406 research outputs found

### Joint cosmological parameters forecast from CFHTLS-cosmic shear and CMB data

We present a prospective analysis of a combined cosmic shear and cosmic
microwave background data set, focusing on a Canada France Hawaii Telescope
Legacy Survey (CFHTLS) type lensing survey and the current WMAP-1 year and CBI
data. We investigate the parameter degeneracies and error estimates of a seven
parameters model, for the lensing alone as well as for the combined
experiments. The analysis is performed using a Monte Carlo Markov Chain
calculation, allowing for a more realistic estimate of errors and degeneracies
than a Fisher matrix approach. After a detailed discussion of the relevant
statistical techniques, the set of the most relevant 2 and 3-dimensional
lensing contours are given. It is shown that the combined cosmic shear and CMB
is particularly efficient to break some parameter degeneracies. The principal
components directions are computed and it is found that the most orthogonal
contours between the two experiments are for the parameter pairs
(Omega_m,sigma_8), (h,ns) and (ns,nrun), where ns and nrun are the slope of the
primordial mass power spectrum and the running spectral index respectively. It
is shown that an improvement of a factor 2 is expected on the running spectral
index from the combined data sets. Forecasts for error improvements from a wide
field space telescope lensing survey are also given.Comment: 16 pages, 11 figures. Submitted to Astronomy & Astrophysic

### Wide-field cosmic shear surveys

We present the current status of cosmic shear based on all surveys done so
far. Taken together, they cover more about 70 deg$^2$ and concern more than 3
million galaxies with accurate shape measurement. Theoretical expectations,
observational results and their cosmological interpretations are discussed in
the framework of standard cosmology and CDM scenarios. The potentials of the
next generation cosmic shear surveys are discussed.Comment: To appear in SPIE Conference 4847 Astronomical Telescopes and
Instrumentation. Kona, August 22-28 2002. Ed

### First cosmic shear results from the Canada-France-Hawaii Telescope Wide Synoptic Legacy Survey

We present the first measurements of the weak gravitational lensing signal
induced by the large scale mass distribution from data obtained as part of the
ongoing Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). The data used in
this analysis are from the Wide Synoptic Survey, which aims to image ~170
square degree in five filters. We have analysed ~22 deg2 (31 pointings) of i'
data spread over two of the three survey fields. These data are of excellent
quality and the results bode well for the remainder of the survey: we do not
detect a significant `B'-mode, suggesting that residual systematics are
negligible at the current level of accuracy. Assuming a Cold Dark Matter model
and marginalising over the Hubble parameter h=[0.6,0.8], the source redshift
distribution and systematics, we constrain sigma_8, the amplitude of the matter
power spectrum. At a fiducial matter density Omega_m=0.3 we find
sigma_8=0.85+-0.06. This estimate is in excellent agreement with previous
studies. Combination of our results with those from the Deep component of the
CFHTLS enables us to place a constraint on a constant equation of state for the
dark energy, based on cosmic shear data alone. We find that w_0<-0.8 at 68%
confidence.Comment: Submitted to Ap

### Prospects for weak lensing/cosmic shear with VLTs

The present status of weak lensing analyses of clusters of galaxies and of
cosmic shear surveys are presented and discussed. We focus on the impact of
very large telescopes on present-day and future surveys and compare their
potential with HST or wide field 4 meter telescopes.Comment: To appear in SPIE Conference 4834. Astronomical Telescopes and
Instrumentation. Kona, August 22-28 200

### Scalar-field quintessence by cosmic shear: CFHT data analysis and forecasts for DUNE

A light scalar field, minimally or not-minimally coupled to the metric field,
is a well-defined candidate for the dark energy, overcoming the coincidence
problem intrinsic to the cosmological constant and avoiding the difficulties of
parameterizations. We present a general description of the weak gravitational
lensing valid for every metric theory of gravity, including vector and tensor
perturbations for a non-flat spatial metric. Based on this description, we
investigate two minimally-coupled scalar field quintessence models using
VIRMOS-Descart and CFHTLS cosmic shear data, and forecast the constraints for
the proposed space-borne wide-field imager DUNE.Comment: 7 pages, 4 figures. To appear in proceedings of IRGAC06 (Barcelona,
July 06

### Dark energy constraints and correlations with systematics from CFHTLS weak lensing, SNLS supernovae Ia and WMAP5

We combine measurements of weak gravitational lensing from the CFHTLS-Wide
survey, supernovae Ia from CFHT SNLS and CMB anisotropies from WMAP5 to obtain
joint constraints on cosmological parameters, in particular, the dark energy
equation of state parameter w. We assess the influence of systematics in the
data on the results and look for possible correlations with cosmological
parameters.
We implement an MCMC algorithm to sample the parameter space of a flat CDM
model with a dark-energy component of constant w. Systematics in the data are
parametrised and included in the analysis. We determine the influence of
photometric calibration of SNIa data on cosmological results by calculating the
response of the distance modulus to photometric zero-point variations. The weak
lensing data set is tested for anomalous field-to-field variations and a
systematic shape measurement bias for high-z galaxies.
Ignoring photometric uncertainties for SNLS biases cosmological parameters by
at most 20% of the statistical errors, using supernovae only; the parameter
uncertainties are underestimated by 10%. The weak lensing field-to-field
variance pointings is 5%-15% higher than that predicted from N-body
simulations. We find no bias of the lensing signal at high redshift, within the
framework of a simple model. Assuming a systematic underestimation of the
lensing signal at high redshift, the normalisation sigma_8 increases by up to
8%. Combining all three probes we obtain -0.10<1+w<0.06 at 68% confidence
(-0.18<1+w<0.12 at 95%), including systematic errors. Systematics in the data
increase the error bars by up to 35%; the best-fit values change by less than
0.15sigma. [Abridged]Comment: 14 pages, 10 figures. Revised version, matches the one to be
published in A&A. Modifications have been made corresponding to the referee's
suggestions, including reordering of some section

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