3,085 research outputs found
Point-Source Power in 3 Year Wilkinson Microwave Anisotropy Probe Data
Using a set of multifrequency cross spectra computed from the 3 year WMAP sky maps, we fit for the unresolved point-source contribution. For a white-noise power spectrum, we find a Q-band amplitude of A = 0.011 ± 0.001 μK^2 sr (antenna temperature), significantly smaller than the value of 0.017 ± 0.002 μK^2 sr used to correct the spectra in the WMAP release. Modifying the point-source correction in this way largely resolves the discrepancy that Eriksen et al. found between the WMAP V- and W-band power spectra. Correcting the co-added WMAP spectrum for both the low-l power excess due to a suboptimal likelihood approximation—also reported by Eriksen et al.—and the high-l power deficit due to oversubtracted point sources—presented in this Letter—we find that the net effect in terms of cosmological parameters is an ~0.7 σ shift in n_s to larger values. For the combination of WMAP, BOOMERANG, and ACBAR data, we find ns = 0.969 ± 0.016, lowering the significance of n_s ≠ 1 from ~2.7 σ to ~2.0 σ
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
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
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
The scalar perturbation spectral index n_s: WMAP sensitivity to unresolved point sources
Precision measurement of the scalar perturbation spectral index, n_s, from
the Wilkinson Microwave Anisotropy Probe temperature angular power spectrum
requires the subtraction of unresolved point source power. Here we reconsider
this issue. First, we note a peculiarity in the WMAP temperature likelihood's
response to the source correction: Cosmological parameters do not respond to
increased source errors. An alternative and more direct method for treating
this error term acts more sensibly, and also shifts n_s by ~0.3 sigma closer to
unity. Second, we re-examine the source fit used to correct the power spectrum.
This fit depends strongly on the galactic cut and the weighting of the map,
indicating that either the source population or masking procedure is not
isotropic. Jackknife tests appear inconsistent, causing us to assign large
uncertainties to account for possible systematics. Third, we note that the WMAP
team's spectrum was computed with two different weighting schemes: uniform
weights transition to inverse noise variance weights at l = 500. The fit
depends on such weighting schemes, so different corrections apply to each
multipole range. For the Kp2 mask used in cosmological analysis, we prefer
source corrections A = 0.012 +/- 0.005 muK^2 for uniform weighting and A =
0.015 +/- 0.005 muK^2 for N_obs weighting. Correcting WMAP's spectrum
correspondingly, we compute cosmological parameters with our alternative
likelihood, finding n_s = 0.970 +/- 0.017 and sigma_8 = 0.778 +/- 0.045 . This
n_s is only 1.8 sigma from unity, compared to the ~2.6 sigma WMAP 3-year
result. Finally, an anomalous feature in the source spectrum at l<200 remains,
most strongly associated with W-band.Comment: 9 pages, 10 figures, 3 tables. Submitted to Ap
Evidence of vorticity and shear at large angular scales in the WMAP data: a violation of cosmological isotropy?
Motivated by the large-scale asymmetry observed in the cosmic microwave
background sky, we consider a specific class of anisotropic cosmological models
-- Bianchi type VII_h -- and compare them to the WMAP first-year data on large
angular scales. Remarkably, we find evidence of a correlation which is ruled
out as a chance alignment at the 3sigma level. The best fit Bianchi model
corresponds to x=0.55, Omega_0=0.5, a rotation axis in the direction
(l,b)=(222degr,-62degr), shear (sigma/H)_0=2.4e-10 and a right--handed
vorticity (omega/H)_0=6.1e-10. Correcting for this component greatly reduces
the significance of the large-scale power asymmetry, resolves several anomalies
detected on large angular scales (ie. the low quadrupole amplitude and
quadrupole/octopole planarity and alignment), and can account for a
non--Gaussian "cold spot" on the sky. Despite the apparent inconsistency with
the best-fit parameters required in inflationary models to account for the
acoustic peaks, we consider the results sufficiently provocative to merit
further consideration.Comment: 4 pages, 3 figures; emulateapj.cls; ApJL accepted version plus fixed
error in vorticity calculation (sqrt(2) off in Table 1, abstract, and
conclusions); basic conclusions unchange
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
Diversity promotes production of ryegrass-clover leys through inclusion of competitive forb species
Highly productive temporary grasslands in Europe are usually composed of only a few plant species, and are typically dominated by perennial ryegrass-clover mixtures. Including additional competitive forb species holds potential for enhancing productivity in temporary grasslands, but requires further demonstration. In a grassland biodiversity experiment, one or all of the three forb species: chicory (Cichorium intybus L.), caraway (Carum carvi L.) and plantain (Plantago lanceolata L.), were grown in different proportions with the perennial ryegrass (Lolium perenne L.)-red clover (Trifolium pratense L.)mixture under two slurry application levels (0 and 250 kg total N ha-1 year-1). Dry matter (DM) yield and botanical composition were determined in 2014 and 2015. Results showed that plantain-containing mixtures significantly increased DM yield by on average 9.5% (20% plantain in seed mixture) to 13.6% (60% plantain) compared to the ryegrass-clover mixture, while other mixtures with forb species produced yields similar to that of the ryegrass-clover mixture. These effects were independent of slurry application and consistent over two years. Moreover, plantain-containing mixtures produced higher yield than
chicory- and caraway-containing mixtures, through greater biomass of plantain and/or complementary effects on red clover. These findings firstly demonstrate that increasing species diversity through including certain competitive forbs promotes production of ryegrass-clover mixtures
Power Asymmetry in Cosmic Microwave Background Fluctuations from Full Sky to Sub-degree Scales: Is the Universe Isotropic?
We repeat and extend the analysis of Eriksen et al 2004 and Hansen et al 2004
testing the isotropy of the Cosmic Microwave Background (CMB) fluctuations. We
find that the hemispherical power asymmetry previously reported for the largest
scales l=2-40 extend to much smaller scales. In fact, for the full multipole
range l=2-600, significantly more power is found in the hemisphere centered at
(theta=107 deg., phi=226 deg.) in galactic co-latitude and longitude than in
the opposite hemisphere consistent with the previously detected direction of
asymmetry for l=2-40. We adopt a model selection test where the direction and
amplitude of asymmetry as well as the multipole range are free parameters. A
model with an asymmetric distribution of power for l=2-600 is found to be
preferred over the isotropic model at the 0.4% significance level taking into
account the additional parameters required to describe it. A similar direction
of asymmetry is found independently in all six subranges of 100 multipoles
between l=2-600 and none of our 9800 isotropic simulated maps show a similarly
consistent direction of asymmetry over such a large multipole range. No known
systematic effects or foregrounds are found to be able to explain the
asymmetry.Comment: Submitted to Ap
Isotropy of the early universe from CMB anisotropies
The acoustic peak in the CMB power spectrum is sensitive to causal processes
and cosmological parameters in the early universe up to the time of last
scattering. We provide limits on correlated spatial variations of the peak
height and peak position and interpret these as constraints on the spatial
variation of the cosmological parameters (baryon density, cold dark matter
density and cosmological constant as well as the amplitude and tilt of the
original fluctuations). We utilize recent work of Hansen, Banday and Gorski
(HBG) who have studied the spatial isotropy of the power spectrum as measured
by WMAP by performing the power spectrum analysis on smaller patches of the
sky. We find that there is no statistically significant correlated asymmetry of
the peak. HBG have also provided preliminary indications of a preferred
direction in the lower angular momentum range(~ 2-40) and we show how possible
explanations of this asymmetry are severely constrained by the data on the
acoustic peak. Finally we show a possible non-gaussian feature in the data,
associated with a difference in the northern and southern galactic hemispheres.Comment: 14 pages, 3 figures, v.2 adds an extra relevant reference and commen
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