82 research outputs found
B-Mode contamination by synchrotron emission from 3-years WMAP data
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-years 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% 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%
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 (T/S>0.3). Such regions allow to be measured directly which approximately corresponds to the
limit imposed by using a sky coverage of 15%. This opens interesting
perspectives to investigate the inflationary model space in lowest emission
regions.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter
The synchrotron foreground and CMB temperature-polarization cross correlation power spectrum from the first year WMAP data
We analyse the temperature-polarization cross-correlation in the Galactic
synchrotron template that we have recently developed, and between the template
and 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 contamined by synchrotron, no evidence for
contamination is found in the multipole range which is most relevant for the
fit of the cosmological optical depth.Comment: Accepted for pubblication on MNRAS Lette
Polarized Diffuse Emission at 2.3 GHz in a High Galactic Latitude Area
Polarized diffuse emission observations at 2.3 GHz in a high Galactic
latitude area are presented. The 2\degr X 2\degr field, centred in
(\alpha=5^h,\delta=-49\degr), is located in the region observed by the
BOOMERanG experiment. Our observations has been carried out with the Parkes
Radio telescope and represent the highest frequency detection done to date in
low emission areas. Because of a weaker Faraday rotation action, the high
frequency allows an estimate of the Galactic synchrotron contamination of the
Cosmic Microwave Background Polarization (CMBP) that is more reliable than that
done at 1.4 GHz. We find that the angular power spectra of the E- and B-modes
have slopes of \beta_E = -1.46 +/- 0.14 and \beta_B = -1.87 +/- 0.22,
indicating a flattening with respect to 1.4 GHz. Extrapolated up to 32 GHz, the
E-mode spectrum is about 3 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
degrees). We find that the CMBP B-mode should be stronger than synchrotron
contamination at 90 GHz for models with T/S > 0.01. This low level could move
down to 60-70 GHz the optimal window for CMBP measures.Comment: 5 pages, 6 figures, accepted for publication in MNRAS Letter
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), 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 --mode component
of the cosmological signal on large--scale, even in models with
low--reionization (). Detection of the weaker --mode on the
largest scales () might be jeopardized unless the value found by WMAP is confirmed, and . For lower levels of the
gravitational--wave background the --mode seems to be accessible only at the
peak and in selected low--synchrotron emission areas.Comment: 13 pages, 14 figures, accepted for pubblications by MNRAS. For a
version with full resolution color figures see
http://sp0rt.bo.iasf.cnr.it:8080/Docs/Public/papers.ph
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
with a sort of instrumental polarization beam 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 -mode--like pattern, the
contamination does not depend on the scanning strategy and the instrumental
polarization map does not have -mode contamination, making axisymmetric
systems suitable to detect the faint -mode signal of the Cosmic Microwave
Background Polarization. The -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
-mode is negligible in the -range of interest for CMBP large angular
scale investigations (multipole ).Comment: 9 pages, accepted for publication on A&
Observations of the diffuse near-IR sky emission with a balloon-borne infrared telescope (TRIP)
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 is
larger than that of the Sun illumination () by a factor , 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.Comment: 12 pages, 11 figures. Accepted for publication in A&
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 with slopes \beta_E = -1.97 \pm 0.08 and
\beta_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.Comment: 13 pages, 11 figures, accepted for publication in MNRA
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