We review the scientific objectives and the present status cosmic shear studies. We discuss the future prospects and the role cosmic shear could play in a precision cosmology era.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The measurement of weak gravitational lensing is currently limited to a precision of $\sim$10% by instabilities in galaxy shape measurement techniques and uncertainties in their calibration. The potential of large, on-going and future cosmic shear surveys will only be realised with the development of more accurate image analysis methods. We present a description of several possible shear measurement methods using the linear “shapelets” decomposition. Shapelets provides a complete reconstruction of any galaxy image, including higher-order shape moments that can be used to generalise the KSB method to arbitrary order. Many independent shear estimators can then be formed for each object, using linear combinations of shapelet coefficients. These estimators can be treated separately, to improve their overall calibration; or combined in more sophisticated ways, to eliminate various instabilities and a calibration bias. We apply several methods to simulated astronomical images containing a known input shear, and demonstrate the dramatic improvement in shear recovery using shapelets. A complete IDL software package to perform image analysis and manipulation in shapelet space can be downloaded from www.astro.caltech.edu/~rjm/shapelets/.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present a direct detection of the growth of large-scale structure, using weak gravitational lensing and photometric redshift data from the COMBO-17 survey. Deep $R$-band imaging of two $0.5\times0.5$ square degree fields is used to provide shear estimates for over 52000 galaxies; these are combined with photometric redshift estimates from our 17 band survey, in order to obtain a 3-D shear field. We discuss how theoretical models for evolving matter power spectra and correlation functions cab be used to find a best fit to this 3-D shear field. We present the detection of the evolution of the power, and measurements of the rate of evolution for $0<z<1$. We discuss future refinements which will improve the accuracy with which the effect can be measured.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present our cosmic shear analysis of the Galaxy Evolution from Morphology and SEDs (GEMS) survey. Imaged with the Advanced Camera for Surveys (ACS) on HST, GEMS provides high resolution imaging spanning some 800 square arcmins in the Chandra Deep Field South (CDFS). We discuss the benefits of using space-based data for weak lensing studies and show that the ACS is a very powerful instrument in this regard. We find that we are not limited by systematic errors arising from the anisotropic ACS point spread function distortion and use our cosmic shear results to place joint constraints on the matter density parameter $\Omega_m$ and the amplitude of the matter power spectrum $\sigma_8$, finding $\sigma_8(\Omega_m/0.3)^{0.62}=0.73 \pm 0.12$.

To investigate the impact of atmospheric seeing on weak lensing analysis we compare the shear measured from CDFS galaxies resolved by the COMBO-17 survey and imaged by GEMS. We find good agreement between the two surveys and a higher dispersion in the intrinsic ellipticity distribution of COMBO-17. This dispersion implies that a space-based cosmic shear analysis would yield higher signal-to-noise results compared to a ground-based cosmic shear analysis of the same galaxy sample.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Cosmic shear is an essential cosmological tool, breaking degeneracies inherent to CMB data and providing an independent check of cosmological parameters. Upcoming cosmic shear surveys with photometric redshift information will enable tighter constraints to be placed on cosmological parameters, and allow us to explore how dark matter evolves. A Monte Carlo method to rapidly simulate mock surveys enables us to estimate the covariance matrix for the shear correlation functions, and hence the expected errors on cosmological parameter estimates given survey specifications. We also make brief remarks on the separation of the cosmic shear signal from any due to intrinsic galaxy alignments.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Under the currently popular CDM model, mass plays the major role in evolution of large scale structure of the universe. In order to examine the paradigm based on observations, it would be ideal to use purely mass selected object catalog. Weak lensing surveys enable a blind search of cluster scale objects, and thus could provide such catalogs. We are working on a weak lensing survey using Subaru Prime Focus Camera (Suprime-Cam). In this note, we introduce our survey strategy, and the status as well as the performance of Suprime-Cam as a weak lensing surveyor.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Weak gravitational lensing can be combined with distance information from galaxy redshifts to great effect in 3-D weak lensing. With both shear and redshift information I show how the full 3-D dark matter distribution can be reconstructed and present a first application to the COMBO-17 data-set. In addition, I describe the Jain-Taylor geometric test, taking ratios of galaxy shear at different distances, as a probe of the dark energy in the universe and present a preliminary application to COMBO-17.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Cosmic shear surveys are now collecting photometric redshifts of the sources. We analyse how such photometric redshifts can be used to perform a genuine 3D analysis of the shear fields, with enhanced statistical power over conventional shear analysis on the sky. In particular, 3D lensing has the potential to measure accurately the equation of state of Dark Energy, with a possibility of measuring $w$ with an accuracy of a few percent. Like the microwave background, 3D lensing observables are calculable ab initio, and are largely unaffected by complex astrophysical processes which may limit their power. In this context, we review how 3D information from photometric redshifts can reduce a possible physical systematic effect, arising from intrinsic alignments of galaxies.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We analyse the sensitivity of cosmic shear 2-point statistics to the cosmological parameters, by using Monte Carlo Markov Chain (MCMC) methods. In particular, we investigate degeneracies among parameters and compare them to the CMB ones. Specializing on a Canada France Hawaii Telescope Legacy Survey (CFHTLS) type lensing survey and WMAP-1 year and CBI CMB data, we find cosmic shear information improves CMB cosmological parameters constraints by a factor of 1.5 – 2.5.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present predictions for cosmological parameter constraints from combined measurements of second- and third-order aperture mass statistics of cosmic shear. The generalized third-order aperture mass is introduced and its relation to the convergence bispectrum is given. This quantity contains (in principle) all information about the bispectrum. Using ray-tracing simulations, we perform a Fisher matrix analysis for various cosmological parameters and show that the combination of $\langle M_{\rm ap}^2\rangle$ and $\langle M_{\rm ap}^3\rangle$ improves the parameter estimation significantly.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Lenses acting on the Cosmic Microwave Background can potentially be a very efficient and robust probe of the large-scale matter distribution in the Universe. Their most immediate signature is the way they affect the statistical properties of both the temperature and the polarization fields, in particular they both induce non-Gaussian properties that can be explicitly computed.

Investigations of those effects led to the elaboration of specific reconstruction procedures that aim at mapping the projected mass responsible of the lens effects. These techniques are now on solid ground and are remarkably efficient. However it is likely that our best chance to detect a lensing signal in CMB data in the coming years will be through the cross-correlation patterns they induce between CMB data and tracers of the large-scale structure. Clearly the detection of such an effect would be very fruitful in scrutinizing the gravitational instability picture.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Several recent papers have studied lensing of the CMB by large-scale structures, which probes the projected matter distribution from $z=10^3$ to $z\simeq 0$. This interest is motivated in part by upcoming high resolution, high sensitivity CMB experiments, such as APEX/SZ, ACT, SPT or Planck, which should be sensitive to lensing. In this paper we examine the reconstruction of the large-scale dark matter distribution from lensed CMB temperature anisotropies. We go beyond previous work in using numerical simulations to include higher order, non-Gaussian effects and find that the convergence and its power spectrum are biased, with the bias increasing with the angular resolution. We also study the contamination by the kinetic Sunyaev-Zel'dovich signal, which is spectrally indistinguishable from lensed CMB anisotropies, and find that it leads to an overestimate of the convergence. We finish by estimating the sensitivity of the previously cited experiments and find that all of them could detect the lensing effect, but would be biased at around the 10% level.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the results of a search for gravitational lensing of the cosmic microwave background (CMB) in cross-correlation with the projected density of luminous red galaxies (LRGs). The CMB lensing reconstruction is performed using the first year of Wilkinson Microwave Anisotropy Probe (WMAP) data, and the galaxy maps are obtained using the Sloan Digital Sky Survey (SDSS) imaging data. We find no detection of lensing; our constraint on the galaxy bias derived from the galaxy-convergence cross-spectrum is $b_g=1.81\pm 1.92$ ($1\sigma$, statistical), as compared to the expected result of $b_g\sim 1.7$ for this sample. We discuss possible instrument-related systematic errors and show that the Galactic foregrounds are not important. We do not find any evidence for point source or thermal Sunyaev-Zel'dovich effect contamination.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We consider the CMB bispectrum signal induced by structure formation through the correlation between the Integrated Sachs-Wolfe and the weak lensing effect. We investigate how the bispectrum knowledge can improve our knowledge of the most important cosmological parameters, focusing on the dark energy ones. The bispectrum signal arises at intermediate redshifts, being null at present and infinity, and is characterized by a large scale regime (dominated by linear dynamics of cosmological perturbation) and a small scale one (dominated by density perturbations in a non-linear regime); on the other hand, the effect induced by dark energy on the power spectrum is mostly geometrical and imprinted at redshift close to the present. Because of this, the knowledge of power spectrum and bispectrum yield two complementary informations at very different cosmological epochs, particularly suitable to extract informations about the onset of the cosmic acceleration and dark energy properties that provide it. In order to quantify how much the bispectrum can help the power spectrum in constraining the dark energy parameters, we choose a fiducial model on a three-dimensional space including the following dark energy parameters: dark energy density $\Omega_V$; dark energy equation of state today $w_0$ and dark energy equation of state in the past $w_\infty$ ($w_\infty - w_0$ is related to the first derivative of equation of state). Then we simulate a likelihood analysis showing how contour levels become narrower when bispectrum is included. Preliminary results suggest a consistent improvement on the estimation of dark energy abundance and on dynamical properties of the equation of state. This indicates that the knowledge of the bispectrum in future high resolution and high sensitivity CMB observations could yield a substantial improvement with respect to the traditional analysis based on the power spectrum only.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the theory of weak gravitational lensing in cosmologies with generalized gravity, described in the Lagrangian by a generic function depending on the Ricci scalar and a non-minimally coupled scalar field.

We work out the generalized Poisson equations relating the dynamics of the fluctuating components to the two gauge invariant scalar gravitational potentials, fixing the new contributions from the modified background expansion and fluctuations.

We show how the lensing observables are affected by the cosmic expansion as well as by the presence of the anisotropic stress, which is non-null at the linear level both in scalar-tensor gravity and in theories where the gravitational Lagrangian term features a non-minimal dependence on the Ricci scalar. We derive the generalized expressions for the convergence power spectrum, and illustrate phenomenologically the new effects in Extended Quintessence scenarios, where the scalar field coupled to gravity plays the role of the dark energy.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Scalar-tensor (ST) theories of gravity are the best motivated alternative to general relativity (GR), arising in every high-energy theory attempting to unify all the fundamental interactions. Furthermore, accomodating an arbitrary number of scalar fields, ST theories yield to cosmological scenarios with a dynamical realization of the dark energy. Solar-System experiments and binary-pulsars observations are compatible with very small departures from GR on the local universe ($z\simeq 0$); on cosmological scales, big-bang nucleosynthesis and cosmic microwave background (CMB) observables can admit larger deviations from the predictions of GR. Weak lensing could provide a test for ST theories of gravity on intermediate scales. Based on a code developed to study ST theories on CMB observables, we implemented a plug-in code to compute the convergence power spectrum and some 2-points statistics. Preliminary results using a simple model of ST theory are presented. This study is aimed to constraint classes of ST models.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In this proceeding we present the method and results of the search for galaxy groups or clusters in the vicinity of the line-of-sight towards lensed quasars.We have studied a sample of ten quasars, using deep ESO/VLT FORS1 and ISAAC images, as well as archive HST/WFPC2 and NiCMOS data. We find that there is most probably a galaxy group towards CTQ 414, HE 0230-2130, B 1359+154, H 1413+117, SBS 1520+530 and HE 2149-2745, with masses $\leq$4~10$^{14}$M$_\odot$h$^{-1}$. Considering its photometric redshift, the galaxy group discovered in the field around HE 1104-1805 is associated with the quasar rather than with the lensing potential. We also conclude that the pair LBQS 1429-0053-A and LBQS 1429-0053-B is a genuine binary quasar rather than a lensed quasar.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The statistics of giant arc formation by galaxy clusters has long held promise as a cosmological tool. Progress in this field relies upon advances in modeling, and in observational samples. We introduce several new lens samples from the Red-Sequence Cluster Survey (RCS-1) which provide a significant increase in the total sample of clusters with arcs, while adding several new observational puzzles. The most significant of these observations is that the redshift distribution of clusters which form arcs is unexpectedly skewed to higher redshifts. We also discuss upcoming samples from the ongoing RCS-2 survey and other planned surveys; preliminary results from RCS-2 support this unexpected redshift distribution and deepen the disagreement between theory and observations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Weak gravitational lensing is considered to be one of the most powerful tools to study the mass and the mass distribution of galaxy clusters. However, the mass-sheet degeneracy transformation has limited its success. We present a novel method for a cluster mass reconstruction, which combines weak and strong lensing information on common scales and can as a consequence break the mass-sheet degeneracy. We extend the weak lensing formalism to the inner parts of the cluster, use redshift information of background sources and combine these with the constraints from multiple image systems. We apply the method to N-body simulations as well as to strong and weak lensing ground-based multi-colour data of RX J1347–1145, the most X-ray luminous cluster known to date. If the redshift measurements of background sources (for strong and weak lensing) and the identification of the multiple-image system are correct, we estimate the enclosed cluster mass within $360\: {\rm h}^{-1}\mbox{kpc}$ to $M(<360\: {\rm h}^{-1}\mbox{kpc})= (1.2 \pm 0.3) \times 10^{15} M_{\odot}$. With higher resolution (e.g. HST) imaging data, reliable multiple imaging information could be obtained and the reconstruction further improved.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

I present recent observations from two Hubble Space Telescope(HST)/ACS programs that target the most X–ray luminous and thus (presumably) most massive galaxy clusters at $z{=}0.5$ – the highest redshift at which complete, well–defined samples of such rare systems are available. The first program (GO:9836, PI: R.S. Ellis) exploits a huge mosaic of 41 ACS pointings spanning a 10 Mpc region centered on MS0451-03. This is the largest contiguous space–based image of a cluster to date. I describe a preliminary weak–lensing analysis and a new Keck/DEIMOS redshift catalog of 1000 galaxies in this field. The second program (GO:9722, PI: H. Ebeling) studies the core regions of the twelve most luminous clusters at $z{\ge}0.5$ from the MAssive Cluster Survey (MACS; Ebeling et al. 2001). Multi–color ACS observations in combination with recent Keck/LRIS spectroscopy of gravitational arcs constrain the distribution of mass in the cluster cores, thus laying the foundation for detailed multi–diagnostic (lensing, X–ray, near–infrared, SZE) investigation of this sample. For example, it is of particular interest to explore how the structure and state of relaxation of massive clusters evolved between this sample at $z{\ge}0.5$ that measured by Smith et al. (2004, astro–ph/0403588) at $z{=}0.2$.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html