1,233 research outputs found
What moves sovereign bond markets? The effects of economic news on U.S. and German yields
Economic announcements are an important source of information, containing news that spills over internationally across markets, affecting yields. An analysis of the U.S. and German sovereign bond markets finds that the largest moves in yields are associated with U.S. announcements on labor market conditions, real GDP growth, and consumer sentiment.Bond market ; Bond market - Germany ; International finance
Weak Lensing Mass Reconstruction: Flexion vs Shear
Weak gravitational lensing has proven to be a powerful tool to map directly
the distribution of dark matter in the Universe. The technique, currently used,
relies on the accurate measurement of the gravitational shear that corresponds
to the first-order distortion of the background galaxy images. More recently, a
new technique has been introduced that relies on the accurate measurement of
the gravitational flexion that corresponds to the second-order distortion of
the background galaxy images. This technique should probe structures on smaller
scales than that of a shear analysis. The goal of this paper is to compare the
ability of shear and flexion to reconstruct the dark matter distribution by
taking into account the dispersion in shear and flexion measurements. Our
results show that the flexion is less sensitive than shear for constructing the
convergence maps on scales that are physically feasible for mapping, meaning
that flexion alone not be used to do convergence map reconstruction, even on
small scales.Comment: Submitted to Ap
Gravitational waves from binary systems in circular orbits: Convergence of a dressed multipole truncation
The gravitational radiation originating from a compact binary system in
circular orbit is usually expressed as an infinite sum over radiative multipole
moments. In a slow-motion approximation, each multipole moment is then
expressed as a post-Newtonian expansion in powers of v/c, the ratio of the
orbital velocity to the speed of light. The bare multipole truncation of the
radiation consists in keeping only the leading-order term in the post-Newtonian
expansion of each moment, but summing over all the multipole moments. In the
case of binary systems with small mass ratios, the bare multipole series was
shown in a previous paper to converge for all values v/c < 2/e, where e is the
base of natural logarithms. In this paper, we extend the analysis to a dressed
multipole truncation of the radiation, in which the leading-order moments are
corrected with terms of relative order (v/c)^2 and (v/c)^3. We find that the
dressed multipole series converges also for all values v/c < 2/e, and that it
coincides (within 1%) with the numerically ``exact'' results for v/c < 0.2.Comment: 9 pages, ReVTeX, 1 postscript figur
Gravitational Flexion by Elliptical Dark Matter Haloes
We present equations for the gravitational lensing flexion expected for an
elliptical lens mass distribution. These can be reduced to one-dimensional
finite integrals, thus saving significant computing time over a full
two-dimensional calculation. We estimate constraints on galaxy halo
ellipticities for a range of potential future surveys, finding that the
constraints from the two different types of flexion are comparable and are up
to two orders of magnitude tighter than those from shear. Flexion therefore
appears to be a very promising potential tool for constraining the shapes of
galaxy haloes from future surveys.Comment: 7 pages, 5 figures, submitted to MNRA
New Constraints on the Complex Mass Substructure in Abell 1689 from Gravitational Flexion
In a recent publication, the flexion aperture mass statistic was found to
provide a robust and effective method by which substructure in galaxy clusters
might be mapped. Moreover, we suggested that the masses and mass profile of
structures might be constrained using this method. In this paper, we apply the
flexion aperture mass technique to HST ACS images of Abell 1689. We demonstrate
that the flexion aperture mass statistic is sensitive to small-scale structures
in the central region of the cluster. While the central potential is not
constrained by our method, due largely to missing data in the central
0.5 of the cluster, we are able to place constraints on the masses and
mass profiles of prominent substructures. We identify 4 separate mass peaks,
and use the peak aperture mass signal and zero signal radius in each case to
constrain the masses and mass profiles of these substructures. The three most
massive peaks exhibit complex small-scale structure, and the masses indicated
by the flexion aperture mass statistic suggest that these three peaks represent
the dominant substructure component of the cluster (). Their complex structure indicates that the cluster --
far from being relaxed -- may have recently undergone a merger. The smaller,
subsidiary peak is located coincident with a group of galaxies within the
cluster, with mass . These results are in
excellent agreement with previous substructure studies of this cluster.Comment: 18 pages, 10 figures, MNRAS accepted (7 Dec 2010
Shape, shear and flexion II - Quantifying the flexion formalism for extended sources with the ray-bundle method
Flexion-based weak gravitational lensing analysis is proving to be a useful
adjunct to traditional shear-based techniques. As flexion arises from gradients
across an image, analytic and numerical techniques are required to investigate
flexion predictions for extended image/source pairs. Using the Schwarzschild
lens model, we demonstrate that the ray-bundle method for gravitational lensing
can be used to accurately recover second flexion, and is consistent with
recovery of zero first flexion. Using lens plane to source plane bundle
propagation, we find that second flexion can be recovered with an error no
worse than 1% for bundle radii smaller than {\Delta}{\theta} = 0.01 {\theta}_E
and lens plane impact pararameters greater than {\theta}_E + {\Delta}{\theta},
where {\theta}_E is the angular Einstein radius. Using source plane to lens
plane bundle propagation, we demonstrate the existence of a preferred flexion
zone. For images at radii closer to the lens than the inner boundary of this
zone, indicative of the true strong lensing regime, the flexion formalism
should be used with caution (errors greater than 5% for extended image/source
pairs). We also define a shear zone boundary, beyond which image shapes are
essentially indistinguishable from ellipses (1% error in ellipticity). While
suggestive that a traditional weak lensing analysis is satisfactory beyond this
boundary, a potentially detectable non-zero flexion signal remains.Comment: 14 pages, 13 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Measuring Gravitational Lensing Flexions in Abell 1689 Using an Analytic Image Model
Measuring dark matter substructure within galaxy cluster haloes is a
fundamental probe of the Lambda-CDM model of structure formation. Gravitational
lensing is a technique for measuring the total mass distribution which is
independent of the nature of the gravitating matter, making it a vital tool for
studying these dark-matter dominated objects. We present a new method for
measuring weak gravitational lensing flexions, the gradients of the lensing
shear field, to measure mass distributions on small angular scales. While
previously published methods for measuring flexions focus on measuring derived
properties of the lensed images, such as shapelet coefficients or surface
brightness moments, our method instead fits a
mass-sheet-transformation-invariant Analytic Image Model (AIM) to the each
galaxy image. This simple parametric model traces the distortion of lensed
image isophotes and constrains the flexion fields. We test the AIM method using
simulated data images with realistic noise and a variety of unlensed image
properties, and show that it successfully reproduces the input flexion fields.
We also apply the AIM method for flexion measurement to Hubble Space Telescope
observations of Abell 1689, and detect mass structure in the cluster using
flexions measured with the AIM method.Comment: 44 pages, 4 figures, 3 tables. Accepted to ApJ. V2 (published
version) has minor changes from V1; ApJ 736 (2011
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