2,479 research outputs found
On the recovery of ISW fluctuations using large-scale structure tracers and CMB temperature and polarization anisotropies
In this work we present a method to extract the signal induced by the
integrated Sachs-Wolfe (ISW) effect in the cosmic microwave background (CMB).
It makes use of the Linear Covariance-Based filter introduced by Barreiro et
al., and combines CMB data with any number of large-scale structure (LSS)
surveys and lensing information. It also exploits CMB polarization to reduce
cosmic variance. The performance of the method has been thoroughly tested with
simulations taking into account the impact of non-ideal conditions such as
incomplete sky coverage or the presence of noise. In particular, three galaxy
surveys are simulated, whose redshift distributions peak at low (), intermediate () and high redshift (). The
contribution of each of the considered data sets as well as the effect of a
mask and noise in the reconstructed ISW map is studied in detail. When
combining all the considered data sets (CMB temperature and polarization, the
three galaxy surveys and the lensing map), the proposed filter successfully
reconstructs a map of the weak ISW signal, finding a perfect correlation with
the input signal for the ideal case and around 80 per cent, on average, in the
presence of noise and incomplete sky coverage. We find that including CMB
polarization improves the correlation between input and reconstruction although
only at a small level. Nonetheless, given the weakness of the ISW signal, even
modest improvements can be of importance. In particular, in realistic
situations, in which less information is available from the LSS tracers, the
effect of including polarisation is larger. For instance, for the case in which
the ISW signal is recovered from CMB plus only one survey, and taking into
account the presence of noise and incomplete sky coverage, the improvement in
the correlation coefficient can be as large as 10 per cent.Comment: 17 pages, 15 figures, accepted for publication in MNRA
On the void explanation of the Cold Spot
The integrated Sachs-Wolfe (ISW) contribution induced on the cosmic microwave
background by the presence of a supervoid as the one detected by Szapudi et al.
(2015) is reviewed in this letter in order to check whether it could explain
the Cold Spot (CS) anomaly. Two different models, previously used for the same
purpose, are considered to describe the matter density profile of the void: a
top hat function and a compensated profile produced by a Gaussian potential.
The analysis shows that, even enabling ellipticity changes or different values
for the dark-energy equation of state parameter , the ISW contribution
due to the presence of the void does not reproduce the properties of the CS.
Finally, the probability of alignment between the void and the CS is also
questioned as an argument in favor of a physical connection between these two
phenomena
Analytic Framework for Students' Use of Mathematics in Upper-Division Physics
Many students in upper-division physics courses struggle with the
mathematically sophisticated tools and techniques that are required for
advanced physics content. We have developed an analytical framework to assist
instructors and researchers in characterizing students' difficulties with
specific mathematical tools when solving the long and complex problems that are
characteristic of upper-division. In this paper, we present this framework,
including its motivation and development. We also describe an application of
the framework to investigations of student difficulties with direct integration
in electricity and magnetism (i.e., Coulomb's Law) and approximation methods in
classical mechanics (i.e., Taylor series). These investigations provide
examples of the types of difficulties encountered by advanced physics students,
as well as the utility of the framework for both researchers and instructors.Comment: 17 pages, 4 figures, 3 tables, in Phys. Rev. - PE
Integrated Sachs-Wolfe map recovery from NVSS and WMAP 7yr data
We present a map of the Cosmic Microwave Background (CMB) anisotropies
induced by the late Integrated Sachs Wolfe effect. The map is constructed by
combining the information of the WMAP 7-yr CMB data and the NRAO VLA Sky Survey
(NVSS) through a linear filter. This combination improves the quality of the
map that would be obtained using information only from the Large Scale
Structure data. In order to apply the filter, a given cosmological model needs
to be assumed. In particular, we consider the standard LCDM model. As a test of
consistency, we show that the reconstructed map is in agreemet with the assumed
model, which is also favoured against a scenario where no correlation between
the CMB and NVSS catalogue is considered.Comment: 6 pages, 4 figures. Minor revision, accepted for publication in MNRA
Exploring two-spin internal linear combinations for the recovery of the CMB polarization
We present a methodology to recover cosmic microwave background (CMB)
polarization in which the quantity is linearly combined at
different frequencies using complex coefficients. This is the most general
linear combination of the and Stokes parameters which preserves the
physical coherence of the residual contribution on the CMB estimation. The
approach is applied to the internal linear combination (ILC) and the internal
template fitting (ITF) methodologies. The variance of of the resulting map
is minimized to compute the coefficients of the linear combination. One of the
key aspects of this procedure is that it serves to account for a global
frequency-dependent shift of the polarization phase. Although in the standard
case, in which no global E-B transference depending on frequency is expected in
the foreground components, minimizing is
similar to minimizing and separately (as previous methodologies proceed), multiplying
and by different coefficients induces arbitrary changes in the
polarization angle and it does not preserve the coherence between the spinorial
components. The approach is tested on simulations, obtaining a similar residual
level with respect to the one obtained with other implementations of the ILC,
and perceiving the polarization rotation of a toy model with the frequency
dependence of the Faraday rotation.Comment: 14 pages, 8 figures, 2 tables. Accepted for publication in MNRA
Radial derivatives as a test of pre-Big-Bang events on the Planck data
Although the search for azimutal patterns in cosmological surveys is useful
to characterise some effects depending exclusively on an angular distance
within the standard model, they are considered as a key distinguishing feature
of some exotic scenarios, such as bubble collisions or conformal cyclic
cosmology (CCC). In particular, the CCC is a non-stardard framework which
predicts circular patterns on the CMB intensity fluctuations. Motivated by some
previous works which explore the presence of radial gradients, we apply a
methodology based on the radial derivatives to the latest release of
\textit{Planck} data. The new approach allows exhaustive studies to be
performed at all sky directions at a HEALPix resolution of . Specifically, two different analyses are performed focusing on weight
functions in both small (up to a -degree radius) and large scales. We
present a comparison between our results and those shown by An et al. (2017),
and An et al. (2018). In addition, a possible polarization counterpart of these
circular patterns is also analysed for the most promising case. Taking into
account the limitations to characterize the significance of the results,
including the possibility of suffering a look-elsewhere effect, no strong
evidence of the kind of circular patterns expected from CCC is found in the
\textit{Planck} data for either the small or the large scales.Comment: 8 figures, 4 table
Bayesian inference methodology for Primordial Power Spectrum reconstructions from Large Scale Structure
We use Bayesian inference and nested sampling to develop a non-parametric
method to reconstruct the primordial power spectrum from
Large Scale Structure (LSS) data. The performance of the method is studied by
applying it to simulations of the clustering of two different object
catalogues, low- (ELGs) and high- (QSOs), and considering two different
photometric errors. These object clusterings are derived from different
templates of the primordial power spectrum motivated by models of inflation:
the Standard Model power law characterized by the two parameters and
; a local feature template; and a global oscillatory template. Our
reconstruction method involves sampling knots in the log
plane. We use two statistical tests to examine the
reconstructions for signs of primordial features: a global test comparing the
evidences and a novel local test quantifying the power of the hypothesis test
between the power law model and the marginalized probability over model.
The method shows good performance in all scenarios considered. In particular,
the tests show no feature detection for the SM. The method is able to detect
power spectrum deviations at a level of for all considered
features, combining either the low- or the high- redshift bins. Other
scenarios with different redshift bins, photometric errors, feature amplitudes
and detection levels are also discussed. In addition, we include a first
application to real data from the Sloan Digital Sky Survey Luminous Red Galaxy
Data Release 4 (SDSS LRG 04), finding no preference for deviations from the
primordial power law. The method is flexible, model independent, and suitable
for its application to existing and future LSS catalogues.Comment: 39 pages, 21 figures, submitted to JCA
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