217 research outputs found
Is the cold spot responsible for the CMB North-South asymmetry?
Several intriguing phenomena, unlikely within the standard inflationary
cosmology, were reported in the cosmic microwave background (CMB) data from
WMAP and appear to be uncorrelated. Two of these phenomena, termed CMB
anomalies, are representative of their disparate nature: the North-South
asymmetry in the CMB angular-correlation strength, inconsistent with an
isotropic universe, and the cold spot, producing a significant deviation from
Gaussianity. We find a cause-effect relationship between them, at medium
angular scales (l = 11 - 20): we show that a successive diminution of the cold
spot (absolute-value) temperature implies a monotonic decrease of the
North-South asymmetry power, and moreover we find that the cold spot supplies
60% of such power.Comment: 5 pages, 2 Postscript figure
Mapping possible non-Gaussianity in the Planck maps
[Abridged.] It is conceivable that no single statistical estimator can be
sensitive to all forms and levels of non-Gaussianity that may be present in
observed CMB data. In recent works a statistical procedure based upon the
calculation of the skewness and kurtosis of the patches of CMB sky-sphere has
been proposed and used to find out significant large-angle deviation from
Gaussianity in the foreground-reduced WMAP maps. Here we address the question
as to how the analysis of Gaussianity of WMAP maps is modified if the
foreground-cleaned Planck maps are used, therefore extending and complementing
the previous analyses in several regards. We carry out a new analysis of
Gaussianity with the available nearly full-sky foreground-cleaned Planck maps.
As the foregrounds are cleaned through different component separation
procedures, each of the resulting Planck maps is then tested for Gaussianity.
We determine quantitatively the effects for Gaussianity of masking the
foreground-cleaned Planck maps with the INPMASK, VALMASK, and U73 Planck masks.
We show that although the foreground-cleaned Planck maps present significant
deviation from Gaussianity of different degrees when the less severe INPMASK
and VALMASK are used, they become consistent with Gaussianity as detected by
our indicator when masked with the union U73 mask. A slightly smaller
consistency with Gaussianity is found when the indicator is employed, which
seems to be associated with large-angle anomalies reported by the Planck team.
Finally, we examine the robustness of the Gaussianity analyses with respect to
the noise pixel's as given by the Planck team, and show that no appreciable
changes arise when is incorporated into the maps. The results of our analyses
provide important information about the suitability of the foreground-cleaned
Planck maps as Gaussian reconstructions of the CMB sky.Comment: 10 pages, 4 figures. V2: Version to appear in A&A (2014),
reformatted, typos corrected, references added, a word added in the titl
A method to search for topological signatures in the angular distribution of cosmic objects
We present a method to search for large angular-scale correlations, termed
topological signatures, in the angular distribution of cosmic objects, which
does not depend on cosmological models or parameters and is based only on the
angular coordinates of the objects. In order to explore Cosmic Microwave
Background temperature fluctuations data, we applied this method to simulated
distributions of objects in thin spherical shells located in three different
multiply-connected Euclidean 3-spaces (, , and ), and found
that the topological signatures due to these topologies can be revealed even if
their intensities are small. We show how to detect such signatures for the
cases of full-sky and partial-sky distributions of objects. This method can
also be applied to other ensembles of cosmic objects, like galaxies or quasars,
in order to reveal possible angular-scale correlations in their distributions.Comment: 11 pages, 18 figures. To appear in A&
A note on the large-angle anisotropies in the WMAP cut-sky maps
Recent analyses of the WMAP data seem to indicate the possible presence of
large-angle anisotropy in the Universe. If confirmed, these can have important
consequences for our understanding of the Universe. A number of attempts have
recently been made to establish the reality and nature of such anisotropies in
the CMB data. Among these is a directional indicator recently proposed by the
authors. A distinctive feature of this indicator is that it can be used to
generate a sky map of the large-scale anisotropies of the CMB maps. Applying
this indicator to full-sky temperature maps we found a statistically
significant preferred direction. The full-sky maps used in these analyses are
known to have residual foreground contamination as well as complicated noise
properties. Thus, here we performed the same analysis for a map where regions
with high foreground contamination were removed. We find that the main feature
of the full-sky analysis, namely the presence of a significant axis of
asymmetry, is robust with respect to this masking procedure. Other subtler
anomalies of the full-sky are on the other hand no longer present.Comment: 10 pages, 3 figeres. We performed a similar analysis of
arXiv:astro-ph/0511666 by considering the LILC map with a Kp2 sky cut, and
find that the presence of a significant axis of asymmetry is robust with
respect to this masking procedur
Primordial Non-Gaussianities of inflationary step-like models
We use Minkowski Functionals to explore the presence of non-Gaussian
signatures in simulated cosmic microwave background (CMB) maps. Precisely, we
analyse the non-Gaussianities produced from the angular power spectra emerging
from a class of inflationary models with a primordial step-like potential. This
class of models are able to perform the best-fit of the low- `features',
revealed first in the CMB angular power spectrum by the WMAP experiment and
then confirmed by the Planck collaboration maps. Indeed, such models generate
oscillatory features in the primordial power spectrum of scalar perturbations,
that are then imprinted in the large scales of the CMB field. Interestingly, we
discover Gaussian deviations in the CMB maps simulated from the power spectra
produced by these models, as compared with Gaussian CDM maps.
Moreover, we also show that the kind and level of the non-Gaussianities
produced in these simulated CMB maps are compatible with that found in the four
foreground-cleaned Planck maps. Our results indicate that inflationary models
with a step-like potential are not only able to improve the best-fit respect to
the CDM model accounting well for the `features' observed in the CMB
angular power spectrum, but also suggesting a possible origin for certain
non-Gaussian signatures observed in the Planck data.Comment: 15 pages, 9 figure
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