We propose to use a simple observable, the fractional area of "hot spots" in weak gravitational lensing mass maps which are detected with high significance, to determine background cosmological parameters. Because these high-convergence regions are directly related to the physical nonlinear structures of the universe, they derive cosmological information mainly from the nonlinear regime of density fluctuations. We show that in combination with future cosmic microwave background anisotropy measurements, this method can place constraints on cosmological parameters that are comparable to those from the redshift distribution of galaxy cluster abundances. The main advantage of the statistic proposed in this paper is that projection effects, normally the main source of uncertainty when determining the presence and the mass of a galaxy cluster, here serve as a source of information.
Here we present results from a maximum likelihood analysis of galaxy-galaxy weak lensing effects as measured in a 12.5' x 12.5' field obtained at the Nordic Optical Telescope, on La Palma, Spain. The analysis incorporates photometric redshifts and gives circular velocities consistent with previous weak lensing work.
Analysing the weak lensing distortions of the images of faint background galaxies provides a means to constrain the mass distribution of cluster galaxies and potentially to test the extent of their dark matter halos as a function of the density of the environment. Here I describe simulations of observational data and present a maximum likelihood method to infer the average properties of an ensemble of cluster galaxies.
Underlying cosmologies with deceleration parameter, $q_0=-0.51^{+0.03}_{-0.24},$ may be interpreted as having $q_0=-0.55,$ on the basis of weak gravitational lensing effects.
We present the main results of a numerical study of weak lensing cluster counting. We examine the scaling with cosmology of the projected-density-peak mass function. Our main conclusion is that the projected-peak and the three-dimensional mass functions scale with cosmology in an astonishingly close way. This means that, despite being derived from a two-dimensional field, the weak lensing cluster abundance can be used to constrain cosmology in the same way as the three-dimensional mass function probed by other types of surveys.
In a series of articles, we have shown that the newly discovered plasma-redshift cosmology gives a simpler, more accurate and consistent explanation of many cosmological phenomena than the big-bang cosmology. The SNe Ia observations are in better agreement with the magnitude-redshift relation predicted by the plasma redshift than that predicted by the multi-parameter big-bang cosmology. No deceleration or expansion parameters are needed. The plasma-redshift cosmology is flat and quasi-static on a large scale. The Hubble constant is no longer an expansion parameter, but is instead a measure of …
We present an integral field spectroscopy survey of rich clusters of galaxies aimed at studying their lensing properties. Thanks to knowledge of the spectroscopic caracteristics of more than three families of multiple images in a single lens, one is able in principle to derive constraints on the geometric cosmological parameters. We show that this ambitious program is feasible and present some new results, in particular the redshift measurement of the giant arc in A2667 and the resdshift confirmation of the counter-image of the radial arc in MS2137--23. Prospects for the future of such program…
Measured time delays between the images of a gravitationally lensed source can lead to a determination of the Hubble constant ($H_o$), but only if the lensing mass distribution is well understood. The inability to sufficiently constrain galaxy mass models results in large uncertainties on the derived $H_o$, and severely hampers the cosmological application of this otherwise elegant method. At the same time, lensing must compete with new techniques that have the potential to measure the Hubble constant to within a few percent by the middle of the decade. In this letter we re-evaluate the role o…
The morphology of galaxy clusters reflects the epoch at which they formed and hence depends on the value of the mean cosmological density, Omega. Recent studies have shown that the distribution of dark matter in clusters can be mapped from analysis of the small distortions in the shapes of background galaxies induced by weak gravitational lensing in the cluster potential. We construct new statistics to quantify the morphology of clusters which are insensitive to limitations in the mass reconstruction procedure. By simulating weak gravitational lensing in artificial clusters grown in numerical …
We present a method for removal of the contaminating effects of intrinsic galaxy alignments, in measurements of cosmic shear from multi-colour weak lensing surveys. The method down-weights pairs which are likely to be close in three dimensions, based on spectroscopic or photometric redshifts. Results are dramatic: the intrinsic contamination of the low-redshift Sloan photometric redshift survey could be 80 times the lensing signal, but this can be almost completely removed, leaving random shot noise errors of the order of 10%. Intrinsic galaxy alignments, although an annoying contaminant for c…
The idea that we live in a Universe undergoing a period of acceleration is a strongly held notion in cosmology. As this can, potentially, be explained with a modification to General Relativity we look at current cosmological data with the purpose of testing aspects of gravity. Firstly we constrain a phenomenological model (mDGP) motivated by a possible extra dimension. This is characterised by $α$ which interpolates between (LCDM) and (the Dvali Gabadadze Porrati (DGP) model). In addition, we analyse general signatures of modified gravity given by the growth parameter $γ$ and power spectrum pa…
Weak gravitational lensing and the Sunyaev-Zel'dovich effect provide complementary information on the composition of clusters of galaxies. Preliminary results from cluster SZ observations with the Very Small Array are presented. A Bayesian approach to combining this data with wide field lensing data is then outlined; this allows the relative probabilities of cluster models of varying complexity to be computed. A simple simulation is used to demonstrate the importance of cluster model selection in cosmological parameter determination.
With future wide and deep cosmological sky surveys, a large number of gravitationally lensed, multiply imaged systems will be found. In addition to multiply imaged galaxies and quasars, sources will include transient events like supernovae and gamma ray bursts in which case very accurate time delay measurements are possible. Also, large numbers of systems with several lensed sources behind a single lens will be observed. In this paper, we review and compare different possibilities of using future strong lensing data to probe lens matter distributions and to determine the Hubble parameter and t…
Recent discoveries by the Sloan Digital Sky Survey (SDSS) of four bright redshift z=6 quasars could constrain the mechanism by which the supermassive black holes powering these sources are assembled. Here we compute the probability that the fluxes of the quasars are strongly amplified by gravitational lensing, and therefore the likelihood that the black hole masses are overestimated when they are inferred assuming Eddington luminosities. The poorly-constrained shape of the intrinsic quasar luminosity function (LF) at redshift z=6 results in a large range of possible lensing probabilities. If t…
Significant adjustments to the values of the cosmological parameters estimated from high-redshift Type Ia Supernovædata are reported, almost an order of magnitude greater than previously found. They arise from the effects of weak gravitational lensing on observations of high-redshift sources. The lensing statistics used have been obtained from computations of the three-dimensional shear in a range of cosmological N-body simulations, from which it is estimated that cosmologies with an underlying deceleration parameter q_0 = -0.51 +0.03/-0.24 may be interpreted as having q_0 = -0.55 (appropriate…
We study the sensitivity of weak lensing by large scale structures to the evolution of dark energy. We explore a 2-parameters model of dark energy evolution, inspired by tracking quintessence models. To this end, we compute the likelihood of a few representative models with varying and non varying equation of states. Based on an earlier work, we show that the evolution of dark energy has a much stronger impact on the non-linear structure growth than on the angular diameter distance, which makes large scale structure measurements a very efficient probe of this evolution. For the different model…
(abridged) We present the first results of our deep survey of lensing clusters aimed at constraining the abundance of star-forming galaxies at z~6-10. Deep near-IR photometry of two lensing clusters (A1835 and AC114) was obtained with ISAAC/VLT. These images, combined with existing data in the optical bands, including HST images, were used to select very high redshift candidates at z>~6 among the optical-dropouts. We have identified 18(8) first and second-category optical dropouts in A1835 (AC114), detected in more than one filter up to H(Vega)~23.8 (AB~25.2,uncorrected for lensing). Among the…
Recently, it has been shown that it is possible to reconstruct the projected mass distribution of a cluster from weak lensing provided that both the geometry of the universe and the probability distribution of galaxy redshifts are known; actually, when additional photometric data are taken to be available, the galaxy redshift distribution could be determined jointly with the cluster mass from the weak lensing analysis. In this paper we develop, in the spirit of a ``thought experiment,'' a method to constrain the geometry of the universe from weak lensing, provided that the redshifts of the sou…
We study the potential of a large future weak-lensing survey to constrain dark energy properties by using both the number counts of detected galaxy clusters (sensitive primarily to density fluctuations on small scales) and tomographic shear-shear correlations (restricted to large scales). We use the Fisher matrix formalism, assume a flat universe and parameterize the equation of state of dark energy by w(a)=w_0+w_a(1-a), to forecast the expected statistical errors from either observable, and from their combination. We show that the covariance between these two observables is small, and argue t…
Weak gravitational lensing surveys measure the distortion of the image of distant sources due to the deflections of light rays by the fluctuations of the gravitational potential along the line of sight. Since they probe the non-linear matter power spectrum itself at medium redshift such surveys are complimentary to both galaxy surveys (which follow stellar light) and cosmic microwave background observations (which probe the linear regime at high redshift). Ongoing CMB experiments such as WMAP and the future Planck satellite mission will measure the standard cosmological parameters with unprece…
We present a new geometrical method which uses weak gravitational lensing effects in clusters to constrain the cosmological parameters Omega and Lambda. On each background galaxy, a cluster induces a convergence and a shear terms, which depend on the cluster projected potential, and on the cosmological parameters (Omega,Lambda), through the angular distance ratio D_{LS}/D_{OS}. To disentangle the effects of these three quantities, we compare the relative values of the ellipticities for each triplet of galaxies located at about the same position in the lens plane, but having different color red…
We explore the dependence of weak lensing phenomena on the background cosmology. We first generalise the relation between $P_ψ(ω)$, the angular power spectrum of the distortion, and the power spectrum of density fluctuations to non-flat cosmologies. We then compute $P_ψ$ for various illustrative models. A useful cosmological discriminator is the growth of $P_ψ$ with source redshift which is much stronger in low matter density models, and especially in $Λ$-dominated models. With even crude redshift information (say from broad band colours) it should be possible to constrain the cosmological wor…
Analysing the weak lensing distortions of the images of faint background galaxies provides a means to constrain the average mass distribution of cluster galaxies and potentially to test the extent of their dark matter haloes as a function of the density of their environment. The observable image distortions are a consequence of the interplay between the effects of a global cluster mass distribution and the perturbations due to individual cluster galaxies. Starting from a reconstruction of the cluster mass distribution with conventional techniques, we apply a maximum likelihood method to infer …
Weak gravitational lensing is responsible for the shearing and magnification of the images of high-redshift sources due to the presence of intervening matter. The distortions are due to fluctuations in the gravitational potential, and are directly related to the distribution of matter and to the geometry and dynamics of the Universe. As a consequence, weak gravitational lensing offers unique possibilities for probing the Dark Matter and Dark Energy in the Universe. In this review, we summarise the theoretical and observational state of the subject, focussing on the statistical aspects of weak …
In this paper, we study the cosmological implications of the 100 square degree Weak Lensing survey (the CFHTLS-Wide, RCS, VIRMOS-DESCART and GaBoDS surveys). We combine these weak lensing data with the cosmic microwave background (CMB) measurements from the WMAP5, BOOMERanG, CBI, VSA, ACBAR, the SDSS LRG matter power spectrum and the Type Ia Supernoave (SNIa) data with the "Union" compilation (307 sample), using the Markov Chain Monte Carlo method to determine the cosmological parameters. Our results show that the ΛCDM model remains a good fit to all of these data. For the dynamical dark energ…
We investigate the potentiality of using strong lensing clusters to constrain the cosmological parameters Omega_m and Omega_lambda. The existence of a multiple image system with known redshift allows, for a given (Omega_m, Omega_lambda) cosmology, absolute calibration of the total mass deduced from lens modelling. Recent Hubble Space Telescope (HST) observations of galaxy clusters reveal a large number of multiple images, which are predicted to be at different redshifts. If it is possible to measure spectroscopically the redshifts of many multiple images then one can in principle constrain (Om…
Cosmic shear leads to a correlation of the observed ellipticities of galaxies, an effect which is used to place constraints on cosmological parameters, and to explore the evolution of dark matter and dark energy in the universe. However, a possible systematic contaminant of the lensing signal is intrinsic galaxy alignment, with a correlation length of a few Mpc. Hirata & Seljak (2004) have recently demonstrated that for some models of intrinsic distortions, there may also be a cross-correlation between the intrinsic and lensing signals, which may dominate the intrinsic signal, and suppress the…
We measure the logarithmic scatter in mass at fixed richness for clusters in the maxBCG cluster catalog, an optically selected cluster sample drawn from SDSS imaging data. Our measurement is achieved by demanding consistency between available weak lensing and X-ray measurements of the maxBCG clusters, and the X-ray luminosity--mass relation inferred from the 400d X-ray cluster survey, a flux limited X-ray cluster survey. We find σ_{\ln M|N_{200}}=0.45^{+0.20}_{-0.18} (95% CL) at N_{200} ~ 40, where N_{200} is the number of red sequence galaxies in a cluster. As a byproduct of our analysis, we …
The knowledge of the redshift of multiple images in cluster-lenses allows to determine precisely the total projected mass within the Einstein radius. The observation of various multiple images in a same cluster is opening new possibilities to constrain the curvature of the universe. Indeed, although the influence of $Ω_m$ and $Ω_λ$ on the images formation is of the second order, observations of many multiple images at different redshifts formed by a regular cluster-lens should allow to constrain very accurately the mass distribution of the cluster and to start to be sensitive to the cosmologic…
Many multiply--imaged quasars have been found over the years, but none so far with image separation in excess of $8\arcsec$. The absence of such large splittings has been used as a test of cosmological models: the standard Cold Dark Matter model has been excluded on the basis that it predicts far too many large--separation double images. These studies assume that the lensing structure has the mass profile of a singular isothermal sphere. However, such large splittings would be produced by very massive systems such as clusters of galaxies, for which other gravitational lensing data suggest less…
We consider the cosmological constraints on theories in which there exists a nontrivial coupling between the dark matter sector and the sector responsible for the acceleration of the universe, in light of the most recent supernovae, large scale structure and cosmic microwave background data. For a variety of models, we show that the strength of the coupling of dark matter to a quintessence field is constrained to be less than 7% of the coupling to gravity. We also show that long range interactions between fermionic dark matter particles mediated by a light scalar with a Yukawa coupling are con…
Observers have demonstrated that it is now feasible to measure the cosmic microwave background (CMB) temperature at high redshifts. We explore the possible constraints on cosmology which might ultimately be derived from such measurements. Besides providing a consistency check on standard and alternative cosmologies, possibilities include: constraints on the inhomogeneity and anisotropy of the universe at intermediate redshift $z ^<_\sim 10$; an independent probe of peculiar motions with respect to the Hubble flow; and constraining the epoch of reionization. We argue that the best possibility i…
We discuss the possibility that, besides the usual gravitational lensing, there may exist a sort of gravitational waveguiding in cosmology which could explain some anomalous phenomena which cannot be understood by the current gravitational lensing models as the existence of "brothers" objects having different brilliancy but similar spectra and redshifts posed on the sky with large angular distance. Furthermore, such a phenomena could explain the huge luminosities coming from quasars using the cosmological structures as selfoc-type or planar waveguide. We describe the gravitational waveguide th…
I present an overview of strong and weak gravitational lensing by galaxy clusters. After briefly introducing the principles of gravitational lensing, I discuss the main lessons learned from lensing on the mass distribution in clusters and their relation to cosmology.
It has recently been suggested that a scale invariant "unparticle" sector with a non-trivial infrared fixed point may couple to the Standard Model (SM) via higher dimensional operators. The weakness of such interactions hides the the unparticle phenomena at low energies. We demonstrate how cosmology and astrophysics can place significant bounds on the strength of unparticle-SM interactions. We also discuss the possibility of a having a non-negligible unparticle relic density today.
Upcoming wide-area surveys in the submillimetre regime will allow the construction of complete galaxy cluster samples through their thermal Sunyaev-Zel'dovich effect. We propose an analytic method to predict the number of gravitationally lensed giant arcs produced by the cluster sample expected to be detectable for the Planck satellite. The statistics of lensed arcs can be used to constrain cosmological parameters. This computation implies the choice of an analytic cluster model which has to reproduce the lensing properties of realistic galaxy clusters. Comparing the results of analytic comput…
Cosmic strings of the GUT scale, generically formed during the SSB of supersymmetric hybrid inflation, are compatible with the most recent CMB data. The strong constraints on the allowed cosmic strings contribution to the measured temperature anisotropies impose limits on the free parameters of the inflationary models, namely the mass scales and the couplings.
The Einstein-Aether theory provides a simple, dynamical mechanism for breaking Lorentz invariance. It does so within a generally covariant context and may emerge from quantum effects in more fundamental theories. The theory leads to a preferred frame and can have distinct experimental signatures. In this letter, we perform a comprehensive study of the cosmological effects of the Einstein-Aether theory and use observational data to constrain it. Allied to previously determined consistency and experimental constraints, we find that an Einstein-Aether universe can fit experimental data over a wid…
We analyze the constraints on neutrino mass spectra with extra sterile neutrinos as implied by the LSND experiment. The various mass related observables in neutrinoless double beta decay, tritium beta decay and cosmology are discussed. Both neutrino oscillation results as well as recent cosmological neutrino mass bounds are taken into account. We find that some of the allowed mass patterns are severely restricted by the current constraints, in particular by the cosmological constraints on the total sum of neutrino masses and by the non-maximality of the solar neutrino mixing angle. Furthermore…
