3,274 research outputs found
Bias to CMB Lensing Reconstruction from Temperature Anisotropies due to Large-Scale Galaxy Motions
Gravitational lensing of the cosmic microwave background (CMB) is expected to
be amongst the most powerful cosmological tools for ongoing and upcoming CMB
experiments. In this work, we investigate a bias to CMB lensing reconstruction
from temperature anisotropies due to the kinematic Sunyaev-Zel'dovich (kSZ)
effect, that is, the Doppler shift of CMB photons induced by Compton-scattering
off moving electrons. The kSZ signal yields biases due to both its own
intrinsic non-Gaussianity and its non-zero cross-correlation with the CMB
lensing field (and other fields that trace the large-scale structure). This
kSZ-induced bias affects both the CMB lensing auto-power spectrum and its
cross-correlation with low-redshift tracers. Furthermore, it cannot be removed
by multifrequency foreground separation techniques because the kSZ effect
preserves the blackbody spectrum of the CMB. While statistically negligible for
current datasets, we show that it will be important for upcoming surveys, and
failure to account for it can lead to large biases in constraints on neutrino
masses or the properties of dark energy. For a Stage 4 CMB experiment, the bias
can be as large as 15% or 12% in cross-correlation with LSST galaxy
lensing convergence or galaxy overdensity maps, respectively, when the maximum
temperature multipole used in the reconstruction is ,
and about half of that when . Similarly, we find that
the CMB lensing auto-power spectrum can be biased by up to several percent.
These biases are many times larger than the expected statistical errors.
Reducing can significantly mitigate the bias at the cost of a
decrease in the overall lensing reconstruction signal-to-noise.
Polarization-only reconstruction may be the most robust mitigation strategy.Comment: Updated to match published version and fixed typo. Improved study of
secondary contractions and end-to-end simulation
Rethinking CMB foregrounds: systematic extension of foreground parameterizations
Future high-sensitivity measurements of the cosmic microwave background (CMB)
anisotropies and energy spectrum will be limited by our understanding and
modeling of foregrounds. Not only does more information need to be gathered and
combined, but also novel approaches for the modeling of foregrounds,
commensurate with the vast improvements in sensitivity, have to be explored.
Here, we study the inevitable effects of spatial averaging on the spectral
shapes of typical foreground components, introducing a moment approach, which
naturally extends the list of foreground parameters that have to be determined
through measurements or constrained by theoretical models. Foregrounds are
thought of as a superposition of individual emitting volume elements along the
line of sight and across the sky, which then are observed through an
instrumental beam. The beam and line of sight averages are inevitable. Instead
of assuming a specific model for the distributions of physical parameters, our
method identifies natural new spectral shapes for each foreground component
that can be used to extract parameter moments (e.g., mean, dispersion,
cross-terms, etc.). The method is illustrated for the superposition of
power-laws, free-free spectra, gray-body and modified blackbody spectra, but
can be applied to more complicated fundamental spectral energy distributions.
Here, we focus on intensity signals but the method can be extended to the case
of polarized emission. The averaging process automatically produces
scale-dependent spectral shapes and the moment method can be used to propagate
the required information across scales in power spectrum estimates. The
approach is not limited to applications to CMB foregrounds but could also be
useful for the modeling of X-ray emission in clusters of galaxies.Comment: 19 pages, 8 figures, accepted by MNRAS, minor revision
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