4,992 research outputs found
The two-and three-point correlation functions of the polarized five-year WMAP sky maps
We present the two- and three-point real space correlation functions of the
five-year WMAP sky maps, and compare the observed functions to simulated LCDM
concordance model ensembles. In agreement with previously published results, we
find that the temperature correlation functions are consistent with
expectations. However, the pure polarization correlation functions are
acceptable only for the 33GHz band map; the 41, 61, and 94 GHz band correlation
functions all exhibit significant large-scale excess structures. Further, these
excess structures very closely match the correlation functions of the two
(synchrotron and dust) foreground templates used to correct the WMAP data for
galactic contamination, with a cross-correlation statistically significant at
the 2sigma-3sigma confidence level. The correlation is slightly stronger with
respect to the thermal dust template than with the synchrotron template.Comment: 10 pages, 5 figures, published in ApJ. v2: New title, minor changes
to appendix, and fixed some typos. v3: Matches version published in Ap
Real space tests of the statistical isotropy and Gaussianity of the WMAP CMB data
ABRIDGED: We introduce and analyze a method for testing statistical isotropy
and Gaussianity and apply it to the WMAP CMB foreground reduced, temperature
maps, and cross-channel difference maps. We divide the sky into regions of
varying size and shape and measure the first four moments of the one-point
distribution within these regions, and using their simulated spatial
distributions we test the statistical isotropy and Gaussianity hypotheses. By
randomly varying orientations of these regions, we sample the underlying CMB
field in a new manner, that offers a richer exploration of the data content,
and avoids possible biasing due to a single choice of sky division. The
statistical significance is assessed via comparison with realistic Monte-Carlo
simulations.
We find the three-year WMAP maps to agree well with the isotropic, Gaussian
random field simulations as probed by regions corresponding to the angular
scales ranging from 6 deg to 30 deg at 68% confidence level. We report a
strong, anomalous (99.8% CL) dipole ``excess'' in the V band of the three-year
WMAP data and also in the V band of the WMAP five-year data (99.3% CL). We
notice the large scale hemispherical power asymmetry, and find that it is not
highly statistically significant in the WMAP three-year data (<~ 97%) at scales
l <= 40. The significance is even smaller if multipoles up to l=1024 are
considered (~90% CL). We give constraints on the amplitude of the
previously-proposed CMB dipole modulation field parameter. We easily detect the
residual foregrounds in cross-band difference maps at rms level <~ 7 \mu K (at
scales >~ 6 deg) and limit the systematical uncertainties to <~ 1.7 \mu K (at
scales >~ 30 deg).Comment: 20 pages, 20 figures; more tests added; updated to match the version
to be published in JCA
Asymmetries in the CMB anisotropy field
We report on the results from two independent but complementary statistical
analyses of the WMAP first-year data, based on the power spectrum and N-point
correlation functions. We focus on large and intermediate scales (larger than
about 3 degrees) and compare the observed data against Monte Carlo ensembles
with WMAP-like properties. In both analyses, we measure the amplitudes of the
large-scale fluctuations on opposing hemispheres and study the ratio of the two
amplitudes. The power-spectrum analysis shows that this ratio for WMAP, as
measured along the axis of maximum asymmetry, is high at the 95%-99% level
(depending on the particular multipole range included). The axis of maximum
asymmetry of the WMAP data is weakly dependent on the multipole range under
consideration but tends to lie close to the ecliptic axis. In the N-point
correlation function analysis we focus on the northern and southern hemispheres
defined in ecliptic coordinates, and we find that the ratio of the large-scale
fluctuation amplitudes is high at the 98%-99% level. Furthermore, the results
are stable with respect to choice of Galactic cut and also with respect to
frequency band. A similar asymmetry is found in the COBE-DMR map, and the axis
of maximum asymmetry is close to the one found in the WMAP data.Comment: 6 pages, 5 figures; version to appear in ApJ, textual improvements,
added reference
Testing for Non-Gaussianity in the Wilkinson Microwave Anisotropy Probe Data: Minkowski Functionals and the Length of the Skeleton
The three Minkowski functionals and the recently defined length of the
skeleton are estimated for the co-added first-year Wilkinson Microwave
Anisotropy Probe (WMAP) data and compared with 5000 Monte Carlo simulations,
based on Gaussian fluctuations with the a-priori best-fit running-index power
spectrum and WMAP-like beam and noise properties. Several power
spectrum-dependent quantities, such as the number of stationary points, the
total length of the skeleton, and a spectral parameter, gamma, are also
estimated. While the area and length Minkowski functionals and the length of
the skeleton show no evidence for departures from the Gaussian hypothesis, the
northern hemisphere genus has a chi^2 that is large at the 95% level for all
scales. For the particular smoothing scale of 3.40 degrees FWHM it is larger
than that found in 99.5% of the simulations. In addition, the WMAP genus for
negative thresholds in the northern hemisphere has an amplitude that is larger
than in the simulations with a significance of more than 3 sigma. On the
smallest angular scales considered, the number of extrema in the WMAP data is
high at the 3 sigma level. However, this can probably be attributed to the
effect of point sources. Finally, the spectral parameter gamma is high at the
99% level in the northern Galactic hemisphere, while perfectly acceptable in
the southern hemisphere. The results provide strong evidence for the presence
of both non-Gaussian behavior and an unexpected power asymmetry between the
northern and southern hemispheres in the WMAP data.Comment: 17 pages, 10 figures, accepted for publication in Ap
Constraints on mode couplings and modulation of the CMB with WMAP data
We investigate a possible asymmetry in the statistical properties of the
cosmic microwave background temperature field and to do so we construct an
estimator aiming at detecting a dipolar modulation. Such a modulation is found
to induce correlations between multipoles with . Applying this
estimator, to the V and W bands of the WMAP data, we found a significant
detection in the V band. We argue however that foregrounds and in particular
point sources are the origin of this signal.Comment: 14 pages, 14 figure
I. The Isotopic Foldy-Wouthuysen Representation and Chiral Symmetry
The paper introduces the isotopic Foldy-Wouthuysen representation. This
representation was used to derive equations for massive interacting fermion
fields. When the interaction Hamiltonian commutes with the matrix, these
equations possess chiral invariance irrespective of whether fermions have mass
or are massless. The isotopic Foldy-Wouthuysen representation preserves the
vector and axial currents irrespective of the fermion mass value. In the Dirac
representation, the axial current is preserved only for massless fermions. In
the isotopic Foldy-Wouthuysen representation, the ground state of fermions
(vacuum) turns out to be degenerate, and therefore there is the possibility of
spontaneously breaking parity (P - symmetry). This study considers the example
of constructing a chirally symmetric quantum electrodynamics framework in the
isotopic Foldy-Wouthuysen representation. A number of physical processes are
calculated in the lowest orders of the perturbation theory. Final results of
the calculations agree with the results of the standard quantum
electrodynamics.Comment: 37 pages, 9 figure
Increasing evidence for hemispherical power asymmetry in the five-year WMAP data
(Abridged)Motivated by the recent results of Hansen et al. (2008) concerning
a noticeable hemispherical power asymmetry in the WMAP data on small angular
scales, we revisit the dipole modulated signal model introduced by Gordon et
al. (2005). This model assumes that the true CMB signal consists of a Gaussian
isotropic random field modulated by a dipole, and is characterized by an
overall modulation amplitude, A, and a preferred direction, p. Previous
analyses of this model has been restricted to very low resolution due to
computational cost. In this paper, we double the angular resolution, and
compute the full corresponding posterior distribution for the 5-year WMAP data.
The results from our analysis are the following: The best-fit modulation
amplitude for l <= 64 and the ILC data with the WMAP KQ85 sky cut is A=0.072
+/- 0.022, non-zero at 3.3sigma, and the preferred direction points toward
Galactic coordinates (l,b) = (224 degree, -22 degree) +/- 24 degree. The
corresponding results for l <~ 40 from earlier analyses was A = 0.11 +/- 0.04
and (l,b) = (225 degree,-27 degree). The statistical significance of a non-zero
amplitude thus increases from 2.8sigma to 3.3sigma when increasing l_max from
40 to 64, and all results are consistent to within 1sigma. Similarly, the
Bayesian log-evidence difference with respect to the isotropic model increases
from Delta ln E = 1.8 to Delta ln E = 2.6, ranking as "strong evidence" on the
Jeffreys' scale. The raw best-fit log-likelihood difference increases from
Delta ln L = 6.1 to Delta ln L = 7.3. Similar, and often slightly stronger,
results are found for other data combinations. Thus, we find that the evidence
for a dipole power distribution in the WMAP data increases with l in the 5-year
WMAP data set, in agreement with the reports of Hansen et al. (2008).Comment: 6 pages, 2 figures; added references and minor comments. Accepted for
publication in Ap
Chandra X-ray Observatory Arcsecond Imaging of the Young, Oxygen-rich Supernova Remnant 1E0102.2-7219
We present observations of the young, Oxygen-rich supernova remnant
1E0102.2-7219 taken by the Chandra X-ray Observatory during Chandra's Orbital
Activation and Checkout phase. The boundary of the blast wave shock is clearly
seen for the first time, allowing the diameter of the remnant and the mean
blast wave velocity to be determined accurately. The prominent X-ray bright
ring of material may be the result of the reverse shock encountering ejecta;
the radial variation of O VII vs. O VIII emission indicates an ionizing shock
propagating inwards, possibly through a strong density gradient in the ejecta.
We compare the X-ray emission to Australia Telescope Compact Array 6 cm radio
observations (Amy and Ball) and to archival Hubble Space Telescope [O III]
observations. The ring of radio emission is predominantly inward of the outer
blast wave, consistent with an interpretation as synchrotron radiation
originating behind the blast wave, but outward of the bright X-ray ring of
emission. Many (but not all) of the prominent optical filaments are seen to
correspond to X-ray bright regions. We obtain an upper limit of ~9e33 erg/s (3
sigma) on any potential pulsar X-ray emission from the central region.Comment: Accepted for pulication in Ap. J. Letters. 4 pages, 6 figures (one
color figure). Formatted with emulateapj5. Revised to incorporate copyediting
changes. High-resolution postscript (3.02MB) and tiff versions of the color
figure are available from
http://chandra.harvard.edu/photo/cycle1/0015multi/index.htm
Anomalous variance in the WMAP data and Galactic Foreground residuals
A previous work (Monteser\'in et al. 2008) estimated the CMB variance from
the three-year WMAP data, finding a lower value than expected from Gaussian
simulations using the WMAP best-fit cosmological model. We repeat the analysis
on the five-year WMAP data using a new estimator with lower bias and variance.
Our results confirm this anomaly at higher significance, namely with a p-value
of 0.31%. We perform the analysis using different exclusion masks, showing that
a particular region of the sky near the Galactic plane shows a higher variance
than 95.58% of the simulations whereas the rest of the sky has a lower variance
than 99.96% of the simulations. The relative difference in variance between
both regions is bigger than in 99.64% of the simulations. This anisotropic
distribution of power seems to be causing the anomaly since the model assumes
isotropy. Furthermore, this region has a clear frequency dependence between
41GHz and 61GHz or 94GHz suggesting that Galactic foreground residuals could be
responsible for the anomaly. Moreover, removing the quadrupole and the octopole
from data and simulations the anomaly disappears. The variance anomaly and the
previously reported quadrupole and octopole alignment seem therefore to be
related and could have a common origin. We discuss different possible causes
and Galactic foreground residuals seem to be the most likely one. These
residuals would affect the estimation of the angular power spectrum from the
WMAP data, which is used to generate Gaussian simulations, giving rise to an
inconsistency between the estimated and expected CMB variance. If the presence
of residuals is confirmed, the estimation of the cosmological parameters could
be affected.Comment: Accepted for publication in MNRAS. Analysis section rewritten. New
exclusion masks are used finding a high variance region. Relation to the
Quadrupole-Octopole alignment foun
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