point functions of the CIB itself ought to be
negligible.
Keywords
astro-ph.CO, astro-ph.CO
Sponsorship
Science and Technology Facilities Council (ST/S000623/1)
Embargo Lift Date
2025-06-21
Identifiers
This record's DOI: https://doi.org/10.17863/CAM.85676
This record's URL: https://www.repository.cam.ac.uk/handle/1810/338268
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