I. S. Ferreira

Alignment Tests for low CMB multipoles

We investigate the large scale anomalies in the angular distribution of the cosmic microwave background radiation as measured by WMAP using several tests. These tests, based on the multipole vector expansion, measure correlations between the phases of the multipoles as expressed by the directions of the multipole vectors and their associated normal planes. We have computed the probability distribution functions for 46 such tests, for the multipoles l=2-5. We confirm earlier findings that point to a high level of alignment between l=2 (quadrupole) and l=3 (octopole), but with our tests we do not find significant planarity in the octopole. In addition, we have found other possible anomalies in the alignment between the octopole and the l=4 (hexadecupole) components, as well as in the planarity of l=4 and l=5. We introduce the notion of a global anomaly statistic to estimate the relevance of the low-multipoles tests of non-Gaussianity. We show that, as a result of these tests, the CMB maps which are most widely used for cosmological analysis lie within the {approx}10% of randomly generated maps with lowest global anomaly statistics.

ON THE LARGE-SCALE ANGULAR DISTRIBUTION OF SHORT GAMMA-RAY BURSTS

We investigate the large-scale angular distribution of the short gamma-ray bursts (SGRBs) from BATSE experiment, using a new coordinate-free method. The analyses performed take into account the angular correlations induced by the nonuniform sky exposure during the experiment, and the uncertainty in the measured angular coordinates. Comparing the large-scale angular correlations from the data with those expected from simulations using the exposure function, we find similar features. In addition, confronting the large-angle correlations computed from the data with those obtained from simulated maps produced under the assumption of statistical isotropy, we found that they are incompatible at 95% confidence level. However, such differences are restricted to the angular scales 36°-45°, which are likely to be due to the nonuniform sky exposure. This result strongly suggests that the set of SGRBs from BATSE are intrinsically isotropic. Moreover, we also investigated a possible large-angle correlation of these data with the supergalactic plane. No evidence for such large-scale anisotropy was found.

Searching for primordial non-Gaussianity in Planck CMB maps using a combined estimator

The extensive search for deviations from Gaussianity in cosmic microwave background radiation (CMB) data is very important due to the information about the very early moments of the universe encoded there. Recent analyses from Planck CMB data do not exclude the presence of non-Gaussianity of small amplitude, although they are consistent with the Gaussian hypothesis. The use of different techniques is essential to provide information about types and amplitudes of non-Gaussianities in the CMB data. In particular, we find interesting to construct an estimator based upon the combination of two powerful statistical tools that appears to be sensitive enough to detect tiny deviations from Gaussianity in CMB maps. This estimator combines the Minkowski functionals with a Neural Network, maximizing a tool widely used to study non-Gaussian signals with a reinforcement of another tool designed to identify patterns in a data set. We test our estimator by analyzing simulated CMB maps contaminated with different amounts of local primordial non-Gaussianity quantified by the dimensionless parameter f NL. We apply it to these sets of CMB maps and find 98% of chance of positive detection, even for small intensity local non-Gaussianity like f NL = 38±18, the current limit from Planck data for large angular scales. Additionally, we test the suitability to distinguish between primary and secondary non-Gaussianities: first we train the Neural Network with two sets, one of nearly Gaussian CMB maps (|f NL| ≤ 10) but contaminated with realistic inhomogeneous Planck noise (i.e., secondary non-Gaussianity) and the other of non-Gaussian CMB maps, that is, maps endowed with weak primordial non-Gaussianity (28 ≤ f NL ≤ 48); after that we test an ensemble composed of CMB maps either with one of these non-Gaussian contaminations, and find out that our method successfully classifies ~ 95% of the tested maps as being CMB maps containing primordial or secondary non-Gaussianity. Furthermore, we analyze the foreground-cleaned Planck maps obtaining constraints for non-Gaussianity at large-angles that are in good agreement with recent constraints. Finally, we also test the robustness of our estimator including cut-sky masks and realistic noise maps measured by Planck, obtaining successful results as well.

The Cosmic Foreground Explorer (COFE): A balloon-borne microwave polarimeter to characterize polarized foregrounds

The COsmic Foreground Explorer (COFE) is a balloon-borne microwave polarimeter designed to measure the low-frequency and low-‘ characteristics of dominant diffuse polarized foregrounds. Short duration balloon flights from the Northern and Southern Hemispheres will allow the telescope to cover up to 80% of the sky with an expected sensitivity per pixel better than 100 lK/deg 2 from 10 GHz to 20 GHz. This is an important effort toward characterizing the polarized foregrounds for future CMB experiments, in particular the ones that aim to detect primordial gravity wave signatures in the CMB polarization angular power spectrum. 2006 Elsevier B.V. All rights reserved.

Probing cosmological isotropy with Planck Sunyaev–Zeldovich galaxy clusters

We probe the hypothesis of cosmological isotropy using the Planck Sunyaev-Zeldovich (PSZ) galaxy clusters data set. Our analyses consist on a hemispherical comparison of the clusters angular distribution, searching for a preferred direction in the large-scale structure of the Universe. We obtain a maximal dipolar signal at the direction (l; b) = (53:44 ; 41:81 ) whose antipode points toward (l; b) = (233:44 ; 41:81 ). Interestingly, this antipode is marginally consistent with the anomalous Cold Spot found in the Cosmic Microwave Background, located at (l; b) ’ (209 ; 57 ), which might be possibly aligned with a supervoid at z 0:2 with 200 Mpc=h of radius. The statistical significance of this result is assessed with ensembles of Monte Carlo realisations, finding that only a small number of runs are able to reproduce a close direction to this one, hence rejecting the null hypothesis of such direction being a random fluctuation of the data. Moreover, the PSZ catalogue presents a mild discrepancy with the isotropic realisations unless we correct some e ects, such as the non-uniform exposure function of Planck’s observational strategy, on the simulated data sets. We also perform a similar analysis to a smaller, albeit optimised sub-sample of PSZ sources, finding a better concordance with isotropic realisations, yet no correlation with the supervoid is obtained this time. Thus, we conclude that the dipole anisotropy found on galaxy clusters angular distribution can be partially attributed to an anomalous feature in the large-scale structure, though the significance of this result is su ciently reduced when corrections to systematic e ects are taken into account.

A Neural-Network based estimator to search for primordial non-Gaussianity in Planck CMB maps

We present an upgraded combined estimator, based on Minkowski Functionals and Neural Networks, with excellent performance in detecting primordial non-Gaussianity in simulated maps that also contain a weighted mixture of Galactic contaminations, besides real pixels noise from Planck cosmic microwave background radiation data. We rigorously test the efficiency of our estimator considering several plausible scenarios for residual non-Gaussianities in the foreground-cleaned Planck maps, with the intuition to optimize the training procedure of the Neural Network to discriminate between contaminations with primordial and secondary non-Gaussian signatures. We look for constraints of primordial local non-Gaussianity at large angular scales in the foreground-cleaned Planck maps. For the

The 2.3 GHz continuum survey of the GEM project

\mathtt{SMICA}

Digital complex correlator for a C-band polarimetry survey

map we found

Local analyses of Planck maps with Minkowski Functionals

{f}_{\rm \,NL} = 33 \pm 23

Isotropy analyses of the Planck convergence map

, at