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E. Carretti

Publications and source records attributed to E. Carretti.

At least 127 records · Page 7Linked to original sources
arXiv2004

High Galactic latitude polarized emission at 1.4 GHz and implications for cosmic microwave background observations

We analyse the polarized emission at 1.4 GHz in a 3x3 deg^2 area at high Galactic latitude (b ~ -40deg). The region, centred in (RA=5h, Dec=-49deg), was observed with the Australia Telescope Compact Array radio-interferometer, whose 3-30 arcmin angular sensitivity range allows the study of scales appropriate for CMB Polarization (CMBP) investigations. The angular behavior of the diffuse emission is analysed through the E- and B-mode power spectra. These follow a power law $C^X_l \propto l^{β_X}$ with slopes β_E = -1.97 \pm 0.08 and β_B = -1.98 \pm 0.07. The emission is found to be about a factor 25 fainter than in Galactic plane regions. The comparison of the power spectra with other surveys indicates that this area is intermediate between strong and negligible Faraday rotation effects. A similar conclusion can be reached by analysing both the frequency and Galactic latitude behaviors of the diffuse Galactic emission of the 408-1411 MHz Leiden survey data. We present an analysis of the Faraday rotation effects on the polarized power spectra, and find that the observed power spectra can be enhanced by a transfer of power from large to small angular scales. The extrapolation of the spectra to 32 and 90GHz of the CMB window suggests that Galactic synchrotron emission leaves the CMBP E-mode uncontaminated at 32GHz. The level of the contamination at 90GHz is expected to be more than 4 orders of magnitude below the CMBP spectrum. Extrapolating to the relevant angular scales, this region also appears adequate for investigation of the CMBP B-modes for models with tensor/scalar fluctuation power ratio T/S>0.01. We also identify polarized point sources in the field, providing a 9 object list which is complete down to the polarized flux limit of S^p_lim = 2 mJy.

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arXiv2004

Effects of Thermal Fluctuations in the SPOrt Experiment

The role of systematic errors induced by thermal fluctuations is analyzed for the SPOrt experiment with the aim at estimating their impact on the measurement of the Cosmic Microwave Background Polarization (CMBP). The transfer functions of the antenna devices from temperature to data fluctuations are computed, by writing them in terms of both instrument and thermal environment parameters. In addition, the corresponding contamination maps are estimated, along with their polarized power spectra, for different behaviours of the instabilities. The result is that thermal effects are at a negligible level even for fluctuations correlated with the Sun illumination provided their frequency $f_{tf}$ is larger than that of the Sun illumination ($f_{day}$) by a factor $f_{tf} / f_{day} > 30$, which defines a requirement for the statistical properties of the temperature behaviour as well. The analysis with actual SPOrt operative parameters shows that the instrument is only weakly sensitive to temperature instabilities, the main contribution coming from the cryogenic stage. The contamination on the E-mode spectrum does not significantly pollute the CMBP signal and no specific data cleaning seems to be needed.

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arXiv2004

Antenna Instrumental Polarization and its Effects on E- and B-Modes for CMBP Observations

We analyze the instrumental polarization generated by the antenna system (optics and feed horn) due to the unpolarized sky emission. Our equations show that it is given by the convolution of the unpolarized emission map $T_b(θ, ϕ)$ with a sort of instrumental polarization beam $Π$ defined by the co- and cross-polar patterns of the antenna. This result is general, it can be applied to all antenna systems and is valid for all schemes to detect polarization, like correlation and differential polarimeters. The axisymmetric case is attractive: it generates an $E$-mode--like $Π$ pattern, the contamination does not depend on the scanning strategy and the instrumental polarization map does not have $B$-mode contamination, making axisymmetric systems suitable to detect the faint $B$-mode signal of the Cosmic Microwave Background Polarization. The $E$-mode of the contamination only affects the FWHM scales leaving the larger ones significantly cleaner. Our analysis is also applied to the SPOrt experiment where we find that the contamination of the $E$-mode is negligible in the $\ell$-range of interest for CMBP large angular scale investigations (multipole $\ell < 10$).

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arXiv2004

A polarized synchrotron template for CMBP experiments after WMAP data

We build template maps for the polarized Galactic--synchrotron emission on large angular scales (FWHM =~7$^\circ$), in the 20-90 GHz microwave range, by using WMAP data. The method, presented in a recent work, requires a synchrotron total intensity survey and the {\it polarization horizon} to model the polarized intensity and a starlight polarization map to model polarization angles. The basic template is obtained directly at 23 GHz with about 94% sky--coverage by using the synchrotron map released by the WMAP team. Extrapolations to 32, 60 and 90 GHz are performed by computing a synchrotron spectral index map, which strongly reduces previous uncertainties in passing from low (1.4 GHz) to microwave frequencies. Differing from low frequency data, none of our templates presents relevant structures out of the Galactic Plane. Our map at 90 GHz suggests that the synchrotron emission at high Galactic latitudes is low enough to allow a robust detection of the $E$--mode component of the cosmological signal on large--scale, even in models with low--reionization ($τ= 0.05$). Detection of the weaker $B$--mode on the largest scales ($\ell < 10$) might be jeopardized unless the value $τ= 0.17$ found by WMAP is confirmed, and $T/S > 0.1$. For lower levels of the gravitational--wave background the $B$--mode seems to be accessible only at the $\ell \sim 100$ peak and in selected low--synchrotron emission areas.

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arXiv2004

The Sky Polarization Observatory

SPOrt is an ASI-funded experiment specifically designed to measure the sky polarization at 22, 32 and 90 GHz, which was selected in 1997 by ESA to be flown on the International Space Station. Starting in 2006 and for at least 18 months, it will be taking direct and simultaneous measurements of the Stokes parameters Q and U at 660 sky pixels, with FWHM=7 degrees. Due to development efforts over the past few years, the design specifications have been significantly improved with respect to the first proposal. Here we present an up-to-date description of the instrument, which now warrants a pixel sensitivity of 1.7 microK for the polarization of the cosmic background radiation, assuming two years of observations. We discuss SPOrt scientific goals in the light of WMAP results, in particular in connection with the emerging double-reionization cosmological scenario.

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arXiv2003

Polarization observations in a low synchrotron emission field at 1.4 GHz

We present the first observation of the diffuse polarized synchrotron radiation of a patch ($\sim 3^\circ \times 3^\circ$) in the BOOMERanG field, one of the areas with the lowest CMB foreground emission. The work has been carried out with the Australia Telescope Compact Array at 1.4 GHz with 3.4 arcmin resolution and sensitivity of $\sim 0.18$ mJy beam$^{-1}$. The mean polarized signal has been found to be $P_{rms} = \sqrt{(Q_{rms}^2 + U_{rms}^2)} = 11.6 \pm 0.6$ mK, nearly one order of magnitude below than in the Galactic Plane. Extrapolations to frequencies of interest for cosmological investigations suggest that polarized synchrotron foreground noise should allow the detection of the CMB Polarization $E$--mode already at 32 GHz and make us confident that, at 90 GHz, it is accessible with no relevant foreground contamination. Last but not least, even the $B$--mode detection for $T/S > 0.01$ is not ruled out in such a low emission patch.

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arXiv2003

An iterative destriping technique for diffuse background polarization data

We describe a simple but effective iterative procedure specifically designed to destripe Q and U Stokes parameter data as those collected by the SPOrt experiment onboard the International Space Station (ISS). The method is general enough to be useful for other experiments, both in polarization and total intensity. The only requirement for the algorithm to work properly is that the receiver knee frequency must be lower than the signal modulation frequency, corresponding in our case to the ISS orbit period. Detailed performances of the technique are presented in the context of the SPOrt experiment, both in terms of added rms noise and residual correlated noise.

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arXiv2003

A New approach for a Galactic Synchrotron Polarized Emission Template in the Microwave Range

We present a new approach in modelling the polarized Galactic synchrotron emission in the microwave range (20-100 GHz), where this radiation is expected to play the leading role in contaminating the Cosmic Microwave Background (CMB) data. Our method is based on real surveys and aims at providing the real spatial distributions of both polarized intensity and polarization angles. Its main features are the modelling of a polarization horizon to determine the polarized intensity and the use of starlight optical data to model the polarization angle pattern. Our results are consistent with several existing data, and our template is virtually free from Faraday rotation effects as required at frequencies in the cosmological window.

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arXiv2003

The BaR-SPOrt Experiment

BaR-SPOrt (Balloon-borne Radiometers for Sky Polarisation Observations) is an experiment to measure the linearly polarized emission of sky patches at 32 and 90 GHz with sub-degree angular resolution. It is equipped with high sensitivity correlation polarimeters for simultaneous detection of both the U and Q stokes parameters of the incident radiation. On-axis telescope is used to observe angular scales where the expected polarization of the Cosmic Microwave Background (CMBP) peaks. This project shares most of the know-how and sophisticated technology developed for the SPOrt experiment onboard the International Space Station. The payload is designed to flight onboard long duration stratospheric balloons both in the Northern and Southern hemispheres where low foreground emission sky patches are accessible. Due to the weakness of the expected CMBP signal (in the range of microK), much care has been spent to optimize the instrument design with respect to the systematics generation, observing time efficiency and long term stability. In this contribution we present the instrument design, and first tests on some components of the 32 GHz radiometer.

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arXiv2002

SPOrt: an Experiment Aimed at Measuring the Large Scale Cosmic Microwave Background Polarization

SPOrt (Sky Polarization Observatory) is a space experiment to be flown on the International Space Station during Early Utilization Phase aimed at measuring the microwave polarized emission with FWHM = 7deg, in the frequency range 22-90 GHz. The Galactic polarized emission can be observed at the lower frequencies and the polarization of Cosmic Microwave Background (CMB) at 90 GHz, where contaminants are expected to be less important. The extremely low level of the CMB Polarization signal (< 1 uK) calls for intrinsically stable radiometers. The SPOrt instrument is expressly devoted to CMB polarization measurements and the whole design has been optimized for minimizing instrumental polarization effects. In this contribution we present the receiver architecture based on correlation techniques, the analysis showing its intrinsic stability and the custom hardware development carried out to detect such a low signal.

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arXiv2002

Polarization angular spectra of Galactic synchrotron emission on arcminute scales

We study the angular power spectra of the polarized component of the Galactic synchrotron emission in the 28-deg^2 Test Region of the Southern Galactic Plane Survey at 1.4 GHz. These data were obtained by the Australia Telescope Compact Array and allow us to investigate angular power spectra down to arcminute scales. We find that, at this frequency, the polarization spectra for E- and B-modes seem to be affected by Faraday rotation produced in compact foreground screens. A different behavior is shown by the angular spectrum of the polarized intensity PI=\sqrt{Q^2+U^2}. This is well fitted by a power law with slope \~1.7, which agrees with higher frequency results and can probably be more confidently extrapolated to the cosmological window.

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arXiv2001

Power Spectrum Analysis of the ESP Galaxy Redshift Survey

We measure the power spectrum of the galaxy distribution in the ESO Slice Project (ESP) galaxy redshift survey. We develope a technique to describe the survey window function analytically, and then deconvolve it from the measured power spectrum using a variant of the Lucy method. We test the whole deconvolution procedure on ESP mock catalogues drawn from large N-body simulations, and find that it is reliable for recovering the correct amplitude and shape of $P(k)$ at $k> 0.065 h$ Mpc$^{-1}$. In general, the technique is applicable to any survey composed by a collection of circular fields with arbitrary pattern on the sky, as typical of surveys based on fibre spectrographs. The estimated power spectrum has a well-defined power-law shape $k^n$ with $n\simeq -2.2$ for $k\ge 0.2 h$ Mpc$^{-1}$, and a smooth bend to a flatter shape ($n\simeq -1.6$) for smaller $k$'s. The smallest wavenumber, where a meaningful reconstruction can be performed ($k\sim 0.06 h$ Mpc$^{-1}$), does not allow us to explore the range of scales where other power spectra seem to show a flattening and hints for a turnover. We also find, by direct comparison of the Fourier transforms, that the estimate of the two-point correlation function $ξ(s)$ is much less sensitive to the effect of a problematic window function as that of the ESP, than the power spectrum. Comparison to other surveys shows an excellent agreement with estimates from blue-selected surveys. In particular, the ESP power spectrum is virtually indistinguishable from that of the Durham-UKST survey over the common range of $k$'s, an indirect confirmation of the quality of the deconvolution technique applied.

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arXiv2001

Limits Due to Instrumental Polarisation in CMB Experiments at Microwave Wavelengths

An extended analysis of some instrumental polarisation sources has been done, as a consequence of the renewed interest in extremely sensitive polarisation measurements stimulated by Cosmic Microwave Background experiments. The case of correlation polarimeters, being them more suitable than other configurations, has been studied in detail and the algorithm has been derived to calculate their intrinsic sensitivity limit due to device characteristics as well as to the operating environment. The atmosphere emission, even though totally unpolarised, has been recognized to be the most important source of sensitivity degradation for ground based experiments. This happens through receiver component losses (mainly in the OMT), which generate instrumental polarisation in genuinely uncorrelated signals. The relevant result is that, also in best conditions (cfr. Antarctica), integration times longer than ~40s are not allowed on ground without modulation techniques. Finally, basic rules to estimate the maximum modulation period for each instrumental configuration have been provided.

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arXiv2000

The angular power spectra of polarized Galactic synchrotron

We derive the angular power spectra of intensity and polarization of Galactic synchrotron emission in the range 36 < l < 10^3 from the Parkes survey mapping the southern Galactic plane at 2.4 GHz. The polarization spectra of both electric and magnetic parity up to l \simeq 10^3 are approximated very well by power laws with slope coefficients \simeq 1.4, quite different from the CMB spectra. We show that no problem should arise from Galactic synchrotron for measurements of CMB polarization in the cosmological window.

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arXiv2000

Dynamic Work Distribution for PM Algorithm

Although poor for small dynamic scales, the Particle-Mesh (PM) model allows in astrophysics good insight for large dynamic scales at low computational cost. Furthermore, it is possible to employ a very high number of particles to get high mass resolution. These properties could be exploited by suitable parallelization of the algorithm. In PM there are two types of data: the particle data, i.e. position and velocity, which are stored in one-dimensional arrays of N elements, and the grid data, i.e. density and force, which are stored in three-dimensional arrays $M\times M\times M$ in size. Since individual particles can change cell under the action of gravitational force, parallelization is a real challenge on parallel machine and must account for the machine architecture. We have implemented a dynamic work distribution through agenda parallelism. By subdividing the work in small tasks, the implementation is well balanced, scalable and efficient also for clustered particle distributions. In this contribution we describe this efficient, load balanced, parallel implementation of PM algorithm on Cray T3E at CINECA and show its performances on cosmological simulation results.

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arXiv1999

The SPOrt Project: an Experimental Overview

The Sky Polarization Observatory (SPOrt) is presented as a project aimed to measure the diffuse sky polarized emission, from the International Space Station, in the frequency range 20-90 GHz with 7 degrees of HPBW. The SPOrt experimental configuration is described with emphasis on the aspects that make SPOrt the first European scientific payload operating at microwave wavelengths.

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arXiv1999

The SPOrt Project: Cosmological and Astrophysical Goals

We present the cosmological and astrophysical objectives of the SPOrt mission, which is scheduled for flying on the International Space Station (ISS) in the year 2002 with the purpose of measuring the diffuse sky polarized radiation in the microwave region. We discuss the problem of disentangling the cosmic background polarized signal from the Galactic foregrounds.

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