Showing papers by "Paolo Natoli published in 2002"

Search for non-Gaussian signals in the BOOMERANG maps: Pixel-space analysis

Abstract: We search the BOOMERANG (Balloon Observations Of Millimetric Extragalactic Radiation ANd Geophysics) maps of the anisotropy of the cosmic microwave background (CMB) for deviations from Gaussianity. In this Letter, we focus on analysis techniques in pixel space and compute skewness, kurtosis, and Minkowski functionals for the BOOMERANG maps and for Gaussian simulations of the CMB sky. We do not find any significant deviation from Gaussianity in the high galactic latitude section of the 150 GHz map. We do find deviations from Gaussianity at lower latitudes and at 410 GHz, and we ascribe them to Galactic dust contamination. Using non-Gaussian simulations of instrumental systematic effects, of foregrounds, and of sample non-Gaussian cosmological models, we set upper limits to the non-Gaussian component of the temperature field in the BOOMERANG maps. For fluctuations distributed as a 1 degree of freedom χ2 mixed to the main Gaussian component, our upper limits are in the few percentile range.

Non-iterative methods to estimate the in-flight noise properties of CMB detectors

Abstract: We present a new approach for statistical inference on noise properties of CMB anisotropy data. We consider a Maximum Likelihood parametric estimator to recover the full dependence structure of the noise process. We also consider a semiparametric procedure which is only sensitive to the low frequency behavior of the noise spectral density. Both approaches are statistically robust and computationally convenient in the case of long memory noise, even under nonstationary circumstances. We show that noise properties can be consistently derived by such procedures without resorting to currently used iterative noise-signal methods. More importantly, we show that optimal (GLS) CMB maps can be obtained from the observed timestream with the only knowledge of the noise memory parameter, the outcome of our estimators.

Testing for non-Gaussianity of the cosmic microwave background in harmonic space: an empirical process approach

Abstract: We present a new, model-independent approach for measuring non-Gaussianity of the Cosmic Microwave Background (CMB) anisotropy pattern. Our approach is based on the empirical distribution function of the normalized spherical harmonic expansion coefficients a_lm of a nearly full-sky CMB map, like the ones expected from forthcoming satellite experiments. Using a set of Kolmogorov-Smirnov type tests, we check for Gaussianity and independency of the a_lm. We test the method on two non-Gaussian toy-models of the CMB, one generated in spherical harmonic space and one in pixel (real) space. We also provide some rigorous results, possibly of independent interest, on the exact distribution of the spherical harmonic coefficients normalized by an estimated angular power spectrum.

CMB power spectrum estimation for the Planck Surveyor

Abstract: We use an iterative generalized least squares map-making algorithm, in conjunction with Monte Carlo techniques, to obtain estimates of the angular power spectrum from cosmic microwave background (CMB) maps. This is achieved by characterizing and removing the instrumental noise contribution in multipole space. This technique produces unbiased estimates and can be applied to an arbitrary experiment. In this paper, we use it on realistic simulations of Planck Low Frequency Instrument (LFI) observations, showing that it can lead to fast and reliable estimation of the CMB angular power spectrum from megapixel maps.

CMB polarization: Scientific case and data analysis issues

Abstract: We review the science case for studying CMB polarization. We then discuss the main issues related to the analysis of forth-coming polarized CMB data, such as those expected from balloon-borne (e.g. BOOMERanG) and satellite (e.g., Planck) experiments.

Ellipticity analysis of the BOOMERanG CMB maps

Abstract: The properties of the Cosmic Microwave Background (CMB) maps carry valuable cosmological information. Here we report the results of the analysis hot and cold CMB anisotropy spots in the BOOMERanG 150 GHz map in terms of number, area, ellipticity, vs. temperature threshold. We carried out this analysis for the map obtained by summing independent measurement channels (signal plus noise map) and for a comparison map (noise only map) obtained by differencing the same channels. The anisotropy areas (spots) have been identified for both maps for various temperature thresholds and a catalog of the spots has been produced. The orientation (obliquity) of the spots is random for both maps. We computed the mean elongation of spots obtained from the maps at a given temperature threshold using a simple estimator. We found that for the sum map there is a region of temperature thresholds where the average elongation is not dependent on the threshold. Its value is ~ 2.3 for cold areas and ~ 2.2 for hot areas. This is a non-trivial result. The bias of the estimator is less than 0.4 for areas of size less than 30', and smaller for larger areas. The presence of noise also biases the ellipticity by less than 0.3. These biases have not been subtracted in the results quoted above. The threshold independent and random obliquity behaviour in the sum map is stable against pointing reconstruction accuracy and noise level of the data, thus confirming that these are actual properties of the dataset. The data used here give a hint of high ellipticity for the largest spots. Analogous elongation properties of CMB anisotropies had been detected for COBE-DMR 4-year data. If this is due to geodesics mixing, it would point to a non zero curvature of the Universe.