115 research outputs found
A Monte Carlo comparison between template-based and Wiener-filter CMB dipole estimators
We review and compare two different CMB dipole estimators discussed in the
literature, and assess their performances through Monte Carlo simulations. The
first method amounts to simple template regression with partial sky data, while
the second method is an optimal Wiener filter (or Gibbs sampling)
implementation. The main difference between the two methods is that the latter
approach takes into account correlations with higher-order CMB temperature
fluctuations that arise from non-orthogonal spherical harmonics on an
incomplete sky, which for recent CMB data sets (such as Planck) is the dominant
source of uncertainty. For an accepted sky fraction of 81% and an angular CMB
power spectrum corresponding to the best-fit Planck 2018 CDM model, we
find that the uncertainty on the recovered dipole amplitude is about six times
smaller for the Wiener filter approach than for the template approach,
corresponding to 0.5 and 3K, respectively. Similar relative differences
are found for the corresponding directional parameters and other sky fractions.
We note that the Wiener filter algorithm is generally applicable to any dipole
estimation problem on an incomplete sky, as long as a statistical and
computationally tractable model is available for the unmasked higher-order
fluctuations. The methodology described in this paper forms the numerical basis
for the most recent determination of the CMB solar dipole from Planck, as
summarized by arXiv:2007.04997.Comment: 8 pages, 10 figures, submitted to A&
Cosmoglobe DR1. III. First full-sky model of polarized synchrotron emission from all WMAP and Planck LFI data
We present the first model of full-sky polarized synchrotron emission that is
derived from all WMAP and Planck LFI frequency maps. The basis of this analysis
is the set of end-to-end reprocessed Cosmoglobe Data Release 1 sky maps
presented in a companion paper, which have significantly lower instrumental
systematics than the legacy products from each experiment. We find that the
resulting polarized synchrotron amplitude map has an average noise rms of
at 30 GHz and FWHM, which is 30% lower than
the recently released BeyondPlanck model that included only LFI+WMAP Ka-V data,
and 29% lower than the WMAP K-band map alone. The mean -to- power
spectrum ratio is , with amplitudes consistent with those measured
previously by Planck and QUIJOTE. Assuming a power law model for the
synchrotron spectral energy distribution, and using the -- plot method,
we find a full-sky inverse noise-variance weighted mean of
between Cosmoglobe DR1 K-band and 30 GHz, in
good agreement with previous estimates. In summary, the novel Cosmoglobe DR1
synchrotron model is both more sensitive and systematically cleaner than
similar previous models, and it has a more complete error description that is
defined by a set of Monte Carlo posterior samples. We believe that these
products are preferable over previous Planck and WMAP products for all
synchrotron-related scientific applications, including simulation, forecasting
and component separation.Comment: 15 pages, 15 figures, submitted to A&
Connective tissue growth factor is activated by gastrin and involved in gastrin-induced migration and invasion
Cosmoglobe DR1 results. I. Improved Wilkinson Microwave Anisotropy Probe maps through Bayesian end-to-end analysis
We present Cosmoglobe Data Release 1, which implements the first joint
analysis of WMAP and Planck LFI time-ordered data, processed within a single
Bayesian end-to-end framework. This framework builds directly on a similar
analysis of the LFI measurements by the BeyondPlanck collaboration, and
approaches the CMB analysis challenge through Gibbs sampling of a global
posterior distribution, simultaneously accounting for calibration, mapmaking,
and component separation. The computational cost of producing one complete
WMAP+LFI Gibbs sample is 812 CPU-hr, of which 603 CPU-hrs are spent on WMAP
low-level processing; this demonstrates that end-to-end Bayesian analysis of
the WMAP data is computationally feasible. We find that our WMAP posterior mean
temperature sky maps and CMB temperature power spectrum are largely consistent
with the official WMAP9 results. Perhaps the most notable difference is that
our CMB dipole amplitude is , which is $11\
\mathrm{\mu K}2.5\ {\sigma}$ higher than
BeyondPlanck; however, it is in perfect agreement with the HFI-dominated Planck
PR4 result. In contrast, our WMAP polarization maps differ more notably from
the WMAP9 results, and in general exhibit significantly lower large-scale
residuals. We attribute this to a better constrained gain and transmission
imbalance model. It is particularly noteworthy that the W-band polarization sky
map, which was excluded from the official WMAP cosmological analysis, for the
first time appears visually consistent with the V-band sky map. Similarly, the
long standing discrepancy between the WMAP K-band and LFI 30 GHz maps is
finally resolved, and the difference between the two maps appears consistent
with instrumental noise at high Galactic latitudes. All maps and the associated
code are made publicly available through the Cosmoglobe web page.Comment: 65 pages, 61 figures. Data available at cosmoglobe.uio.no. Submitted
to A&
BeyondPlanck II. CMB map-making through Gibbs sampling
We present a Gibbs sampling solution to the map-making problem for CMB
measurements, building on existing destriping methodology. Gibbs sampling
breaks the computationally heavy destriping problem into two separate steps;
noise filtering and map binning. Considered as two separate steps, both are
computationally much cheaper than solving the combined problem. This provides a
huge performance benefit as compared to traditional methods, and allows us for
the first time to bring the destriping baseline length to a single sample. We
apply the Gibbs procedure to simulated Planck 30 GHz data. We find that gaps in
the time-ordered data are handled efficiently by filling them with simulated
noise as part of the Gibbs process. The Gibbs procedure yields a chain of map
samples, from which we may compute the posterior mean as a best-estimate map.
The variation in the chain provides information on the correlated residual
noise, without need to construct a full noise covariance matrix. However, if
only a single maximum-likelihood frequency map estimate is required, we find
that traditional conjugate gradient solvers converge much faster than a Gibbs
sampler in terms of total number of iterations. The conceptual advantages of
the Gibbs sampling approach lies in statistically well-defined error
propagation and systematic error correction, and this methodology forms the
conceptual basis for the map-making algorithm employed in the BeyondPlanck
framework, which implements the first end-to-end Bayesian analysis pipeline for
CMB observations.Comment: 11 pages, 10 figures. All BeyondPlanck products and software will be
released publicly at http://beyondplanck.science during the online release
conference (November 18-20, 2020). Connection details will be made available
at the same website. Registration is mandatory for the online tutorial, but
optional for the conferenc
BeyondPlanck VII. Bayesian estimation of gain and absolute calibration for CMB experiments
We present a Bayesian calibration algorithm for CMB observations as
implemented within the global end-to-end BeyondPlanck (BP) framework, and apply
this to the Planck Low Frequency Instrument (LFI) data. Following the most
recent Planck analysis, we decompose the full time-dependent gain into a sum of
three orthogonal components: One absolute calibration term, common to all
detectors; one time-independent term that can vary between detectors; and one
time-dependent component that is allowed to vary between one-hour pointing
periods. Each term is then sampled conditionally on all other parameters in the
global signal model through Gibbs sampling. The absolute calibration is sampled
using only the orbital dipole as a reference source, while the two relative
gain components are sampled using the full sky signal, including the orbital
and Solar CMB dipoles, CMB fluctuations, and foreground contributions. We
discuss various aspects of the data that influence gain estimation, including
the dipole/polarization quadrupole degeneracy and anomalous jumps in the
instrumental gain. Comparing our solution to previous pipelines, we find good
agreement in general, with relative deviations of -0.84% (-0.67%) for 30 GHz,
-0.14% (0.02%) for 44 GHz and -0.69% (-0.08%) for 70 GHz, compared to Planck
2018 (NPIPE). The deviations we find are within expected error bounds, and we
attribute them to differences in data usage and general approach between the
pipelines. In particular, the BP calibration is performed globally, resulting
in better inter-frequency consistency. Additionally, WMAP observations are used
actively in the BP analysis, which breaks degeneracies in the Planck data set
and results in better agreement with WMAP. Although our presentation and
algorithm are currently oriented toward LFI processing, the procedure is fully
generalizable to other experiments.Comment: 18 pages, 15 figures. All BeyondPlanck products and software will be
released publicly at http://beyondplanck.science during the online release
conference (November 18-20, 2020). Connection details will be made available
at the same website. Registration is mandatory for the online tutorial, but
optional for the conferenc
BeyondPlanck X. Planck LFI frequency maps with sample-based error propagation
We present Planck LFI frequency sky maps derived within the BeyondPlanck
framework. This framework draws samples from a global posterior distribution
that includes instrumental, astrophysical and cosmological parameters, and the
main product is an entire ensemble of frequency sky map samples. This ensemble
allows for computationally convenient end-to-end propagation of low-level
instrumental uncertainties into higher-level science products. We show that the
two dominant sources of LFI instrumental systematic uncertainties are
correlated noise and gain fluctuations, and the products presented here support
- for the first time - full Bayesian error propagation for these effects at
full angular resolution. We compare our posterior mean maps with traditional
frequency maps delivered by the Planck collaboration, and find generally good
agreement. The most important quality improvement is due to significantly lower
calibration uncertainties in the new processing, as we find a fractional
absolute calibration uncertainty at 70 GHz of , which is nominally 40 times smaller than that reported by Planck
2018. However, the original Planck 2018 estimate has a non-trivial statistical
interpretation, and this further illustrates the advantage of the new framework
in terms of producing self-consistent and well-defined error estimates of all
involved quantities without the need of ad hoc uncertainty contributions. We
describe how low-resolution data products, including dense pixel-pixel
covariance matrices, may be produced directly from the posterior samples
without the need for computationally expensive analytic calculations or
simulations. We conclude that posterior-based frequency map sampling provides
unique capabilities in terms of low-level systematics modelling and error
propagation, and may play an important role for future CMB B-mode experiments.
(Abridged.)Comment: 32 pages, 23 figures, data available from
https://www.cosmoglobe.uio.no
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