64 research outputs found
General CMB and Primordial Bispectrum Estimation I: Mode Expansion, Map-Making and Measures of f_NL
We present a detailed implementation of two bispectrum estimation methods
which can be applied to general non-separable primordial and CMB bispectra. The
method exploits bispectrum mode decompositions on the domain of allowed
wavenumber or multipole values. Concrete mode examples constructed from
symmetrised tetrahedral polynomials are given, demonstrating rapid convergence
for known bispectra. We use these modes to generate simulated CMB maps of high
resolution (l > 2000) given an arbitrary primordial power spectrum and
bispectrum or an arbitrary late-time CMB angular power spectrum and bispectrum.
By extracting coefficients for the same separable basis functions from an
observational map, we are able to present an efficient and general f_NL
estimator for a given theoretical model. The estimator has two versions
comparing theoretical and observed coefficients at either primordial or late
times, thus encompassing a wider range of models, including secondary
anisotropies, lensing and cosmic strings. We provide examples and validation of
both f_NL estimation methods by direct comparison with simulations in a
WMAP-realistic context. In addition, we show how the full bispectrum can be
extracted from observational maps using these mode expansions, irrespective of
the theoretical model under study. We also propose a universal definition of
the bispectrum parameter F_NL for more consistent comparison between
theoretical models. We obtain WMAP5 estimates of f_NL for the equilateral model
from both our primordial and late-time estimators which are consistent with
each other, as well as with results already published in the literature. These
general bispectrum estimation methods should prove useful for the analysis of
nonGaussianity in the Planck satellite data, as well as in other contexts.Comment: 41 pages, 17 figure
A high performance cost-effective digital complex correlator for an X-band polarimetry survey
The detailed knowledge of the Milky Way radio emission is important to characterize galactic foregrounds masking extragalactic and cosmological signals. The update of the global sky models describing radio emissions over a very large spectral band requires high sensitivity experiments capable of observing large sky areas with long integration times. Here, we present the design of a new 10 GHz (X-band) polarimeter digital back-end to map the polarization components of the galactic synchrotron radiation field of the Northern Hemisphere sky. The design follows the digital processing trends in radio astronomy and implements a large bandwidth (1 GHz) digital complex cross-correlator to extract the Stokes parameters of the incoming synchrotron radiation field. The hardware constraints cover the implemented VLSI hardware description language code and the preliminary results. The implementation is based on the simultaneous digitized acquisition of the Cartesian components of the two linear receiver polarization channels. The design strategy involves a double data rate acquisition of the ADC interleaved parallel bus, and field programmable gate array device programming at the register transfer mode. The digital core of the back-end is capable of processing 32 Gbps and is built around an Altera field programmable gate array clocked at 250 MHz, 1 GSps analog to digital converters and a clock generator. The control of the field programmable gate array internal signal delays and a convenient use of its phase locked loops provide the timing requirements to achieve the target bandwidths and sensitivity. This solution is convenient for radio astronomy experiments requiring large bandwidth, high functionality, high volume availability and low cost. Of particular interest, this correlator was developed for the Galactic Emission Mapping project and is suitable for large sky area polarization continuum surveys. The solutions may also be adapted to be used at signal processing subsystem levels for large projects like the square kilometer array testbeds
CMB Anisotropy Constraints on Flat-Lambda and Open CDM Cosmogonies from DMR, UCSB South Pole, Python, ARGO, MAX, White Dish, OVRO, and SuZIE Data
We use joint likelihood analyses of combinations of fifteen cosmic microwave
background (CMB) anisotropy data sets from the DMR, UCSB South Pole 1994,
Python I--III, ARGO, MAX 4 and 5, White Dish, OVRO, and SuZIE experiments to
constrain cosmogonies. We consider open and spatially-flat-Lambda cold dark
matter cosmogonies, with nonrelativistic-mass density parameter Omega_0 in the
range 0.1--1, baryonic-mass density parameter Omega_B in the range
(0.005--0.029) h^{-2}, and age of the universe t_0 in the range (10--20) Gyr.
Marginalizing over all parameters but Omega_0, the data favor Omega_0 \simeq
0.9--1 (0.4--0.6) flat-Lambda (open) models. The range in deduced Omega_0
values is partially a consequence of the different combinations of
smaller-angular-scale CMB anisotropy data sets used in the analyses, but more
significantly a consequence of whether the DMR quadrupole moment is accounted
for or ignored in the analysis. For both flat-Lambda and open models, after
marginalizing over all other parameters, a lower Omega_B h^2 \simeq
0.005--0.009 is favored. This is also marginally at odds with estimates from
more recent CMB anisotropy data and some estimates from standard
nucleosynthesis theory and observed light element abundances. For both sets of
models a younger universe with t_0 \simeq 12--15 Gyr is favored, consistent
with other recent non-CMB indicators. We emphasize that since we consider only
a small number of data sets, these results are tentative. More importantly, the
analyses here do not rule out the currently favored flat-Lambda model with
Omega_0 \sim 0.3, nor the larger Omega_B h^2 values favored by some other data.Comment: 25 pages, 10 figures, submitted to ApJ; the abstract here is slightly
abridge
Python I, II, and III CMB Anisotropy Measurement Constraints on Open and Flat-Lambda CDM Cosmogonies
We use Python I, II, and III cosmic microwave background anisotropy data to
constrain cosmogonies. We account for the Python beamwidth and calibration
uncertainties. We consider open and spatially-flat-Lambda cold dark matter
cosmogonies, with nonrelativistic-mass density parameter Omega_0 in the range
0.1--1, baryonic-mass density parameter Omega_B in the range (0.005--0.029)
h^{-2}, and age of the universe t_0 in the range (10--20) Gyr. Marginalizing
over all parameters but Omega_0, the combined Python data favors an open
(spatially-flat-Lambda) model with Omega_0 simeq 0.2 (0.1). At the 2 sigma
confidence level model normalizations deduced from the combined Python data are
mostly consistent with those drawn from the DMR, UCSB South Pole 1994, ARGO,
MAX 4 and 5, White Dish, and SuZIE data sets.Comment: 20 pages, 7 figures, accepted by Ap
CMB polarimetry with BICEP: instrument characterization, calibration, and performance
BICEP is a ground-based millimeter-wave bolometric array designed to target
the primordial gravity wave signature on the polarization of the cosmic
microwave background (CMB) at degree angular scales. Currently in its third
year of operation at the South Pole, BICEP is measuring the CMB polarization
with unprecedented sensitivity at 100 and 150 GHz in the cleanest available 2%
of the sky, as well as deriving independent constraints on the diffuse
polarized foregrounds with select observations on and off the Galactic plane.
Instrument calibrations are discussed in the context of rigorous control of
systematic errors, and the performance during the first two years of the
experiment is reviewed.Comment: 12 pages, 15 figures, updated version of a paper accepted for
Millimeter and Submillimeter Detectors and Instrumentation for Astronomy IV,
Proceedings of SPIE, 7020, 200
Simulation of non-Gaussian CMB maps
A simple method is presented for the rapid simulation of
statistically-isotropic non-Gaussian maps of CMB temperature fluctuations with
a given power spectrum and analytically-calculable bispectrum and higher-order
polyspectra. The th-order correlators of the pixel values may also be
calculated analytically. The cumulants of the simulated map may be used to
obtain an expression for the probability density function of the pixel
temperatures. The statistical properties of the simulated map are determined by
the univariate non-Gaussian distribution from which pixel values are drawn
independently in the first stage of the simulation process. We illustrate the
method using a non-Gaussian distribution derived from the wavefunctions of the
harmonic oscillator. The basic simulation method is easily extended to produce
non-Gaussian maps with a given power spectrum and diagonal bispectrum.Comment: 10 pages, 8 figures (3 coloured), replaced with version accepted by
MNRAS. Figure 3 is not included but a complete version of the paper with high
resolution figures can be downloaded from
(http://www.mrao.cam.ac.uk/~graca/Ngsims/
Absolute polarization angle calibration using polarized diffuse Galactic emission observed by BICEP
We present a method of cross-calibrating the polarization angle of a
polarimeter using BICEP Galactic observations. \bicep\ was a ground based
experiment using an array of 49 pairs of polarization sensitive bolometers
observing from the geographic South Pole at 100 and 150 GHz. The BICEP
polarimeter is calibrated to +/-0.01 in cross-polarization and less than +/-0.7
degrees in absolute polarization orientation. BICEP observed the temperature
and polarization of the Galactic plane (R.A= 100 degrees ~ 270 degrees and Dec.
= -67 degrees ~ -48 degrees). We show that the statistical error in the 100 GHz
BICEP Galaxy map can constrain the polarization angle offset of WMAP Wband to
0.6 degrees +\- 1.4 degrees. The expected 1 sigma errors on the polarization
angle cross-calibration for Planck or EPIC are 1.3 degrees and 0.3 degrees at
100 and 150 GHz, respectively. We also discuss the expected improvement of the
BICEP Galactic field observations with forthcoming BICEP2 and Keck
observations.Comment: 13 pages, 10 figures and 2 tables. To appear in Proceedings of SPIE
Astronomical Telescopes and Instrumentation 201
Searching for non-Gaussianity in the VSA data
We have tested Very Small Array (VSA) observations of three regions of sky
for the presence of non-Gaussianity, using high-order cumulants, Minkowski
functionals, a wavelet-based test and a Bayesian joint power
spectrum/non-Gaussianity analysis. We find the data from two regions to be
consistent with Gaussianity. In the third region, we obtain a 96.7% detection
of non-Gaussianity using the wavelet test. We perform simulations to
characterise the tests, and conclude that this is consistent with expected
residual point source contamination. There is therefore no evidence that this
detection is of cosmological origin. Our simulations show that the tests would
be sensitive to any residual point sources above the data's source subtraction
level of 20 mJy. The tests are also sensitive to cosmic string networks at an
rms fluctuation level of (i.e. equivalent to the best-fit observed
value). They are not sensitive to string-induced fluctuations if an equal rms
of Gaussian CDM fluctuations is added, thereby reducing the fluctuations due to
the strings network to rms . We especially highlight the usefulness
of non-Gaussianity testing in eliminating systematic effects from our data.Comment: Minor corrections; accepted for publication to MNRA
Recommended from our members
Characterization of the BICEP Telescope for High-precision Cosmic Microwave Background Polarimetry
The Background Imaging of Cosmic Extragalactic Polarization (BICEP) experiment was designed specifically to search for the signature of inflationary gravitational waves in the polarization of the cosmic microwave background (CMB). Using a novel small-aperture refractor and 49 pairs of polarization-sensitive bolometers, BICEP has completed three years of successful observations at the South Pole beginning in 2006 February. To constrain the amplitude of the inflationary B-mode polarization, which is expected to be at least 7 orders of magnitude fainter than the 3 K CMB intensity, precise control of systematic effects is essential. This paper describes the characterization of potential systematic errors for the BICEP experiment, supplementing a companion paper on the initial cosmological results. Using the analysis pipelines for the experiment, we have simulated the impact of systematic errors on the B-mode polarization measurement. Guided by these simulations, we have established benchmarks for the characterization of critical instrumental properties including bolometer relative gains, beam mismatch, polarization orientation, telescope pointing, sidelobes, thermal stability, and timestream noise model. A comparison of the benchmarks with the measured values shows that we have characterized the instrument adequately to ensure that systematic errors do not limit BICEP's two-year results, and identifies which future refinements are likely necessary to probe inflationary B-mode polarization down to levels below a tensor-to-scalar ratio r = 0.1.Astronom
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