F. Stivoli

Component separation methods for the PLANCK mission

Context. The PLANCK satellite will map the full sky at nine frequencies from 30 to 857 GHz. The CMB intensity and polarization that are its prime targets are contaminated by foreground emission. n nAims. The goal of this paper is to compare proposed methods for separating CMB from foregrounds based on their different spectral and spatial characteristics, and to separate the foregrounds into “components” with different physical origins (Galactic synchrotron, free-free and dust emissions; extra-galactic and far-IR point sources; Sunyaev-Zeldovich effect, etc.) n nMethods. A component separation challenge has been organised, based on a set of realistically complex simulations of sky emission. Several methods including those based on internal template subtraction, maximum entropy method, parametric method, spatial and harmonic cross correlation methods, and independent component analysis have been tested. n nResults. Different methods proved to be effective in cleaning the CMB maps of foreground contamination, in reconstructing maps of diffuse Galactic emissions, and in detecting point sources and thermal Sunyaev-Zeldovich signals. The power spectrum of the residuals is, on the largest scales, four orders of magnitude lower than the input Galaxy power spectrum at the foreground minimum. The CMB power spectrum was accurately recovered up to the sixth acoustic peak. The point source detection limit reaches 100 mJy, and about 2300 clusters are detected via the thermal SZ effect on two thirds of the sky. We have found that no single method performs best for all scientific objectives. n nConclusions. We foresee that the final component separation pipeline for PLANCK will involve a combination of methods and iterations between processing steps targeted at different objectives such as diffuse component separation, spectral estimation, and compact source extraction.

EBEX: A balloon-borne CMB polarization experiment

EBEX is a NASA-funded balloon-borne experiment designed to measure the polarization of the cosmic microwave background (CMB). Observations will be made using 1432 transition edge sensor (TES) bolometric detectors read out with frequency multiplexed SQuIDs. EBEX will observe in three frequency bands centered at 150, 250, and 410 GHz, with 768, 384, and 280 detectors in each band, respectively. This broad frequency coverage is designed to provide valuable information about polarized foreground signals from dust. The polarized sky signals will be modulated with an achromatic half wave plate (AHWP) rotating on a superconducting magnetic bearing (SMB) and analyzed with a fixed wire grid polarizer. EBEX will observe a patch covering ~1% of the sky with 8 resolution, allowing for observation of the angular power spectrum from l = 20 to 1000. This will allow EBEX to search for both the primordial B-mode signal predicted by inflation and the anticipated lensing B-mode signal. Calculations to predict EBEX constraints on r using expected noise levels show that, for a likelihood centered around zero and with negligible foregrounds, 99% of the area falls below r = 0.035. This value increases by a factor of 1.6 after a process of foreground subtraction. This estimate does not include systematic uncertainties. An engineering flight was launched in June, 2009, from Ft. Sumner, NM, and the long duration science flight in Antarctica is planned for 2011. These proceedings describe the EBEX instrument and the North American engineering flight.

WMAP 3‐yr data with Correlated Component Analysis: anomalous emission and impact of component separation on the CMB power spectrum

Correlated Component Analysis (CCA) allows us to estimate how the different diffuse emissions mix in observations by cosmic microwave background (CMB) experiments, also taking into account complementary information from other surveys. It is especially useful for dealing with possible additional components for which little or no prior information exists. An application of CCA to the Wilkinson Microwave Anisotropy Probe (WMAP) maps assuming that only the canonical Galactic emissions (synchrotron, free–free and thermal dust) 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 a component, namely a power law as is expected if it is flat synchrotron, and two spectral shapes that may fit the spinning dust emission: a parabola in the logxa0S− logxa0ν plane and a grey body. If the spatial distribution of the additional (‘anomalous’) component is not constrained a priori, it is found to be always tightly correlated with thermal dust, but the correlation is not perfect. 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 those obtained by the WMAP team, although at least one of the models gives a significantly higher quadrupole moment than found by WMAP. Taking foreground modelling uncertainties into account, we find that the mean quadrupole amplitude for the three ‘good’ models is less than 1σ below the expectation from the standard Λcold dark matter (ΛCDM) 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, which is stable with respect to the foreground parametrization we adopted. We also present a first, albeit preliminary, all-sky template of the ‘anomalous emission’.

Maximum likelihood algorithm for parametric component separation in cosmic microwave background experiments

We discuss an approach to the component separation of microwave, multifrequency sky maps as those typically produced from cosmic microwave background (CMB) anisotropy data sets. The algorithm is based on the two-step, parametric, likelihood-based technique recently elaborated on by Eriksen et al., where the foreground spectral parameters are estimated prior to the actual separation of the components. In contrast with the previous approaches, we accomplish the former task with help of an analytically derived likelihood function for the spectral parameters, which, we show, yields estimates equal to the maximum likelihood values of the full multidimensional data problem. We then use these estimates to perform the second step via the standard, generalized-least-squares-like procedure. We demonstrate that the proposed approach is equivalent to a direct maximization of the full data likelihood, which is recast in a computationally tractable form. We use the corresponding curvature matrices to characterize statistical properties of the recovered parameters. We incorporate in the formalism some of the essential features of the CMB data sets, such as inhomogeneous pixel domain noise, unknown map offsets as well as calibration errors and study their consequences for the separation. We find that the calibration is likely to have a dominant effect on the precision of the spectral parameter determination for a realistic CMB experiment. We apply the algorithm to simulated data and discuss the results. Our focus is on partial sky, total intensity and polarization, CMB experiments such as planned balloon-borne and ground-based efforts, however, the techniques presented here should be also applicable to the full-sky data as for instance, those produced by the Wilkinson Microwave Anisotropy Probe (WMAP) satellite and anticipated from the Planck mission.

Cosmic microwave background signal in Wilkinson Microwave Anisotropy Probe three-year 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.

Separating polarized cosmological and galactic emissions for cosmic microwave background B-mode polarization experiments

The detection and characterization of the B mode of Cosmic Microwave Background (CMB) polarization anisotropies will not be possible without a high precision removal of the foreground contamination present in the microwave band. In this work we study the relevance of the component separation technique based on the Independent Component Analysis (ICA) for this purpose 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 centered at 40 degrees in right ascension and -45 in declination, 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 foreground templates simulated in accordance with the existing observations in the radio and infrared bands, as well as the Wilkinson Microwave Anisotropy Probe (WMAP) and Archeops data and model the CMB emission adopting the current best fit cosmological model, with an amplitude of primordial gravitational waves either set to zero or 10%. 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, i.e., where the errors and biases introduced by the separation are found to be comparable or lower than the uncertainty due to the cosmic variance and instrumental noise. 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. Although our conclusions are limited by the absence of systematics in the simulated data, these results indicate that these component separation techniques could play a

EBEX: the E and B Experiment

The E and B Experiment, EBEX, is a Cosmic Microwave Background polarization experiment designed to detect or set upper limits on the signature of primordial gravity waves. Primordial gravity waves are predicted to be produced by inflation, and a measurement of the power spectrum of these gravity waves is a measurement of the energy scale of inflation. EBEX has sufficient sensitivity to detect or set an upper limit at 95% confidence on the energy scale of inflation of < 1.4 × 1016 GeV. This article reviews our strategy for achieving our science goals and discusses the implementation of the instrument.

Framework for performance forecasting and optimization of CMB B -mode observations in the presence of astrophysical foregrounds

We present a formalism for performance forecasting and optimization of future cosmic microwave background (CMB) experiments. We implement it in the context of nearly full sky, multifrequency, B-mode polarization observations, incorporating statistical uncertainties due to the CMB sky statistics, instrumental noise, as well as the presence of the foreground signals. We model the effects of a subtraction of these using a parametric maximum likelihood technique and optimize the instrumental configuration with predefined or arbitrary observational frequency channels, constraining either a total number of detectors or a focal plane area. We showcase the proposed formalism by applying it to two cases of experimental setups based on the CMBpol and COrE mission concepts looked at as dedicated B-mode experiments. We find that, if the models of the foregrounds available at the time of the optimization are sufficiently precise, the procedure can help to either improve the potential scientific outcome of the experiment by a factor of a few, while allowing one to avoid excessive hardware complexity, or simplify the instrument design without compromising its science goals. However, our analysis also shows that even if the available foreground models are not considered to be sufficiently reliable, the proposed procedure can guide a design of more robust experimental setups. While better suited to cope with a plausible, greater complexity of the foregrounds than that foreseen by the models, these setups could ensure science results close to the best achievable, should the models be found to be correct.

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 here