S. Cortiglioni

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 3° x 3° area at high Galactic latitude (b ∼ -40°). The region, centred in (a = 5 h , δ = -49°), 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 the E- and B-mode angular power spectra. These follow a power law C X l lβ X with slopes β E = -1.97 ± 0.08 and β B = -1.98 ± 0.07. 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 CMBP E-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 CMBP B-modes for models with tensor-to-scalar fluctuation power ratio T/S ≥ 0.01. We also identify polarized point sources in the field, providing a nine object list, which is complete down to the polarized flux limit of S p lim = 2 mJy.

The Sky Polarization Observatory

Abstract 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°. 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 μK 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.

The power-law behaviours of angular spectra of polarized Galactic synchrotron

Abstract We study the angular power spectra of polarized Galactic synchrotron in the range 10≲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 |b|≃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≳0.05.

Limits due to instrumental polarisation in CMB experiments at microwave wavelengths

Abstract 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 recognised 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 ∼40 s are not allowed on ground without modulation techniques. Finally, basic rules to estimate the maximum modulation period for each instrumental configuration have been provided.

The Parkes Galactic Meridian Survey: observations and CMB polarization foreground analysis

We present observations and cosmic microwave background (CMB) foreground analysis of the Parkes Galactic Meridian Survey, an investigation of the Galactic latitude behaviour of the polarized synchrotron emission at 2.3 GHz with the Parkes Radio Telescope. The survey consists of a 5 degrees wide strip along the Galactic meridian l = 254 degrees extending from the Galactic plane to the South Galactic pole. We identify three zones distinguished by polarized emission properties: the disc, the halo and a transition region connecting them. The halo section lies at latitudes vertical bar b vertical bar > 40 degrees and has weak and smooth polarized emission mostly at large scale with steep angular power spectra of median slope beta(med) similar to -2.6. The disc region covers the latitudes vertical bar b vertical bar <20 degrees and has a brighter, more complex emission dominated by the small scales with flatter spectra of median slope beta(med) = -1.8. The transition region has steep spectra as in the halo, but the emission increases towards the Galactic plane from halo to disc levels. The change of slope and emission structure at b similar to -20 degrees is sudden, indicating a sharp disc-halo transition. The whole halo section is just one environment extended over 50 degrees with very low emission which, once scaled to 70 GHz, is equivalent to the CMB B-mode emission for a tensor-toscalar perturbation power ratio r(halo) = (3.3 +/- 0.4) x 10(-3). Applying a conservative cleaning procedure, we estimate an r detection limit of delta r similar to 2 x 10(-3) at 70 GHz (3 sigma confidence limit) and, assuming a dust polarization fraction of <12 per cent, dr similar to 1 x 10(-2) at 150 GHz. The 150-GHz limit matches the goals of planned sub-orbital experiments, which can therefore be conducted at this high frequency. The 70-GHz limit is close to the goal of proposed next-generation space missions, which thus might not strictly require space-based platforms.

A polarized synchrotron template for cosmic microwave background polarization experiments based on WMAP data

We build template maps for the polarized Galactic--synchrotron emission on large angular scales (FWHM =~7

POLARIZATION OBSERVATIONS IN A LOW SYNCHROTRON EMISSION FIELD AT 1.4 GHZ

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B‐mode contamination by synchrotron emission from 3‐yr Wilkinson Microwave Anisotropy Probe data

), 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

A new approach for a Galactic synchrotron polarized emission template in the microwave range

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Polarized diffuse emission at 2.3 GHz in a high Galactic latitude area

--mode component of the cosmological signal on large--scale, even in models with low--reionization (