53,002 research outputs found
Steerable wavelet analysis of CMB structures alignment
This paper reviews the application of a novel methodology for analysing the
isotropy of the universe by probing the alignment of local structures in the
CMB. The strength of the proposed methodology relies on the steerable wavelet
filtering of the CMB signal. One the one hand, the filter steerability renders
the computation of the local orientation of the CMB features affordable in
terms of computation time. On the other hand, the scale-space nature of the
wavelet filtering allows to explore the alignment of the local structures at
different scales, probing possible different phenomena. We present the WMAP
first-year data analysis recently performed by the same authors (Wiaux et al.),
where an extremely significant anisotropy was found. In particular, a preferred
plane was detected, having a normal direction with a northern end position
close to the northern end of the CMB dipole axis. In addition, a most preferred
direction was found in that plane, with a northern end direction very close to
the north ecliptic pole. This result synthesised for the first time previously
reported anomalies identified in the direction of the dipole and the ecliptic
poles axes. In a forthcoming paper (Vielva et al.), we have extended our
analysis to the study of individual frequency maps finding first indications
for discarding foregrounds as the origin of the anomaly. We have also tested
that the preferred orientations are defined by structures homogeneously
distributed in the sky, rather than from localised regions. We have also
analysed the WMAP 3-year data, finding the same anomaly pattern, although at a
slightly lower significance level.Comment: 14 pages, 8 figures. Proceedings of the Fundamental Physics With CMB
workshop, UC Irvine, March 23-25, 2006, to be published in New Astronomy
Review
Alignment and signed-intensity anomalies in WMAP data
Significant alignment and signed-intensity anomalies of local features of the
cosmic microwave background (CMB) are detected on the three-year WMAP data,
through a decomposition of the signal with steerable wavelets on the sphere.
Firstly, an alignment analysis identifies two mean preferred planes in the sky,
both with normal axes close to the CMB dipole axis. The first plane is defined
by the directions toward which local CMB features are anomalously aligned. A
mean preferred axis is also identified in this plane, located very close to the
ecliptic poles axis. The second plane is defined by the directions anomalously
avoided by local CMB features. This alignment anomaly provides further insight
on recent results (Wiaux et al. 2006). Secondly, a signed-intensity analysis
identifies three mean preferred directions in the southern galactic hemisphere
with anomalously high or low temperature of local CMB features: a cold spot
essentially identified with a known cold spot (Vielva et al. 2004), a second
cold spot lying very close to the southern end of the CMB dipole axis, and a
hot spot lying close to the southern end of the ecliptic poles axis. In both
analyses, the anomalies are observed at wavelet scales corresponding to angular
sizes around 10 degress on the celestial sphere, with global significance
levels around 1%. Further investigation reveals that the alignment and
signed-intensity anomalies are only very partially related. Instrumental noise,
foreground emissions, as well as some form of other systematics, are strongly
rejected as possible origins of the detections. An explanation might still be
envisaged in terms of a global violation of the isotropy of the Universe,
inducing an intrinsic statistical anisotropy of the CMB.Comment: 12 pages, 7 figures. Accepted for publication in MNRAS. Small changes
made (including the new subsection 3.4) to match the final versio
Cross-correlation of the CMB and radio galaxies in real, harmonic and wavelet spaces: detection of the integrated Sachs-Wolfe effect and dark energy constraints
We report the first detection of the ISW effect in wavelet space, at scales
in the sky around 7 degrees with a significance of around 3.3 sigma, by
cross-correlating the WMAP first-year data and the NRAO VLA Sky Survey (NVSS).
In addition, we present a detailed comparison among the capabilities of three
different techniques for two different objectives: to detect the ISW and to put
constraints in the nature of the dark energy. The three studied techniques are:
the cross-angular power spectrum (CAPS, harmonic space), the correlation
function (CCF, real space) and the covariance of the Spherical Mexican Hat
Wavelet (SMHW) coefficients (CSMHW, wavelet space). We prove that the CSMHW is
expected to provide a higher detection of the ISW effect for a certain scale.
This prediction has been corroborated by the analysis of the data. The SMHW
analysis shows that the cross-correlation signal is caused neither by
systematic effects nor foreground contamination. However, by taking into
account the information encoded in all the multipoles/scales/angles, the CAPS
provides slightly better constraints than the SMHW in the cosmological
parameters that define the nature of the dark energy. The limits provided by
the CCF are wider than for the other two methods. Two different cases have been
studied: 1) a flat Lambda-CDM universe and 2) a flat universe with an equation
of state parameter different from -1. In the first case, the CAPS provides (for
a bias value of b = 1.6) 0.59 < Lambda density < 0.84 (at 1 sigma CL).
Moreover, the CAPS rejects the range Lambda density < 0.1 at 3.5 sigma, which
is the highest detection of the dark energy reported up to date. In the second
case, the CAPS gives 0.50 < dark energy density < 0.82 and -1.16 < w < 0.43 (at
1 sigma CL).Comment: 12 pages, 7 figures, accepted for publication in MNRAS. Analysis
redone. Changes in the estimation of the cosmological parametres. Additional
comparison between wavelets and more standard technique
Three body resonances in two meson-one baryon systems
We report four 's and three 's, in the 1500 - 1800 MeV
region, as two meson - one baryon S-wave resonances. We solve Faddeev
equations in the coupled channel approach. The invariant mass of one of the
meson-baryon pairs and that of the three particles have been varied and peaks
in the squared three body -matrix have been found very close to the existing
= -1, low lying baryon resonances. The input two-body
-matrices for meson-meson and meson-baryon interaction have been calculated
by solving the Bethe-Salpeter equation with the potentials obtained in the
chiral unitary approach.Comment: corrected version, new channels evaluated, new references adde
CCD photometry in the region of NGC 6994: the remains of an old open cluster
We present the results of BV(RI)_KC CCD photometry down to V=21 mag in the
region of NGC 6994. To our knowledge, no photometry has previously been
reported for this object and we find evidences that it is a poor and sparse old
open cluster, with a minimum angular diameter of 9 arcmin, i.e. larger than the
3 arcmin originally assigned to it. We obtain a color excess E(B-V) = 0.07 +/-
0.02 mag by means of the BVI_(C) technique. Based on the theoretical isochrones
from VandenBergh (1985) that are in better agreement with our data, we estimate
for this cluster a distance from the Sun of 620 pc (Vo-Mv = 9 +/- 0.25 mag) and
an age lying within the range of 2 - 3 Gyr, adopting solar metallicity. Thus,
the corresponding cluster's Galactocentric distance is 8.1 kpc and is placed at
about 350 pc below the Galactic plane. According to this results, NGC 6994
belongs to the old open cluster population located in the outer disk and at
large distances from the Galactic plane, and must have suffered significant
individual dynamical evolution, resulting in mass segregation and evaporation
of low mass stars.Comment: 10 pages including 11 figures and 1 table. Accepted for publication
in Astronomy & Astrophysic
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
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