156 research outputs found
CMB Observations: improvements of the performance of correlation radiometers by signal modulation and synchronous detection
Observation of the fine structures (anisotropies, polarization, spectral
distortions) of the Cosmic Microwave Background (CMB) is hampered by
instabilities, 1/f noise and asymmetries of the radiometers used to carry on
the measurements. Addition of modulation and synchronous detection allows to
increase the overall stability and the noise rejection of the radiometers used
for CMB studies. In this paper we discuss the advantages this technique has
when we try to detect CMB polarization. The behaviour of a two channel
correlation receiver to which phase modulation and synchronous detection have
been added is examined. Practical formulae for evaluating the improvements are
presented.Comment: 18 pages, 3 figures, New Astronomy accepte
Far infrared polarimeter with very low instrumental polarization
After a short analysis of the main problems involved in the construction of a
Far Infrared polarimeter with very low instrumental noise, we describe the
instrument that will be employed at MITO telescope to search for calibration
sources and investigate polarization near the CMB anisotropy peaks in the next
campaign (Winter 2002-03).Comment: 9 pages, 5 figures, to appear in SPIE conference proceedings
"Astronomical telescopes and instrumentation
Recent results and perspectives on cosmology and fundamental physics from microwave surveys
Recent cosmic microwave background data in temperature and polarization have
reached high precision in estimating all the parameters that describe the
current so-called standard cosmological model. Recent results about the
integrated Sachs-Wolfe effect from cosmic microwave background anisotropies,
galaxy surveys, and their cross-correlations are presented. Looking at fine
signatures in the cosmic microwave background, such as the lack of power at low
multipoles, the primordial power spectrum and the bounds on non-Gaussianities,
complemented by galaxy surveys, we discuss inflationary physics and the
generation of primordial perturbations in the early Universe. Three important
topics in particle physics, the bounds on neutrinos masses and parameters, on
thermal axion mass and on the neutron lifetime derived from cosmological data
are reviewed, with attention to the comparison with laboratory experiment
results. Recent results from cosmic polarization rotation analyses aimed at
testing the Einstein equivalence principle are presented. Finally, we discuss
the perspectives of next radio facilities for the improvement of the analysis
of future cosmic microwave background spectral distortion experiments.Comment: 27 pages, 9 figures. Review Article. International Journal of Modern
Physics D, in press. [Will appear also on the proceedings of the Fourteenth
Marcel Grossmann Meeting University of Rome "La Sapienza" - Rome, July 12-18,
2015 (http://www.icra.it/mg/mg14/), eds. Robert T. Jantzen, Kjell Rosquist,
Remo Ruffini. World Scientific, Singapore
Puzzling large-scale polarization in the galaxy cluster Abell 523
Large-scale magnetic fields reveal themselves through diffuse synchrotron
sources observed in galaxy clusters such as radio halos. Total intensity
filaments of these sources have been observed in polarization as well, but only
in three radio halos out of about one hundred currently known. In this paper we
analyze new polarimetric Very Large Array data of the diffuse emission in the
galaxy cluster Abell 523 in the frequency range 1-2 GHz. We find for the first
time evidence of polarized emission on scales of ~ 2.5 Mpc. Total intensity
emission is observed only in the central part of the source, likely due to
observational limitations. To look for total intensity emission beyond the
central region, we combine these data with single-dish observations from the
Sardinia Radio Telescope and we compare them with multi-frequency total
intensity observations obtained with different instruments, including the LOw
Frequency ARray and the Murchison Widefield Array. By analysing the rotation
measure properties of the system and utilizing numerical simulations, we infer
that this polarized emission is associated with filaments of the radio halo
located in the outskirts of the system, in the peripheral region closest to the
observer.Comment: 14 pages, 12 figures, accepted for publication on MNRA
SWIPE: a bolometric polarimeter for the Large-Scale Polarization Explorer
The balloon-borne LSPE mission is optimized to measure the linear
polarization of the Cosmic Microwave Background at large angular scales. The
Short Wavelength Instrument for the Polarization Explorer (SWIPE) is composed
of 3 arrays of multi-mode bolometers cooled at 0.3K, with optical components
and filters cryogenically cooled below 4K to reduce the background on the
detectors. Polarimetry is achieved by means of large rotating half-wave plates
and wire-grid polarizers in front of the arrays. The polarization modulator is
the first component of the optical chain, reducing significantly the effect of
instrumental polarization. In SWIPE we trade angular resolution for
sensitivity. The diameter of the entrance pupil of the refractive telescope is
45 cm, while the field optics is optimized to collect tens of modes for each
detector, thus boosting the absorbed power. This approach results in a FWHM
resolution of 1.8, 1.5, 1.2 degrees at 95, 145, 245 GHz respectively. The
expected performance of the three channels is limited by photon noise,
resulting in a final sensitivity around 0.1-0.2 uK per beam, for a 13 days
survey covering 25% of the sky.Comment: In press. Copyright 2012 Society of Photo-Optical Instrumentation
Engineers. One print or electronic copy may be made for personal use only.
Systematic reproduction and distribution, duplication of any material in this
paper for a fee or for commercial purposes, or modification of the content of
the paper are prohibite
Cosmological Parameters from Pre-Planck CMB Measurements
Recent data from the WMAP, ACT and SPT experiments provide precise
measurements of the cosmic microwave background temperature power spectrum over
a wide range of angular scales. The combination of these observations is well
fit by the standard, spatially flat LCDM cosmological model, constraining six
free parameters to within a few percent. The scalar spectral index, n_s =
0.9690 +/- 0.0089, is less than unity at the 3.6 sigma level, consistent with
simple models of inflation. The damping tail of the power spectrum at high
resolution, combined with the amplitude of gravitational lensing measured by
ACT and SPT, constrains the effective number of relativistic species to be
N_eff = 3.28 +/- 0.40, in agreement with the standard model's three species of
light neutrinos.Comment: 5 pages, 4 figure
The Atacama Cosmology Telescope: Galactic Dust Structure and the Cosmic PAH Background in Cross-correlation with WISE
We present a cross-correlation analysis between resolution total
intensity and polarization observations from the Atacama Cosmology Telescope
(ACT) at 150 and 220 GHz and 15 mid-infrared photometry from the Wide-field
Infrared Survey Explorer (WISE) over 107 12.512.5 patches
of sky. We detect a spatially isotropic signal in the WISEACT
cross power spectrum at 30 significance that we interpret as the
correlation between the cosmic infrared background at ACT frequencies and
polycyclic aromatic hydrocarbon (PAH) emission from galaxies in WISE, i.e., the
cosmic PAH background. Within the Milky Way, the Galactic dust spectra are
generally well-described by power laws in over the range 1010, but there is evidence both for variability in the power law index and
for non-power law behavior in some regions. We measure a positive correlation
between WISE total intensity and ACT -mode polarization at 10006000 at 3 in each of 35 distinct 100 deg regions
of the sky, suggesting alignment between Galactic density structures and the
local magnetic field persists to sub-parsec physical scales in these regions.
The distribution of amplitudes in this range across all 107 regions
is biased to positive values, while there is no evidence for such a bias in the
spectra. This work constitutes the highest- measurements of the
Galactic dust spectrum to date and indicates that cross-correlation with
high-resolution mid-infrared measurements of dust emission is a promising tool
for constraining the spatial statistics of dust emission at millimeter
wavelengths.Comment: 20 pages, 14 figures, submitted to Ap
The Atacama Cosmology Telescope: Temperature and Gravitational Lensing Power Spectrum Measurements from Three Seasons of Data
We present the temperature power spectra of the cosmic microwave background
(CMB) derived from the three seasons of data from the Atacama Cosmology
Telescope (ACT) at 148 GHz and 218 GHz, as well as the cross-frequency spectrum
between the two channels. We detect and correct for contamination due to the
Galactic cirrus in our equatorial maps. We present the results of a number of
tests for possible systematic error and conclude that any effects are not
significant compared to the statistical errors we quote. Where they overlap, we
cross-correlate the ACT and the South Pole Telescope (SPT) maps and show they
are consistent. The measurements of higher-order peaks in the CMB power
spectrum provide an additional test of the Lambda CDM cosmological model, and
help constrain extensions beyond the standard model. The small angular scale
power spectrum also provides constraining power on the Sunyaev-Zel'dovich
effects and extragalactic foregrounds. We also present a measurement of the CMB
gravitational lensing convergence power spectrum at 4.6-sigma detection
significance.Comment: 21 pages; 20 figures, Submitted to JCAP, some typos correcte
The Atacama Cosmology Telescope: Sunyaev-Zel'dovich Selected Galaxy Clusters at 148 GHz from Three Seasons of Data
[Abridged] We present a catalog of 68 galaxy clusters, of which 19 are new
discoveries, detected via the Sunyaev-Zel'dovich effect (SZ) at 148 GHz in the
Atacama Cosmology Telescope (ACT) survey of 504 square degrees on the celestial
equator. A subsample of 48 clusters within the 270 square degree region
overlapping SDSS Stripe 82 is estimated to be 90% complete for M_500c > 4.5e14
Msun and 0.15 < z < 0.8. While matched filters are used to detect the clusters,
the sample is studied further through a "Profile Based Amplitude Analysis"
using a single filter at a fixed \theta_500 = 5.9' angular scale. This new
approach takes advantage of the "Universal Pressure Profile" (UPP) to fix the
relationship between the cluster characteristic size (R_500) and the integrated
Compton parameter (Y_500). The UPP scalings are found to be nearly identical to
an adiabatic model, while a model incorporating non-thermal pressure better
matches dynamical mass measurements and masses from the South Pole Telescope. A
high signal to noise ratio subsample of 15 ACT clusters is used to obtain
cosmological constraints. We first confirm that constraints from SZ data are
limited by uncertainty in the scaling relation parameters rather than sample
size or measurement uncertainty. We next add in seven clusters from the ACT
Southern survey, including their dynamical mass measurements based on galaxy
velocity dispersions. In combination with WMAP7 these data simultaneously
constrain the scaling relation and cosmological parameters, yielding \sigma_8 =
0.829 \pm 0.024 and \Omega_m = 0.292 \pm 0.025. The results include
marginalization over a 15% bias in dynamical mass relative to the true halo
mass. In an extension to LCDM that incorporates non-zero neutrino mass density,
we combine our data with WMAP7+BAO+Hubble constant measurements to constrain
\Sigma m_\nu < 0.29 eV (95% C. L.).Comment: 32 pages, 21 figures To appear in J. Cosmology and Astroparticle
Physic
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