809 research outputs found
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 \nu>1GHz are reviewed. By exploiting all the most relevant data on
the polarized emission of ERS we study the frequency dependence of polarization
properties of ERS between 1.4 and 86GHz. For flat-spectrum sources the median
(mean) fractional polarization increases from 1.5% (2-2.5%) at 1.4GHz to 2.5-3%
(3-3.5%) at \nu>10GHz. Steep-spectrum sources are typically more polarized,
especially at high frequencies where Faraday depolarization is less relevant.
As a general result, we do not find that the fractional polarization of ERS
depends on the total flux density at high radio frequencies, i.e >20GHz.
Moreover, in this frequency range, current data suggest a moderate increase of
the fractional polarization of ERS with frequency. A formalism to estimate ERS
number counts in polarization and the contribution of unresolved polarized ERS
to angular power spectra at Cosmic Microwave Background (CMB) frequencies is
also developed and discussed. As a first application, we present original
predictions for the Planck satellite mission. Our current results show that
only a dozen polarized ERS will be detected by the Planck Low Frequency
Instrument (LFI), and a few tens by the High Frequency Instrument (HFI). As for
CMB power spectra, ERS should not be a strong contaminant to the CMB E-mode
polarization at frequencies \nu>70GHz. On the contrary, they can become a
relevant constraint for the detection of the cosmological B--mode polarization
if the tensor-to-scalar ratio is <0.01.Comment: 14 pages, 7 figures. Accepted for publication in Advances in
Astronomy, Special Issue: "Astrophysical Foregrounds in Microwave Surveys",
editor-in-chief C. Burigana, (www.hindawi.com
Statistics of the fractional polarisation of compact radio sources in Planck maps
In this work we apply the stacking technique to estimate the average
fractional polarisation from 30 to 353 GHz of a primary sample of 1560 compact
sources - essentially all radio sources - detected in the 30 GHz Planck all-sky
map and listed in the second version of the Planck Catalogue of Compact Sources
(PCCS2). We divide our primary sample in two subsamples according to whether
the sources lay (679 sources) or not (881 sources) inside the sky region
defined by the Planck Galactic mask (fsky ~ 60 per cent) and the area around
the Magellanic Clouds. We find that the average fractional polarisation of
compact sources is approximately constant (with frequency) in both samples
(with a weighted mean over all the channels of 3.08 per cent outside and 3.54
per cent inside the Planck mask). In the sky region outside the adopted mask,
we also estimate the {\mu} and {\sigma} parameters for the log-normal
distribution of the fractional polarisation, finding a weighted mean value over
all the Planck frequency range of 1.0 for {\sigma} and 0.7 for {\mu} (that
would imply a weighted mean value for the median fractional polarisation of 1.9
per cent).Comment: 12 pages, 7 figures, 2 tables, MNRAS in pres
Statistics of the fractional polarisation of extragalactic dusty sources in Planck HFI maps
We estimate the average fractional polarisation at 143, 217 and 353 GHz of a
sample of 4697 extragalactic dusty sources by applying stacking technique. The
sample is selected from the second version of the Planck Catalogue of Compact
Sources at 857 GHz, avoiding the region inside the Planck Galactic mask (fsky ~
60 per cent). We recover values for the mean fractional polarisation at 217 and
353 GHz of (3.10 \pm 0.75) per cent and (3.65 \pm 0.66) per cent, respectively,
whereas at 143 GHz we give a tentative value of (3.52 \pm 2.48) per cent. We
discuss the possible origin of the measured polarisation, comparing our new
estimates with those previously obtained from a sample of radio sources. We
test different distribution functions and we conclude that the fractional
polarisation of dusty sources is well described by a log-normal distribution,
as determined in the radio band studies. For this distribution we estimate
{\mu}_{217GHz} = 0.3 \pm 0.5 (that would correspond to a median fractional
polarisation of {\Pi}_{med} = (1.3 \pm 0.7) per cent) and {\mu}_{353GHz} = 0.7
\pm 0.4 ({\Pi}_{med} = (2.0 \pm 0.8) per cent), {\sigma}_{217GHz} = 1.3 \pm 0.2
and {\sigma}_{353GHz} = 1.1 \pm 0.2. With these values we estimate the source
number counts in polarisation and the contribution given by these sources to
the CMB B-mode angular power spectrum at 217, 353, 600 and 800 GHz. We conclude
that extragalactic dusty sources might be an important contaminant for the
primordial B-mode at frequencies > 217 GHz.Comment: arXiv admin note: text overlap with arXiv:1703.0995
Angular Correlations of the X-Ray Background and Clustering of Extragalactic X-Ray Sources
The information content of the autocorrelation function (ACF) of intensity
fluctuations of the X-ray background (XRB) is analyzed. The tight upper limits
set by ROSAT deep survey data on the ACF at arcmin scales imply strong
constraints on clustering properties of X-ray sources at cosmological distances
and on their contribution to the soft XRB. If quasars have a clustering radius
r_0=12-20 Mpc (H_0=50), and their two point correlation function, is constant
in comoving coordinates as indicated by optical data, they cannot make up more
40-50% of the soft XRB (the maximum contribution may reach 80% in the case of
stable clustering, epsilon=0). Active Star-forming (ASF) galaxies clustered
like normal galaxies, with r_0=10-12 Mpc can yield up to 20% or up to 40% of
the soft XRB for epsilon=-1.2 or epsilon=0, respectively. The ACF on degree
scales essentially reflects the clustering properties of local sources and is
proportional to their volume emissivity. The upper limits on scales of a few
degrees imply that hard X-ray selected AGNs have r_0<25 Mpc if epsilon=0 or
r_0<20 Mpc if epsilon=-1.2. No significant constraints are set on clustering of
ASF galaxies, due to their low local volume emissivity. The possible signal on
scales >6 deg, if real, may be due to AGNs with r_0=20 Mpc; the contribution
from clusters of galaxies with r_0~50 Mpc is a factor 2 lower.Comment: ApJ, in press (20 July 1993); 28 pages, TeX, ASTRPD-93-2-0
Contributions of point extragalactic sources to the Cosmic Microwave Background bispectrum
All the analyses of Cosmic Microwave Background (CMB) temperature maps
up--to--date show that CMB anisotropies follow a Gaussian distribution. On the
other hand, astrophysical foregrounds which hamper the detection of the CMB
angular power spectrum, are not Gaussian distributed on the sky. Therefore,
they should give a sizeable contribution to the CMB bispectrum. In fact, the
first year data of the Wilkinson Microwave Anisotropy Probe (WMAP) mission have
allowed the {\it first} detection of the extragalactic source contribution to
the CMB bispectrum at 41 GHz and, at the same time, much tighter limits than
before to non--Gaussian primordial fluctuations. In view of the above and for
achieving higher precision in current and future CMB measurements of
non--Gaussianity, in this paper we discuss a comprehensive assessment of the
bispectrum due to either uncorrelated and clustered extragalactic point sources
in the whole frequency interval around the CMB intensity peak. Our
calculations, based on current cosmological evolution models for sources, show
that the reduced angular bispectrum due to point sources, , should be
detectable in all WMAP and Planck frequency channels. We also find agreement
with the results on at 41 GHz coming from the analysis of the first
year WMAP data. Moreover, by comparing with the primordial reduced CMB
bispectrum, we find that only the peak value of the primordial bispectrum
(which appears at ) results greater than in a frequency
window around the intensity peak of the CMB. The amplitude of this window
basically depends on the capability of the source detection algorithms (i.e.,
on the achievable flux detection limit, , for sources).Comment: 26 pages, 6 Figures, use AasTex5.0, ApJ, in press, Oct. 10, 2003
Issu
Wavelets Applied to CMB Maps: a Multiresolution Analysis for Denoising
Analysis and denoising of Cosmic Microwave Background (CMB) maps are
performed using wavelet multiresolution techniques. The method is tested on
maps with resolution resembling the
experimental one expected for future high resolution space observations.
Semianalytic formulae of the variance of wavelet coefficients are given for the
Haar and Mexican Hat wavelet bases. Results are presented for the standard Cold
Dark Matter (CDM) model. Denoising of simulated maps is carried out by removal
of wavelet coefficients dominated by instrumental noise. CMB maps with a
signal-to-noise, , are denoised with an error improvement factor
between 3 and 5. Moreover we have also tested how well the CMB temperature
power spectrum is recovered after denoising. We are able to reconstruct the
's up to with errors always below in cases with
.Comment: latex file 9 pages + 5 postscript figures + 1 gif figure (figure 6),
to be published in MNRA
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