1,223 research outputs found
Efficient data structures for masks on 2D grids
This article discusses various methods of representing and manipulating
arbitrary coverage information in two dimensions, with a focus on space- and
time-efficiency when processing such coverages, storing them on disk, and
transmitting them between computers. While these considerations were originally
motivated by the specific tasks of representing sky coverage and cross-matching
catalogues of astronomical surveys, they can be profitably applied in many
other situations as well.Comment: accepted by A&
Circular scans for CMB anisotropy observation and analysis
A number of experiments for measuring anisotropies of the Cosmic Microwave
Background use scanning strategies in which temperature fluctuations are
measured along circular scans on the sky. It is possible, from a large number
of such intersecting circular scans, to build two-dimensional sky maps for
subsequent analysis. However, since instrumental effects --- especially the
excess low-frequency 1/f noise --- project onto such two-dimensional maps in a
non-trivial way, we discuss the analysis approach which focuses on information
contained in the individual circular scans. This natural way of looking at CMB
data from experiments scanning on the circles combines the advantages of
elegant simplicity of Fourier series for the computation of statistics useful
for constraining cosmological scenarios,and superior efficiency in analysing
and quantifying most of the crucial instrumental effects.Comment: 10 pages, 5 figures (.ps), submitted to MNRA
CMB Polarization Systematics Due to Beam Asymmetry: Impact on Inflationary Science
CMB polarization provides a unique window into cosmological inflation; the
amplitude of the B-mode polarization from last scattering is uniquely sensitive
to the energetics of inflation. However, numerous systematic effects arising
from optical imperfections can contaminate the observed B-mode power spectrum.
In particular, systematic effects due to the coupling of the underlying
temperature and polarization fields with elliptical or otherwise asymmetric
beams yield spurious systematic signals. This paper presents a non-perturbative
analytic calculation of some of these signals. We show that results previously
derived in real space can be generalized, formally, by including infinitely
many higher-order corrections to the leading order effects. These corrections
can be summed and represented as analytic functions when a fully Fourier-space
approach is adopted from the outset. The formalism and results presented in
this paper were created to determine the susceptibility of CMB polarization
probes of the primary gravitational wave signal but can be easily extended to
the analysis of gravitational lensing of the CMB.Comment: 14 pages, 11 figures, 6 tables. Minor corrections included to match
published versio
Three-Point Statistics from a New Perspective
Multipole expansion of spatial three-point statistics is introduced as a tool
for investigating and displaying configuration dependence. The novel
parametrization renders the relation between bi-spectrum and three-point
correlation function especially transparent as a set of two-dimensional Hankel
transforms. It is expected on theoretical grounds, that three-point statistics
can be described accurately with only a few multipoles. In particular, we show
that in the weakly non-linear regime, the multipoles of the reduced bispectrum,
, are significant only up to quadrupole. Moreover, the non-linear bias in
the weakly non-linear regime only affects the monopole order of these
statistics. As a consequence, a simple, novel set of estimators can be
constructed to constrain galaxy bias. In addition, the quadrupole to dipole
ratio is independent of the bias, thus it becomes a novel diagnostic of the
underlying theoretical assumptions: weakly non-linear gravity and perturbative
local bias. To illustrate the use of our approach, we present predictions based
on both power law, and CDM models. We show that the presently favoured
SDSS-WMAP concordance model displays strong ``baryon bumps'' in the 's.
Finally, we sketch out three practical techniques estimate these novel
quantities: they amount to new, and for the first time edge corrected,
estimators for the bispectrum.Comment: 5 pages 6 figures, ApL accepte
CMB Polarization Systematics Due to Beam Asymmetry: Impact on Inflationary Science
CMB polarization provides a unique window into cosmological inflation; the
amplitude of the B-mode polarization from last scattering is uniquely sensitive
to the energetics of inflation. However, numerous systematic effects arising
from optical imperfections can contaminate the observed B-mode power spectrum.
In particular, systematic effects due to the coupling of the underlying
temperature and polarization fields with elliptical or otherwise asymmetric
beams yield spurious systematic signals. This paper presents a non-perturbative
analytic calculation of some of these signals. We show that results previously
derived in real space can be generalized, formally, by including infinitely
many higher-order corrections to the leading order effects. These corrections
can be summed and represented as analytic functions when a fully Fourier-space
approach is adopted from the outset. The formalism and results presented in
this paper were created to determine the susceptibility of CMB polarization
probes of the primary gravitational wave signal but can be easily extended to
the analysis of gravitational lensing of the CMB.Comment: 14 pages, 11 figures, 6 tables. Minor corrections included to match
published versio
- …