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We study the contamination of the B-mode of the cosmic microwave background polarization (CMBP) by Galactic synchrotron in the lowest emission regions of the sky. The 22.8-GHz polarization map of the 3-yr Wilkinson Microwave Anisotropy Probe ( WMAP) data release is used to identify and analyse such regions. Two areas are selected with signal-to-noise ratio S/N < 2 and S/N < 3, covering ∼16 and ∼26 per cent fraction of the sky, respectively. The polarization power spectra of these two areas are dominated by the sky signal on large angular scales (multipoles ℓ < 15), while the noise prevails on degree scales. Angular extrapolations show that the synchrotron emission competes with the CMBP B-mode signal for tensor-to-scalar perturbation power ratio at 70 GHz in the 16 per cent lowest emission sky (S/N < 2 area). These values worsen by a factor ∼5 in the S/N < 3 region. The novelty is that our estimates regard the whole lowest emission regions and outline a contamination better than that of the whole high Galactic latitude sky found by the WMAP team . Such regions allow to be measured directly which approximately corresponds to the limit imposed by using a sky coverage of 15 per cent. This opens interesting perspectives on the investigation of the inflationary model space in lowest emission regions. [ABSTRACT FROM AUTHOR]

We present results of polarization observations at 1.4 GHz of the two fields imaged by the DASI experiment ( and , respectively). Data were taken with the Australia Telescope Compact Array with 3.4-arcmin resolution and ∼0.18-mJy beam−1 sensitivity. The emission is dominated by point sources, and we do not find evidence for diffuse synchrotron radiation even after source subtraction. This allows to estimate an upper limit of the diffuse polarized emission. The extrapolation to 30 GHz suggests that the synchrotron radiation is lower than the polarized signal measured by the DASI experiment by at least two orders of magnitude. This further supports the conclusions drawn by the DASI team itself about the negligible Galactic foreground contamination in their data set, improving by a factor of ∼5 the upper limit estimated by Leitch et al. The dominant point-source emission allows us to estimate the contamination of the cosmic microwave background (CMB) by extragalactic foregrounds. We computed the power spectrum of their contribution, and its extrapolation to 30 GHz provides a framework where the CMB signal should dominate. However, our results do not match the conclusions of the DASI team about the negligibility of point-source contamination, suggesting taking into account a source subtraction from the DASI data. [ABSTRACT FROM AUTHOR]

Polarized diffuse emission observations at 1.4 GHz in a high Galactic latitude area of the Northern celestial hemisphere are presented. The field, centred at , has Galactic coordinates and is located in the region selected as northern target of the Balloon-borne Radiometers for Sky Polarization Observations experiment. Observations have been performed with the Effelsberg 100-m telescope. We find that the angular power spectra of the E and B modes have slopes of and , respectively. Because of the very high Galactic latitude and the smooth emission, a weak Faraday rotation action is expected, which allows both a fair extrapolation to cosmic microwave background polarization (CMBP) frequencies and an estimate of the contamination by the Galactic synchrotron emission. We extrapolate the E-mode spectrum up to 32 GHz and confirm the possibility to safely detect the CMBP E-mode signal in the Ka band found in another low-emission region. Extrapolated up to 90 GHz, the Galactic synchrotron B mode looks to compete with the cosmic signal only for models with a tensor-to-scalar perturbation power ratio , which is even lower than the T/ S value of 0.01 found to be accessible in the only other high Galactic latitude area investigated to date. This suggests that values as low as might be accessed at high Galactic latitudes. Such low-emission values can allow a significant redshift of the best frequency to detect the CMBP B mode, also reducing the contamination by Galactic dust, and opening interesting perspectives to investigate inflation models. [ABSTRACT FROM AUTHOR]

Polarized diffuse emission observations at 2.3 GHz in a high Galactic latitude area are presented. The field, centred at , is located in the region observed by the BOOMERanG experiment. Our observations were carried out with the Parkes radio telescope, and represent the highest frequency detection to date in a low-emission area. Because of the weaker Faraday rotation effect, the high frequency allows an estimate of the Galactic synchrotron contamination of the cosmic microwave background polarization (CMBP) which is more reliable than that achieved at 1.4 GHz. We find that the angular power spectra of the E- and B-modes have slopes of and , indicating a flattening with respect to 1.4 GHz. Extrapolated up to 32 GHz, the E-mode spectrum is about three orders of magnitude lower than that of the CMBP, allowing a clean detection even at this frequency. The best improvement concerns the B-mode, for which our single-dish observations provide the first estimate of the contamination on angular scales close to the CMBP peak (about 2°). We find that the CMBP B-mode should be stronger than the synchrotron contamination at 90 GHz for models with tensor-to-scalar perturbation ratio . This low level could move down to 60–70 GHz the optimal window for CMBP measurements. [ABSTRACT FROM AUTHOR]

We analyse the polarized emission at 1.4 GHz in a 3°× 3° area at high Galactic latitude. The region, centred in, was observed with the Australia Telescope Compact Array (ATCA) radio-interferometer, whose 3–30 arcmin angular sensitivity range allows the study of scales appropriate for cosmic microwave background polarization (CMBP) investigations. The angular behaviour of the diffuse emission is analysed through theE- andB-mode angular power spectra. These follow a power lawCXℓ∝ℓβ X with slopesand. The emission is found to be approximately 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 behaviours 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 90 GHz of the cosmic microwave background (CMB) window suggests that Galactic synchrotron emission leaves the CMBPE-mode uncontaminated at 32 GHz. The level of the contamination at 90 GHz 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 CMBPB-modes for models with tensor-to-scalar fluctuation power ratio. We also identify polarized point sources in the field, providing a nine object list, which is complete down to the polarized flux limit ofSplim= 2 mJy. [ABSTRACT FROM AUTHOR]

We build template maps for the polarized Galactic synchrotron emission on large angular scales (7° full width at half maximum), in the 20–90 GHz microwave range, by using Wilkinson Microwave Anisotropy Probe ( WMAP) data. The method, presented in recent work, requires a synchrotron total-intensity survey and the 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 per cent 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 present 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 robust detection of the E-mode component of the cosmological signal on large scale, even in models with low reionization . Detection of the weaker B-mode on the largest scales might be jeopardized unless the value found by WMAP is confirmed, and tensor-to-scalar fluctuation power ratio . For lower levels of the gravitational-wave background the B-mode seems to be accessible only at the peak and in selected low-synchrotron emission areas. [ABSTRACT FROM AUTHOR]

ABSTRACT We present a new approach to 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 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. [ABSTRACT FROM AUTHOR]

We analyse the temperature–polarization cross-correlation in the Galactic synchrotron template that we have recently developed, and between the template and cosmic microwave background (CMB) temperature maps derived from WMAP data. Since the polarized synchrotron template itself uses WMAP data, we can estimate residual synchrotron contamination in the CMB angular spectrum. While appears to be contaminated by synchrotron, no evidence for contamination is found in the multipole range which is most relevant for the fit of the cosmological optical depth. [ABSTRACT FROM AUTHOR]

We study the angular power spectra of polarized Galactic synchrotron in the range 10&lsim;l≤800, at several frequencies between 0.4 and 2.7 GHz and at several Galactic latitudes up to near the North Galactic Pole. Electric- and magnetic-parity polarization spectra are found to have slopes around αE,B=1.4–1.5 in the Parkes and Effelsberg Galactic-Plane surveys, but strong local fluctuations of αE,B are found at &z.sfnc;b&z.sfnc;≃10° from the 1.4 GHz Effelsberg survey. The CPIl spectrum, which is insensitive to the polarization direction, is somewhat steeper, being αPI=1.6–1.8 for the same surveys. The low-resolution multifrequency survey of Brouw and Spoelstra [A&AS 26 (1976) 129] shows some flattening of the spectra below 1 GHz, more intense for CE,Bl than for CPIl. In no case we find evidence for really steep spectra. The extrapolation to the cosmological window shows that at 90 GHz the detection of E-mode harmonics in the cosmic background radiation should not be disturbed by synchrotron, even around l≃10 for a reionization optical depth τri&gsim;0.05. [Copyright &y& Elsevier]