M. Tucci

Limits on the detectability of the CMB B-mode polarization imposed by foregrounds

We investigate which practical constraints are imposed by foregrounds on the detection of the B-mode polarization generated by gravitational waves, in the case of experiments of the type currently being planned. As the B-mode signal is probably dominated by foregrounds at all frequencies, the detection of the cosmological component depends drastically on our ability to remove foregrounds. We provide an analytical expression with which to estimate the level of the residual polarization for Galactic foregrounds, according to the method employed for their subtraction. We interpret this result in terms of the lower limit of the tensor-to-scalar ratio r that allows us to disentangle the cosmological B-mode polarization from the foreground contribution. Polarized emission from extragalactic radio sources and gravitational lensing is also taken into account. As a first approach, we consider the ideal limit of an instrumental noise-free experiment: for full-sky coverage and a resolution of 1°, we obtain a limit of r ∼ 10 -4 . This value can be improved by high-resolution experiments and, in principle, there is no clear fundamental limit on the detectability of the polarization of gravitational waves. Our analysis is also applied to planned or hypothetical future polarization experiments, taking into account expected noise levels.

Predictions on the high-frequency polarization properties of extragalactic radio sources and implications for polarization measurements of the cosmic microwave background

We present a method to simulate the polarization properties of extragalactic radio sources at microwave frequencies. Polarization measurements of nearly 2 x 10 6 sources at 1.4 GHz are provided by the NVSS survey. Using this catalogue and the GB6 survey, we study the distribution of the polarization degree of both steep- and flat-spectrum sources. We find that the polarization degree is anticorrelated with the flux density for the former population, while no correlation is detected for the latter. The available high-frequency data are exploited to determine the frequency dependence of the distribution of polarization degrees. Using such information and the evolutionary model developed by Toffolatti and coworkers, we estimate the polarization power spectra of extragalactic radio sources at ≥30 GHz and their contamination of CMB polarization maps. Two distinct methods to compute point-source polarization spectra are presented, extending and improving the one generally used in previous analyses. While extragalactic radio sources can significantly contaminate the CMB E-mode power spectrum only at low frequencies (ν? 30 GHz), they can severely constrain the detectability of the CMB B mode up to ν ≃ 100 GHz.

Cross-correlation of the CMB and radio galaxies in real, harmonic and wavelet spaces: detection of the integrated Sachs-Wolfe effect and dark energy constraints

We report on the first detection of the integrated Sachs-Wolfe (ISW) effect in wavelet space, at scales in the sky around 0 7° with a significance 3.3σ, by cross-correlating the Wilkinson Microwave Anisotropy Probe (WMAP) first-year data and the National Radio Astronomy Observatories (NRAO) Very Large Array (VLA) Sky Survey (NVSS). In addition, we present a detailed comparison of the capabilities of three different techniques for two different objectives: to detect the ISW effect and to put constraints on the nature of the dark energy. The three studied techniques are the cross-angular power spectrum (CAPS; harmonic space), the correlation function (CCF; real space) and the covariance of the spherical Mexican hat wavelet (SMHW) coefficients (CSMHW; wavelet space). We prove that the CSMHW is expected to provide a higher detection (in terms of the signal-to-noise ratio) of the ISW effect for a certain scale. However, the detection achieved by the CAPS is the lowest, being the signal-to-noise ratio dispersed among a wide multipole range. The CCF provides an intermediate detection level. This prediction has been corroborated by the analysis of the data. The SMHW analysis shows that the cross-correlation signal is caused neither by systematic effects nor foreground contamination. However, by taking into account the information encoded in all the multipoles/scales/angles, the CAPS provides slightly better constraints than the SMHW in the cosmological parameters that define the nature of the dark energy. The limits provided by the CCF are wider than for the other two methods, although the three of them give similar confidence levels (CLs). Two different cases have been studied: (i) a flat A cold dark matter universe; (ii) a flat universe with an equation of state parameter that, although it does not change with time, could take values different from - 1. In the first case, the CAPS provides (for a bias value of b = 1.6) Ω Λ = 0.73 +0.11 -0.14 (at la CL). Moreover, the CAPS rejects the range Ω Λ < 0.1 at 3.5σ, which is the highest detection of dark energy reported to date. In the second case, the CAPS gives Ω DE = 0.70 +0.12 -0.20 and w = -0.75 +0.32 -0.41 (at la CL). This is the first estimation of the equation of state of dark energy made through the cross-correlation of the cosmic microwave background (CMB) and the nearby galaxy density distribution. It also provides an independent estimation from that made by the WMAP team using the CMB and large-scale structure.

The Impact of Polarized Extragalactic Radio Sources on the Detection of CMB Anisotropies in Polarization

Recent polarimetric surveys of extragalactic radio sources (ERS) at frequencies ν≳1 GHz are reviewed. By exploiting all the most relevant data we study the frequency dependence of polarization properties of ERS between 1.4 and 86 GHz. For flat-spectrum sources the median (mean) fractional polarization increases from 1.5% (2–2.5%) at 1.4 GHz to 2.5–3% (3–3.5%) at νg10 GHz. Steep-spectrum sources are typically more polarized, especially at high frequencies where Faraday depolarization is less relevant. Current data suggest that at high radio frequencies (ν≥20) GHz the fractional polarization of ERS does not depend on total flux density and moderately increases with frequency. We estimate ERS number counts in polarization and the contribution of unresolved polarized ERS to angular power spectra. A first application is for the Planck satellite mission: we predict that only a dozen polarized ERS will be detected by the Planck LFI, and a few tens by the HFI. As for CMB power spectra, ERS should not be a strong contaminant to the CMB E-mode polarization at ν≳70 GHz, but they can become a relevant constraint for the detection of the cosmological B-mode polarization if the tensor-to-scalar ratio is ≲0.01.

Radio source calibration for the Very Small Array and other cosmic microwave background instruments at around 30 GHz

Accurate calibration of data is essential for the current generation of CMB experiments. Using data from the Very Small Array (VSA), we describe procedures which will lead to an accuracy of 1 percent or better for experiments such as the VSA and CBI. Particular attention is paid to the stability of the receiver systems, the quality of the site and frequent observations of reference sources. At 30 GHz the careful correction for atmospheric emission and absorption is shown to be essential for achieving 1 percent precision. The sources for which a 1 percent relative flux density calibration was achieved included Cas A, Cyg A, Tau A and NGC7027 and the planets Venus, Jupiter and Saturn. A flux density, or brightness temperature in the case of the planets, was derived at 33 GHz relative to Jupiter which was adopted as the fundamental calibrator. A spectral index at ~30 GHz is given for each. Cas A,Tau A, NGC7027 and Venus were examined for variability. Cas A was found to be decreasing at

Statistical Tests for CHDM and ΛCDM Cosmologies

0.394 \pm 0.019

Multifrequency spectral analysis of extragalactic radio sources in the 33‐GHz VSA catalogue: sources with flattening and upturn spectrum

percent per year over the period March 2001 to August 2004. In the same period Tau A was decreasing at

The SPOrt experiment

0.22\pm 0.07

Characterization of polarimetric and total intensity behaviour of a complete sample of PACO radio sources in the radio bands

percent per year. A survey of the published data showed that the planetary nebula NGC7027 decreased at

SPOrt: an experiment aimed at measuring the large scale cosmic microwave background polarization

0.16\pm 0.04