128 research outputs found
Hunting B modes in CMB polarization observations
In Chapter 1, I will introduce the current cosmological model and review the theoretical aspects of the CMB anisotropies and the present status of the observations. In Chapter 2, I will focus on the diffuse emissions of our Galaxy in the microwaves, expected to be a serious contamination for the CMB studies. The separation of these diffuse components and the CMB cleaning will be the main topic of Chapter 3, where I will describe a few algorithms I\u2019ve worked on during my Phd . Finally, in Chapter 4, I will present a couple of applications of these methods aimed at B mode recovery
WMAP 3yr data with the CCA: anomalous emission and impact of component separation on the CMB power spectrum
The Correlated Component Analysis (CCA) allows us to estimate how the
different diffuse emissions mix in CMB experiments, exploiting also
complementary information from other surveys. It is especially useful to deal
with possible additional components. An application of CCA to WMAP maps
assuming that only the canonical Galactic emissions are present, highlights the
widespread presence of a spectrally flat "synchrotron" component, largely
uncorrelated with the synchrotron template, suggesting that an additional
foreground is indeed required. We have tested various spectral shapes for such
component, namely a power law as expected if it is flat synchrotron, and two
spectral shapes that may fit the spinning dust emission: a parabola in the logS
- log(frequency) plane, and a grey body. Quality tests applied to the
reconstructed CMB maps clearly disfavour two of the models. The CMB power
spectra, estimated from CMB maps reconstructed exploiting the three surviving
foreground models, are generally consistent with the WMAP ones, although at
least one of them gives a significantly higher quadrupole moment than found by
the WMAP team. Taking foreground modeling uncertainties into account, we find
that the mean quadrupole amplitude for the three "good" models is less than 1
sigma below the expectation from the standard LambdaCDM model. Also the other
reported deviations from model predictions are found not to be statistically
significant, except for the excess power at l~40. We confirm the evidence for a
marked North-South asymmetry in the large scale (l < 20) CMB anisotropies. We
also present a first, albeit preliminary, all-sky map of the "anomalous"
component.Comment: 14 pages, 17 figures, submitted to MNRAS, references adde
CMB signal in WMAP 3yr data with FastICA
We present an application of the fast Independent Component Analysis
(FastICA) to the WMAP 3yr data with the goal of extracting the CMB signal. We
evaluate the confidence of our results by means of Monte Carlo simulations
including CMB, foreground contaminations and instrumental noise specific of
each WMAP frequency band. We perform a complete analysis involving all or a
subset of the WMAP channels in order to select the optimal combination for CMB
extraction, using the frequency scaling of the reconstructed component as a
figure of merit. We found that the combination KQVW provides the best CMB
frequency scaling, indicating that the low frequency foreground contamination
in Q, V and W bands is better traced by the emission in the K band. The CMB
angular power spectrum is recovered up to the degree scale, it is consistent
within errors for all WMAP channel combination considered, and in close
agreement with the WMAP 3yr results. We perform a statistical analysis of the
recovered CMB pattern, and confirm the sky asymmetry reported in several
previous works with independent techniques.Comment: 10 pages, 7 figures, submitted to MNRA
Forecast B-modes detection at large scales in presence of noise and foregrounds
We investigate the detectability of the primordial CMB polarization B-mode
power spectrum on large scales in the presence of instrumental noise and
realistic foreground contamination. We have worked out a method to estimate the
errors on component separation and to propagate them up to the power spectrum
estimation. The performances of our method are illustrated by applying it to
the instrumental specifications of the Planck satellite and to the proposed
configuration for the next generation CMB polarization experiment COrE. We
demonstrate that a proper component separation step is required in order
achieve the detection of B-modes on large scales and that the final sensitivity
to B-modes of a given experiment is determined by a delicate balance between
noise level and residual foregrounds, which depend on the set of frequencies
exploited in the CMB reconstruction, on the signal-to-noise of each frequency
map, and on our ability to correctly model the spectral behavior of the
foreground components. We have produced a flexible software tool that allows
the comparison of performances on B-mode detection of different instrumental
specifications (choice of frequencies, noise level at each frequency, etc.) as
well as of different proposed approaches to component separation.Comment: 7 pages, 2 tables, 1 figure, accepted by MNRA
Component Separation in Polarization with FastICA
FastICA is a blind technique aimed to separate different components in CMB experiments, with a very few assumptions on the signals to recover. Since current knowledge about foregrounds in polarization are very poor, this kind of technique can pla y a crucial role in forecoming CMB experiments. Recent and ongoing developments of the method are presented her
Maximum likelihood, parametric component separation and CMB B-mode detection in suborbital experiments
We investigate the performance of the parametric Maximum Likelihood component
separation method in the context of the CMB B-mode signal detection and its
characterization by small-scale CMB suborbital experiments. We consider
high-resolution (FWHM=8') balloon-borne and ground-based observatories mapping
low dust-contrast sky areas of 400 and 1000 square degrees, in three frequency
channels, 150, 250, 410 GHz, and 90, 150, 220 GHz, with sensitivity of order 1
to 10 micro-K per beam-size pixel. These are chosen to be representative of
some of the proposed, next-generation, bolometric experiments. We study the
residual foreground contributions left in the recovered CMB maps in the pixel
and harmonic domain and discuss their impact on a determination of the
tensor-to-scalar ratio, r. In particular, we find that the residuals derived
from the simulated data of the considered balloon-borne observatories are
sufficiently low not to be relevant for the B-mode science. However, the
ground-based observatories are in need of some external information to permit
satisfactory cleaning. We find that if such information is indeed available in
the latter case, both the ground-based and balloon-borne experiments can detect
the values of r as low as ~0.04 at 95% confidence level. The contribution of
the foreground residuals to these limits is found to be then subdominant and
these are driven by the statistical uncertainty due to CMB, including E-to-B
leakage, and noise. We emphasize that reaching such levels will require a
sufficient control of the level of systematic effects present in the data.Comment: 18 pages, 12 figures, 6 table
A Statistical Analysis of the "Internal Linear Combination" Method in Problems of Signal Separation as in CMB Observations
AIMS: The separation of foreground contamination from cosmic microwave
background (CMB) observations is one of the most challenging and important
problem of digital signal processing in Cosmology. In literature, various
techniques have been presented, but no general consensus about their real
performances and properties has been reached. This is due to the
characteristics of these techniques that have been studied essentially through
numerical simulations based on semi-empirical models of the CMB and the
Galactic foregrounds. Such models often have different level of sophistication
and/or are based on different physical assumptions (e.g., the number of the
Galactic components and the level of the noise). Hence, a reliable comparison
is difficult. What actually is missing is a statistical analysis of the
properties of the proposed methodologies. Here, we consider the "Internal
Linear Combination" method (ILC) which, among the separation techniques,
requires the smallest number of "a priori" assumptions. This feature is of
particular interest in the context of the CMB polarization measurements at
small angular scales where the lack of knowledge of the polarized backgrounds
represents a serious limit. METHODS: The statistical characteristics of ILC are
examined through an analytical approach and the basic conditions are fixed in a
way to work satisfactorily. RESULTS: ILC provides satisfactory results only
under rather restrictive conditions. This is a critical fact to take into
consideration in planning the future ground-based observations (e.g., with
ALMA) where, contrary to the satellite experiments, there is the possibility to
have a certain control of the experimental conditions.Comment: A version of this manuscript without figures has been accepted for
publication by A&A. A & A 2008, accepte
Multi-resolution internal template cleaning: An application to the Wilkinson Microwave Anisotropy Probe 7-yr polarization data
Cosmic microwave background (CMB) radiation data obtained by different
experiments contain, besides the desired signal, a superposition of microwave
sky contributions. We present a fast and robust method, using a wavelet
decomposition on the sphere, to recover the CMB signal from microwave maps. An
application to \textit{WMAP} polarization data is presented, showing its good
performance particularly in very polluted regions of the sky. The applied
wavelet has the advantages of requiring little computational time in its
calculations, being adapted to the \textit{HEALPix} pixelization scheme, and
offering the possibility of multi-resolution analysis. The decomposition is
implemented as part of a fully internal template fitting method, minimizing the
variance of the resulting map at each scale. Using a characterization
of the noise, we find that the residuals of the cleaned maps are compatible
with those expected from the instrumental noise. The maps are also comparable
to those obtained from the \textit{WMAP} team, but in our case we do not make
use of external data sets. In addition, at low resolution, our cleaned maps
present a lower level of noise. The E-mode power spectrum is
computed at high and low resolution; and a cross power spectrum
is also calculated from the foreground reduced maps of temperature given by
\textit{WMAP} and our cleaned maps of polarization at high resolution. These
spectra are consistent with the power spectra supplied by the \textit{WMAP}
team. We detect the E-mode acoustic peak at , as predicted by
the standard model. The B-mode power spectrum is
compatible with zero.Comment: 8 pages, 6 figures. Some changes have been done from the original
manuscript. This paper is accepted by MNRA
Separating polarized cosmological and galactic emissions for CMB B-mode polarization experiments
In this work we study the relevance of the component separation technique
based on the Independent Component Analysis (ICA) and investigate its
performance in the context of a limited sky coverage observation and from the
viewpoint of our ability to differentiate between cosmological models with
different primordial B-mode content. We focus on the low Galactic emission sky
patch, corresponding to the target of several operating and planned CMB
experiments and which, in many respects, adequately represents a typical
"clean" high latitude sky. We consider two fiducial observations, one operating
at low (40, 90 GHz) and one at high (150, 350 GHz) frequencies and thus
dominated by the synchrotron and thermal dust emission, respectively. We use a
parallel version of the FASTICA code to explore a substantial parameter space
including Gaussian pixel noise level, observed sky area and the amplitude of
the foreground emission and employ large Monte Carlo simulations to quantify
errors and biases pertinent to the reconstruction for different choices of the
parameter values. We identify a large subspace of the parameter space for which
the quality of the CMB reconstruction is excellent. For both the cosmological
models, with and without the primordial gravitational waves, we find that
FASTICA performs extremely well even in the cases when the B mode CMB signal is
up to a few times weaker than the foreground contamination and the noise
amplitude is comparable with the total CMB polarized emission. In addition we
discuss limiting cases of the noise and foreground amplitudes, for which the
ICA approach fails.Comment: 19 pages, 12 figures, 5 tables, replaced to match published versio
Blind component separation for polarized observations of the CMB
We present in this paper the PolEMICA (Polarized Expectation-Maximization
Independent Component Analysis) algorithm which is an extension to polarization
of the SMICA (Spectral Matching Independent Component Analysis) temperature
multi-detectors multi-components (MD-MC) component separation method
(Delabrouille et al. 2003). This algorithm allows us to estimate blindly in
harmonic space multiple physical components from multi-detectors polarized sky
maps. Assuming a linear noisy mixture of components we are able to reconstruct
jointly the anisotropies electromagnetic spectra of the components for each
mode T, E and B, as well as the temperature and polarization spatial power
spectra, TT, EE, BB, TE, TB and EB for each of the physical components and for
the noise on each of the detectors. PolEMICA is specially developed to estimate
the CMB temperature and polarization power spectra from sky observations
including both CMB and foreground emissions. This has been tested intensively
using as a first approach full sky simulations of the Planck satellite
polarized channels for a 14-months nominal mission assuming a simplified linear
sky model including CMB, and optionally Galactic synchrotron emission and a
Gaussian dust emission. Finally, we have applied our algorithm to more
realistic Planck full sky simulations, including synchrotron, realistic dust
and free-free emissions.Comment: 20 pages, 21 figures, 1 table, TeX file, accepted for publication in
MNRA
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