New insights into foreground analysis of the WMAP five-year data using FASTICA (original) (raw)
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Foreground analysis of the WMAP three-year data with FASTICA
2008
We present an analysis of the foreground emission present in the WMAP 3-year data as determined by the method of Independent Component Analysis. We derived coupling coefficients between the WMAP data and foreground templates which are then used to infer the spectral behaviour for three foreground components -- synchrotron, anomalous dust-correlated emission and free-free. For the first two components, we
Model independent foreground power spectrum estimation using WMAP 5-year data
Physical Review D, 2009
In this paper, we propose & implement on WMAP 5-year data, a model independent approach of foreground power spectrum estimation for multifrequency observations of CMB experiments. Recently a model independent approach of CMB power spectrum estimation was proposed by . This methodology demonstrates that CMB power spectrum can be reliably estimated solely from WMAP data without assuming any template models for the foreground components. In the current paper, we extend this work to estimate the galactic foreground power spectrum using the WMAP 5 year maps following a self contained analysis. We apply the model independent method in harmonic basis to estimate the foreground power spectrum and frequency dependence of combined foregrounds. We also study the behaviour of synchrotron spectral index variation over different regions of the sky. We compare our results with those obtained from MEM foreground maps which are formed in pixel space. We find that relative to our model independent estimates MEM maps overestimates the foreground power close to galactic plane and underestimates it at high latitudes.
Foreground Maps in WMAP frequency bands
Arxiv preprint arXiv: …, 2010
This paper provides full sky maps of foreground emission in all WMAP channels, with very low residual contamination from the Cosmic Microwave Background (CMB) anisotropies and controlled level of instrumental noise. Foreground maps are ...
Non-Gaussian foreground residuals of the WMAP first-year maps
Monthly Notices of the Royal Astronomical Society, 2006
We investigate the effect of foreground residuals in the WMAP data (Bennett et al. 2003a) by adding foreground contamination to Gaussian ensembles of CMB signal and noise maps. We evaluate a set of non-Gaussian estimators on the contaminated ensembles to determine with what accuracy any residual in the data can be constrained using higher order statistics. We apply the estimators to the raw and cleaned Q, V, and W band first year maps. The foreground subtraction method applied to clean the data in Bennett et al. (2003b) appears to have induced a correlation between the power spectra and normalized bispectra of the maps which is absent in Gaussian simulations. It also appears to increase the correlation between the ∆ℓ = 1 inter-ℓ bispectrum of the cleaned maps and the foreground templates. In a number of cases the significance of the effect is above the 98% confidence level.
Foreground analysis of the Wilkinson Microwave Anisotropy Probe 3-yr data with fastica
Monthly Notices of the Royal Astronomical Society, 2008
We present an analysis of the foreground emission present in the Wilkinson Microwave Anisotropy Probe (WMAP) 3-yr data as determined by the method of Independent Component Analysis. The WMAP data averaged at each frequency are used together with the standard foreground emission templates as inputs to the FASTICA algorithm. The returned coefficients can be interpreted as coupling coefficients between the WMAP data and foreground templates. These results are then used to infer the spectral behaviour for three foreground components -synchrotron, anomalous dust-correlated emission and free-free. For the first two components, we find values consistent with previous results although slightly steeper. We confirm the inconsistency in the scaling between the Hα template and free-free emission at K and Ka bands where an electron temperature of ∼4000 K is indicated. We also see evidence of significantly flatter spectral behaviour to higher frequencies than expected theoretically and previously noted by Dobler et al., but only when analysing the Kp2 sky coverage.
Blind and non-blind source detection in WMAP 5-year maps
Monthly Notices of The Royal Astronomical Society, 2008
We have analyzed the efficiency in source detection and flux density estimation of blind and non-blind detection techniques exploiting the MHW2 filter applied to the Wilkinson Microwave Anisotropy Probe (WMAP) 5-year maps. A comparison with the AT20G Bright Source Sample (Massardi et al. 2008), with a completeness limit of 0.5 Jy and accurate flux measurements at 20 GHz, close to the lowest frequency of WMAP maps, has allowed us to assess the completeness and the reliability of the samples detected with the two approaches, as well as the accuracy of flux and error estimates, and their variations across the sky. The uncertainties on flux estimates given by our procedure turned out to be about a factor of 2 lower than the rms differences with AT20G measurements, consistent with the smoothing of the fluctuation field yielded by map filtering. Flux estimates were found to be essentially unbiased except that, close to the detection limit, a substantial fraction of fluxes are found to be inflated by the contribution of underlying positive fluctuations. This is consistent with expectations for the Eddington bias associated to the true errors on flux density estimates. The blind and non-blind approaches are found to be complementary: each of them allows the detection of sources missed by the other. Combining results of the two methods on the WMAP 5-year maps we have expanded the non-blindly generated New Extragalactic WMAP Point Source (NEWPS) catalogue (Lopez-Caniego et al. 2007) that was based on WMAP 3-year maps. After having removed the probably spurious objects not identified with known radio sources, the new version of the NEWPS catalogue, NEWPS_5yr comprises 484 sources detected with a signal-to-noise ratio SNR>5.
Foreground removal usingfastica: a showcase of LOFAR-EoR
Monthly Notices of the Royal Astronomical Society, 2012
We introduce a new implementation of the FASTICA algorithm on simulated Low Frequency Array Epoch of Reionization data with the aim of accurately removing the foregrounds and extracting the 21-cm reionization signal. We find that the method successfully removes the foregrounds with an average fitting error of 0.5 per cent and that the 2D and 3D power spectra are recovered across the frequency range. We find that for scales above several point spread function scales, the 21-cm variance is successfully recovered though there is evidence of noise leakage into the reconstructed foreground components. We find that this blind independent component analysis technique provides encouraging results without the danger of prior foreground assumptions.
The Angular Power Spectrum of the First-Year WMAP Data Reanalysed
2004
We measure the angular power spectrum of the WMAP first-year temperature anisotropy maps. We use SpICE (Spatially Inhomogeneous Correlation Estimator) to estimate Cl's for multipoles l=2-900 from all possible cross-correlation channels. Except for the map-making stage, our measurements provide an independent analysis of that by Hinshaw etal (2003). Despite the different methods used, there is virtually no difference between the two measurements for l < 700 ; the highest l's are still compatible within 1-sigma errors. We use a novel intra-bin variance method to constrain Cl errors in a model independent way. When applied to WMAP data, the intra-bin variance estimator yields diagonal errors 10% larger than those reported by the WMAP team for 100 < l < 450. This translates into a 2.4 sigma detection of systematics since no difference is expected between the SpICE and the WMAP team estimator window functions in this multipole range. With our measurement of the Cl's and errors, we get chi^2/d.o.f. = 1.042 for a best-fit LCDM model, which has a 14% probability, whereas the WMAP team obtained chi^2/d.o.f. = 1.066, which has a 5% probability. We assess the impact of our results on cosmological parameters using Markov Chain Monte Carlo simulations. From WMAP data alone, assuming spatially flat power law LCDM models, we obtain the reionization optical depth tau = 0.145 +/- 0.067, spectral index n_s = 0.99 +/- 0.04, Hubble constant h = 0.67 +/- 0.05, baryon density Omega_b h^2 = 0.0218 +/- 0.0014, cold dark matter density Omega_{cdm} h^2 = 0.122 +/- 0.018, and sigma_8 = 0.92 +/- 0.12, consistent with a reionization redshift z_{re} = 16 +/- 5 (68% CL).
Monthly Notices of the Royal Astronomical Society, 2012
The WMAP satellite has provided high resolution, high signal to noise ratio maps of the sky in five main frequency bands ranging from 23 to 94 GHz. These maps consist in noisy observations a mixture of Cosmic Microwave Background (CMB) anisotropies and of other astrophysical foreground emissions. We present a new foreground-cleaned CMB map, as well as a new estimation of the angular power spectrum of CMB temperature anisotropies, based on 7 years of observations of the sky by WMAP. The method used to extract the CMB signal is based on an implementation of minimum variance linear combination of WMAP channels and of external full-sky foreground maps, on a frame of spherical wavelets called needlets. The use of spherical needlets makes possible localised filtering both in pixel space and harmonic space, so that the ILC weights are adjusted as a function of location on the sky and of angular scale. Our CMB power spectrum estimate is computed using cross power spectra between CMB maps obtained from different individual years of observation. The CMB power spectrum is corrected for low-level biases originating from the ILC method and from foreground residual emissions, by making use of realistic simulations of the whole analysis pipeline. Our error bars, compatible with those obtained by the WMAP collaboration, are obtained from the combination of two terms: the internal scatter of individual C ℓ in each ℓ bin, and a term originating from uncertainties in our correction for biases due to empirical correlations between CMB and foregrounds, as well as to residual foregrounds in the CMB maps. Our power spectrum is essentially compatible, within error bars, with the result obtained by the WMAP collaboration, although it is systematically lower at the lowest multipoles, more than expected considering that the two estimates are based on the same original data. Exhaustive investigations of the presence of a possible bias in our estimate fail to explain the difference. Comparison with several other analyses confirm the existence of differences in the large scale CMB power, which are significant enough that until the origin of this discrepancy is understood, some caution is recommended in scientific work relying much on the exact value of the CMB power spectrum in the Sachs-Wolfe plateau.