914 research outputs found
Path Integral Marginalization for Cosmology: Scale Dependent Galaxy Bias & Intrinsic Alignments
We present a path-integral likelihood formalism that extends parameterized
likelihood analyses to include continuous functions. The method finds the
maximum likelihood point in function-space, and marginalizes over all possible
functions, under the assumption of a Gaussian-distributed function-space. We
apply our method to the problem of removing unknown systematic functions in two
topical problems for dark energy research : scale-dependent galaxy bias in
redshift surveys; and galaxy intrinsic alignments in cosmic shear surveys. We
find that scale-dependent galaxy bias will degrade information on cosmological
parameters unless the fractional variance in the bias function is known to 10%.
Measuring and removing intrinsic alignments from cosmic shear surveys with a
flat-prior can reduce the dark energy Figure-of-Merit by 20%, however provided
that the scale and redshift-dependence is known to better than 10% with a
Gaussian-prior, the dark energy Figure-of-Merit can be enhanced by a factor of
two with no extra assumptions.Comment: 11 pages, 4 figures, submitted to MNRA
The vacuum energy with non-ideal boundary conditions via an approximate functional equation
We discuss the vacuum energy of a quantized scalar field in the presence of
classical surfaces, defining bounded domains ,
where the field satisfies ideal or non-ideal boundary conditions. For the
electromagnetic case, this situation describes the conductivity correction to
the zero-point energy. Using an analytic regularization procedure, we obtain
the vacuum energy for a massless scalar field at zero temperature in the
presence of a slab geometry with Dirichlet
boundary conditions. To discuss the case of non-ideal boundary conditions, we
employ an asymptotic expansion, based on an approximate functional equation for
the Riemann zeta-function, where finite sums outside their original domain of
convergence are defined. Finally, to obtain the Casimir energy for a massless
scalar field in the presence of a rectangular box, with lengths and
, i.e., with non-ideal boundary
conditions, we employ an approximate functional equation of the Epstein
zeta-function.Comment: 10 page
Systematic effects on dark energy from 3D weak shear
We present an investigation into the potential effect of systematics inherent
in multi-band wide field surveys on the dark energy equation of state
determination for two 3D weak lensing methods. The weak lensing methods are a
geometric shear-ratio method and 3D cosmic shear. The analysis here uses an
extension of the Fisher matrix framework to jointly include photometric
redshift systematics, shear distortion systematics and intrinsic alignments. We
present results for DUNE and Pan-STARRS surveys. We show that assuming
systematic parameters are fixed, but possibly biased, results in potentially
large biases in dark energy parameters. We quantify any potential bias by
defining a Bias Figure of Merit. We also show the effect on the dark energy
Figure of Merit of marginalising over each systematic parameter individually.
We find that the largest effect on the Figure of Merit comes from uncertainty
in the photometric redshift systematic parameters. These can reduce the Figure
of Merit by up to a factor of 2 to 4 in both 3D weak lensing methods, if no
informative prior on the systematic parameters is applied. Shear distortion
systematics have a smaller overall effect. Intrinsic alignment effects can
reduce the Figure of Merit by up to a further factor of 2. This, however, is a
worst case scenario. By including prior information on systematic parameters
the Figure of Merit can be recovered to a large extent. We conclude that, as a
rule of thumb, given a realistic current understanding of intrinsic alignments
and photometric redshifts, then including all three primary systematic effects
reduces the Figure of Merit by at most a factor of 2, but that in reality this
factor should be much less. [abridged]Comment: 20 pages, 11 figures, submitted to MNRA
Cosmic shear analysis of archival HST/ACS data: I. Comparison of early ACS pure parallel data to the HST/GEMS Survey
This is the first paper of a series describing our measurement of weak
lensing by large-scale structure using archival observations from the Advanced
Camera for Surveys (ACS) on board the Hubble Space Telescope (HST).
In this work we present results from a pilot study testing the capabilities
of the ACS for cosmic shear measurements with early parallel observations and
presenting a re-analysis of HST/ACS data from the GEMS survey and the GOODS
observations of the Chandra Deep Field South (CDFS). We describe our new
correction scheme for the time-dependent ACS PSF based on observations of
stellar fields. This is currently the only technique which takes the full time
variation of the PSF between individual ACS exposures into account. We estimate
that our PSF correction scheme reduces the systematic contribution to the shear
correlation functions due to PSF distortions to < 2*10^{-6} for galaxy fields
containing at least 10 stars. We perform a number of diagnostic tests
indicating that the remaining level of systematics is consistent with zero for
the GEMS and GOODS data confirming the success of our PSF correction scheme.
For the parallel data we detect a low level of remaining systematics which we
interpret to be caused by a lack of sufficient dithering of the data.
Combining the shear estimate of the GEMS and GOODS observations using 96
galaxies arcmin^{-2} with the photometric redshift catalogue of the GOODS-MUSIC
sample, we determine a local single field estimate for the mass power spectrum
normalisation sigma_{8,CDFS}=0.52^{+0.11}_{-0.15} (stat) +/- 0.07 (sys) (68%
confidence assuming Gaussian cosmic variance) at fixed Omega_m=0.3 for a
LambdaCDM cosmology. We interpret this exceptionally low estimate to be due to
a local under-density of the foreground structures in the CDFS.Comment: Version accepted for publication in Astronomy & Astrophysics with 28
pages, 25 figures. A version with full resolution figures can be downloaded
from http://www.astro.uni-bonn.de/~schrabba/papers/cosmic_shear_acs1_v2.pd
Cluster Masses Accounting for Structure along the Line of Sight
Weak gravitational lensing of background galaxies by foreground clusters
offers an excellent opportunity to measure cluster masses directly without
using gas as a probe. One source of noise which seems difficult to avoid is
large scale structure along the line of sight. Here I show that, by using
standard map-making techniques, one can minimize the deleterious effects of
this noise. The resulting uncertainties on cluster masses are significantly
smaller than when large scale structure is not properly accounted for, although
still larger than if it was absent altogether.Comment: 5 pages, 5 figure
Spatial matter density mapping of the STAGES Abell A901/2 supercluster field with 3D lensing
We present weak lensing data from the Hubble Space Telescope(HST)/Space Telescope A901/902 Galaxy Evolution Survey (STAGES) survey to study the three-dimensional spatial distribution of matter and galaxies in the Abell 901/902 supercluster complex. Our method improves over the existing 3D lensing mapping techniques by calibrating and removing redshift bias and accounting for the effects of the radial elongation of 3D structures. We also include the first detailed noise analysis of a 3D lensing map, showing that even with deep HST-quality data, only the most massive structures, for example M200âł 1015Mâh-1 at z⌠0.8, can be resolved in 3D with any reasonable redshift accuracy (Îzâ 0.15). We compare the lensing map to the stellar mass distribution and find luminous counterparts for all mass peaks detected with a peak significance >3Ï. We see structures in and behind the z= 0.165 foreground supercluster, finding structure directly behind the A901b cluster at z⌠0.6 and also behind the south-west (SW) group at z⌠0.7. This 3D structure viewed in projection has no significant impact on recent mass estimates of A901b or the SW group components SWa and SWb. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS
Mapping the 3-D dark matter with weak lensing in COMBO-17
We present a 3-dimensional lensing analysis of the z=0.16 supercluster
A901/2, resulting in a 3-D map of the dark matter distribution within a 3 X
10^{5} [Mpc]^3 volume from the COMBO-17 survey. We perform a chi^2-fit of
isothermal spheres to the tangential shear pattern around each cluster as a
function of redshift to estimate the 3-D positions and masses of the main
clusters in the supercluster from lensing alone. We then present the first 3-D
map of the dark matter gravitational potential field, Phi, using the
Kaiser-Squires (1993) and Taylor (2001) inversion methods. These maps clearly
show the potential wells of the main supercluster components, including a new
cluster behind A902, and demonstrates the applicability of 3-D dark matter
mapping and projection free-mass-selected cluster finding to current data.
Finally, we develop the halo model of dark matter and galaxy clustering and
compare this with the auto-and cross-correlation functions of the 3-D
gravitational potential, galaxy number densities and galaxy luminosity
densities measured in the A901/2 field. We find significant anti-correlations
between the gravitational potential field and the galaxy number density and
luminosities, as expected due to baryonic infall into dark matter
concentrations. We find good agreement with the halo model for the number
densities and luminosity correlation functions.Comment: Submitted to MNRAS; 21 pages, 18 figure
A Comparative Analysis of Rare Sternalis Muscles: A Case Report
The sternalis muscle is a rare variant in the anterior chest wall located anterior to the vertical muscle. It was found in two cadavers during routine cadaveric dissection of 20 bodies. This finding provided an opportunity to perform a comparative anatomical analysis between a unilateral sternalis muscle on a female versus a bilateral sternalis muscle on a male. Having a better understanding of the anatomical variants can be extremely useful, precisely to avoid misdiagnosing tumors and to assist in landmark identification during surgeries
Ultra-deep catalog of X-ray groups in the Extended Chandra Deep Field South
Ultra-deep observations of ECDF-S with Chandra and XMM-Newton enable a search
for extended X-ray emission down to an unprecedented flux of
ergs s cm. We present the search for the extended emission on
spatial scales of 32 in both Chandra and XMM data, covering
0.3 square degrees and model the extended emission on scales of arcminutes. We
present a catalog of 46 spectroscopically identified groups, reaching a
redshift of 1.6. We show that the statistical properties of ECDF-S, such as
logN-logS and X-ray luminosity function are broadly consistent with LCDM, with
the exception that dn/dz/d test reveals that a redshift range of
in ECDF-S is sparsely populated. The lack of nearby structure,
however, makes studies of high-redshift groups particularly easier both in
X-rays and lensing, due to a lower level of clustered foreground. We present
one and two point statistics of the galaxy groups as well as weak-lensing
analysis to show that the detected low-luminosity systems are indeed low-mass
systems. We verify the applicability of the scaling relations between the X-ray
luminosity and the total mass of the group, derived for the COSMOS survey to
lower masses and higher redshifts probed by ECDF-S by means of stacked weak
lensing and clustering analysis, constraining any possible departures to be
within 30% in mass. Abridged.Comment: 20 pages, 21 figures, 3 tables, to match the journal versio
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