189 research outputs found
The CMB Derivatives of Planck's Beam Asymmetry
We investigate the anisotropy in cosmic microwave background Planck maps due
to the coupling between its beam asymmetry and uneven scanning strategy.
Introducing a pixel space estimator based on the temperature gradients, we find
a highly significant (~20 \sigma) preference for these to point along ecliptic
latitudes. We examine the scale dependence, morphology and foreground
sensitivity of this anisotropy, as well as the capability of detailed Planck
simulations to reproduce the effect, which is crucial for its removal, as we
demonstrate in a search for the weak lensing signature of cosmic defects.Comment: 5 pages, 9 figures Published in MNRA
A close examination of cosmic microwave background mirror-parity after Planck
Previous claims of significant evidence for mirror-parity in the large-scale
cosmic microwave background (CMB) data from the Wilkinson Microwave Anisotropy
Probe (WMAP) experiment have been recently echoed in the first study of
isotropy and statistics of CMB data from Planck. We revisit these claims with a
careful analysis of the latest data available. We construct statistical
estimators in both harmonic and pixel space, test them on simulated data with
and without mirror-parity symmetry, apply different Galactic masks, and study
the dependence of the results on arbitrary choices of free parameters. We
confirm that the data exhibit evidence for odd mirror-parity at a significance
which reaches as high as ~ 99 per cent C.L., under some circumstances. However,
given the inherent biases in the pixel-based statistic and the dependence of
both pixel and harmonic space statistics on the particular form of Galactic
masking and other a-posteriori choices, we conclude that these results are not
in significant tension with the predictions of the concordance cosmological
model.Comment: 9 pages, 5 figures, minor changes, as published in MNRA
Studying the Peculiar Velocity Bulk Flow in a Sparse Survey of Type-Ia SNe
Studies of the peculiar velocity bulk flow based on different tools and
datasets have been consistent so far in their estimation of the direction of
the flow, which also happens to lie in close proximity to several features
identified in the cosmic microwave background, providing motivation to use new
compilations of type-Ia supernovae measurements to pinpoint it with better
accuracy and up to higher redshift. Unfortunately, the peculiar velocity field
estimated from the most recent Union2.1 compilation suffers from large
individual errors, poor sky coverage and low redshift-volume density. We show
that as a result, any naive attempt to calculate the best-fit bulk flow and its
significance will be severely biased. Instead, we introduce an iterative method
which calculates the amplitude and the scatter of the direction of the best-fit
bulk flow as deviants are successively removed and take into account the
sparsity of the data when estimating the significance of the result. Using 200
supernovae up to a redshift of z=0.2, we find that while the amplitude of the
bulk flow is marginally consistent with the value expected in a LCDM universe
given the large bias, the scatter of the direction is significantly low (at >=
99.5 C.L.) when compared to random simulations, supporting the quest for a
cosmological origin.Comment: 7 pages, 6 figures; typos fixed; clarifications made; important
references adde
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