135 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
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
Cosmological Constraints with Clustering-Based Redshifts
We demonstrate that observations lacking reliable redshift information, such
as photometric and radio continuum surveys, can produce robust measurements of
cosmological parameters when empowered by clustering-based redshift estimation.
This method infers the redshift distribution based on the spatial clustering of
sources, using cross-correlation with a reference dataset with known redshifts.
Applying this method to the existing SDSS photometric galaxies, and projecting
to future radio continuum surveys, we show that sources can be efficiently
divided into several redshift bins, increasing their ability to constrain
cosmological parameters. We forecast constraints on the dark-energy
equation-of-state and on local non-gaussianity parameters. We explore several
pertinent issues, including the tradeoff between including more sources versus
minimizing the overlap between bins, the shot-noise limitations on binning, and
the predicted performance of the method at high redshifts. Remarkably, we find
that, once this technique is implemented, constraints on dynamical dark energy
from the SDSS imaging catalog can be competitive with, or better than, those
from the spectroscopic BOSS survey and even future planned experiments.
Further, constraints on primordial non-Gaussianity from future large-sky
radio-continuum surveys can outperform those from the Planck CMB experiment,
and rival those from future spectroscopic galaxy surveys. The application of
this method thus holds tremendous promise for cosmology.Comment: 7 pages, 3 figures, 2 tables; to be submitted to MNRA
- …