7,196 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
Kramers equation for a charged Brownian particle: The exact solution
We report the exact fundamental solution for Kramers equation associated to a
brownian gas of charged particles, under the influence of homogeneous
(spatially uniform) otherwise arbitrary, external mechanical, electrical and
magnetic fields. Some applications are presented, namely the
hydrothermodynamical picture for Brownian motion in the long time regime.Comment: minor correction
Some Good Reasons to Use Matched Filters for the Detection of Point Sources in CMB Maps
In this draft we comment on the results concerning the performances of
matched filters, scale adaptive filters and Mexican hat wavelet that recently
appeared in literature in the context of point source detection in Cosmic
Microwave Background maps. In particular, we show that, contrary to what has
been claimed, the use of the matched filters still appear to be the most
reliable and efficient method to disantangle point sources from the
backgrounds, even when using detection criterion that, differently from the
classic thresholding rule, takes into account not only the height of
the peaks in the signal corresponding to the candidate sources but also their
curvature.Comment: Replacement after submission to A&A and referee's comments. Astronomy
and Astrophysics, in press, JNL/2003/473
A linear filter to reconstruct the ISW effect from CMB and LSS observations
The extraction of a signal from some observational data sets that contain
different contaminant emissions, often at a greater level than the signal
itself, is a common problem in Astrophysics and Cosmology. The signal can be
recovered, for instance, using a simple Wiener filter. However, in certain
cases, additional information may also be available, such as a second
observation which correlates to a certain level with the sought signal. In
order to improve the quality of the reconstruction, it would be useful to
include as well this additional information. Under these circumstances, we have
constructed a linear filter, the linear covariance-based filter, that extracts
the signal from the data but takes also into account the correlation with the
second observation. To illustrate the performance of the method, we present a
simple application to reconstruct the so-called Integrated Sachs-Wolfe effect
from simulated observations of the Cosmic Microwave Background and of
catalogues of galaxies.Comment: 8 pages, 6 figures, accepted for publication in the IEEE Journal of
Selected Topics in Signal Processin
Non-Gaussianity analysis on local morphological measures of WMAP data
The decomposition of a signal on the sphere with the steerable wavelet
constructed from the second Gaussian derivative gives access to the
orientation, signed-intensity, and elongation of the signal's local features.
In the present work, the non-Gaussianity of the WMAP temperature data of the
cosmic microwave background (CMB) is analyzed in terms of the first four
moments of the statistically isotropic random fields associated with these
local morphological measures, at wavelet scales corresponding to angular sizes
between 27.5 arcminutes and 30 degrees on the celestial sphere. While no
detection is made neither in the orientation analysis nor in the elongation
analysis, a strong detection is made in the excess kurtosis of the
signed-intensity of the WMAP data. The non-Gaussianity is observed with a
significance level below 0.5% at a wavelet scale corresponding to an angular
size around 10 degrees, and confirmed at neighbour scales. This supports a
previous detection of an excess of kurtosis in the wavelet coefficient of the
WMAP data with the axisymmetric Mexican hat wavelet (Vielva et al. 2004).
Instrumental noise and foreground emissions are not likely to be at the origin
of the excess of kurtosis. Large-scale modulations of the CMB related to some
unknown systematics are rejected as possible origins of the detection. The
observed non-Gaussianity may therefore probably be imputed to the CMB itself,
thereby questioning the basic inflationary scenario upon which the present
concordance cosmological model relies. Taking the CMB temperature angular power
spectrum of the concordance cosmological model at face value, further analysis
also suggests that this non-Gaussianity is not confined to the directions on
the celestial sphere with an anomalous signed-intensity.Comment: 10 pages, 3 figures. Version 2 includes minor changes to match
version accepted for publication in MNRA
Collision-free inverse kinematics of a 7 link cucumber picking robot
The paper presents results of research on inverse kinematics algorithms to be used in a functional model of a cucumber harvesting robot consisting of a redundant manipulator with one prismatic and six rotational joints (P6R). Within a first generic approach, the inverse kinematics problem was reformulated as a non-linear programming problem and solved with a generic algorithm. Solutions were easily obtained, but the considerable calculation time needed to solve the problem prevented on line implementation. To circumvent this problem, a second, less generic approach was developed consisting of a mixed numerical-analytic solution of the inverse kinematics problem exploiting the particular structure of the P6R manipulator. This approach facilitated rapid and robust calculation of the inverse kinematics of the cucumber harvester. During the early stages of the cucumber harvesting project, this inverse kinematics algorithm was used to off-line evaluate the ability of the robot to harvest cucumbers using 3D-information of a cucumber crop obtained in a real greenhouse. Thereafter, the algorithm was employed successfully in a functional model of the cucumber harvester to determine if cucumbers were hanging within the reachable workspace of the robot and to determine a collision-free harvest posture to be used for motion control of the manipulator during harvesting
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
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