Probing satellite haloes with weak gravitational lensing
NASA Astrophysics Data System (ADS)
Gillis, Bryan R.; Hudson, Michael J.; Hilbert, Stefan; Hartlap, Jan
2013-02-01
We demonstrate the possibility of detecting tidal stripping of dark matter subhaloes within galaxy groups using weak gravitational lensing. We have run ray-tracing simulations on galaxy catalogues from the Millennium Simulation to generate mock shape catalogues. The ray-tracing catalogues assume a halo model for galaxies and groups using various models with different distributions of mass between galaxy and group haloes to simulate different stages of group evolution. Using these mock catalogues, we forecast the lensing signals that will be detected around galaxy groups and satellite galaxies, as well as test two different methods for isolating the satellites' lensing signals. A key challenge is to determine the accuracy to which group centres can be identified. We show that with current and ongoing surveys, it will possible to detect stripping in groups of mass 1012-1015 M⊙.
Baryons, neutrinos, feedback and weak gravitational lensing
NASA Astrophysics Data System (ADS)
Harnois-Déraps, Joachim; van Waerbeke, Ludovic; Viola, Massimo; Heymans, Catherine
2015-06-01
The effect of baryonic feedback on the dark matter mass distribution is generally considered to be a nuisance to weak gravitational lensing. Measurements of cosmological parameters are affected as feedback alters the cosmic shear signal on angular scales smaller than a few arcminutes. Recent progress on the numerical modelling of baryon physics has shown that this effect could be so large that, rather than being a nuisance, the effect can be constrained with current weak lensing surveys, hence providing an alternative astrophysical insight on one of the most challenging questions of galaxy formation. In order to perform our analysis, we construct an analytic fitting formula that describes the effect of the baryons on the mass power spectrum. This fitting formula is based on three scenarios of the OverWhelmingly Large hydrodynamical simulations. It is specifically calibrated for z < 1.5, where it models the simulations to an accuracy that is better than 2 per cent for scales k < 10 h Mpc-1 and better than 5 per cent for 10 < k < 100 h Mpc-1. Equipped with this precise tool, this paper presents the first constraint on baryonic feedback models using gravitational lensing data, from the Canada France Hawaii Telescope Lensing Survey (CFHTLenS). In this analysis, we show that the effect of neutrino mass on the mass power spectrum is degenerate with the baryonic feedback at small angular scales and cannot be ignored. Assuming a cosmology precision fixed by WMAP9, we find that a universe with massless neutrinos is rejected by the CFHTLenS lensing data with 85-98 per cent confidence, depending on the baryon feedback model. Some combinations of feedback and non-zero neutrino masses are also disfavoured by the data, although it is not yet possible to isolate a unique neutrino mass and feedback model. Our study shows that ongoing weak gravitational lensing surveys (KiDS, HSC and DES) will offer a unique opportunity to probe the physics of baryons at galactic scales, in addition to the expected constraints on the total neutrino mass.
Weak Gravitational Lensing Systematics from Image Combination
NASA Astrophysics Data System (ADS)
Shapiro, C.; Rowe, B. T. P.; Goodsall, T.; Hirata, C.; Fucik, J.; Rhodes, J.; Seshadri, S.; Smith, R.
2013-12-01
Extremely accurate shape measurements of galaxy images are needed to probe dark energy properties with weak gravitational lensing surveys. To increase survey area with a fixed observing time and pixel count, images from surveys such as the Wide Field Infrared Survey Telescope (WFIRST) or Euclid will necessarily be undersampled and therefore distorted by aliasing. Oversampled, unaliased images can be obtained by combining multiple, dithered exposures of the same source with a suitable reconstruction algorithm. Any such reconstruction must minimally distort the reconstructed images for weak lensing analyses to be unbiased. In this paper, we use the image combination (IMCOM) algorithm of Rowe, Hirata, and Rhodes to investigate the effect of image combination on shape measurements (size and ellipticity). We simulate dithered images of sources with varying amounts of ellipticity and undersampling, reconstruct oversampled output images from them using IMCOM, and measure shape distortions in the output. Our simulations show that IMCOM creates no significant distortions when the relative offsets between dithered images are precisely known. Distortions increase with the uncertainty in those offsets, but become problematic only with relatively poor astrometric precision; e.g., for images similar to those from the Astrophysics Focused Telescope Asset (AFTA) implementation of WFIRST, combining eight undersampled images (sampling ratio Q = 1) with highly pessimistic uncertainty in astrometric registration (σd ~ 10-3 pixels) yields an rms shear error of O(10-4). Our analysis pipeline is adapted from that of the Precision Projector Laboratory—a joint project between NASA Jet Propulsion Laboratory and Caltech that characterizes image sensors using laboratory emulations of astronomical data.
Atomic Inference from Weak Gravitational Lensing Data
Marshall, Phil; /KIPAC, Menlo Park
2005-12-14
We present a novel approach to reconstructing the projected mass distribution from the sparse and noisy weak gravitational lensing shear data. The reconstructions are regularized via the knowledge gained from numerical simulations of clusters, with trial mass distributions constructed from n NFW profile ellipsoidal components. The parameters of these ''atoms'' are distributed a priori as in the simulated clusters. Sampling the mass distributions from the atom parameter probability density function allows estimates of the properties of the mass distribution to be generated, with error bars. The appropriate number of atoms is inferred from the data itself via the Bayesian evidence, and is typically found to be small, reecting the quality of the data. Ensemble average mass maps are found to be robust to the details of the noise realization, and succeed in recovering the demonstration input mass distribution (from a realistic simulated cluster) over a wide range of scales. As an application of such a reliable mapping algorithm, we comment on the residuals of the reconstruction and the implications for predicting convergence and shear at specific points on the sky.
NASA Astrophysics Data System (ADS)
Tsukamoto, Naoki; Kitamura, Takao; Nakajima, Koki; Asada, Hideki
2014-09-01
The gravitational lensing effects in the weak gravitational field by exotic lenses have been investigated intensively to find nonluminous exotic objects. Gravitational lensing based on 1/rn fall-off metric, as a one-parameter model that can treat by hand both the Schwarzschild lens (n =1) and the Ellis wormhole (n =2) in the weak field, has been recently studied. Only for n=1 case, however, it has been explicitly shown that effects of relativistic lens images by the strong field on the light curve can be neglected. We discuss whether relativistic images by the strong field can be neglected for n>1 in the Tangherlini spacetime which is one of the simplest models for our purpose. We calculate the divergent part of the deflection angle for arbitrary n and the regular part for n=1, 2 and 4 in the strong field limit, the deflection angle for arbitrary n under the weak gravitational approximation. We also compare the radius of the Einstein ring with the radii of the relativistic Einstein rings for arbitrary n. We conclude that the images in the strong gravitational field have little effect on the total light curve and that the time-symmetric demagnification parts in the light curve will appear even after taking account of the images in the strong gravitational field for n>1.
The general theory of secondary weak gravitational lensing
NASA Astrophysics Data System (ADS)
Clarkson, Chris
2015-09-01
Weak gravitational lensing is normally assumed to have only two principle effects: a magnification of a source and a distortion of the sources shape in the form of a shear. However, further distortions are actually present owing to changes in the gravitational field across the scale of the ray bundle of light propagating to us, resulting in the familiar arcs in lensed images. This is normally called the flexion, and is approximated by Taylor expanding the shear and magnification across the image plane. However, the physical origin of this effect arises from higher-order corrections in the geodesic deviation equation governing the gravitational force between neighbouring geodesics so involves derivatives of the Riemann tensor. We show that integrating the second-order geodesic deviation equation results in a `Hessian map' for gravitational lensing, which is a higher-order addition to the Jacobi map. We derive the general form of the Hessian map in an arbitrary spacetime paying particular attention to the separate effects of local Ricci versus non-local Weyl curvature. We then specialise to the case of a perturbed FLRW model, and give the general form of the Hessian for the first time. This has a host of new contributions which could in principle be used as tests for modified gravity.
Weak Gravitational Lensing from Regular Bardeen Black Holes
NASA Astrophysics Data System (ADS)
Ghaffarnejad, Hossein; niad, Hassan
2015-09-01
In this article we study weak gravitational lensing of regular Bardeen black hole which has scalar charge g and mass m. We investigate the angular position and magnification of non-relativistic images in two cases depending on the presence or absence of photon sphere. Defining dimensionless charge parameter q=g/2m we seek to disappear photon sphere in the case of |q|>{24?5}/{125} for which the space time metric encounters strongly with naked singularities. We specify the basic parameters of lensing in terms of scalar charge by using the perturbative method and found that the parity of images is different in two cases: (a) The strongly naked singularities is present in the space time. (b) singularity of space time is weak or is eliminated (the black hole lens).
Weak Gravitational Lensing from Regular Bardeen Black Holes
NASA Astrophysics Data System (ADS)
Ghaffarnejad, Hossein; niad, Hassan
2016-03-01
In this article we study weak gravitational lensing of regular Bardeen black hole which has scalar charge g and mass m. We investigate the angular position and magnification of non-relativistic images in two cases depending on the presence or absence of photon sphere. Defining dimensionless charge parameter q= {g}/{2m} we seek to disappear photon sphere in the case of |q|>{24√5}/{125} for which the space time metric encounters strongly with naked singularities. We specify the basic parameters of lensing in terms of scalar charge by using the perturbative method and found that the parity of images is different in two cases: (a) The strongly naked singularities is present in the space time. (b) singularity of space time is weak or is eliminated (the black hole lens).
Combining Strong and Weak Gravitational Lensing in Abell 1689
NASA Astrophysics Data System (ADS)
Limousin, Marceau; Richard, Johan; Jullo, Eric; Kneib, Jean-Paul; Fort, Bernard; Soucail, Genevive; Elasdttir, rds; Natarajan, Priyamvada; Ellis, Richard S.; Smail, Ian; Czoske, Oliver; Smith, Graham P.; Hudelot, Patrick; Bardeau, Sbastien; Ebeling, Harald; Egami, Eiichi; Knudsen, Kirsten K.
2007-10-01
We present a reconstruction of the mass distribution of galaxy cluster Abell 1689 at z=0.18 using detected strong lensing features from deep ACS observations and extensive ground based spectroscopy. Earlier analyses have reported up to 32 multiply imaged systems in this cluster, of which only 3 were spectroscopically confirmed. In this work, we present a parametric strong lensing mass reconstruction using 34 multiply imaged systems of which 24 have newly determined spectroscopic redshifts, which is a major step forward in building a robust mass model. In turn, the new spectroscopic data allows a more secure identification of multiply imaged systems. The resultant mass model enables us to reliably predict the redshifts of additional multiply imaged systems for which no spectra are currently available, and to use the location of these systems to further constrain the mass model. Using our strong lensing mass model, we predict on larger scale a shear signal which is consistent with that inferred from our large scale weak lensing analysis derived using CFH12K wide field images. Thanks to a new method for reliably selecting a well defined background lensed galaxy population, we resolve the discrepancy found between the NFW concentration parameters derived from earlier strong and weak lensing analysis. The derived parameters for the best fit NFW profile is found to be c200=7.6+/-1.6 and r200=2.16+/-0.10 h-170 Mpc (corresponding to a 3D mass equal to M200=[1.32+/-0.2]1015 h70 Msolar). The large number of new constraints incorporated in this work makes Abell 1689 the most reliably reconstructed cluster to date. This well calibrated mass model, which we here make publicly available, will enable us to exploit Abell 1689 efficiently as a gravitational telescope, as well as to potentially constrain cosmology. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. Also based on observations from the NASA/ESA Hubble Space Telescope (programs 9289 and 10150) obtained at the Space Telescope Science Institute, which is operated by AURA under NASA contract NAS5-26555.
Accurate modeling of weak lensing with the stochastic gravitational lensing method
NASA Astrophysics Data System (ADS)
Kainulainen, Kimmo; Marra, Valerio
2011-01-01
We revise and extend the stochastic gravitational lensing method (the sGL method) first introduced by Kainulainen and Marra [Phys. Rev. DPRVDAQ1550-7998 80, 123020 (2009)10.1103/PhysRevD.80.123020]. Here we include a realistic halo-mass function and density profiles to model the distribution of mass between and within galaxies, galaxy groups, and galaxy clusters. We also introduce a modeling of the filamentary large-scale structures and a method to embed halos into these structures. We show that the sGL method naturally reproduces the weak lensing results for the Millennium simulation. The strength of the sGL method is that a numerical code based on it can compute the lensing probability distribution function (PDF) for a given inhomogeneous model universe in a few seconds. This makes it a useful tool to study how lensing depends on cosmological parameters and its impact on observations. The sGL method can also be used to simulate the effect of a wide array of systematic biases on the observable lensing PDF. As an example we show how simple selection effects may reduce the variance of the observed PDF, which could possibly mask opposite effects from very large-scale structures. We also show how a survey like the Joint Dark Energy Mission could constrain the lensing PDF relative to a given cosmological model. The updated turboGL code is available at turboGL.org.
Weak gravitational lensing systematic errors in the dark energy survey
NASA Astrophysics Data System (ADS)
Plazas, Andres Alejandro
Dark energy is one of the most important unsolved problems in modern Physics, and weak gravitational lensing (WL) by mass structures along the line of sight ("cosmic shear") is a promising technique to learn more about its nature. However, WL is subject to numerous systematic errors which induce biases in measured cosmological parameters and prevent the development of its full potential. In this thesis, we advance the understanding of WL systematics in the context of the Dark Energy Survey (DES). We develop a testing suite to assess the performance of the shapelet-based DES WL measurement pipeline. We determine that the measurement bias of the parameters of our Point Spread Function (PSF) model scales as (S/N )-2, implying that a PSF S/N > 75 is needed to satisfy DES requirements. PSF anisotropy suppression also satisfies the requirements for source galaxies with S/N ≳ 45. For low-noise, marginally-resolved exponential galaxies, the shear calibration errors are up to about 0.06% (for shear values ≲ 0.075). Galaxies with S/N ≳ 75 present about 1% errors, sufficient for first-year DES data. However, more work is needed to satisfy full-area DES requirements, especially in the high-noise regime. We then implement tests to validate the high accuracy of the map between pixel coordinates and sky coordinates (astrometric solution), which is crucial to detect the required number of galaxies for WL in stacked images. We also study the effect of atmospheric dispersion on cosmic shear experiments such as DES and the Large Synoptic Survey Telescope (LSST) in the four griz bands. For DES (LSST), we find systematics in the g and r (g, r, and i) bands that are larger than required. We find that a simple linear correction in galaxy color is accurate enough to reduce dispersion shear systematics to insignificant levels in the r ( i) band for DES (LSST). More complex corrections will likely reduce the systematic cosmic-shear errors below statistical errors for LSST r band. However, g-band dispersion effects remain large enough for induced systematics to dominate the statistical error of both surveys, so cosmic-shear measurements should rely on the redder bands.
Constraining modified gravitational theories by weak lensing with Euclid
Martinelli, Matteo; Calabrese, Erminia; De Bernardis, Francesco; Melchiorri, Alessandro; Pagano, Luca; Scaramella, Roberto
2011-01-15
Future proposed satellite missions such as Euclid can offer the opportunity to test general relativity on cosmic scales through mapping of the galaxy weak-lensing signal. In this paper we forecast the ability of these experiments to constrain modified gravity scenarios such as those predicted by scalar-tensor and f(R) theories. We find that Euclid will improve constraints expected from the Planck satellite on these modified theories of gravity by 2 orders of magnitude. We discuss parameter degeneracies and the possible biases introduced by modifications to gravity.
Gravitational lensing beyond the weak-field approximation
Perlick, Volker
2014-01-14
Gravitational lensing is considered in the full spacetime formalism of general relativity, assuming that the light rays are lightlike geodesics in a Lorentzian manifold. The review consists of three parts. The first part is devoted to spherically symmetric and static spacetimes. In particular, an exact lens map for this situation is discussed. The second part is on axisymmetric and stationary spacetimes. It concentrates on the investigation of the photon region, i.e., the region filled by spherical lightlike geodesics, in the Kerr spacetime. The photon region is of crucial relevance for the formation of a shadow. Finally, the third part briefly addresses two topics that apply to spacetimes without symmetry, namely Fermat’s principle and the exact lens map of Frittelli and Newman.
Turner, E.L.
1988-07-01
For several years astronomers have devoted considerable effort to finding and studying a class of celestial phenomena whose very existence depends on rare cosmic accidents. These are gravitational-lens events, which occur when two or more objects at different distances from the earth happen to lie along the same line of sight and so coincide in the sky. The radiation from the more distant object, typically a quasar, is bent by the gravitational field of the foreground object. The bending creates a cosmic mirage: distorted or multiple images of the background object. Such phenomena may reveal many otherwise undetectable features of the image source, of the foreground object and of the space lying between them. Such observations could help to resolve several fundamental questions in cosmology. In the past decade theoretical and observational research on gravitational lenses has grown rapidly and steadily. At this writing at least 17 candidate lens systems have been discussed in the literature. Of the 17 lens candidates reported so far in professional literature, only five are considered to have been reliably established by subsequent observations. Another three are generally regarded as weak or speculative cases with less than 50 percent chance of actually being lens systems. In the remaining nine cases the evidence is mixed or is sparse enough so that the final judgment could swing either way. As might be concluded, little of the scientific promise of gravitational lenses has yet been realized. The work has not yielded a clear value for the proportionality constant or any of the other fundamental cosmological parameter. 7 figs.
Weak gravitational lensing as a method to constrain unstable dark matter
Wang Meiyu; Zentner, Andrew R.
2010-12-15
The nature of the dark matter remains a mystery. The possibility of an unstable dark matter particle decaying to invisible daughter particles has been explored many times in the past few decades. Meanwhile, weak gravitational lensing shear has gained a lot of attention as a probe of dark energy, though it was previously considered a dark matter probe. Weak lensing is a useful tool for constraining the stability of the dark matter. In the coming decade a number of large galaxy imaging surveys will be undertaken and will measure the statistics of cosmological weak lensing with unprecedented precision. Weak lensing statistics are sensitive to unstable dark matter in at least two ways. Dark matter decays alter the matter power spectrum and change the angular diameter distance-redshift relation. We show how measurements of weak lensing shear correlations may provide the most restrictive, model-independent constraints on the lifetime of unstable dark matter. Our results rely on assumptions regarding nonlinear evolution of density fluctuations in scenarios of unstable dark matter and one of our aims is to stimulate interest in theoretical work on nonlinear structure growth in unstable dark matter models.
Lincoln, Don
2015-06-24
In a long line of intellectual triumphs, Einstein’s theory of general relativity was his greatest and most imaginative. It tells us that what we experience as gravity can be most accurately described as the bending of space itself. This idea leads to consequences, including gravitational lensing, which is caused by light traveling in this curved space. This is works in a way analogous to a lens (and hence the name). In this video, Fermilab’s Dr. Don Lincoln explains a little general relativity, a little gravitational lensing, and tells us how this phenomenon allows us to map out the matter of the entire universe, including the otherwise-invisible dark matter.
Rotation of the cosmic microwave background polarization from weak gravitational lensing.
Dai, Liang
2014-01-31
When a cosmic microwave background (CMB) photon travels from the surface of last scatter through spacetime metric perturbations, the polarization vector may rotate about its direction of propagation. This gravitational rotation is distinct from, and occurs in addition to, the lensing deflection of the photon trajectory. This rotation can be sourced by linear vector or tensor metric perturbations and is fully coherent with the curl deflection field. Therefore, lensing corrections to the CMB polarization power spectra as well as the temperature-polarization cross correlations due to nonscalar perturbations are modified. The rotation does not affect lensing by linear scalar perturbations, but needs to be included when calculations go to higher orders. We present complete results for weak lensing of the full-sky CMB power spectra by general linear metric perturbations, taking into account both deflection of the photon trajectory and rotation of the polarization. For the case of lensing by gravitational waves, we show that the B modes induced by the rotation largely cancel those induced by the curl component of deflection. PMID:24580435
WEAK GRAVITATIONAL LENSING AS A PROBE OF PHYSICAL PROPERTIES OF SUBSTRUCTURES IN DARK MATTER HALOS
Shirasaki, Masato
2015-02-01
We propose a novel method to select satellite galaxies in outer regions of galaxy groups or clusters using weak gravitational lensing. The method is based on the theoretical expectation that the tangential shear pattern around satellite galaxies would appear with negative values at an offset distance from the center of the main halo. We can thus locate the satellite galaxies statistically with an offset distance of several lensing smoothing scales by using the standard reconstruction of surface mass density maps from weak lensing observation. We test the idea using high-resolution cosmological simulations. We show that subhalos separated from the center of the host halo are successfully located even without assuming the position of the center. For a number of such subhalos, the characteristic mass and offset length can be also estimated on a statistical basis. We perform a Fisher analysis to show how well upcoming weak lensing surveys can constrain the mass density profile of satellite galaxies. In the case of the Large Synoptic Survey Telescope with a sky coverage of 20,000deg{sup 2}, the mass of the member galaxies in the outer region of galaxy clusters can be constrained with an accuracy of ?0.1 dex for galaxy clusters with mass 10{sup 14} h {sup 1} M {sub ?} at z = 0.15. Finally we explore the detectability of tidal stripping features for subhalos having a wide range of masses of 10{sup 11}-10{sup 13} h {sup 1} M {sub ?}.
Improving PSF modelling for weak gravitational lensing using new methods in model selection
NASA Astrophysics Data System (ADS)
Rowe, Barnaby
2010-05-01
A simple theoretical framework for the description and interpretation of spatially correlated modelling residuals is presented, and the resulting tools are found to provide a useful aid to model selection in the context of weak gravitational lensing. The description is focused upon the specific problem of modelling the spatial variation of a telescope point spread function (PSF) across the instrument field of view, a crucial stage in lensing data analysis, but the technique may be used to rank competing models wherever data are described empirically. As such it may, with further development, provide useful extra information when used in combination with existing model selection techniques such as the Akaike and Bayesian information criteria, or the Bayesian evidence. Two independent diagnostic correlation functions are described, and the interpretation of these functions is demonstrated by using a simulated PSF anisotropy field. The efficacy of these diagnostic functions as an aid to the correct choice of empirical model is then demonstrated by analysing results for a suite of Monte Carlo simulations of random PSF fields with varying degrees of spatial structure, and it is shown how the diagnostic functions can be related to requirements for precision cosmic shear measurement. The limitations of the technique, and opportunities for improvements and applications to fields other than weak gravitational lensing, are discussed.
Hirata, Christopher M.; Cutler, Curt
2010-06-15
Gravitational wave sources are a promising cosmological standard candle because their intrinsic luminosities are determined by fundamental physics (and are insensitive to dust extinction). They are, however, affected by weak lensing magnification due to the gravitational lensing from structures along the line of sight. This lensing is a source of uncertainty in the distance determination, even in the limit of perfect standard candle measurements. It is commonly believed that the uncertainty in the distance to an ensemble of gravitational wave sources is limited by the standard deviation of the lensing magnification distribution divided by the square root of the number of sources. Here we show that by exploiting the non-Gaussian nature of the lensing magnification distribution, we can improve this distance determination, typically by a factor of 2-3; we provide a fitting formula for the effective distance accuracy as a function of redshift for sources where the lensing noise dominates.
Resource Letter GL-1: Gravitational Lensing
NASA Astrophysics Data System (ADS)
Treu, Tommaso; Marshall, Philip J.; Clowe, Douglas
2012-09-01
This Resource Letter provides a guide to a selection of the literature on gravitational lensing and its applications. Journal articles, books, popular articles, and websites are cited for the following topics: foundations of gravitational lensing, foundations of cosmology, history of gravitational lensing, strong lensing, weak lensing, and microlensing.
NASA Astrophysics Data System (ADS)
Harnois-Draps, Joachim; van Waerbeke, Ludovic
2015-07-01
Numerical N-body simulations play a central role in the assessment of weak gravitational lensing statistics, residual systematics and error analysis. In this paper, we investigate and quantify the impact of finite simulation volume on weak lensing two- and four-point statistics. These finite support (FS) effects are modelled for several estimators, simulation box sizes and source redshifts, and validated against a new large suite of 500 N-body simulations. The comparison reveals that our theoretical model is accurate to better than 5 per cent for the shear correlation function ?+(?) and its error. We find that the most important quantities for FS modelling are the ratio between the measured angle ? and the angular size of the simulation box at the source redshift, ?box(zs), or the multipole equivalent ?/?box(zs). When this ratio reaches 0.1, independently of the source redshift, the shear correlation function ?+ is suppressed by 5, 10, 20 and 25 per cent for Lbox = 1000, 500, 250 and 147 h-1 Mpc, respectively. The same effect is observed in ?-(?), but at much larger angles. This has important consequences for cosmological analyses using N-body simulations and should not be overlooked. We propose simple semi-analytic correction strategies that account for shape noise and survey masks, generalizable to any weak lensing estimator. From the same simulation suite, we revisit the existing non-Gaussian covariance matrix calibration of the shear correlation function, and propose a new one based on the 9-year Wilkinson Microwave Anisotropy Probe)+baryon acoustic oscillations+supernova cosmology. Our calibration matrix is accurate at 20 per cent down to the arcminute scale, for source redshifts in the range 0 < z < 3, even for the far off-diagonal elements. We propose, for the first time, a parametrization for the full ?- covariance matrix, also 20 per cent accurate for most elements.
Gravitational Lensing by Kerr-Sen Dilaton-Axion Black Hole in the Weak Deflection Limit
Gyulchev, G. N.; Yazadjiev, S. S.
2010-11-25
We investigate analytically gravitational lensing by charged, stationary, axially symmetric Kerr-Sen dilaton-axion black hole in the weak deflection limit. Approximate solutions to the lightlike equations of motion are present up to and including third-order terms in M/b, a/b and r{sub {alpha}}/b, where M is the black hole mass, a is the angular momentum, r{sub {alpha}}= Q{sup 2}/M,Q being the charge and b is the impact parameter of the light ray. We compute the positions of the two weak field images up to post-Newtonian order. The shift of the critical curves as a function of the lens angular momentum is found, and it is shown that they decrease slightly with the increase of the charge. The lensing observables are compared to these characteristics for particular cases as Schwarzschild and Kerr black holes as well as the Gibbons-Maeda-Garfinkle-Horowitz-Strominger black hole.
Constraints on the shapes of galaxy dark matter haloes from weak gravitational lensing
NASA Astrophysics Data System (ADS)
van Uitert, E.; Hoekstra, H.; Schrabback, T.; Gilbank, D. G.; Gladders, M. D.; Yee, H. K. C.
2012-09-01
We study the shapes of galaxy dark matter haloes by measuring the anisotropy of the weak gravitational lensing signal around galaxies in the second Red-sequence Cluster Survey (RCS2). We determine the average shear anisotropy within the virial radius for three lens samples: the "all" sample, which contains all galaxies with 19 < mr' < 21.5, and the "red" and "blue" samples, whose lensing signals are dominated by massive low-redshift early-type and late-type galaxies, respectively. To study the environmental dependence of the lensing signal, we separate each lens sample into an isolated and clustered part and analyse them separately. We address the impact of several complications on the halo ellipticity measurement, including PSF residual systematics in the shape catalogues, multiple deflections, and the clustering of lenses. We estimate that the impact of these is small for our lens selections. Furthermore, we measure the azimuthal dependence of the distribution of physically associated galaxies around the lens samples. We find that these satellites preferentially reside near the major axis of the lenses, and constrain the angle between the major axis of the lens and the average location of the satellites to ⟨θ⟩ = 43.7° ± 0.3° for the "all" lenses, ⟨θ⟩ = 41.7° ± 0.5° for the "red" lenses and ⟨θ⟩ = 42.0° ± 1.4° for the "blue" lenses. We do not detect a significant shear anisotropy for the average "red" and "blue" lenses, although for the most elliptical "red" and "blue" galaxies it is marginally positive and negative, respectively. For the "all" sample, we find that the anisotropy of the galaxy-mass cross-correlation function ⟨f - f45⟩ = 0.23 ± 0.12, providing weak support for the view that the average galaxy is embedded in, and preferentially aligned with, a triaxial dark matter halo. Assuming an elliptical Navarro-Frenk-White profile, we find that the ratio of the dark matter halo ellipticity and the galaxy ellipticity fh = eh/eg = 1.50-1.01+1.03, which for a mean lens ellipticity of 0.25 corresponds to a projected halo ellipticity of eh = 0.38-0.25+0.26 if the halo and the lens are perfectly aligned. For isolated galaxies of the "all" sample, the average shear anisotropy increases to ⟨f-f45⟩ = 0.51-0.25+0.26 and fh = 4.73-2.05+2.17, whilst for clustered galaxies the signal is consistent with zero. These constraints provide lower limits on the average dark matter halo ellipticity, as scatter in the relative position angle between the galaxies and the dark matter haloes is expected to reduce the shear anisotropy by a factor ~2.
TOPICAL REVIEW Gravitational lensing
NASA Astrophysics Data System (ADS)
Bartelmann, Matthias
2010-12-01
Gravitational lensing has developed into one of the most powerful tools for the analysis of the dark universe. This review summarizes the theory of gravitational lensing, its main current applications and representative results achieved so far. It has two parts. In the first, starting from the equation of geodesic deviation, the equations of thin and extended gravitational lensing are derived. In the second, gravitational lensing by stars and planets, galaxies, galaxy clusters and large-scale structures is discussed and summarized.
Probing Dark Energy via Weak Gravitational Lensing with the Supernova Acceleration Probe (SNAP)
Albert, J.; Aldering, G.; Allam, S.; Althouse, W.; Amanullah, R.; Annis, J.; Astier, P.; Aumeunier, M.; Bailey, S.; Baltay, C.; Barrelet, E.; Basa, S.; Bebek, C.; Bergstom, L.; Bernstein, G.; Bester, M.; Besuner, B.; Bigelow, B.; Blandford, R.; Bohlin, R.; Bonissent, A.; /Caltech /LBL, Berkeley /Fermilab /SLAC /Stockholm U. /Paris, IN2P3 /Marseille, CPPM /Marseille, Lab. Astrophys. /Yale U. /Pennsylvania U. /UC, Berkeley /Michigan U. /Baltimore, Space Telescope Sci. /Indiana U. /Caltech, JPL /Australian Natl. U., Canberra /American Astron. Society /Chicago U. /Cambridge U. /Saclay /Lyon, IPN
2005-08-08
SNAP is a candidate for the Joint Dark Energy Mission (JDEM) that seeks to place constraints on the dark energy using two distinct methods. The first, Type Ia SN, is discussed in a separate white paper. The second method is weak gravitational lensing, which relies on the coherent distortions in the shapes of background galaxies by foreground mass structures. The excellent spatial resolution and photometric accuracy afforded by a 2-meter space-based observatory are crucial for achieving the high surface density of resolved galaxies, the tight control of systematic errors in the telescope's Point Spread Function (PSF), and the exquisite redshift accuracy and depth required by this project. These are achieved by the elimination of atmospheric distortion and much of the thermal and gravity loads on the telescope. The SN and WL methods for probing dark energy are highly complementary and the error contours from the two methods are largely orthogonal. The nominal SNAP weak lensing survey covers 1000 square degrees per year of operation in six optical and three near infrared filters (NIR) spanning the range 350 nm to 1.7 {micro}m. This survey will reach a depth of 26.6 AB magnitude in each of the nine filters and allow for approximately 100 resolved galaxies per square arcminute, {approx} 3 times that available from the best ground-based surveys. Photometric redshifts will be measured with statistical accuracy that enables scientific applications for even the faint, high redshift end of the sample. Ongoing work aims to meet the requirements on systematics in galaxy shape measurement, photometric redshift biases, and theoretical predictions.
Zhang Pengjie
2010-09-10
The galaxy intrinsic alignment is a severe challenge to precision cosmic shear measurement. We propose self-calibrating the induced gravitational shear-galaxy intrinsic ellipticity correlation (the GI correlation) in weak lensing surveys with photometric redshift measurements. (1) We propose a method to extract the intrinsic ellipticity-galaxy density cross-correlation (I-g) from the galaxy ellipticity-density measurement in the same redshift bin. (2) We also find a generic scaling relation to convert the extracted I-g correlation to the necessary GI correlation. We perform a concept study under simplified conditions and demonstrate its capability to significantly reduce GI contamination. We discuss the impact of various complexities on the two key ingredients of the self-calibration technique, namely the method for extracting the I-g correlation and the scaling relation between the I-g and the GI correlation. We expect that none of them will likely be able to completely invalidate the proposed self-calibration technique.
NASA Astrophysics Data System (ADS)
Rhodes, Jason
The nature of dark energy, thought to be driving the accelerating expansion of the Universe, is one of the most compelling mysteries in all of science. Determining the equation-of-state of dark energy to 1% accuracy is currently a leading goal for many planned cosmological surveys and numerical simulations of structure formation are required to make predictions and help mitigate systematics for upcoming surveys such as NASA’s Wide-Field Infrared Survey Telescope (WFIRST), ESA’s Euclid and the Large Synoptic Survey Telescope (LSST). We propose to: 1) Enhance our weak lensing simulation pipeline, SUNGLASS, to include galaxy intrinsic alignments 2) Develop and test intrinsic alignment mitigation techniques 3) Generate high precision covariance matrices and determine the precision required to measure the equation-of-state of dark energy to 1% 4) Develop a covariance emulator Our SUNGLASS pipeline (Simulated UNiverses for Gravitational Lensing Analysis and Shear Surveys; Kiessling et al. 2011a) is able to produce Monte Carlo suites of numerical simulations and rapidly generates mock weak lensing galaxy shear catalogues. We propose to enhance the SUNGLASS pipeline to include realistic galaxy properties using the Galacticus software (Benson 2012). With the realistic galaxy properties made available from Galacticus, we will be able to place realistic intrinsic alignment (IA) signals, where galaxy shapes are correlated due to their physical proximity, into the mock catalogues. Using the SUNGLASS/Galacticus catalogues, we propose to reduce the degrees of freedom in a plausible IA model and find optimal methods of controlling IA through removal techniques and modeling. It is currently unknown how accurate a covariance matrix needs to be in order to measure the equation-of-state of dark energy to 1%. We will directly generate the matrices with 10^4 independent N-body realizations for a LCDM cosmology to test how errors propagate through the non-linear modes and compare results with Gaussian estimates. We will also determine how accurate the inverse covariance matrix needs to be to measure dark energy to 1%. Future missions will require cosmology dependent covariance matrices, so we will need simulations at up to 10^4 points in parameter space. The ~10^8 simulations needed (10^4 realizations at up to 10^4 points in parameter space) would take a prohibitively large amount of time and computing resources. To reduce the number of realizations required in the future, while sampling the plausible parameter space, we will develop and test an emulator that does not compromise on the accuracy of the inverse covariance matrix. The developments and investigations proposed here are absolutely essential for the success of future telescope missions in determining the dark energy equation-of-state to an accuracy of 1%. The SUNGLASS pipeline is uniquely placed to tackle all of these problems in a rapid and computationally efficient way and the developments proposed will result in a pipeline that is able to drive a cosmology telescope mission from the development phase all the way through to accurate data analysis.
NASA Astrophysics Data System (ADS)
Niemi, Sami-Matias; Kitching, Thomas D.; Cropper, Mark
2015-12-01
One of the most powerful techniques to study the dark sector of the Universe is weak gravitational lensing. In practice, to infer the reduced shear, weak lensing measures galaxy shapes, which are the consequence of both the intrinsic ellipticity of the sources and of the integrated gravitational lensing effect along the line of sight. Hence, a very large number of galaxies is required in order to average over their individual properties and to isolate the weak lensing cosmic shear signal. If this `shape noise' can be reduced, significant advances in the power of a weak lensing surveys can be expected. This paper describes a general method for extracting the probability distributions of parameters from catalogues of data using Voronoi cells, which has several applications, and has synergies with Bayesian hierarchical modelling approaches. This allows us to construct a probability distribution for the variance of the intrinsic ellipticity as a function of galaxy property using only photometric data, allowing a reduction of shape noise. As a proof of concept the method is applied to the CFHTLenS survey data. We use this approach to investigate trends of galaxy properties in the data and apply this to the case of weak lensing power spectra.
Weak gravitational lensing due to large-scale structure of the universe
NASA Technical Reports Server (NTRS)
Jaroszynski, Michal; Park, Changbom; Paczynski, Bohdan; Gott, J. Richard, III
1990-01-01
The effect of the large-scale structure of the universe on the propagation of light rays is studied. The development of the large-scale density fluctuations in the omega = 1 universe is calculated within the cold dark matter scenario using a smooth particle approximation. The propagation of about 10 to the 6th random light rays between the redshift z = 5 and the observer was followed. It is found that the effect of shear is negligible, and the amplification of single images is dominated by the matter in the beam. The spread of amplifications is very small. Therefore, the filled-beam approximation is very good for studies of strong lensing by galaxies or clusters of galaxies. In the simulation, the column density was averaged over a comoving area of approximately (1/h Mpc)-squared. No case of a strong gravitational lensing was found, i.e., no 'over-focused' image that would suggest that a few images might be present. Therefore, the large-scale structure of the universe as it is presently known does not produce multiple images with gravitational lensing on a scale larger than clusters of galaxies.
Cosmology with weak lensing surveys.
Munshi, Dipak; Valageas, Patrick
2005-12-15
Weak gravitational lensing is responsible for the shearing and magnification of the images of high-redshift sources due to the presence of intervening mass. Since the lensing effects arise from deflections of the light rays due to fluctuations of the gravitational potential, they can be directly related to the underlying density field of the large-scale structures. Weak gravitational surveys are complementary to both galaxy surveys and cosmic microwave background observations as they probe unbiased nonlinear matter power spectra at medium redshift. Ongoing CMBR experiments such as WMAP and a future Planck satellite mission will measure the standard cosmological parameters with unprecedented accuracy. The focus of attention will then shift to understanding the nature of dark matter and vacuum energy: several recent studies suggest that lensing is the best method for constraining the dark energy equation of state. During the next 5 year period, ongoing and future weak lensing surveys such as the Joint Dark Energy Mission (JDEM; e.g. SNAP) or the Large-aperture Synoptic Survey Telescope will play a major role in advancing our understanding of the universe in this direction. In this review article, we describe various aspects of probing the matter power spectrum and the bi-spectrum and other related statistics with weak lensing surveys. This can be used to probe the background dynamics of the universe as well as the nature of dark matter and dark energy. PMID:16286284
NASA Astrophysics Data System (ADS)
Jee, Myungkook James
2006-06-01
Clusters of galaxies, the largest gravitationally bound objects in the Universe, are useful tracers of cosmic evolution, and particularly detailed studies of still-forming clusters at high-redshifts can considerably enhance our understanding of the structure formation. We use two powerful methods that have become recently available for the study of these distant clusters: spaced- based gravitational weak-lensing and high-resolution X-ray observations. Detailed analyses of five high-redshift (0.8 < z < 1.3) clusters are presented based on the deep Advanced Camera for Surveys (ACS) and Chandra X-ray images. We show that, when the instrumental characteristics are properly understood, the newly installed ACS on the Hubble Space Telescope (HST) can detect subtle shape distortions of background galaxies down to the limiting magnitudes of the observations, which enables the mapping of the cluster dark matter in unprecedented high-resolution. The cluster masses derived from this HST /ACS weak-lensing study have been compared with those from the re-analyses of the archival Chandra X-ray data. We find that there are interesting offsets between the cluster galaxy, intracluster medium (ICM), and dark matter centroids, and possible scenarios are discussed. If the offset is confirmed to be uniquitous in other clusters, the explanation may necessitate major refinements in our current understanding of the nature of dark matter, as well as the cluster galaxy dynamics. CL0848+4452, the highest-redshift ( z = 1.27) cluster yet detected in weak-lensing, has a significant discrepancy between the weak- lensing and X-ray masses. If this trend is found to be severe and common also for other X-ray weak clusters at redshifts beyond the unity, the conventional X-ray determination of cluster mass functions, often inferred from their immediate X-ray properties such as the X-ray luminosity and temperature via the so-called mass-luminosity (M-L) and mass-temperature (M-T) relations, will become highly unstable in this redshift regime. Therefore, the relatively unbiased weak-lensing measurements of the cluster mass properties can be used to adequately calibrate the scaling relations in future high-redshift cluster investigations.
CFHTLenS: the relation between galaxy dark matter haloes and baryons from weak gravitational lensing
NASA Astrophysics Data System (ADS)
Velander, Malin; van Uitert, Edo; Hoekstra, Henk; Coupon, Jean; Erben, Thomas; Heymans, Catherine; Hildebrandt, Hendrik; Kitching, Thomas D.; Mellier, Yannick; Miller, Lance; Van Waerbeke, Ludovic; Bonnett, Christopher; Fu, Liping; Giodini, Stefania; Hudson, Michael J.; Kuijken, Konrad; Rowe, Barnaby; Schrabback, Tim; Semboloni, Elisabetta
2014-01-01
We present a study of the relation between dark matter halo mass and the baryonic content of their host galaxies, quantified through galaxy luminosity and stellar mass. Our investigation uses 154 deg2 of Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) lensing and photometric data, obtained from the CFHT Legacy Survey. To interpret the weak lensing signal around our galaxies, we employ a galaxy-galaxy lensing halo model which allows us to constrain the halo mass and the satellite fraction. Our analysis is limited to lenses at redshifts between 0.2 and 0.4, split into a red and a blue sample. We express the relationship between dark matter halo mass and baryonic observable as a power law with pivot points of 10^{11} h_{70}^{-2} L_{{⊙}} and 2× 10^{11} h_{70}^{-2} M_{{⊙}} for luminosity and stellar mass, respectively. For the luminosity-halo mass relation, we find a slope of 1.32 ± 0.06 and a normalization of 1.19^{+0.06}_{-0.07}× 10^{13} h_{70}^{-1} M_{{⊙}} for red galaxies, while for blue galaxies the best-fitting slope is 1.09^{+0.20}_{-0.13} and the normalization is 0.18^{+0.04}_{-0.05}× 10^{13} h_{70}^{-1} M_{{⊙}}. Similarly, we find a best-fitting slope of 1.36^{+0.06}_{-0.07} and a normalization of 1.43^{+0.11}_{-0.08}× 10^{13} h_{70}^{-1} M_{{⊙}} for the stellar mass-halo mass relation of red galaxies, while for blue galaxies the corresponding values are 0.98^{+0.08}_{-0.07} and 0.84^{+0.20}_{-0.16}× 10^{13} h_{70}^{-1} M_{{⊙ }}. All numbers convey the 68 per cent confidence limit. For red lenses, the fraction which are satellites inside a larger halo tends to decrease with luminosity and stellar mass, with the sample being nearly all satellites for a stellar mass of 2× 109 h_{70}^{-2} M_{{⊙}}. The satellite fractions are generally close to zero for blue lenses, irrespective of luminosity or stellar mass. This, together with the shallower relation between halo mass and baryonic tracer, is a direct confirmation from galaxy-galaxy lensing that blue galaxies reside in less clustered environments than red galaxies. We also find that the halo model, while matching the lensing signal around red lenses well, is prone to overpredicting the large-scale signal for faint and less massive blue lenses. This could be a further indication that these galaxies tend to be more isolated than assumed.
Gravitational lensing in quasar samples
NASA Astrophysics Data System (ADS)
Claeskens, Jean-François; Surdej, Jean
The first cosmic mirage was discovered approximately 20 years ago as the double optical counterpart of a radio source. This phenomenon had been predicted some 70 years earlier as a consequence of General Relativity. We present here a summary of what we have learnt since. The applications are so numerous that we had to concentrate on a few selected aspects of this new field of research. This review is focused on strong gravitational lensing, i.e. the formation of multiple images, in QSO samples. It is intended to give the reader an up-to-date status of the observations and to present an overview of its most interesting potential applications in cosmology and astrophysics, as well as numerous important results achieved so far. The first section follows an intuitive approach to the basics of gravitational lensing and is developed in view of our interest in multiply imaged quasars. The astrophysical and cosmological applications of gravitational lensing are outlined in Sect. 2 and the most important results are presented in Sect. 5. Sections 3 and 4 are devoted to the observations. Finally, conclusions are summarized in the last section. We have tried to avoid duplication with existing (and excellent) introductions to the field of gravitational lensing. For this reason, we did not concentrate on the individual properties of specific lens models, as these are already well presented in Narayan and Bartelmann (1996) and on a more intuitive ground in Refsdal and Surdej (1994). Wambsganss (1998) proposes a broad view on gravitational lensing in astronomy; the reviews by Fort and Mellier (1994) and Hattori et al. (1999) deal with lensing by galaxy clusters; microlensing in the Galaxy and the local group is reviewed by Paczynski (1996) and a general panorama on weak lensing is given by Bartelmann and Schneider (1999) and Mellier (1999). The monograph on the theory of gravitational lensing by Schneider, Ehlers and Falco (1992) also remains a reference in the field.
Aberration in gravitational lensing
Sereno, M.
2008-10-15
It is known that a relative translational motion between the deflector and the observer affects gravitational lensing. In this paper, a lens equation is obtained to describe such effects on actual lensing observables. Results can be easily interpreted in terms of aberration of light rays. Both radial and transverse motions with relativistic velocities are considered. The lens equation is derived by first considering geodesic motion of photons in the rest-frame Schwarzschild space-time of the lens, and, then, light-ray detection in the moving observer's frame. Because of the transverse motion images are displaced and distorted in the observer's celestial sphere, whereas the radial velocity along the line of sight causes an effective rescaling of the lens mass. The Einstein ring is distorted to an ellipse whereas the caustics in the source plane are still pointlike. Either for null transverse motion or up to linear order in velocities, the critical curve is still a circle with its radius corrected by a factor (1+z{sub d}) with respect to the static case, z{sub d} being the relativistic Doppler shift of the deflector. From the observational point of view, the orbital motion of the Earth can cause potentially observable corrections of the order of the {mu}arcsec in lensing towards the supermassive black hole at the Galactic center. On a cosmological scale, tangential peculiar velocities of a cluster of galaxies bring about a typical flexion in images of background galaxies in the weak lensing regime but future measurements seem to be too challenging.
Aberration in gravitational lensing
NASA Astrophysics Data System (ADS)
Sereno, M.
2008-10-01
It is known that a relative translational motion between the deflector and the observer affects gravitational lensing. In this paper, a lens equation is obtained to describe such effects on actual lensing observables. Results can be easily interpreted in terms of aberration of light rays. Both radial and transverse motions with relativistic velocities are considered. The lens equation is derived by first considering geodesic motion of photons in the rest-frame Schwarzschild space-time of the lens, and, then, light-ray detection in the moving observer’s frame. Because of the transverse motion images are displaced and distorted in the observer’s celestial sphere, whereas the radial velocity along the line of sight causes an effective rescaling of the lens mass. The Einstein ring is distorted to an ellipse whereas the caustics in the source plane are still pointlike. Either for null transverse motion or up to linear order in velocities, the critical curve is still a circle with its radius corrected by a factor (1+zd) with respect to the static case, zd being the relativistic Doppler shift of the deflector. From the observational point of view, the orbital motion of the Earth can cause potentially observable corrections of the order of the μarcsec in lensing towards the supermassive black hole at the Galactic center. On a cosmological scale, tangential peculiar velocities of a cluster of galaxies bring about a typical flexion in images of background galaxies in the weak lensing regime but future measurements seem to be too challenging.
Taylor, James E.; Massey, Richard J.; Leauthaud, Alexie; Tanaka, Masayuki; George, Matthew R.; Rhodes, Jason; Ellis, Richard; Scoville, Nick; Kitching, Thomas D.; Capak, Peter; Finoguenov, Alexis; Ilbert, Olivier; Kneib, Jean-Paul; Jullo, Eric; Koekemoer, Anton M.
2012-04-20
Gravitational lensing can provide pure geometric tests of the structure of spacetime, for instance by determining empirically the angular diameter distance-redshift relation. This geometric test has been demonstrated several times using massive clusters which produce a large lensing signal. In this case, matter at a single redshift dominates the lensing signal, so the analysis is straightforward. It is less clear how weaker signals from multiple sources at different redshifts can be stacked to demonstrate the geometric dependence. We introduce a simple measure of relative shear which for flat cosmologies separates the effect of lens and source positions into multiplicative terms, allowing signals from many different source-lens pairs to be combined. Applying this technique to a sample of groups and low-mass clusters in the COSMOS survey, we detect a clear variation of shear with distance behind the lens. This represents the first detection of the geometric effect using weak lensing by multiple, low-mass groups. The variation of distance with redshift is measured with sufficient precision to constrain the equation of state of the universe under the assumption of flatness, equivalent to a detection of a dark energy component {Omega}{sub X} at greater than 99% confidence for an equation-of-state parameter -2.5 {<=} w {<=} -0.1. For the case w = -1, we find a value for the cosmological constant density parameter {Omega}{sub {Lambda}} = 0.85{sup +0.044}{sub -}0{sub .19} (68% CL) and detect cosmic acceleration (q{sub 0} < 0) at the 98% CL. We consider the systematic uncertainties associated with this technique and discuss the prospects for applying it in forthcoming weak-lensing surveys.
Tuning Gravitationally Lensed Standard Sirens
NASA Astrophysics Data System (ADS)
Jnsson, J.; Goobar, A.; Mrtsell, E.
2007-03-01
Gravitational waves emitted by chirping supermassive black hole binaries could in principle be used to obtain very accurate distance determinations. Provided they have an electromagnetic counterpart from which the redshift can be determined, these standard sirens could be used to build a high-redshift Hubble diagram. Errors in the distance measurements will most likely be dominated by gravitational lensing. We show that the (de)magnification due to inhomogeneous foreground matter will increase the scatter in the measured distances by a factor of ~10. We propose to use optical and IR data of the foreground galaxies to minimize the degradation from weak lensing. We find that the net effect of correcting the estimated distances for lensing is comparable to increasing the sample size by a factor of 3 when using the data to constrain cosmological parameters.
NASA Astrophysics Data System (ADS)
Wang, Wenting; White, Simon D. M.; Mandelbaum, Rachel; Henriques, Bruno; Anderson, Michael E.; Han, Jiaxin
2016-03-01
We use weak gravitational lensing to measure mean mass profiles around locally brightest galaxies (LBGs). These are selected from the Seventh Data Release of the Sloan Digital Sky Survey spectroscopic and photometric catalogues to be brighter than any neighbour projected within 1.0 Mpc and differing in redshift by <1000 km s-1. Most (>83 per cent) are expected to be the central galaxies of their dark matter haloes. Previous stacking analyses have used this LBG sample to measure mean Sunyaev-Zeldovich flux and mean X-ray luminosity as a function of LBG stellar mass. In both cases, a simulation of the formation of the galaxy population was used to estimate effective halo mass for LBGs of given stellar mass, allowing the derivation of scaling relations between the gas properties of haloes and their mass. By comparing results from a variety of simulations to our lensing data, we show that this procedure has significant model dependence reflecting: (i) the failure of any given simulation to reproduce observed galaxy abundances exactly; (ii) a dependence on the cosmology underlying the simulation; and (iii) a dependence on the details of how galaxies populate haloes. We use our lensing results to recalibrate the scaling relations, eliminating most of this model dependence and explicitly accounting both for residual modelling uncertainties and for observational uncertainties in the lensing results. The resulting scaling relations link the mean gas properties of dark haloes to their mass over an unprecedentedly wide range, 1012.5 < M500/M⊙ < 1014.5, and should fairly and robustly represent the full halo population.
NASA Astrophysics Data System (ADS)
Wittman, David M.; Jain, B.; Jarvis, M.; Knox, L.; Margoniner, V.; Takada, M.; Tyson, J.; Zhan, H.; LSST Weak Lensing Science Collaboration
2006-12-01
Constraining dark energy parameters with weak lensing is one of the primary science goals of the LSST. The LSST Weak Lensing Science Collaboration has been formed with the goal of optimizing the weak lensing science by optimizing the survey cadence; working with Data Management to insure high-quality pipeline processing which will meet our needs; developing the necessary analysis tools well before the onset of data-taking; participating in high-fidelity simulations to test the system end-to-end; and analyzing the real dataset as it becomes available. We review the major weak lensing probes, the twoand three-point shear correlations, and how they constrain dark energy parameters. We also review the possibility of going beyond dark energy models and testing gravity with the LSST data. To realize the promise of the awesome LSST statistical precision, we must ensure that systematic errors are kept under control. We review the major sources of systematics and our plans for mitigation. We present data that demonstrate that these sources of systematics can be kept to a level smaller than the statistical error.
NASA Astrophysics Data System (ADS)
Taylor, James E.; Massey, Richard J.; Leauthaud, Alexie; George, Matthew R.; Rhodes, Jason; Kitching, Thomas D.; Capak, Peter; Ellis, Richard; Finoguenov, Alexis; Ilbert, Olivier; Jullo, Eric; Kneib, Jean-Paul; Koekemoer, Anton M.; Scoville, Nick; Tanaka, Masayuki
2012-04-01
Gravitational lensing can provide pure geometric tests of the structure of spacetime, for instance by determining empirically the angular diameter distance-redshift relation. This geometric test has been demonstrated several times using massive clusters which produce a large lensing signal. In this case, matter at a single redshift dominates the lensing signal, so the analysis is straightforward. It is less clear how weaker signals from multiple sources at different redshifts can be stacked to demonstrate the geometric dependence. We introduce a simple measure of relative shear which for flat cosmologies separates the effect of lens and source positions into multiplicative terms, allowing signals from many different source-lens pairs to be combined. Applying this technique to a sample of groups and low-mass clusters in the COSMOS survey, we detect a clear variation of shear with distance behind the lens. This represents the first detection of the geometric effect using weak lensing by multiple, low-mass groups. The variation of distance with redshift is measured with sufficient precision to constrain the equation of state of the universe under the assumption of flatness, equivalent to a detection of a dark energy component ? X at greater than 99% confidence for an equation-of-state parameter -2.5 <= w <= -0.1. For the case w = -1, we find a value for the cosmological constant density parameter ?? = 0.85+0.044 -0.19 (68% CL) and detect cosmic acceleration (q 0 < 0) at the 98% CL. We consider the systematic uncertainties associated with this technique and discuss the prospects for applying it in forthcoming weak-lensing surveys. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by AURA Inc. under the NASA contract NAS 5-26555; the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan; the European Southern Observatory under the Large Program 175.A-0839, Chile; Kitt Peak National Observatory, Cerro Tololo Inter-American Observatory, and the National Optical Astronomy Observatory, which are operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation.
Gravitational lensing in plasmic medium
NASA Astrophysics Data System (ADS)
Bisnovatyi-Kogan, G. S.; Tsupko, O. Yu.
2015-07-01
The influence of plasma on different effects of gravitational lensing is reviewed. Using the Hamiltonian approach for geometrical optics in a medium in the presence of gravity, an exact formula for the photon deflection angle by a black hole (or another body with a Schwarzschild metric) embedded in plasma with a spherically symmetric density distribution is derived. The deflection angle in this case is determined by the mutual combination of different factors: gravity, dispersion, and refraction. While the effects of deflection by the gravity in vacuum and the refractive deflection in a nonhomogeneous medium are well known, the new effect is that, in the case of a homogeneous plasma, in the absence of refractive deflection, the gravitational deflection differs from the vacuum deflection and depends on the photon frequency. In the presence of a plasma nonhomogeneity, the chromatic refractive deflection also occurs, so the presence of plasma always makes gravitational lensing chromatic. In particular, the presence of plasma leads to different angular positions of the same image if it is observed at different wavelengths. It is discussed in detail how to apply the presented formulas for the calculation of the deflection angle in different situations. Gravitational lensing in plasma beyond the weak deflection approximation is also considered.
Quasars and gravitational lenses.
Turner, E L
1984-03-23
Despite the expenditure of large amounts of telescope time and other resources, most of the fundamental questions concerning quasi-stellar objects (quasars) remain unanswered. A complex phenomenology of radio, infrared, optical, and x-ray properties has accumulated but has not yielded even a satisfactory classification system. The large red shifts (distances) of quasars make them very valuable tools for studying cosmology and the properties of intervening matter in the Universe through observations of absorption lines and gravitational lenses. PMID:17759346
Multiple gravitational lensing
NASA Astrophysics Data System (ADS)
Nottale, L.; Chauvineau, B.
1986-07-01
The authors develop a new approach for solving the Optical Scalar Equations in inhomogeneous cosmology. In terms of the "optical distance" (Nottale and Hammer, 1984), the propagation of a light beam diameter is linear in a Friedmann universe, while it is given by a simple equation in regions of higher or lower density than the mean cosmological density. This formalism is used to find a general formula for the global Ricci amplification by multiple gravitational lenses: In most situations, this differs significantly from the product of the amplifications by each individual lens.
Nbody Simulations and Weak Gravitational Lensing using new HPC-Grid resources: the PI2S2 project
NASA Astrophysics Data System (ADS)
Becciani, U.; Antonuccio-Delogu, V.; Costa, A.; Comparato, M.
2008-08-01
We present the main project of the new grid infrastructure and the researches, that have been already started in Sicily and will be completed by next year. The PI2S2 project of the COMETA consortium is funded by the Italian Ministry of University and Research and will be completed in 2009. Funds are from the European Union Structural Funds for Objective 1 regions. The project, together with a similar project called Trinacria GRID Virtual Laboratory (Trigrid VL), aims to create in Sicily a computational grid for e-science and e-commerce applications with the main goal of increasing the technological innovation of local enterprises and their competition on the global market. PI2S2 project aims to build and develop an e-Infrastructure in Sicily, based on the grid paradigm, mainly for research activity using the grid environment and High Performance Computer systems. As an example we present the first results of a new grid version of FLY a tree Nbody code developed by INAF Astrophysical Observatory of Catania, already published in the CPC program Library, that will be used in the Weak Gravitational Lensing field.
NASA Astrophysics Data System (ADS)
Blake, Chris; Joudaki, Shahab; Heymans, Catherine; Choi, Ami; Erben, Thomas; Harnois-Deraps, Joachim; Hildebrandt, Hendrik; Joachimi, Benjamin; Nakajima, Reiko; van Waerbeke, Ludovic; Viola, Massimo
2016-03-01
The unknown nature of `dark energy' motivates continued cosmological tests of large-scale gravitational physics. We present a new consistency check based on the relative amplitude of non-relativistic galaxy peculiar motions, measured via redshift-space distortion, and the relativistic deflection of light by those same galaxies traced by galaxy-galaxy lensing. We take advantage of the latest generation of deep, overlapping imaging and spectroscopic data sets, combining the Red Cluster Sequence Lensing Survey, the Canada-France-Hawaii Telescope Lensing Survey, the WiggleZ Dark Energy Survey and the Baryon Oscillation Spectroscopic Survey. We quantify the results using the `gravitational slip' statistic EG, which we estimate as 0.48 ± 0.10 at z = 0.32 and 0.30 ± 0.07 at z = 0.57, the latter constituting the highest redshift at which this quantity has been determined. These measurements are consistent with the predictions of General Relativity, for a perturbed Friedmann-Robertson-Walker metric in a Universe dominated by a cosmological constant, which are EG = 0.41 and 0.36 at these respective redshifts. The combination of redshift-space distortion and gravitational lensing data from current and future galaxy surveys will offer increasingly stringent tests of fundamental cosmology.
NASA Astrophysics Data System (ADS)
Liesenborgs, J.; de Rijcke, S.; Dejonghe, H.; Bekaert, P.
2011-03-01
Gravitational lenses are a spectacular astrophysical phenomenon, a cosmic mirage caused by the gravitational deflection of light in which multiple images of a same background object can be seen. Their beauty is only exceeded by their usefulness, as the gravitational lens effect is a direct probe of the total mass of the deflecting object. Furthermore, since the image configuration arising from the gravitational lens effect depends on the exact gravitational potential of the deflector, it even holds the promise of learning about the distribution of the mass. In this presentation, a method for extracting the information encoded in the images and reconstructing the mass distribution is presented. Being a non-parametric method, it avoids making a priori assumptions about the shape of the mass distribution. At the core of the procedure lies a genetic algorithm, an optimization strategy inspired by Darwin's principle of ``survival of the fittest''. One only needs to specify a criterion to decide if one particular trial solution is deemed better than another, and the genetic algorithm will ``breed'' appropriate solutions to the problem. In a similar way, one can create a multi-objective genetic algorithm, capable of optimizing several fitness criteria at the same time. This provides a very flexible way to incorporate all the available information in the gravitational lens system: not only the positions and shapes of the multiple images are used, but also the so-called ``null space'', i.e. the area in which no such images can be seen. The effectiveness of this approach is illustrated using simulated data, which allows one to compare the reconstruction to the true mass distribution.
Measuring neutrino masses with weak lensing
Wong, Yvonne Y. Y.
2006-11-17
Weak gravitational lensing of distant galaxies by large scale structure (LSS) provides an unbiased way to map the matter distribution in the low redshift universe. This technique, based on the measurement of small distortions in the images of the source galaxies induced by the intervening LSS, is expected to become a key cosmological probe in the future. We discuss how future lensing surveys can probe the sum of the neutrino masses at the 0 05 eV level.
EDITORIAL: Focus on Gravitational Lensing
NASA Astrophysics Data System (ADS)
Jain, Bhuvnesh
2007-11-01
Gravitational lensing emerged as an observational field following the 1979 discovery of a doubly imaged quasar lensed by a foreground galaxy. In the 1980s and '90s dozens of other multiply imaged systems were observed, as well as time delay measurements, weak and strong lensing by galaxies and galaxy clusters, and the discovery of microlensing in our galaxy. The rapid pace of advances has continued into the new century. Lensing is currently one of best techniques for finding and mapping dark matter over a wide range of scales, and also addresses broader cosmological questions such as understanding the nature of dark energy. This focus issue of New Journal of Physics presents a snapshot of current research in some of the exciting areas of lensing. It provides an occasion to look back at the advances of the last decade and ahead to the potential of the coming years. Just about a decade ago, microlensing was discovered through the magnification of stars in our galaxy by invisible objects with masses between that of Jupiter and a tenth the mass of the Sun. Thus a new component of the mass of our galaxy, dubbed MACHOs, was established (though a diffuse, cold dark matter-like component is still needed to make up most of the galaxy mass). More recently, microlensing led to another exciting discovery—of extra-solar planets with masses ranging from about five times that of Earth to that of Neptune. We can expect many more planets to be discovered through ongoing surveys. Microlensing is the best technique for finding Earth mass planets, though it is not as productive overall as other methods and does not allow for follow up observations. Beyond planet hunting, microlensing has enabled us to observe previously inaccessible systems, ranging from the surfaces of other stars to the accretion disks around the black holes powering distant quasars. Galaxies and galaxy clusters at cosmological distances can produce dramatic lensing effects: multiple images of background galaxies or quasars which are strongly magnified and sheared. In the last decade, double and quadruply imaged systems due to galactic lenses have been studied with optical and radio observations. An interesting result obtained from the flux ratio 'anomalies' of quadruply imaged systems is the statistical detection of dark sub-clumps in galaxy halos. More broadly, while we have learned a lot about the mass distribution in lens galaxies and improved time delay constraints on the Hubble constant, the limitations of cosmological studies with strong lensing due to uncertainties in lens mass models have also come to be appreciated. That said, progress will no doubt continue with qualitative advances in observations such as astrometric counterparts to the flux anomalies, clever ideas such as the use of spectroscopic signatures to assemble the SLACS lens sample, and combining optical imaging, spectroscopy and radio data to continue the quest for a set of golden lenses to measure the Hubble constant. Galaxy clusters are a fascinating arena for studying the distribution of dark and baryonic matter. Weak and strong lensing information can be combined with dynamical information from the spectroscopic measurements of member galaxies and x-ray/Sunyaev Zeldovich measurements of the hot ionized gas. Hubble Space Telescope observations have yielded spectacular images of clusters, such as Abell 1689, which has over a hundred multiply imaged arcs. Mass measurements have progressed to the level of 10 percent accuracy for several clusters. Unfortunately, it is unclear if one can do much better for individual clusters given inherent limitations such as unknown projection effects. The statistical study of clusters is likely to remain a promising way to study dark matter, gravity theories, and cosmology. Techniques to combine weak and strong lensing information to obtain the mass distribution of clusters have also advanced, and work continues on parameter-free techniques that are agnostic to the relation of cluster light and mass. An interesting twist in cluster lensing was provided by the post-merger Bullet Cluster (identified as 1E0657-558). In this and other merging clusters, the lensing mass is displaced from the baryonic center of mass, presenting a challenge to theories that attempt to explain away dark matter by positing a modification to the law of gravity. Detailed modeling and multi-wavelength data on these systems will provide interesting limits on dark matter as well as the possibility of a major surprise. Other advances may come from the gravitational telescope effect of galaxy clusters: regions with very high magnification can be used to image proto-galaxies at z ~ 10. Statistical studies of galaxy and cluster lenses and of invisible, diffuse large-scale structures via weak lensing have come into their own in recent years. A census of the mass distribution at low redshift has been made using the technique of galaxy galaxy lensing: the mean mass profiles of galaxies and clusters have been measured using the weak tangential shear imprinted on background galaxies. These can be correlated with a variety of luminous tracers to study galaxy/cluster properties at a level of detail not possible until recently. Equally impressive is the measurement of excess mass correlations out to ~30 Mpc from these halos, requiring measurements of shear signals below 0.01%. These measurements account for the total matter density inferred from the CMB plus other observations, thus providing a direct measure of dark matter in the present day universe. Cosmic shear refers to the more challenging measurement of shear shear correlations without the use of foreground objects to orient the shear. The first detections of such correlations were published in 2001; since then measurements from arcminute to degree scales have been made with much improved accuracy. Theoretical techniques of lensing tomography and advances in analysis methods to eliminate systematic errors have progressed rapidly. That cosmic shear is now regarded as a key element of major missions aimed at probing dark energy is a feat of scientific persuasion—a decade ago not many believed it was realistic to even detect this tiny shear signal, let alone measure it with the percent-level accuracy needed to advance dark energy measurements. If weak lensing measurements deliver on their promise, then, in combination with other imaging and spectroscopic probes, they may well impact fundamental physics and cosmology. For example they may find evidence for an evolving dark energy component or signatures of departures from general relativity. These exciting prospects rest on new optical surveys planned for the next five years which will image a thousand square degrees or more of the sky to redshifts ~1 (compared to about a hundred square degrees imaged currently). Further, through photometric redshifts based on galaxy colors, lensing tomography methods will be applied to learn about the three-dimensional distribution of dark matter. Lensing measurements in other wavelengths, such as planned 21-cm surveys and CMB lensing, would add valuable diversity to measurement techniques. The case for the next generation optical surveys from the ground and space is compelling as well: they will produce another order of magnitude in data quantity and deliver images with minimal distortions due to the atmosphere and telescope optics. The coming decade therefore has the potential for exciting discoveries in gravitational lensing. Focus on Gravitational Lensing Contents A Bayesian approach to strong lensing modelling of galaxy clusters E Jullo, J-P Kneib, M Limousin, Á Elíasdóttir, P J Marshall and T Verdugo Probing dark energy with cluster counts and cosmic shear power spectra: including the full covariance Masahiro Takada and Sarah Bridle How robust are the constraints on cosmology and galaxy evolution from the lens-redshift test? Pedro R Capelo and Priyamvada Natarajan Dark energy constraints from cosmic shear power spectra: impact of intrinsic alignments on photometric redshift requirements Sarah Bridle and Lindsay King An integral-field spectroscopic strong lens survey Adam S Bolton and Scott Burles Is there a quad problem among optical gravitational lenses? Masamune Oguri Cluster mass estimators from CMB temperature and polarization lensing Wayne Hu, Simon DeDeo and Chris Vale
Cosmological applications of gravitational lensing
NASA Astrophysics Data System (ADS)
Schmidt, Robert W.
2000-06-01
In this thesis we use the gravitational lensing effect as a tool to tackle two rather different cosmological topics: the nature of the dark matter in galaxy halos, and the rotation of the universe. Firstly, we study the microlensing effect in the gravitational lens systems Q0957+561 and Q2237+0305. In these systems the light from the quasar shines directly through the lensing galaxy. Due to the relative motion of the quasar, the lensing galaxy, and the observer compact objects in the galaxy or galaxy halo cause brightness fluctuations of the light from the background quasar. We compare light curve data from a monitoring program of the double quasar Q0957+561 at the 3.5m telescope at Apache Point Observatory from 1995 to 1998 (Colley, Kundic & Turner 2000) with numerical simulations to test whether the halo of the lensing galaxy consists of massive compact objects (MACHOs). This test was first proposed by Gott (1981). We can exclude MACHO masses from 10^-6 M_sun up to 10^-2 M_sun for quasar sizes of less than 3x10^14 h_60^-0.5 cm if the MACHOs make up at least 50% of the dark halo. Secondly, we present new light curve data for the gravitationally lensed quadruple quasar Q2237+0305 taken at the 3.5m telescope at Apache Point Observatory from June 1995 to January 1998. Although the images were taken under variable, often poor seeing conditions and with coarse pixel sampling, photometry is possible for the two brighter quasar images A and B with the help from HST observations. We find independent evidence for a brightness peak in image A of 0.4 to 0.5 mag with a duration of at least 100 days, which indicates that microlensing has taken place in the lensing galaxy. Finally, we use the weak gravitational lensing effect to put limits on a class of Goedel-type rotating cosmologies described by Korotky & Obukhov (1996). In weak lensing studies the shapes of thousands of background galaxies are measured and averaged to reveal coherent gravitational distortions of the galaxy shapes by foreground matter distributions, or by the large-scale structure of space-time itself. We calculate the predicted shear as a function of redshift in Goedel-type rotating cosmologies and compare this to the upper limit on cosmic shear gamma_limit of approximately 0.04 from weak lensing studies. We find that Goedel-type models cannot have larger rotations omega than H_0=6.1x10^-11 h_60/year if this shear limit is valid for the whole sky. In dieser Arbeit benutze ich den Gravitationslinseneffekt als ein Werkzeug, um zwei recht unterschiedliche kosmologische Fragestellungen zu bearbeiten: die Natur der dunklen Materie in Galaxienhalos und die Rotation des Universums. Zuerst untersuche ich den Mikrolinseneffekt in den Gravitationlinsensystemen Q0957+561 und Q2237+0305. In diesen Systemen scheint das Licht eines Quasars durch die Linsengalaxie hindurch. Aufgrund der Relativbewegung zwischen Quasar, Linsengalaxie und Beobachter verursachen kompakte Objekte innerhalb der Galaxie oder dem Galaxienhalo Helligkeitsfluktuationen des Hintergrundquasars. Ich vergleiche die am 3.5m Teleskop des Apache Point Observatory zwischen 1995 und 1998 gewonnene Lichtkurve des Doppelquasars Q0957+561 (Colley, Kundic & Turner 2000) mit numerischen Simulationen, um zu untersuchen, ob der Halo der Linsengalaxie aus massiven kompakten Objekten (MACHOs) besteht. Dieser Test wurde zuerst von Gott (1981) vorgeschlagen. Ich kann MACHO-Massen von 10^-6 M_sun bis zu 10^-2 M_sun ausschliessen, sofern der Quasar kleiner ist als 3x10^14 h_60^-0.5 cm und MACHOs mehr als 50% des dunklen Halos ausmachen. Im zweiten Teil der Arbeit stelle ich neue Beobachtungsdaten fuer den Vierfachquasar Q2237+0305 vor, die am 3.5m Teleskop des Apache Point Observatory zwischen Juni 1995 und Januar 1998 gewonnen wurden. Obwohl die Daten bei veraenderlichen, oft schlechten Seeing Bedingungen und grober Pixelaufloesung aufgenommen wurden, ist die Photometrie der beiden helleren Quasarbilder A und B mit Hilfe von HST-Beobachtungen moeglich. Ich finde ein Helligkeitsmaximum in Bild A mit einer Amplitu
Gravitational lensing properties of cosmological black holes
NASA Astrophysics Data System (ADS)
Zakharov, A. F.; Capozziello, S.; Stornaiolo, C.
If really such objects like cosmological black holes exist they may be studied with a standard technique like strong and weak gravitational lensing. Cosmological voids can be explained as the result the collapse of large perturbations into black hole with masses of the order of 1014Mȯ and the expansion of the universe. The resulting image of the universe is that it is more homogeneous than expected from present observations. In this paper we discuss some lensing properties related to the cosmological black holes (CBHs), namely we consider differences in gravitational lensing for point like mass and extended mass distributions. We consider the singular isothermal sphere model as a toy (illustrative) model for an extended distribution of dark matter and a slightly more complicated isothermal sphere with a core.
NASA Astrophysics Data System (ADS)
Leauthaud, Alexie; J. Benson, Andrew; Civano, Francesca; L. Coil, Alison; Bundy, Kevin; Massey, Richard; Schramm, Malte; Schulze, Andreas; Capak, Peter; Elvis, Martin; Kulier, Andrea; Rhodes, Jason
2015-01-01
Understanding the relationship between galaxies hosting active galactic nuclei (AGN) and the dark matter haloes in which they reside is key to constraining how black hole fuelling is triggered and regulated. Previous efforts have relied on simple halo mass estimates inferred from clustering, weak gravitational lensing, or halo occupation distribution modelling. In practice, these approaches remain uncertain because AGN, no matter how they are identified, potentially live a wide range of halo masses with an occupation function whose general shape and normalization are poorly known. In this work, we show that better constraints can be achieved through a rigorous comparison of the clustering, lensing, and cross-correlation signals of AGN hosts to the fiducial stellar-to-halo mass relation (SHMR) derived for all galaxies, irrespective of nuclear activity. Our technique exploits the fact that the global SHMR can be measured with much higher accuracy than any statistic derived from AGN samples alone. Using 382 moderate luminosity X-ray AGN at z < 1 from the COSMOS field, we report the first measurements of weak gravitational lensing from an X-ray-selected sample. Comparing this signal to predictions from the global SHMR, we find that, contrary to previous results, most X-ray AGN do not live in medium size groups - nearly half reside in relatively low mass haloes with M200b 1012.5 M?. The AGN occupation function is well described by the same form derived for all galaxies but with a lower normalization - the fraction of haloes with AGN in our sample is a few per cent. The number of AGN satellite galaxies scales as a power law with host halo mass with a power-law index ? = 1. By highlighting the relatively `normal' way in which moderate luminosity X-ray AGN hosts occupy haloes, our results suggest that the environmental signature of distinct fuelling modes for luminous quasars compared to moderate luminosity X-ray AGN is less obvious than previously claimed.
Gravitational Lenses in the Classroom
ERIC Educational Resources Information Center
Ros, Rosa M.
2008-01-01
It is not common to introduce current astronomy in school lessons. This article presents a set of experiments about gravitational lenses. It is normal to simulate them by means of computers, but it is very simple to simulate similar effects using a drinking glass full of liquid or using only the glass base. These are, of course, cheap and easy
Gravitational Lenses in the Classroom
ERIC Educational Resources Information Center
Ros, Rosa M.
2008-01-01
It is not common to introduce current astronomy in school lessons. This article presents a set of experiments about gravitational lenses. It is normal to simulate them by means of computers, but it is very simple to simulate similar effects using a drinking glass full of liquid or using only the glass base. These are, of course, cheap and easy…
HUBBLE'S TOP TEN GRAVITATIONAL LENSES
NASA Technical Reports Server (NTRS)
2002-01-01
The NASA Hubble Space Telescope serendipitous survey of the sky has uncovered exotic patterns, rings, arcs and crosses that are all optical mirages produced by a gravitational lens, nature's equivalent of having giant magnifying glass in space. Shown are the top 10 lens candidates uncovered in the deepest 100 Hubble fields. Hubble's sensitivity and high resolution allow it to see faint and distant lenses that cannot be detected with ground-based telescopes whose images are blurred by Earth's atmosphere. [Top Left] - HST 01248+0351 is a lensed pair on either side of the edge-on disk lensing galaxy. [Top Center] - HST 01247+0352 is another pair of bluer lensed source images around the red spherical elliptical lensing galaxy. Two much fainter images can be seen near the detection limit which might make this a quadruple system. [Top Right] - HST 15433+5352 is a very good lens candidate with a bluer lensed source in the form of an extended arc about the redder elliptical lensing galaxy. [Middle Far Left] - HST 16302+8230 could be an 'Einstein ring' and the most intriguing lens candidate. It has been nicknamed the 'the London Underground' since it resembles that logo. [Middle Near Left] - HST 14176+5226 is the first, and brightest lens system discovered in 1995 with the Hubble telescope. This lens candidate has now been confirmed spectroscopically using large ground-based telescopes. The elliptical lensing galaxy is located 7 billion light-years away, and the lensed quasar is about 11 billion light-years distant. [Middle Near Right] - HST 12531-2914 is the second quadruple lens candidate discovered with Hubble. It is similar to the first, but appears smaller and fainter. [Middle Far Right] - HST 14164+5215 is a pair of bluish lensed images symmetrically placed around a brighter, redder galaxy. [Bottom Left] - HST 16309+8230 is an edge-on disk-like galaxy (blue arc) which has been significantly distorted by the redder lensing elliptical galaxy. [Bottom Center] - HST 12368+6212 is a blue arc in the Hubble Deep Field (HDF). [Bottom Right] - HST 18078+4600 is a blue arc caused by the gravitational potential of a small group of 4 galaxies. Credit: Kavan Ratnatunga (Carnegie Mellon Univ.) and NASA
WEAK LENSING MASS RECONSTRUCTION: FLEXION VERSUS SHEAR
Pires, S.
2010-11-10
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 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 should not be used to do convergence map reconstruction, even on small scales.
Towards noiseless gravitational lensing simulations
NASA Astrophysics Data System (ADS)
Angulo, Raul E.; Chen, Ruizhu; Hilbert, Stefan; Abel, Tom
2014-11-01
The microphysical properties of the dark matter (DM) particle can, in principle, be constrained by the properties and abundance of substructures in galaxy clusters, as measured through strong gravitational lensing. Unfortunately, there is a lack of accurate theoretical predictions for the lensing signal of these substructures, mainly because of the discreteness noise inherent to N-body simulations. Here, we present a method, dubbed as Recursive-TCM, that is able to provide lensing predictions with an arbitrarily low discreteness noise. This solution is based on a novel way of interpreting the results of N-body simulations, where particles simply trace the evolution and distortion of Lagrangian phase-space volume elements. We discuss the advantages and limitations of this method compared to the widely used density estimators based on cloud-in-cells and adaptive-kernel smoothing. Applying the new method to a cluster-sized DM halo simulated in warm and cold DM scenarios, we show how the expected differences in their substructure population translate into differences in convergence and magnification maps. We anticipate that our method will provide the high-precision theoretical predictions required to interpret and fully exploit strong gravitational lensing observations.
Tomography and weak lensing statistics
Munshi, Dipak; Coles, Peter; Kilbinger, Martin E-mail: peter.coles@astro.cf.ac.uk
2014-04-01
We provide generic predictions for the lower order cumulants of weak lensing maps, and their correlators for tomographic bins as well as in three dimensions (3D). Using small-angle approximation, we derive the corresponding one- and two-point probability distribution function for the tomographic maps from different bins and for 3D convergence maps. The modelling of weak lensing statistics is obtained by adopting a detailed prescription for the underlying density contrast that involves hierarchal ansatz and lognormal distribution. We study the dependence of our results on cosmological parameters and source distributions corresponding to the realistic surveys such as LSST and DES. We briefly outline how photometric redshift information can be incorporated in our results. We also show how topological properties of convergence maps can be quantified using our results.
Gravitational Lensing in TeVe S
NASA Astrophysics Data System (ADS)
Chiu, Mu-Chen; Ko, Chung-Ming; Tian, Yong
Gravitational Lensing is an important tool to understand the "missing mass" problem, especially for Modified Gravity. Recently, Bekenstein proposed a relativistic gravitation theory for Modified Newtonian Dynamics (MOND) paradigm which resolves the "missing mass" problem well on abnormal dynamical behaviors in extragalactic region. Our work follow Bekenstein's approach to investigating gravitational lensing to get theoretical prediction.
LensTools: Weak Lensing computing tools
NASA Astrophysics Data System (ADS)
Petri, A.
2016-02-01
LensTools implements a wide range of routines frequently used in Weak Gravitational Lensing, including tools for image analysis, statistical processing and numerical theory predictions. The package offers many useful features, including complete flexibility and easy customization of input/output formats; efficient measurements of power spectrum, PDF, Minkowski functionals and peak counts of convergence maps; survey masks; artificial noise generation engines; easy to compute parameter statistical inferences; ray tracing simulations; and many others. It requires standard numpy and scipy, and depending on tools used, may require Astropy (ascl:1304.002), emcee (ascl:1303.002), matplotlib, and mpi4py.
Weak Lensing Results of the Merging Cluster A1758
NASA Technical Reports Server (NTRS)
Markevitch, M.; Gonzalez, A. H.; Bradac, M.
2011-01-01
Here we present the weak lensing results of A1758, which is known to have four cluster members undergoing two separate mergers, A1758N and A1758S. Weak lensing results of A1758N agree with previous weak lensing results of clusters lE0657-558 (Bullet cluster) and MACS J0025.4-1222, whose X-ray gas components were found to be largely separated from their clusters' gravitational potentials. A1758N has a geometry that is different from previously published mergers in that one of its X-ray peaks overlays the corresponding gravitational potential and the other X-ray peak is well separated from its cluster's gravitational potential.
Gravitational Lensing Extends SETI Range
NASA Astrophysics Data System (ADS)
Factor, Richard
Microwave SETI (The Search for Extraterrestrial Intelligence) focuses on two primary strategies, the "Targeted Search" and the "All-Sky Survey." Although the goal of both strategies is the unequivocal discovery of a signal transmitted by intelligent species outside our solar system, they pursue the strategies in very different manners and have vastly different requirements. This chapter introduces Gravitational Lensing SETI (GL-SETI), a third strategy. Its goal is the unequivocal discovery of an extraterrestrial signal, with equipment and data processing requirements that are substantially different from the commonly-used strategies. This strategy is particularly suitable for use with smaller radio telescopes and has budgetary requirements suitable for individual researchers.
Cluster masses from CMB and galaxy weak lensing
Lewis, Antony; King, Lindsay
2006-03-15
Gravitational lensing can be used to directly constrain the projected density profile of galaxy clusters. We discuss possible future constraints using lensing of the cosmic microwave background (CMB) temperature and polarization, and compare to results from using galaxy weak lensing. We model the moving lens and kinetic Sunyaev-Zel'dovich signals that confuse the temperature CMB lensing when cluster velocities and angular momenta are unknown, and show how they degrade parameter constraints. The CMB polarization cluster lensing signal is {approx}1 {mu}K for massive clusters and challenging to detect; however it should be significantly cleaner than the temperature signal and may provide the most robust constraints at low noise levels. Galaxy lensing is likely to be much better for constraining cluster masses at low redshift, but for clusters at redshift z > or approx. 1 future CMB lensing observations may be able to do better.
Natural wormholes as gravitational lenses
Cramer, J.G.; Forward, R.L.; Morris, M.S.; Visser, M.; Benford, G.; Landis, G.A. Forward Unlimited, P.O. Box 2783, Malibu, California 90265 Department of Physics and Astronomy, Butler University, Indianapolis, Indiana 46208 Physics Department, Washington University, St. Louis, Missouri 63130-4899 Physics Department, University of California at Irvine, Irvine, California 92717-4575 NASA Lewis Research Center, Mail Code 302-1, Cleveland, Ohio 44135-3191 )
1995-03-15
Once quantum mechanical effects are included, the hypotheses underlying the positive mass theorem of classical general relativity fail. As an example of the peculiarities attendant upon this observation, a wormhole mouth embedded in a region of high mass density might accrete mass, giving the other mouth a net [ital negative] mass of unusual gravitational properties. The lensing of such a gravitationally negative anomalous compact halo object (GNACHO) will enhance background stars with a time profile that is observable and qualitatively different from that recently observed for massive compact halo objects (MACHO's) of positive mass. While the analysis is discussed in terms of wormholes, the observational test proposed is more generally a search for compact negative mass objects of any origin. We recommend that MACHO search data be analyzed for GNACHO's.
Gravitational lensing and polarization in astrophysics
NASA Astrophysics Data System (ADS)
Zakharov, Alexander F.
2016-02-01
We discuss astrophysical problems connected with gravitational lensing where current and future polarimetric observations are very important to clarify theoretical models. Namely, we consider polarization observations for exoplanet searches with gravitational microlensing, optical polarization for gravitational lens systems, polarization signatures of cosmological gravitational waves.
Gravitational lensing of cosmological 21 cm emission
NASA Astrophysics Data System (ADS)
Pourtsidou, A.; Metcalf, R. Benton
2015-04-01
We investigate the feasibility of measuring weak gravitational lensing using 21-cm intensity mapping with special emphasis on the performance of the planned Square Kilometre Array (SKA). We find that the current design for SKA_Mid should be able to measure the evolution of the lensing power spectrum at z 2-3 using this technique. This will be a probe of the expansion history of the Universe and gravity at a unique range in redshift. The signal to noise is found to be highly dependent on evolution of the neutral hydrogen fraction in the Universe with a higher H I density resulting in stronger signal. With realistic models for this, SKA Phase 1 should be capable of measuring the lensing power spectrum and its evolution. The dependence of signal to noise on the area and diameter of the array is quantified. We further demonstrate the applications of this technique by applying it to two specific coupled dark energy models that would be difficult to observationally distinguish without information from this range of redshift. We also investigate measuring the lensing signal with 21 cm emission from the Epoch of Reionization (EoR) using SKA and find that it is unlikely to constrain cosmological parameters because of the small survey size, but could provide a map of the dark matter within a small region of the sky.
Gravitational lensing in fourth order gravity
Capozziello, S.; Troisi, A.; Cardone, V.F.
2006-05-15
Gravitational lensing is investigated in the weak field limit of fourth order gravity in which the Lagrangian of the gravitational field is modified by replacing the Ricci scalar curvature R with an analytical expression f(R). Considering the case of a pointlike lens, we study the behavior of the deflection angle in the case of power-law Lagrangians, i.e. with f(R){proportional_to}R{sup n}. In order to investigate possible detectable signatures, the position of the Einstein ring and the solutions of the lens equation are evaluated considering the change with respect to the standard case. Effects on the amplification of the images and the Paczynski curve in microlensing experiments are also estimated.
Gravitational lensing by rotating naked singularities
Gyulchev, Galin N.; Yazadjiev, Stoytcho S.
2008-10-15
We model massive compact objects in galactic nuclei as stationary, axially symmetric naked singularities in the Einstein-massless scalar field theory and study the resulting gravitational lensing. In the weak deflection limit we study analytically the position of the two weak field images, the corresponding signed and absolute magnifications as well as the centroid up to post-Newtonian order. We show that there are static post-Newtonian corrections to the signed magnification and their sum as well as to the critical curves, which are functions of the scalar charge. The shift of the critical curves as a function of the lens angular momentum is found, and it is shown that they decrease slightly for the weakly naked and vastly for the strongly naked singularities with the increase of the scalar charge. The pointlike caustics drift away from the optical axis and do not depend on the scalar charge. In the strong deflection limit approximation, we compute numerically the position of the relativistic images and their separability for weakly naked singularities. All of the lensing quantities are compared to particular cases as Schwarzschild and Kerr black holes as well as Janis-Newman-Winicour naked singularities.
Lossy compression of weak lensing data
Vanderveld, R. Ali; Bernstein, Gary M.; Stoughton, Chris; Rhodes, Jason; Massey, Richard; Dobke, Benjamin M.
2011-07-12
Future orbiting observatories will survey large areas of sky in order to constrain the physics of dark matter and dark energy using weak gravitational lensing and other methods. Lossy compression of the resultant data will improve the cost and feasibility of transmitting the images through the space communication network. We evaluate the consequences of the lossy compression algorithm of Bernstein et al. (2010) for the high-precision measurement of weak-lensing galaxy ellipticities. This square-root algorithm compresses each pixel independently, and the information discarded is by construction less than the Poisson error from photon shot noise. For simulated space-based images (without cosmicmore » rays) digitized to the typical 16 bits per pixel, application of the lossy compression followed by image-wise lossless compression yields images with only 2.4 bits per pixel, a factor of 6.7 compression. We demonstrate that this compression introduces no bias in the sky background. The compression introduces a small amount of additional digitization noise to the images, and we demonstrate a corresponding small increase in ellipticity measurement noise. The ellipticity measurement method is biased by the addition of noise, so the additional digitization noise is expected to induce a multiplicative bias on the galaxies measured ellipticities. After correcting for this known noise-induced bias, we find a residual multiplicative ellipticity bias of m {approx} -4 x 10-4. This bias is small when compared to the many other issues that precision weak lensing surveys must confront, and furthermore we expect it to be reduced further with better calibration of ellipticity measurement methods.« less
Lossy compression of weak lensing data
Vanderveld, R. Ali; Bernstein, Gary M.; Stoughton, Chris; Rhodes, Jason; Massey, Richard; Dobke, Benjamin M.
2011-07-12
Future orbiting observatories will survey large areas of sky in order to constrain the physics of dark matter and dark energy using weak gravitational lensing and other methods. Lossy compression of the resultant data will improve the cost and feasibility of transmitting the images through the space communication network. We evaluate the consequences of the lossy compression algorithm of Bernstein et al. (2010) for the high-precision measurement of weak-lensing galaxy ellipticities. This square-root algorithm compresses each pixel independently, and the information discarded is by construction less than the Poisson error from photon shot noise. For simulated space-based images (without cosmic rays) digitized to the typical 16 bits per pixel, application of the lossy compression followed by image-wise lossless compression yields images with only 2.4 bits per pixel, a factor of 6.7 compression. We demonstrate that this compression introduces no bias in the sky background. The compression introduces a small amount of additional digitization noise to the images, and we demonstrate a corresponding small increase in ellipticity measurement noise. The ellipticity measurement method is biased by the addition of noise, so the additional digitization noise is expected to induce a multiplicative bias on the galaxies measured ellipticities. After correcting for this known noise-induced bias, we find a residual multiplicative ellipticity bias of m {approx} -4 x 10^{-4}. This bias is small when compared to the many other issues that precision weak lensing surveys must confront, and furthermore we expect it to be reduced further with better calibration of ellipticity measurement methods.
NASA Astrophysics Data System (ADS)
Rhodes, Jason D.; Massey, Richard J.; Albert, Justin; Collins, Nicholas; Ellis, Richard S.; Heymans, Catherine; Gardner, Jonathan P.; Kneib, Jean-Paul; Koekemoer, Anton; Leauthaud, Alexie; Mellier, Yannick; Refregier, Alexander; Taylor, James E.; Van Waerbeke, Ludovic
2007-09-01
We examine the spatial and temporal stability of the Hubble Space Telescope's Advanced Camera for Surveys (ACS) Wide Field Camera (WFC) point-spread function (PSF) using the 2 deg2 COSMOS survey. This is important for studies of weak gravitational lensing, where the ability to deconvolve the PSF from galaxy shapes is of paramount importance. We show that stochastic aliasing of the PSF necessarily occurs during ``drizzling.'' This aliasing is maximal if the output-pixel scale is equal to the input-pixel scale. This source of PSF variation can be significantly reduced by choosing a Gaussian drizzle kernel with a size of 0.8 input pixels and by reducing the output-pixel scale. We show that the PSF is temporally unstable, resulting in an overall slow periodic focus change in the COSMOS images. Using a modified version of the Tiny Tim PSF modeling software, we create grids of undistorted stars over a range of telescope focus values. We then use the approximately 10 well-measured stars in each COSMOS field to pick the best-fit focus value for each field. The Tiny Tim model stars can then be used to perform PSF corrections for weak lensing. We derive a parametric correction for the effect of charge transfer efficiency (CTE) degradation on the shapes of objects in the COSMOS field as a function of observation date, position within the ACS WFC field, and object flux. Finally, we discuss future plans to improve the CTE correction. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555 also based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan; the XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA member states and NASA; the European Southern Observatory, Chile; Kitt Peak National Observatory, Cerro Tololo Inter-American Observatory, and the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation; the National Radio Astronomy Observatory, which is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.; and the Canada-France-Hawaii Telescope, operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique de France, and the University of Hawaii.
Gravitational lensing by straight cosmic strings
NASA Astrophysics Data System (ADS)
Kotvytskiy, A. T.
2015-07-01
We consider effects due to gravitational lensing by hypothetical cosmic strings. We briefly review facts concerning infinite straight strings, obtain the equation for a gravitational lens produced by an infinite string in the classical form, and analyze features of the gravitational lensing for a given object in detail. We consider a finite straight string. We present caustics and critical curves for strings with different lengths and also some images produced by the considered gravitational lens. We propose a method for constructing brightness curves numerically. As an example of the working capacity of this method, we construct a concrete brightness curve for certain gravitational lens parameters.
WEAK-LENSING RESULTS FOR THE MERGING CLUSTER A1758
Ragozzine, B.; Clowe, D.; Markevitch, M.; Gonzalez, A. H.; Bradac, M.
2012-01-10
Here we present the weak-lensing results for A1758, which is known to consist of four subclusters undergoing two separate mergers, A1758N and A1758S. Weak-lensing results for A1758N agree with previous weak-lensing results for clusters 1E0657-558 (Bullet cluster) and MACS J0025.4-1222, whose X-ray gas components were found to be largely separated from their clusters' gravitational potentials. A1758N has a geometry that is different from previously published mergers in that one of its X-ray peaks overlays the corresponding gravitational potential and the other X-ray peak is well separated from its cluster's gravitational potential. The weak-lensing mass peaks of the two northern clusters are separated at the 2.5{sigma} level. We estimate the combined mass of the clusters in A1758N to be (2.2 {+-} 0.5) Multiplication-Sign 10{sup 15} M{sub Sun} and r{sub 200} = 2300{sup +100}{sub -130} kpc. We also detect seven strong-lensing candidates, two of which may provide information that would improve the mass measurements of A1758N.
Gravitational lensing of the CMB with SPTpol
NASA Astrophysics Data System (ADS)
Story, Kyle Tyler; SPTpol Collaboration
2015-01-01
Measurements of gravitational lensing of the cosmic microwave background (CMB) directly probe the projected mass in the universe out to high redshifts. Gravitational lensing encodes a wealth of information in the CMB about the growth and geometry of large-scale structure, which is sensitive to cosmic acceleration (dark energy), the expansion history of the universe and the properties of neutrinos. Additionally, gravitational lensing can be used to improve inflationary gravitational wave searches in the CMB, and constrain the relationship between dark and luminous matter at high redshifts. I will present recent lensing results from the first two years of data from the South Pole Telescope polarimeter (SPTpol) and discuss future opportunities for this powerful technique.
Gravitational lensing in observational cosmology
NASA Astrophysics Data System (ADS)
Nottale, L.
This paper reviews some previous theoretical and observational results concerning the various effects of gravitational lensing, and also presents still unpublished results in this field. The theoretical section deals with the Optical Scalar Equation (OSE) approach. We recall the form of these equations, which relate the deformations of the cross sectional area of a light beam to the material and energetic distribution it encounters, via the two basic contributions to lensing, the matter or Ricci term and the shear term. The introduction of a new distance, the optical distance, allows to write the OSE in a simplified way from which new solutions are easily derived. We demonstrate here that a general form may be obtained for the amplification formula in the exact relativistic treatment, provided the Universe is assumed to be Friedmannian in the mean. New results are also presented concerning the probability distribution of amplifications, the relation from matter term to shear terms (the first ones give the mean of the second ones) and the problem of energy conservation. We recall how our method let to an analytical formula yielding the amplification by any number of lenses placed anywhere along the line of sight and present new general solutions for lensing by large scale density inhomogeneities. The gravitational redshift effects are also considered, either due to the crossing by photons of inhomogeneities, or intrinsic to them ; generalized solutions to the last problem are given. Some observational evidence concerning various lensing effects, either statistical or applying to individual sources, are considered. We first recall how the dependence of the amplification formula on the various physical parameters points towards the optimisation of lensing by very rich clusters of galaxies lying at redshifts around 0.7, which may give rise to very large amplifications for reasonable values of the density parameter. Recent results concerning a statistical effect of amplification of Brightest Cluster Galaxies by foreground clusters are analysed, including the discussion of a selection effect precisely due to gravitational luminosity amplification. It results in an artificial increase of the deceleration parameter of the Universe measured from the Hubble diagram of these objects. We recall our proposal that the sample of distant 3C radiogalaxies of redshift > 1 is strongly perturbed by lensing effects, mostly by foreground clusters of galaxies (i.e. only the luminosity is changed without image multiplication), but also for some objects by galaxies, producing gravitational mirages. The case of 3C324, for which definite evidence for multiple imaging has been recently obtained, is described, including detailed modelling of the lensing configuration. We present a highly significant statistical effect of lensing on absorption line QSOs due to matter lying at the absorption redshifts. Microlensing is also considered, and we recall our recent proposal that the variability of some among the OVV QSOs turning to BL Lac at maximum brightness, like the eruptive object 0846 +51W1, is a consequence of microlensing by stars or compact objects constituting foreground galaxy halos. Finally, discrepant redshift associations are considered. We recall how the case of anomalous quintets of galaxies have been explained by the gravitational lensing effects of quartets halos on background galaxies. Then we present evidence that the Arp QSO-galaxy associations may be the result of the combined lensing effects of several superposed galaxies, groups and clusters. Cet article présente une revue de certains résultats théoriques et observationnels concernant les divers effets de lentille gravitationnelle, complétée par des résultats nouveaux non encore publiés. Dans la partie théorique, nous considérons essentiellement l'approche relativiste employant les équations scalaires optiques. La forme de ces équations est rappelée : elles relient les diverses déformations subies par la section d'un faisceau lumineux au cours de sa propagation, à la distribution matérielle et énergétique qu'il rencontre sur son trajet entre la source et l'observateur. Les deux contributions aux effets d'optique apparaissant dans ces équations (et leurs solutions) sont les termes de matière et les termes de cisaillement. Nous montrons comment une nouvelle distance peut être introduite, la distance optique, en fonction de laquelle les équations se simplifient et de nouvelles solutions analytiques peuvent être établies. En particulier, nous démontrons que la formule d'amplification gravitationnelle peut s'écrire sous une forme très générale sous la simple hypothèse que l'Univers est en moyenne de type Friedmann-Robertson-Walker. De nouveaux résultats sont aussi présentés concernant la distribution de probabilité des amplifications, les rapports entre termes de matière et termes de cisaillement (les premiers donnant la moyenne des seconds), et le problème de la conservation de l'énergie. Nous rappelons comment une formule analytique peut être obtenue pour des amplifications multiples et présentons des solutions nouvelles au problème de l'amplification par des hétérogénéités à très grande échelle. Enfin, les effets de décalages spectraux gravitationnels sont aussi considérés, qu'ils soient dus à des effets de traversée d'excès de densité, ou intrinsèques à ceux-ci ; dans ce dernier cas, une généralisation de solutions déjà connues est proposée. On considère ensuite le problème de la mise en évidence observationnelle des divers effets d'optique gravitationnelle, qu'ils soient de nature statistique ou qu'ils concernent des objets individuels. A la suite d'une analyse décrivant la dépendance de la formule d'amplification en fonction des différents paramètres y intervenant, nous insistons tout particulièrement sur le rôle cosmologique que jouent probablement les amas de galaxies très riches de décalages spectraux autour de 0,7 qui peuvent donner lieu à des amplifications quasi-infinies. La mise en évidence récente d'un effet statistique d'amplification par des amas d'avant-plan sur les galaxies les plus brillantes des amas est rappelée, ainsi que celle d'un important effet de sélection observationnel, précisément dû aux amplifications, qui augmente artificiellement la valeur de q0 mesurée à partir du diagramme de Hubble. L'extrapolation de cet effet à des objets plus lointains nous a conduit à proposer que les radiogalaxies lointaines du catalogue 3C de z < 1 étaient fortement affectées par les effets de lentille gravitationnelle, essentiellement par les amas (qui les amplifient la plupart du temps sans multiplication d'image), mais aussi dans certains cas par des galaxies qui peuvent alors provoquer des effets de mirage. Le cas de 3C324, pour lequel des preuves observationelles de multiplication d'image ont été récemment obtenues, est analysé en particulier ; un modèle détaillé en est présenté. Un autre effet statistique récemment démontré concerne les quasars à raies d'absorption, dont la luminosité est fortement corrélée à l'amplification prédite par de la matière située aux décalages spectraux d'absorption. On considère également les effets de microlentille : nous rappelons notre proposition récente que la variabilité de certains OVVs tels que le BL Lac éruptif 0846 + 51W1 est une conséquence du passage d'étoiles ou d'objets compacts du halo de galaxies intervenantes devant les régions centrales d'un quasar. Le lien entre effets d'optique gravitationnelle et associations de décalages spectraux discordants est évoqué. Le cas des quintets de galaxies discordant a été récemment expliqué par les effets (amplification, agrandissement, changement de densité superficielle d'objets lointains) des halos de groupes compacts de galaxies. Nous démontrons pour finir que les associations QSOsgalaxies de Arp peuvent s'expliquer par les effets de lentille gravitationnelle combinés de plusieurs galaxies, groupes et amas vus en superposition.
Investigations of Galaxy Clusters Using Gravitational Lensing
NASA Astrophysics Data System (ADS)
Wiesner, Matthew P.; Lin, H.; Soares-Santos, M.
2014-01-01
In this dissertation talk I describe my studies of galaxy clustering and gravitational lensing; both are important phenomena which can be used to study the structure and evolution of the universe. First I describe a sample of ten strong-lensing galaxy clusters of mass between 1-30x1014 h-1M?. These clusters were found in the Sloan Digital Sky Survey and were further observed using the WIYN 3.5-m telescope at Kitt Peak National Observatory and the Astrophysical Research Consortium 3.5-m telescope at Apache Point Observatory. Analyses of these clusters showed that the four lowest mass clusters in this sample exhibit overconcentration, that is, the concentration of mass in the centers of the clusters was higher than theory would predict. Second, I describe lens models of three of the strong lenses in this sample using a Bayesian algorithm for lens modeling. Finally I describe measurements of a mass-richness relation for galaxy clusters found at higher median redshift (z?0.6) than has been typical of previous sky surveys. This relation empirically describes how the mass of galaxy clusters is related to the number of galaxies in the cluster. Mass-richness calibration is a key component of cosmology analyses using galaxy clusters; thus this work will be important to studies of cosmology done with this decade's large sky surveys. Galaxy clusters were found using a Voronoi Tessellation cluster finder and masses were measured using stacked weak lensing shear measurements in bins of similar richness. The mass-richness relation was derived using data from the Blanco Cosmology Survey and from the Sloan Digital Sky Survey Stripe 82 coadd, leading to a sample of clusters covering a total sky area of about 400 square degrees.
Strong gravitational lensing by Kiselev black hole
NASA Astrophysics Data System (ADS)
Younas, Azka; Jamil, Mubasher; Bahamonde, Sebastian; Hussain, Saqib
2015-10-01
We investigate the gravitational lensing scenario due to Schwarzschild-like black hole surrounded by quintessence (Kiselev black hole). We work for the special case of Kiselev black hole where we take the state parameter wq=-2/3 . For the detailed derivation and analysis of the bending angle involved in the deflection of light, we discuss three special cases of Kiselev black hole: nonextreme, extreme, and naked singularity. We also calculate the approximate bending angle and compare it with the exact bending angle. We found the relation of bending angles in the decreasing order as: naked singularity, extreme Kiselev black hole, nonextreme Kiselev black hole, and Schwarzschild black hole. In the weak field approximation, we compute the position and total magnification of relativistic images as well.
Lensing of 21-cm fluctuations by primordial gravitational waves.
Book, Laura; Kamionkowski, Marc; Schmidt, Fabian
2012-05-25
Weak-gravitational-lensing distortions to the intensity pattern of 21-cm radiation from the dark ages can be decomposed geometrically into curl and curl-free components. Lensing by primordial gravitational waves induces a curl component, while the contribution from lensing by density fluctuations is strongly suppressed. Angular fluctuations in the 21-cm background extend to very small angular scales, and measurements at different frequencies probe different shells in redshift space. There is thus a huge trove of information with which to reconstruct the curl component of the lensing field, allowing tensor-to-scalar ratios conceivably as small as r~10(-9)-far smaller than those currently accessible-to be probed. PMID:23003237
Gravitational lensing of active galactic nuclei.
Hewitt, J N
1995-01-01
Most of the known cases of strong gravitational lensing involve multiple imaging of an active galactic nucleus. The properties of lensed active galactic nuclei make them promising systems for astrophysical applications of gravitational lensing; in particular, they show structure on scales of milliseconds of arc to tens of seconds of arc, they are variable, and they are polarized. More than 20 cases of strong gravitational lenses are now known, and about half of them are radio sources. High-resolution radio imaging is making possible the development of well-constrained lens models. Variability studies at radio and optical wavelengths are beginning to yield results of astrophysical interest, such as an independent measure of the distance scale and limits on source sizes. PMID:11607613
Atmospheric Dispersion Effects in Weak Lensing Measurements
Plazas, Andrés Alejandro; Bernstein, Gary
2012-10-01
The wavelength dependence of atmospheric refraction causes elongation of finite-bandwidth images along the elevation vector, which produces spurious signals in weak gravitational lensing shear measurements unless this atmospheric dispersion is calibrated and removed to high precision. Because astrometric solutions and PSF characteristics are typically calibrated from stellar images, differences between the reference stars' spectra and the galaxies' spectra will leave residual errors in both the astrometric positions (dr) and in the second moment (width) of the wavelength-averaged PSF (dv) for galaxies.We estimate the level of dv that will induce spurious weak lensing signals in PSF-corrected galaxy shapes that exceed themore » statistical errors of the DES and the LSST cosmic-shear experiments. We also estimate the dr signals that will produce unacceptable spurious distortions after stacking of exposures taken at different airmasses and hour angles. We also calculate the errors in the griz bands, and find that dispersion systematics, uncorrected, are up to 6 and 2 times larger in g and r bands,respectively, than the requirements for the DES error budget, but can be safely ignored in i and z bands. For the LSST requirements, the factors are about 30, 10, and 3 in g, r, and i bands,respectively. We find that a simple correction linear in galaxy color is accurate enough to reduce dispersion shear systematics to insignificant levels in the r band for DES and i band for LSST,but still as much as 5 times than the requirements for LSST r-band observations. More complex corrections will likely be able to reduce the systematic cosmic-shear errors below statistical errors for LSST r band. But g-band effects remain large enough that it seems likely that induced systematics will dominate the statistical errors of both surveys, and cosmic-shear measurements should rely on the redder bands.« less
Atmospheric Dispersion Effects in Weak Lensing Measurements
Plazas, Andrés Alejandro; Bernstein, Gary
2012-10-01
The wavelength dependence of atmospheric refraction causes elongation of finite-bandwidth images along the elevation vector, which produces spurious signals in weak gravitational lensing shear measurements unless this atmospheric dispersion is calibrated and removed to high precision. Because astrometric solutions and PSF characteristics are typically calibrated from stellar images, differences between the reference stars' spectra and the galaxies' spectra will leave residual errors in both the astrometric positions (dr) and in the second moment (width) of the wavelength-averaged PSF (dv) for galaxies.We estimate the level of dv that will induce spurious weak lensing signals in PSF-corrected galaxy shapes that exceed the statistical errors of the DES and the LSST cosmic-shear experiments. We also estimate the dr signals that will produce unacceptable spurious distortions after stacking of exposures taken at different airmasses and hour angles. We also calculate the errors in the griz bands, and find that dispersion systematics, uncorrected, are up to 6 and 2 times larger in g and r bands,respectively, than the requirements for the DES error budget, but can be safely ignored in i and z bands. For the LSST requirements, the factors are about 30, 10, and 3 in g, r, and i bands,respectively. We find that a simple correction linear in galaxy color is accurate enough to reduce dispersion shear systematics to insignificant levels in the r band for DES and i band for LSST,but still as much as 5 times than the requirements for LSST r-band observations. More complex corrections will likely be able to reduce the systematic cosmic-shear errors below statistical errors for LSST r band. But g-band effects remain large enough that it seems likely that induced systematics will dominate the statistical errors of both surveys, and cosmic-shear measurements should rely on the redder bands.
The Sloan Nearby Cluster Weak Lensing Survey
Kubo, Jeffrey M.; Annis, James T.; Hardin, Frances Mei; Kubik, Donna; Lawhorn, Kelsey; Lin, Huan; Nicklaus, Liana; Nelson, Dylan; Reis, Ribamar Rondon de Rezende; Seo, Hee-Jong; Soares-Santos, Marcelle; /Fermilab /Inst. Geo. Astron., Havana /Sao Paulo U. /Fermilab
2009-08-01
We describe and present initial results of a weak lensing survey of nearby (z {approx}< 0.1) galaxy clusters in the Sloan Digital Sky Survey (SDSS). In this first study, galaxy clusters are selected from the SDSS spectroscopic galaxy cluster catalogs of Miller et al. and Berlind et al. We report a total of seven individual low-redshift cluster weak lensing measurements that include A2048, A1767, A2244, A1066, A2199, and two clusters specifically identified with the C4 algorithm. Our program of weak lensing of nearby galaxy clusters in the SDSS will eventually reach {approx}200 clusters, making it the largest weak lensing survey of individual galaxy clusters to date.
Magnified Weak Lensing Cross Correlation Tomography
Ulmer, Melville P., Clowe, Douglas I.
2010-11-30
This project carried out a weak lensing tomography (WLT) measurement around rich clusters of galaxies. This project used ground based photometric redshift data combined with HST archived cluster images that provide the WLT and cluster mass modeling. The technique has already produced interesting results (Guennou et al, 2010,Astronomy & Astrophysics Vol 523, page 21, and Clowe et al, 2011 to be submitted). Guennou et al have validated that the necessary accuracy can be achieved with photometric redshifts for our purposes. Clowe et al titled "The DAFT/FADA survey. II. Tomographic weak lensing signal from 10 high redshift clusters," have shown that for the **first time** via this purely geometrical technique, which does not assume a standard rod or candle, that a cosmological constant is **required** for flat cosmologies. The intent of this project is not to produce the best constraint on the value of the dark energy equation of state, w. Rather, this project is to carry out a sustained effort of weak lensing tomography that will naturally feed into the near term Dark Energy Survey (DES) and to provide invaluable mass calibration for that project. These results will greatly advance a key cosmological method which will be applied to the top-rated ground-based project in the Astro2020 decadal survey, LSST. Weak lensing tomography is one of the key science drivers behind LSST. CO-I Clowe is on the weak lensing LSST committee, and senior scientist on this project, at FNAL James Annis, plays a leading role in the DES. This project has built on successful proposals to obtain ground-based imaging for the cluster sample. By 1 Jan, it is anticipated the project will have accumulated complete 5-color photometry on 30 (or about 1/3) of the targeted cluster sample (public webpage for the survey is available at http://cencos.oamp.fr/DAFT/ and has a current summary of the observational status of various clusters). In all, the project has now been awarded the equivalent of over 60 nights on 4-m class telescopes, which gives concrete evidence of strong community support for this project. The WLT technique is based on the dependence of the gravitational shear signal on the angular diameter distances between the observer, the lens, and the lensed galaxy to measure cosmological parameters. By taking the ratio of measured shears of galaxies with different redshifts around the same lens, one obtains a measurement of the ratios of the angular diameter distances involved. Making these observations over a large range of lenses and background galaxy redshifts will measure the history of the expansion rate of the universe. Because this is a purely geometric measurement, it is insensitive to any form of evolution of objects or the necessity to understand the physics in the early universe. Thus, WLT was identified by the Dark Energy Task Force as perhaps the best method to measure the evolution of DE. To date, however, the conjecture of the DETF has not been experimentally verified, but will be by the proposed project. The primary reason for the lack of tomography measurements is that one must have an exceptional data-set to attempt the measurement. One needs both extremely good seeing (or space observations) in order to minimize the point spread function smearing corrections on weak lensing shear measurements and deep, multi-color data, from B to z, to measure reliable photometric redshifts of the background galaxies being lensed (which are typically too faint to obtain spectroscopic redshifts). Because the entire process from multi-drizzling the HST images, and then creating shear maps, to gathering the necessary ground based observations, to generating photo-zs and then carrying out the tomography is a complicated task, until the creation of our team, nobody has taken the time to connect all the levels of expertise necessary to carry out this project based on HST archival data. Our data are being used in 2 Ph.D. theses. Kellen Murphy, at Ohio University, is using the tomography data along with simulations in a thesis expected to be completed in June 2012. Loic Guennou (thesis advisors, Adami and Le Brun) whose PhD is expected in 2013. In addition, proposals on the European side were submitted to continue spectroscopic calibration of the photo-zs in clusters versus the field and also to provide further z-band coverage for clusters that are within 1 degree of each other so that more than one cluster image can be acquired per exposure. Preliminary results have been presented at 6 conferences in 2010: Murphy and Guennou at the Great Lakes Cosmology Conference, Clowe, Edinburgh and Garching, Durret, Garching, and Mazure, Japan. Despite favorable reviews is not being continued. Hence, this is a final technical report..
Gravitational lenses and dark matter - Theory
NASA Technical Reports Server (NTRS)
Gott, J. Richard, III
1987-01-01
Theoretical models are presented for guiding the application of gravitational lenses to probe the characteristics of dark matter in the universe. Analytical techniques are defined for quantifying the mass associated with lensing galaxies (in terms of the image separation), determining the quantity of dark mass of the lensing bodies, and estimating the mass density of the lenses. The possibility that heavy halos are made of low mass stars is considered, along with the swallowing of central images of black holes or cusps in galactic nuclei and the effects produced on a lensed quasar image by nonbaryonic halos. The observable effects of dense groups and clusters and the characteristics of dark matter strings are discussed, and various types of images which are possible due to lensing phenomena and position are described.
Cosmological constraints from weak lensing non-Gaussian statistics
NASA Astrophysics Data System (ADS)
Liu, Jia; Haiman, Zoltan; Petri, Andrea; Hill, James; Hui, Lam; Kratochvil, Jan Michael; May, Morgan
2016-01-01
Weak gravitational lensing is one of the most promising techniques to probe dark energy. Our work to date suggests that the information in the nonlinear regime exceeds that in the two-point functions. Using the publicly available data from the 154 deg^2 CFHTLenS survey and a large suite of ray-tracing N-body simulations on a grid of 91 cosmological models, we find that constraints from peak counts are comparable to those from the power spectrum, and somewhat tighter when different smoothing scales are combined.I will also introduce the utility of cross-correlating weak galaxy lensing maps with CMB lensing maps, a technique that will be useful to probe structures at an intermediate redshift of 0.9, as larger weak lensing surveys such as HSC, DES, KiDS, Euclid, and LSST come online. We cross-correlate the CFHTLenS galaxy lensing convergence maps with Planck CMB lensing maps. Our results show two sigma tension with the constraints obtained from the Planck temperature measurements. I will discuss possible sources of the tension, including intrinsic alignments, photo-z uncertainties, masking of tSZ in the CMB maps, and the multiplicative bias.
EFFECT OF MASKED REGIONS ON WEAK-LENSING STATISTICS
Shirasaki, Masato; Yoshida, Naoki; Hamana, Takashi
2013-09-10
Sky masking is unavoidable in wide-field weak-lensing observations. We study how masks affect the measurement of statistics of matter distribution probed by weak gravitational lensing. We first use 1000 cosmological ray-tracing simulations to examine in detail the impact of masked regions on the weak-lensing Minkowski Functionals (MFs). We consider actual sky masks used for a Subaru Suprime-Cam imaging survey. The masks increase the variance of the convergence field and the expected values of the MFs are biased. The bias then compromises the non-Gaussian signals induced by the gravitational growth of structure. We then explore how masks affect cosmological parameter estimation. We calculate the cumulative signal-to-noise ratio (S/N) for masked maps to study the information content of lensing MFs. We show that the degradation of S/N for masked maps is mainly determined by the effective survey area. We also perform simple {chi}{sup 2} analysis to show the impact of lensing MF bias due to masked regions. Finally, we compare ray-tracing simulations with data from a Subaru 2 deg{sup 2} survey in order to address if the observed lensing MFs are consistent with those of the standard cosmology. The resulting {chi}{sup 2}/n{sub dof} = 29.6/30 for three combined MFs, obtained with the mask effects taken into account, suggests that the observational data are indeed consistent with the standard {Lambda}CDM model. We conclude that the lensing MFs are a powerful probe of cosmology only if mask effects are correctly taken into account.
Neutrino mass and dark energy from weak lensing.
Abazajian, Kevork N; Dodelson, Scott
2003-07-25
Weak gravitational lensing of background galaxies by intervening matter directly probes the mass distribution in the Universe. This distribution is sensitive to both the dark energy and neutrino mass. We examine the potential of lensing experiments to measure features of both simultaneously. Focusing on the radial information contained in a future deep 4000 deg(2) survey, we find that the expected (1-sigma) error on a neutrino mass is 0.1 eV, if the dark-energy parameters are allowed to vary. The constraints on dark-energy parameters are similarly restrictive, with errors on w of 0.09. PMID:12906650
Trapping light by mimicking gravitational lensing
NASA Astrophysics Data System (ADS)
Liu, Hui; Sheng, Chong; Zhu, Shining; Genov, Dentcho; Nanjing Unversity Collaboration; Louisiana Tech University Collaboration
2014-03-01
One of the most fascinating predictions of the theory of general relativity is the effect of gravitational lensing, the bending of light in close proximity to massive stellar objects. Recently, artificial optical materials have been proposed to study the various aspects of curved spacetimes, including light trapping and Hawking's radiation. However, the development of experiments 'toy' models that simulate gravitational lensing in curved spacetimes remains a challenge, especially for visible light. Here, by utilizing a microstructured optical waveguide around a microsphere, we propose to mimic curved spacetimes caused by gravity, with high precision. We experimentally demonstrate both far-field gravitational lensing effects and the critical phenomenon in close proximity to the photon sphere of astrophysical objects under hydrostatic equilibrium. The proposed microstructured waveguide can be used as an omnidirectional absorber, with potential light harvesting and microcavity applications. This work is published at Nature Photonics 2013, DOI: 10.1038/NPHOTON.2013.247.
Observing long cosmic strings through gravitational lensing
NASA Astrophysics Data System (ADS)
de Laix, Andrew A.
1997-11-01
We consider the gravitational lensing produced by long cosmic strings formed in a grand-unified theory scale phase transition. We derive a formula for the deflection of photons which pass near the strings that reduces to an integral over the light cone projection of the string configuration plus constant terms which are not important for lensing. Our strings are produced by performing numerical simulations of cosmic string networks in flat, Minkowski space ignoring the effects of cosmological expansion. These strings have more small scale structure than those from an expanding universe simulation-fractal dimension 1.3 for Minkowski versus 1.1 for expanding-but share the same qualitative features. Lensing simulations show that for both pointlike and extended objects strings produce patterns unlike more traditional lenses, and, in particluar, the kinks in strings tend to generate demagnified images which reside close to the string. Thus lensing acts as a probe of the small scale structure of a string. Estimates of lensing probablity suggest that for string energy densities consistent with string seeded structure formation, on the order of tens of string lenses should be observed in the Sloan Digital Sky Survey (SDSS) quasar catalog. We propose a search strategy in which string lenses would be identified in the SDSS quasar survey, and the string nature of the lens can be confirmed by the observation of nearby high redshift galaxies which are also be lensed by the string.
Time delay in Swiss cheese gravitational lensing
Chen, B.; Kantowski, R.; Dai, X.
2010-08-15
We compute time delays for gravitational lensing in a flat {Lambda} dominated cold dark matter Swiss cheese universe. We assume a primary and secondary pair of light rays are deflected by a single point mass condensation described by a Kottler metric (Schwarzschild with {Lambda}) embedded in an otherwise homogeneous cosmology. We find that the cosmological constant's effect on the difference in arrival times is nonlinear and at most around 0.002% for a large cluster lens; however, we find differences from time delays predicted by conventional linear lensing theory that can reach {approx}4% for these large lenses. The differences in predicted delay times are due to the failure of conventional lensing to incorporate the lensing mass into the mean mass density of the universe.
NASA Astrophysics Data System (ADS)
Okura, Yuki; Futamase, Toshifumi
2014-09-01
Highly accurate weak lensing analysis is urgently required for planned cosmic shear observations. For this purpose we have eliminated various systematic noises in the measurement. The point-spread function (PSF) effect is one of them. A perturbative approach for correcting the PSF effect on the observed image ellipticities has been previously employed. Here we propose a new non-perturbative approach for PSF correction that avoids the systematic error associated with the perturbative approach. The new method uses an artificial image for measuring shear which has the same ellipticity as the lensed image. This is done by re-smearing the observed galaxy images and observed star images (PSF) with an additional smearing function to obtain the original lensed galaxy images. We tested the new method with simple simulated objects that have Gaussian or Srsic profiles smeared by a Gaussian PSF with sufficiently large size to neglect pixelization. Under the condition of no pixel noise, it is confirmed that the new method has no systematic error even if the PSF is large and has a high ellipticity.
Okura, Yuki; Futamase, Toshifumi E-mail: tof@astr.tohoku.ac.jp
2014-09-10
Highly accurate weak lensing analysis is urgently required for planned cosmic shear observations. For this purpose we have eliminated various systematic noises in the measurement. The point-spread function (PSF) effect is one of them. A perturbative approach for correcting the PSF effect on the observed image ellipticities has been previously employed. Here we propose a new non-perturbative approach for PSF correction that avoids the systematic error associated with the perturbative approach. The new method uses an artificial image for measuring shear which has the same ellipticity as the lensed image. This is done by re-smearing the observed galaxy images and observed star images (PSF) with an additional smearing function to obtain the original lensed galaxy images. We tested the new method with simple simulated objects that have Gaussian or Sérsic profiles smeared by a Gaussian PSF with sufficiently large size to neglect pixelization. Under the condition of no pixel noise, it is confirmed that the new method has no systematic error even if the PSF is large and has a high ellipticity.
Galilean-invariant scalar fields can strengthen gravitational lensing.
Wyman, Mark
2011-05-20
The mystery of dark energy suggests that there is new gravitational physics on long length scales. Yet light degrees of freedom in gravity are strictly limited by Solar System observations. We can resolve this apparent contradiction by adding a Galilean-invariant scalar field to gravity. Called Galileons, these scalars have strong self-interactions near overdensities, like the Solar System, that suppress their dynamical effect. These nonlinearities are weak on cosmological scales, permitting new physics to operate. In this Letter, we point out that a massive-gravity-inspired coupling of Galileons to stress energy can enhance gravitational lensing. Because the enhancement appears at a fixed scaled location for dark matter halos of a wide range of masses, stacked cluster analysis of weak lensing data should be able to detect or constrain this effect. PMID:21668215
Statistics of gravitational lenses - The uncertainties
NASA Technical Reports Server (NTRS)
Mao, Shude
1991-01-01
The assumptions in the analysis of gravitational lensing statistics are examined. Special emphasis is given to the uncertainties in the theoretical predictions. It is shown that a simple redshift cutoff model, which may result from galaxy evolution, can significantly reduce the lensing probability and explain the large mean separation of images in observed gravitational lenses. This effect may affect the constraint on the contribution of the cosmological constant to producing a flat universe from the number counts of the observed lenses. For the Omega(0) = 1 (filled beam) model, the lensing probability of early-type galaxies with finite core radii is reduced roughly by a factor of 2 for high-redshift quasars as compared with the corresponding singular isothermal sphere model. The finite core radius effect is about 20 percent for a lambda-dominated flat universe. It is also shown that the most recent galaxy luminosity function gives lensing probabilities that are smaller than previously estimated roughly by a factor of 3.
Cosmological test using strong gravitational lensing systems
NASA Astrophysics Data System (ADS)
Yuan, C. C.; Wang, F. Y.
2015-09-01
As one of the probes of universe, strong gravitational lensing systems allow us to compare different cosmological models and constrain vital cosmological parameters. This purpose can be reached from the dynamic and geometry properties of strong gravitational lensing systems, for instance, time-delay Δτ of images, the velocity dispersion σ of the lensing galaxies and the combination of these two effects, Δτ/σ2. In this paper, in order to carry out one-on-one comparisons between ΛCDM universe and Rh = ct universe, we use a sample containing 36 strong lensing systems with the measurement of velocity dispersion from the Sloan Lens Advanced Camera for Surveys (SLACS) and Lens Structure and Dynamic survey (LSD) survey. Concerning the time-delay effect, 12 two-image lensing systems with Δτ are also used. In addition, Monte Carlo simulations are used to compare the efficiency of the three methods as mentioned above. From simulations, we estimate the number of lenses required to rule out one model at the 99.7 per cent confidence level. Comparing with constraints from Δτ and the velocity dispersion σ, we find that using Δτ/σ2 can improve the discrimination between cosmological models. Despite the independence tests of these methods reveal a correlation between Δτ/σ2 and σ, Δτ/σ2 could be considered as an improved method of σ if more data samples are available.
Gravitational Lensing of Supernova Neutrinos
Mena, Olga; Mocioiu, Irina; Quigg, Chris; /Fermilab
2006-10-01
The black hole at the center of the galaxy is a powerful lens for supernova neutrinos. In the very special circumstance of a supernova near the extended line of sight from Earth to the galactic center, lensing could dramatically enhance the neutrino flux at Earth and stretch the neutrino pulse.
Hopfield neural network deconvolution for weak lensing measurement
NASA Astrophysics Data System (ADS)
Nurbaeva, G.; Tewes, M.; Courbin, F.; Meylan, G.
2015-05-01
Weak gravitational lensing has the potential to place tight constraints on the equation of the state of dark energy. However, this will only be possible if shear measurement methods can reach the required level of accuracy. We present a new method for measuring the ellipticity of galaxies used in weak lensing surveys. The method makes use of direct deconvolution of the data by the total point spread function (PSF). We adopt a linear algebra formalism that represents the PSF as a Toeplitz matrix. This allows us to solve the convolution equation by applying the Hopfield neural network iterative scheme. The ellipticity of galaxies in the deconvolved images are then measured using second-order moments of the autocorrelation function of the images. To our knowledge, it is the first time full image deconvolution has been used to measure weak lensing shear. We apply our method to the simulated weak lensing data proposed in the GREAT10 challenge and obtain a quality factor of Q = 87. This result is obtained after applying image denoising to the data, prior to the deconvolution. The additive and multiplicative biases on the shear power spectrum are then √{A}= + 0.09 × 10-4 and ℳ/2 = +0.0357, respectively.
Separating weak lensing and intrinsic alignments using radio observations
NASA Astrophysics Data System (ADS)
Whittaker, Lee; Brown, Michael L.; Battye, Richard A.
2015-07-01
We discuss methods for performing weak lensing using radio observations to recover information about the intrinsic structural properties of the source galaxies. Radio surveys provide unique information that can benefit weak lensing studies, such as H I emission, which may be used to construct galaxy velocity maps, and polarized synchrotron radiation; both of which provide information about the unlensed galaxy and can be used to reduce galaxy shape noise and the contribution of intrinsic alignments. Using a proxy for the intrinsic position angle of an observed galaxy, we develop techniques for cleanly separating weak gravitational lensing signals from intrinsic alignment contamination in forthcoming radio surveys. Random errors on the intrinsic orientation estimates introduce biases into the shear and intrinsic alignment estimates. However, we show that these biases can be corrected for if the error distribution is accurately known. We demonstrate our methods using simulations, where we reconstruct the shear and intrinsic alignment auto- and cross-power spectra in three overlapping redshift bins. We find that the intrinsic position angle information can be used to successfully reconstruct both the lensing and intrinsic alignment power spectra with negligible residual bias.
Strong gravitational lensing of gravitational waves in Einstein Telescope
Piórkowska, Aleksandra; Biesiada, Marek; Zhu, Zong-Hong E-mail: marek.biesiada@us.edu.pl
2013-10-01
Gravitational wave experiments have entered a new stage which gets us closer to the opening a new observational window on the Universe. In particular, the Einstein Telescope (ET) is designed to have a fantastic sensitivity that will provide with tens or hundreds of thousand NS-NS inspiral events per year up to the redshift z = 2. Some of such events should be gravitationally lensed by intervening galaxies. We explore the prospects of observing gravitationally lensed inspiral NS-NS events in the Einstein telescope. Being conservative we consider the lens population of elliptical galaxies. It turns out that depending on the local insipral rate ET should detect from one per decade detection in the pessimistic case to a tens of detections per year for the most optimistic case. The detection of gravitationally lensed source in gravitational wave detectors would be an invaluable source of information concerning cosmography, complementary to standard ones (like supernovae or BAO) independent of the local cosmic distance ladder calibrations.
NASA Astrophysics Data System (ADS)
Weinberg, Nevin Nachum
The studies presented herein are on three distinct topics in astrophysics: I. We solve for the evolution of the vertical extent of the convective region of a neutron star atmosphere during a type I X-ray burst. The convective region is well-mixed with ashes of nuclear burning, and its extent determines the burst rise time. We show that the maximum extent of the convective region during photospheric radius expansion (PRE) bursts can be sufficiently great that some ashes of burning are: (1) ejected by the radiation-driven wind during the PRE phase and, (2) exposed at the neutron star surface following the PRE phase. We calculate the expected column density of ashes in hydrogen-like states and find that the resulting photoionization edges should be detectable with current high spectral resolution X-ray telescopes. A detection would probe the burst nuclear burning processes and might enable a measurement of the neutron star gravitational redshift. II. We discuss physical experiments achievable via the monitoring of stellar dynamics near the massive black hole (MBH) at the Galactic center with a next- generation, extremely large telescope (ELT). We use the Markov Chain Monte Carlo method to evaluate the constraints that the monitoring of these orbits will place on the matter content at the Galactic center. We compare these future constraints with those obtained with the current data. We also describe how the monitoring of stellar proper motions can be used to probe directly the masses of isolated stellar remnants near the MBH. III. We calculate the abundance of dark-matter concentrations that are sufficiently overdense to produce a detectable weak-gravitational-lensing signal. Most of these overdensities are virialized halos containing identifiable X-ray and/or optical clusters. However, a significant fraction are nonvirialized, cluster-mass overdensities still in the process of gravitational collapse---these should produce significantly weaker or no X-ray emission. Our predicted abundance of such dark clusters is consistent with the abundance implied by the detection of apparent dark lenses. We also examine the prospect of using weak gravitational lenses to constrain the dark energy equation-of- state.
Weak Lensing from Space I: Instrumentation and Survey Strategy
Rhodes, Jason; Refregier, Alexandre; Massey, Richard; Albert, Justin; Bacon, David; Bernstein, Gary; Ellis, Richard; Jain, Bhuvnesh; Kim, Alex; Lampton, Mike; McKay, Tim; Akerlof, C.; Aldering, G.; Amanullah, R.; Astier, P.; Barrelet, E.; Bebek, C.; Bergstrom, L.; Bercovitz, J.; Bester, M.; Bonissent, A.; Bower, C.; Carithers, W.; Commins, E.; Day, C.; Deustua, S.; DiGennaro, R.; Ealet, A.; Eriksson, M.; Fruchter, A.; Genat, J.-F.; Goldhaber, G.; Goobar, A.; Groom, D.; Harris, S.; Harvey, P.; Heetderks, H.; Holland, S.; Huterer, D.; Karcher, A.; Kolbe, W.; Kreiger, B.; Lafever, R.; Lamoureux, J.; Levi, M.; Devin, D.; Linder, E.; Loken, S.; Malina, R.; McKee, S.; Miquel, R.; Mortsell, E.; Mostek, N.; Mufson, S.; Musser, J.; Nugent, P.; Oluseyi, H.; Pain, R.; Palaio, N.; Pankow, D.; Perlmutter, S.; Pratt, R.; Prieto, E.; Robinson, K.; Roe, N.; Sholl, M.; Schubnell, M.; Smadja, G.; Smoot, G.; Spadafora, A.; Tarle, G.; Tomasch, A.; von der Lippe, H.; Vincent, D.; Walder, J.-P.; Wang, G.
2003-04-23
A wide field space-based imaging telescope is necessary to fully exploit the technique of observing dark matter via weak gravitational lensing. This first paper in a three part series outlines the survey strategies and relevant instrumental parameters for such a mission. As a concrete example of hardware design, we consider the proposed Supernova/Acceleration Probe (SNAP). Using SNAP engineering models, we quantify the major contributions to this telescope's Point Spread Function (PSF). These PSF contributions are relevant to any similar wide field space telescope. We further show that the PSF of SNAP or a similar telescope will be smaller than current ground-based PSFs, and more isotropic and stable over time than the PSF of the Hubble Space Telescope. We outline survey strategies for two different regimes - a ''wide'' 300 square degree survey and a ''deep'' 15 square degree survey that will accomplish various weak lensing goals including statistical studies and dark matter mapping.
Oguri, Masamune; Hennawi, Joseph F.; Gladders, Michael D.; Dahle, Haakon; Natarajan, Priyamvada; Dalal, Neal; Koester, Benjamin P.; Sharon, Keren; Bayliss, Matthew
2009-01-29
We derive radial mass profiles of four strong lensing selected clusters which show prominent giant arcs (Abell 1703, SDSS J1446+3032, SDSS J1531+3414, and SDSS J2111-0115), by combining detailed strong lens modeling with weak lensing shear measured from deep Subaru Suprime-cam images. Weak lensing signals are detected at high significance for all four clusters, whose redshifts range from z = 0.28 to 0.64. We demonstrate that adding strong lensing information with known arc redshifts significantly improves constraints on the mass density profile, compared to those obtained from weak lensing alone. While the mass profiles are well fitted by the universal form predicted in N-body simulations of the {Lambda}-dominated cold dark matter model, all four clusters appear to be slightly more centrally concentrated (the concentration parameters c{sub vir} {approx} 8) than theoretical predictions, even after accounting for the bias toward higher concentrations inherent in lensing selected samples. Our results are consistent with previous studies which similarly detected a concentration excess, and increases the total number of clusters studied with the combined strong and weak lensing technique to ten. Combining our sample with previous work, we find that clusters with larger Einstein radii are more anomalously concentrated. We also present a detailed model of the lensing cluster Abell 1703 with constraints from multiple image families, and find the dark matter inner density profile to be cuspy with the slope consistent with -1, in agreement with expectations.
First measurement of gravitational lensing by cosmic voids in SDSS
NASA Astrophysics Data System (ADS)
Melchior, Peter; Sutter, P. M.; Sheldon, Erin S.; Krause, Elisabeth; Wandelt, Benjamin D.
2014-06-01
We report the first measurement of the diminutive lensing signal arising from matter underdensities associated with cosmic voids. While undetectable individually, by stacking the weak gravitational shear estimates around 901 voids detected in Sloan Digital Sky Survey DR7 by Sutter et al., we find substantial evidence for a depression of the lensing signal compared to the cosmic mean. This depression is most pronounced at the void radius, in agreement with analytical models of void matter profiles. Even with the largest void sample and imaging survey available today, we cannot put useful constraints on the radial dark matter void profile. We invite independent investigations of our findings by releasing data and analysis code to the public at https://github.com/pmelchior/void-lensing.
Computer Modeling of Gravitational Lensing Systems
NASA Astrophysics Data System (ADS)
Naudus, Philip; Wallin, J.; Marshall, P.
2010-01-01
The purpose of this research project is to determine the properties of gravitational lensing systems through the use of computer simulations. Modeling the lens galaxy as a Singular Isothermal Ellipsoid (SIE), we solved the gravitational lens equation for many different source and lens configurations in order to determine the properties of the system which reproduce the observed lensed images. Although exploring the entire parameter space is a computationally intense process, we have shown that solutions can be found relatively quickly by incorporating interaction between a user and the computer (solutions were found within a few minutes in our test cases). For this reason, we are collaborating with Galaxy Zoo to create and deploy an interactive Java applet which will allow non-experts to contribute to the modeling process. This project promises to determine properties of source galaxies in addition to finding the dark matter distributions of lens galaxies.
The geometry of gravitational lensing magnification
NASA Astrophysics Data System (ADS)
Aazami, Amir Babak; Werner, Marcus C.
2016-02-01
We present a definition of unsigned magnification in gravitational lensing valid on arbitrary convex normal neighborhoods of time oriented Lorentzian manifolds. This definition is a function defined at any two points along a null geodesic that lie in a convex normal neighborhood, and foregoes the usual notions of lens and source planes in gravitational lensing. Rather, it makes essential use of the van Vleck determinant, which we present via the exponential map, and Etherington's definition of luminosity distance for arbitrary spacetimes. We then specialize our definition to spacetimes, like Schwarzschild's, in which the lens is compact and isolated, and show that our magnification function is monotonically increasing along any geodesic contained within a convex normal neighborhood.
New optical surveys for gravitationally lensed quasars
NASA Astrophysics Data System (ADS)
Morgan, Nicholas D.
This thesis describes four new optical surveys for gravitationally lensed quasars. Three of these surveys take the form of traditional targeted searches. These include: (1)a ground-based survey targeting 173 radio-loud quasars using the 2.4 m telescope at Michigan-Dartmouth-
Gravitational Lensing: Recent Progress & Future Goals
NASA Technical Reports Server (NTRS)
Brainerd, Tereasa
2001-01-01
This award was intended to provide financial support for an international astrophysics conference on gravitational lensing which was held at Boston University from July 25 to July 30, 1999. Because of the nature of the award, no specific research was proposed, nor was any carried out. The participants at the conference presented results of their on-going research efforts, and written summaries of their presentations have been published by the Astronomical Society of the Pacific as part of their conference series. The reference to the conference proceedings book is Gravitational Lensing: Recent Progress and Future Goals, ASP Conference Series volume 237, eds. T. G. Brainerd and C. S. Kochanek (2001). The ISBN number of this book is 1-58381-074-9. The goal of the conference was to bring together both senior and junior investigators who were actively involved in all aspects of gravitational lensing research. This was the first conference in four years to address gravitational lensing from such a broad perspective (the previous such conference being IAU Symposium 173 held in Melbourne, Australia in July 1995). The conference was attended by 190 participants, who represented of order 70 different institutions and of order 15 different countries. The Scientific Organizing Committee members were Matthias Bartelmann (co-chair), Tereasa Brainerd (co-chair), Ian Browne, Richard Ellis, Nick Kaiser, Yannick Mellier, Sjur Refsdal, HansWalter Rix, Joachim Wambsganss, and Rachel Webster. The Local Organizing Committee members were Tereasa Brainerd (chair), Emilio Falco, Jacqueline Hewitt, Christopher Kochanek, and Irwin Shapiro. The oral sessions were organized around specific applications of gravitational lensing and included invited reviews, invited 'targeted talks', and contributed talks. The review speakers were Roger Blandford, Tereasa Brainerd, Gus Evrard, Nick Kaiser, Guinevere Kaufmann, Chris Kochanek, Charley Lineweaver, Gerry Luppino, Shude Mao, Paul Schechter, Peter Snhneider, amd Ed Turner. The 'targeted talk' speakers were Andy Boden, Ian Browne, Emilio Falco, Harry Ferguson, Bhuvnesh Jain, Christine Jones, Arlie Petters, Hans-Walter Rix, Penny Sackett, Prasenjit Saha, Virginia Trimble, and Joachim Wambsganss. Due to limited time, only 25% of the abstracts which were submitted for consideration as contributed talks could actually be accepted for the final program; those which were not selected as talks were presented as posters, and a special poster viewing session was held to allow participants to present their work. A copy of the complete Final Program of the conference is included in the following pages.
Weak lensing induced by second-order vector mode
NASA Astrophysics Data System (ADS)
Saga, Shohei; Yamauchi, Daisuke; Ichiki, Kiyotomo
2015-09-01
The vector mode of cosmological perturbation theory imprints characteristic signals on the weak lensing signals such as curl and B modes which are never imprinted by the scalar mode. However, the vector mode is neglected in the standard first-order cosmological perturbation theory since it only has a decaying mode. This situation changes if the cosmological perturbation theory is expanded up to second order. The second-order vector and tensor modes are inevitably induced by the product of the first-order scalar modes. We study the effect of the second-order vector mode on the weak lensing curl and B modes. We find that the curl mode induced by the second-order vector mode is comparable to that induced by the primordial gravitational waves with the tensor-to-scalar ratio r =0.1 at ??200 . In this case, the curl mode induced by the second-order vector mode dominates at ?>200 . Furthermore, the B-mode cosmic shear induced by the second-order vector mode dominates on almost all scales. However, we find that the observational signatures of the second-order vector and tensor modes cannot exceed the expected noise of ongoing and upcoming weak lensing measurements. We conclude that the curl and B modes induced by the second-order vector and tensor modes are unlikely to be detected in future experiments.
The Third Gravitational Lensing Accuracy Testing (GREAT3) Challenge Handbook
NASA Astrophysics Data System (ADS)
Mandelbaum, Rachel; Rowe, Barnaby; Bosch, James; Chang, Chihway; Courbin, Frederic; Gill, Mandeep; Jarvis, Mike; Kannawadi, Arun; Kacprzak, Tomasz; Lackner, Claire; Leauthaud, Alexie; Miyatake, Hironao; Nakajima, Reiko; Rhodes, Jason; Simet, Melanie; Zuntz, Joe; Armstrong, Bob; Bridle, Sarah; Coupon, Jean; Dietrich, Jörg P.; Gentile, Marc; Heymans, Catherine; Jurling, Alden S.; Kent, Stephen M.; Kirkby, David; Margala, Daniel; Massey, Richard; Melchior, Peter; Peterson, John; Roodman, Aaron; Schrabback, Tim
2014-05-01
The GRavitational lEnsing Accuracy Testing 3 (GREAT3) challenge is the third in a series of image analysis challenges, with a goal of testing and facilitating the development of methods for analyzing astronomical images that will be used to measure weak gravitational lensing. This measurement requires extremely precise estimation of very small galaxy shape distortions, in the presence of far larger intrinsic galaxy shapes and distortions due to the blurring kernel caused by the atmosphere, telescope optics, and instrumental effects. The GREAT3 challenge is posed to the astronomy, machine learning, and statistics communities, and includes tests of three specific effects that are of immediate relevance to upcoming weak lensing surveys, two of which have never been tested in a community challenge before. These effects include many novel aspects including realistically complex galaxy models based on high-resolution imaging from space; a spatially varying, physically motivated blurring kernel; and a combination of multiple different exposures. To facilitate entry by people new to the field, and for use as a diagnostic tool, the simulation software for the challenge is publicly available, though the exact parameters used for the challenge are blinded. Sample scripts to analyze the challenge data using existing methods will also be provided. See http://great3challenge.info and http://great3.projects.phys.ucl.ac.uk/leaderboard/ for more information.
3D weak lensing with spin wavelets on the ball
NASA Astrophysics Data System (ADS)
Leistedt, Boris; McEwen, Jason D.; Kitching, Thomas D.; Peiris, Hiranya V.
2015-12-01
We construct the spin flaglet transform, a wavelet transform to analyze spin signals in three dimensions. Spin flaglets can probe signal content localized simultaneously in space and frequency and, moreover, are separable so that their angular and radial properties can be controlled independently. They are particularly suited to analyzing cosmological observations such as the weak gravitational lensing of galaxies. Such observations have a unique 3D geometrical setting since they are natively made on the sky, have spin angular symmetries, and are extended in the radial direction by additional distance or redshift information. Flaglets are constructed in the harmonic space defined by the Fourier-Laguerre transform, previously defined for scalar functions and extended here to signals with spin symmetries. Thanks to various sampling theorems, both the Fourier-Laguerre and flaglet transforms are theoretically exact when applied to bandlimited signals. In other words, in numerical computations the only loss of information is due to the finite representation of floating point numbers. We develop a 3D framework relating the weak lensing power spectrum to covariances of flaglet coefficients. We suggest that the resulting novel flaglet weak lensing estimator offers a powerful alternative to common 2D and 3D approaches to accurately capture cosmological information. While standard weak lensing analyses focus on either real- or harmonic-space representations (i.e., correlation functions or Fourier-Bessel power spectra, respectively), a wavelet approach inherits the advantages of both techniques, where both complicated sky coverage and uncertainties associated with the physical modeling of small scales can be handled effectively. Our codes to compute the Fourier-Laguerre and flaglet transforms are made publicly available.
Strong gravitational lensing and dark energy complementarity
Linder, Eric V.
2004-01-21
In the search for the nature of dark energy most cosmological probes measure simple functions of the expansion rate. While powerful, these all involve roughly the same dependence on the dark energy equation of state parameters, with anticorrelation between its present value w{sub 0} and time variation w{sub a}. Quantities that have instead positive correlation and so a sensitivity direction largely orthogonal to, e.g., distance probes offer the hope of achieving tight constraints through complementarity. Such quantities are found in strong gravitational lensing observations of image separations and time delays. While degeneracy between cosmological parameters prevents full complementarity, strong lensing measurements to 1 percent accuracy can improve equation of state characterization by 15-50 percent. Next generation surveys should provide data on roughly 105 lens systems, though systematic errors will remain challenging.
Predicting weak lensing statistics from halo mass reconstructions - Final Paper
Everett, Spencer
2015-08-20
As dark matter does not absorb or emit light, its distribution in the universe must be inferred through indirect effects such as the gravitational lensing of distant galaxies. While most sources are only weakly lensed, the systematic alignment of background galaxies around a foreground lens can constrain the mass of the lens which is largely in the form of dark matter. In this paper, I have implemented a framework to reconstruct all of the mass along lines of sight using a best-case dark matter halo model in which the halo mass is known. This framework is then used to make predictions of the weak lensing of 3,240 generated source galaxies through a 324 arcmin² field of the Millennium Simulation. The lensed source ellipticities are characterized by the ellipticity-ellipticity and galaxy-mass correlation functions and compared to the same statistic for the intrinsic and ray-traced ellipticities. In the ellipticity-ellipticity correlation function, I and that the framework systematically under predicts the shear power by an average factor of 2.2 and fails to capture correlation from dark matter structure at scales larger than 1 arcminute. The model predicted galaxy-mass correlation function is in agreement with the ray-traced statistic from scales 0.2 to 0.7 arcminutes, but systematically underpredicts shear power at scales larger than 0.7 arcminutes by an average factor of 1.2. Optimization of the framework code has reduced the mean CPU time per lensing prediction by 70% to 24 ± 5 ms. Physical and computational shortcomings of the framework are discussed, as well as potential improvements for upcoming work.
Direct shear mapping - a new weak lensing tool
NASA Astrophysics Data System (ADS)
de Burgh-Day, C. O.; Taylor, E. N.; Webster, R. L.; Hopkins, A. M.
2015-08-01
We have developed a new technique called direct shear mapping (DSM) to measure gravitational lensing shear directly from observations of a single background source. The technique assumes the velocity map of an unlensed, stably rotating galaxy will be rotationally symmetric. Lensing distorts the velocity map making it asymmetric. The degree of lensing can be inferred by determining the transformation required to restore axisymmetry. This technique is in contrast to traditional weak lensing methods, which require averaging an ensemble of background galaxy ellipticity measurements, to obtain a single shear measurement. We have tested the efficacy of our fitting algorithm with a suite of systematic tests on simulated data. We demonstrate that we are in principle able to measure shears as small as 0.01. In practice, we have fitted for the shear in very low redshift (and hence unlensed) velocity maps, and have obtained null result with an error of 0.01. This high-sensitivity results from analysing spatially resolved spectroscopic images (i.e. 3D data cubes), including not just shape information (as in traditional weak lensing measurements) but velocity information as well. Spirals and rotating ellipticals are ideal targets for this new technique. Data from any large Integral Field Unit (IFU) or radio telescope is suitable, or indeed any instrument with spatially resolved spectroscopy such as the Sydney-Australian-Astronomical Observatory Multi-Object Integral Field Spectrograph (SAMI), the Atacama Large Millimeter/submillimeter Array (ALMA), the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) and the Square Kilometer Array (SKA).
Spurious Shear in Weak Lensing with LSST
Chang, C.; Kahn, S.M.; Jernigan, J.G.; Peterson, J.R.; AlSayyad, Y.; Ahmad, Z.; Bankert, J.; Bard, D.; Connolly, A.; Gibson, R.R.; Gilmore, K.; Grace, E.; Hannel, M.; Hodge, M.A.; Jee, M.J.; Jones, L.; Krughoff, S.; Lorenz, S.; Marshall, P.J.; Marshall, S.; Meert, A.
2012-09-19
The complete 10-year survey from the Large Synoptic Survey Telescope (LSST) will image {approx} 20,000 square degrees of sky in six filter bands every few nights, bringing the final survey depth to r {approx} 27.5, with over 4 billion well measured galaxies. To take full advantage of this unprecedented statistical power, the systematic errors associated with weak lensing measurements need to be controlled to a level similar to the statistical errors. This work is the first attempt to quantitatively estimate the absolute level and statistical properties of the systematic errors on weak lensing shear measurements due to the most important physical effects in the LSST system via high fidelity ray-tracing simulations. We identify and isolate the different sources of algorithm-independent, additive systematic errors on shear measurements for LSST and predict their impact on the final cosmic shear measurements using conventional weak lensing analysis techniques. We find that the main source of the errors comes from an inability to adequately characterise the atmospheric point spread function (PSF) due to its high frequency spatial variation on angular scales smaller than {approx} 10{prime} in the single short exposures, which propagates into a spurious shear correlation function at the 10{sup -4}-10{sup -3} level on these scales. With the large multi-epoch dataset that will be acquired by LSST, the stochastic errors average out, bringing the final spurious shear correlation function to a level very close to the statistical errors. Our results imply that the cosmological constraints from LSST will not be severely limited by these algorithm-independent, additive systematic effects.
Point mass deflectors in gravitational lenses
NASA Technical Reports Server (NTRS)
Dolan, Joseph F.
1988-01-01
The observed properties of the six systems generally accepted as gravitational lenses are compared with the properties predicted for the images of point-mass and distributed mass deflectors. Taken as a statistical distribution, the characteristics of the six known systems strongly suggest the existence of a super-massive black hole as the effective deflecting mass in one or more of these systems. If the deflecting mass in a gravitational lens is a black hole, the distance to the deflecting mass can be determined directly from the difference in light travel time along the separate image paths. (No direct solution for the distance to the deflecting mass exists when the deflecting mass is a galaxy or a cluster of galaxies). Geometric parallaxes of objects at 1000 Mpc distance are of obvious importance in a wide variety of cosmological studies.
Virbhadra, K. S.; Keeton, C. R.
2008-06-15
We model the massive dark object at the center of the Galaxy as a Schwarzschild black hole as well as Janis-Newman-Winicour naked singularities, characterized by the mass and scalar charge parameters, and study gravitational lensing (particularly time delay, magnification centroid, and total magnification) by them. We find that the lensing features are qualitatively similar (though quantitatively different) for Schwarzschild black holes, weakly naked, and marginally strongly naked singularities. However, the lensing characteristics of strongly naked singularities are qualitatively very different from those due to Schwarzschild black holes. The images produced by Schwarzschild black hole lenses and weakly naked and marginally strongly naked singularity lenses always have positive time delays. On the other hand, strongly naked singularity lenses can give rise to images with positive, zero, or negative time delays. In particular, for a large angular source position the direct image (the outermost image on the same side as the source) due to strongly naked singularity lensing always has a negative time delay. We also found that the scalar field decreases the time delay and increases the total magnification of images; this result could have important implications for cosmology. As the Janis-Newman-Winicour metric also describes the exterior gravitational field of a scalar star, naked singularities as well as scalar star lenses, if these exist in nature, will serve as more efficient cosmic telescopes than regular gravitational lenses.
Cluster mass profiles from weak lensing II
NASA Astrophysics Data System (ADS)
King, L. J.; Schneider, P.
2001-04-01
When a cluster gravitationally lenses faint background galaxies, its tidal gravitational field distorts their shapes (shear effect) and its magnification effect changes the observed number density. In Schneider et al. (\\cite{Schneider00}) we developed likelihood techniques to compare the constraints on cluster mass profiles that can be obtained using the shear and magnification information. This work considered circularly symmetric power-law models for clusters at fairly low redshifts where the redshift distribution of source galaxies could be neglected. Here this treatment is extended to encompass NFW profiles which are a good description of clusters from cosmological N-body simulations, and NFW clusters at higher redshifts where the influence of various scenarios for the knowledge of the redshift distribution are examined. Since in reality the overwhelming majority of clusters have ellipsoidal rather than spherical profiles, the singular isothermal ellipsoid (SIE) is investigated. We also briefly consider the impact of substructure on such a likelihood analysis. In general, we find that the shear information provides a better constraint on the NFW profile under consideration, so this becomes the focus of what follows. The ability to differentiate between the NFW and power-law profiles strongly depends on the size of the data field, and on the number density of galaxies for which an ellipticity can be measured. Combining Monte Carlo simulations with likelihood techniques is a very suitable way to predict whether profiles will be distinguishable, given the field of view and depth of the observations. For higher redshift NFW profiles, there is very little reduction ( ~ 1.5%) in the dispersion of parameter estimates when spectroscopic redshifts, as opposed to photometric redshift estimates, are available for the galaxies used in the lensing analysis.
Gravitational lensing of Type Ia supernovae
NASA Astrophysics Data System (ADS)
Goliath, M.; Mrtsell, E.
2000-08-01
Recently, Holz and Wald [Phys. Rev. D 58 (1998) 063501] have presented a method for determining gravitational lensing effects in inhomogeneous universes. Their use of realistic galaxy models has been limited to the singular, truncated isothermal sphere with a fixed mass. In this paper, their method is generalized to allow for matter distributions more accurately describing the actual properties of galaxies, as derived from observations and /N-body simulations. This includes the density profile proposed by Navarro, Frenk and White, as well as a distribution of galaxy masses. As an example of the possible applications of the method, we consider lensing effects on supernova luminosity distributions. We find that results for different mass distributions of smooth dark matter halos are very similar, making lensing effects predictable for a broad range of halo profiles. We also note, in agreement with other investigations, that one should be able to discriminate smooth halos from a dominant component of dark matter in compact objects. For instance, a sample of 100 supernovae at redshift /z=1 can, with 99% certainty, discriminate the case where all matter is in compact objects from the case where matter is in smooth halos.
MULTIPOLE FORMULAE FOR GRAVITATIONAL LENSING SHEAR AND FLEXION
Bernstein, Gary M.; Nakajima, Reiko E-mail: rnakajima@berkeley.edu
2009-03-10
The gravitational lensing equations for convergence, potential, shear, and flexion are simple in polar coordinates and separate under a multipole expansion once the shear and flexion spinors are rotated into a 'tangential' basis. We use this to investigate whether the useful monopole aperture-mass shear formulae generalize to all multipoles and to flexions. We re-derive the result of Schneider and Bartelmann that the shear multipole m at radius R is completely determined by the mass multipole at R, plus specific moments Q '('m') {sub in} and Q '('m') {sub out} of the mass multipoles internal and external, respectively, to R. The m {>=} 0 multipoles are independent of Q {sub out}. But in contrast to the monopole, the m < 0 multipoles are independent of Q {sub in}. These internal and external mass moments can be determined by shear (and/or flexion) data on the complementary portion of the plane, which has practical implications for lens modeling. We find that the ease of E/B separation in the monopole aperture moments does not generalize to m {ne} 0: the internal monopole moment is the only nonlocal E/B discriminant available from lensing observations. We have also not found practical local E/B discriminants beyond the monopole, though they could exist. We show also that the use of weak-lensing data to constrain a constant shear term near a strong-lensing system is impractical without strong prior constraints on the neighboring mass distribution.
Three Gravitationally Lensed Supernovae Behind Clash Galaxy Clusters
NASA Technical Reports Server (NTRS)
Patel, Brandon; McCully, Curtis; Jha, Saurbh W.; Rodney, Steven A.; Jones, David O.; Graur, Or; Merten, Julian; Zitrin, Adi; Riess, Adam G.; Matheson, Thomas; Sako, Masao; Holoien, Thomas W. -S.; Postman, Marc; Coe, Dan; Bartelmann, Matthias; Balestra, Italo; Benitez, Narciso; Bouwens, Rychard; Bradley, Larry; Broadhurst, Tom; Cenko, Stephen Bradley; Donahue, Megan; Filippenko, Alexei V.; Ford, Holland; Garnavich, Peter; Grillo, Claudio; Infante, Leopoldo; Jouvel, Stephanie; Kelson, Daniel; Koekemoer, Anton; Lahav, Ofer; Lemze, Doron; Maoz, Dan; Medezinski, Elinor; Melchior, Peter; Meneghetti, Massimo; Molino, Alberto; Moustakas, John; Moustakas, Leonidas A.; Nonino, Mario; Rosati, Piero; Seitz, Stella; Strolger, Louis G.; Umetsu, Keiichi; Zheng, Wei
2014-01-01
We report observations of three gravitationally lensed supernovae (SNe) in the Cluster Lensing And Supernova survey with Hubble (CLASH) Multi-Cycle Treasury program. These objects, SN CLO12Car (z = 1.28), SN CLN12Did (z = 0.85), and SN CLA11Tib (z = 1.14), are located behind three different clusters, MACSJ1720.2+3536 (z = 0.391), RXJ1532.9+3021 (z = 0.345), and A383 (z = 0.187), respectively. Each SN was detected in Hubble Space Telescope optical and infrared images. Based on photometric classification, we find that SNe CLO12Car and CLN12Did are likely to be Type Ia supernovae (SNe Ia), while the classification of SN CLA11Tib is inconclusive. Using multi-color light-curve fits to determine a standardized SN Ia luminosity distance, we infer that SN CLO12Car was approx. 1.0 +/- 0.2 mag brighter than field SNe Ia at a similar redshift and ascribe this to gravitational lens magnification. Similarly, SN CLN12Did is approx. 0.2 +/- 0.2 mag brighter than field SNe Ia. We derive independent estimates of the predicted magnification from CLASH strong+weak-lensing maps of the clusters (in magnitude units, 2.5 log10 µ): 0.83 +/- 0.16 mag for SN CLO12Car, 0.28 +/- 0.08 mag for SN CLN12Did, and 0.43 +/- 0.11 mag for SN CLA11Tib. The two SNe Ia provide a new test of the cluster lens model predictions: we find that the magnifications based on the SN Ia brightness and those predicted by the lens maps are consistent. Our results herald the promise of future observations of samples of cluster-lensed SNe Ia (from the ground or space) to help illuminate the dark-matter distribution in clusters of galaxies, through the direct determination of absolute magnifications.
NASA Astrophysics Data System (ADS)
Kirk, D.; Omori, Y.; Benoit-Lévy, A.; Cawthon, R.; Chang, C.; Larsen, P.; Amara, A.; Bacon, D.; Crawford, T. M.; Dodelson, S.; Fosalba, P.; Giannantonio, T.; Holder, G.; Jain, B.; Kacprzak, T.; Lahav, O.; MacCrann, N.; Nicola, A.; Refregier, A.; Sheldon, E.; Story, K. T.; Troxel, M. A.; Vieira, J. D.; Vikram, V.; Zuntz, J.; Abbott, T. M. C.; Abdalla, F. B.; Becker, M. R.; Benson, B. A.; Bernstein, G. M.; Bernstein, R. A.; Bleem, L. E.; Bonnett, C.; Bridle, S. L.; Brooks, D.; Buckley-Geer, E.; Burke, D. L.; Capozzi, D.; Carlstrom, J. E.; Rosell, A. Carnero; Kind, M. Carrasco; Carretero, J.; Crocce, M.; Cunha, C. E.; D'Andrea, C. B.; da Costa, L. N.; Desai, S.; Diehl, H. T.; Dietrich, J. P.; Doel, P.; Eifler, T. F.; Evrard, A. E.; Flaugher, B.; Frieman, J.; Gerdes, D. W.; Goldstein, D. A.; Gruen, D.; Gruendl, R. A.; Honscheid, K.; James, D. J.; Jarvis, M.; Kent, S.; Kuehn, K.; Kuropatkin, N.; Lima, M.; March, M.; Martini, P.; Melchior, P.; Miller, C. J.; Miquel, R.; Nichol, R. C.; Ogando, R.; Plazas, A. A.; Reichardt, C. L.; Roodman, A.; Rozo, E.; Rykoff, E. S.; Sako, M.; Sanchez, E.; Scarpine, V.; Schubnell, M.; Sevilla-Noarbe, I.; Simard, G.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thomas, D.; Wechsler, R. H.; Weller, J.
2016-03-01
We measure the cross-correlation between weak lensing of galaxy images and of the cosmic microwave background (CMB). The effects of gravitational lensing on different sources will be correlated if the lensing is caused by the same mass fluctuations. We use galaxy shape measurements from 139 deg2 of the Dark Energy Survey (DES) Science Verification data and overlapping CMB lensing from the South Pole Telescope (SPT) and Planck. The DES source galaxies have a median redshift of zmed ˜ 0.7, while the CMB lensing kernel is broad and peaks at z ˜ 2. The resulting cross-correlation is maximally sensitive to mass fluctuations at z ˜ 0.44. Assuming the Planck 2015 best-fit cosmology, the amplitude of the DESSPT cross-power is found to be ASPT = 0.88 ± 0.30 and that from DES×Planck to be A_{Planck} = 0.86 ± 0.39, where A = 1 corresponds to the theoretical prediction. These are consistent with the expected signal and correspond to significances of 2.9σ and 2.2σ respectively. We demonstrate that our results are robust to a number of important systematic effects including the shear measurement method, estimator choice, photo-z uncertainty and CMB lensing systematics. We calculate a value of A = 1.08 ± 0.36 for DES×SPT when we correct the observations with a simple IA model. With three measurements of this cross-correlation now existing in the literature, there is not yet reliable evidence for any deviation from the expected LCDM level of cross-correlation. We provide forecasts for the expected signal-to-noise of the combination of the five-year DES survey and SPT-3G.
GLAMER - II. Multiple-plane gravitational lensing
NASA Astrophysics Data System (ADS)
Petkova, Margarita; Metcalf, R. Benton; Giocoli, Carlo
2014-12-01
We present an extension to multiple planes of the gravitational lensing code GLAMER. The method entails projecting the mass in the observed light-cone on to a discrete number of lens planes and inverse ray-shooting from the image to the source plane. The mass on each plane can be represented as haloes, simulation particles, a projected mass map extracted form a numerical simulation or any combination of these. The image finding is done in a source-oriented fashion, where only regions of interest are iteratively refined on an initially coarse image plane grid. The calculations are performed in parallel on shared memory machines. The code is able to handle different types of analytic haloes (NFW, NSIE, power law, etc.), haloes extracted from numerical simulations and clusters constructed from semi-analytic models (MOKA). Likewise, there are several different options for modelling the source(s) which can be distributed throughout the light-cone. The distribution of matter in the light-cone can be either taken from a pre-existing N-body numerical simulations, from halo catalogues, or are generated from an analytic mass function. We present several tests of the code and demonstrate some of its applications such as generating mock images of galaxy and galaxy cluster lenses.
Neutrino halos in clusters of galaxies and their weak lensing signature
Villaescusa-Navarro, Francisco; Peña-Garay, Carlos; Miralda-Escudé, Jordi; Quilis, Vicent E-mail: miralda@icc.ub.es E-mail: vicent.quilis@uv.es
2011-06-01
We study whether non-linear gravitational effects of relic neutrinos on the development of clustering and large-scale structure may be observable by weak gravitational lensing. We compute the density profile of relic massive neutrinos in a spherical model of a cluster of galaxies, for several neutrino mass schemes and cluster masses. Relic neutrinos add a small perturbation to the mass profile, making it more extended in the outer parts. In principle, this non-linear neutrino perturbation is detectable in an all-sky weak lensing survey such as EUCLID by averaging the shear profile of a large fraction of the visible massive clusters in the universe, or from its signature in the general weak lensing power spectrum or its cross-spectrum with galaxies. However, correctly modeling the distribution of mass in baryons and cold dark matter and suppressing any systematic errors to the accuracy required for detecting this neutrino perturbation is severely challenging.
Extreme value statistics of weak lensing shear peak counts
NASA Astrophysics Data System (ADS)
Reischke, R.; Maturi, M.; Bartelmann, M.
2016-02-01
The statistics of peaks in weak gravitational lensing maps is a promising technique to constrain cosmological parameters in present and future surveys. Here we investigate its power when using general extreme value statistics which is very sensitive to the exponential tail of the halo mass function. To this end, we use an analytic method to quantify the number of weak lensing peaks caused by galaxy clusters, large-scale structures and observational noise. Doing so, we further improve the method in the regime of high signal-to-noise ratios dominated by non-linear structures by accounting for the embedding of those counts into the surrounding shear caused by large-scale structures. We derive the extreme value and order statistics for both overdensities (positive peaks) and underdensities (negative peaks) and provide an optimized criterion to split a wide field survey into subfields in order to sample the distribution of extreme values such that the expected objects causing the largest signals are mostly due to galaxy clusters. We find good agreement of our model predictions with a ray-tracing N-body simulation. For a Euclid-like survey, we find tight constraints on σ8 and Ωm with relative uncertainties of ˜10-3. In contrast, the equation of state parameter w0 can be constrained only with a 10 per cent level, and wa is out of reach even if we include redshift information.
The probability distribution of ellipticity: implications for weak lensing measurement
NASA Astrophysics Data System (ADS)
Viola, Massimo
2014-05-01
The weak lensing effect generates spin-2 distortions, referred to as shear, on the observable shape of distant galaxies, induced by intervening gravitational tidal fields. Traditionally, the spin-2 distortion in the light distribution of distant galaxies is measured in terms of a galaxy ellipticity. This is a very good unbiased estimator of the shear field in the limit that a galaxy is measured at infinite signal-to-noise. However, the ellipticity is always defined as a ratio between two quantities (for example, between the polarisation and measurement of the galaxy size, or between the semi-major and semi-minor axis of the galaxy) and therefore requires some non-linear combination of the image pixels. This means, in any realistic case, this would lead to biases in the measurement of the shear (and hence in the cosmological parameters) whenever noise is present in the image. This type of bias can be understood from the particular shape of the 2D probability distribution of the ellipticity of an object measured from data. Moreover this probability distribution can be used to explore strategies for calibration of noise biases in present and future weak lensing surveys (e.g. KiDS, DES, HSC,Euclid, LSST...)
Gravitational lensing with three-dimensional ray tracing
NASA Astrophysics Data System (ADS)
Killedar, M.; Lasky, P. D.; Lewis, G. F.; Fluke, C. J.
2012-02-01
High-redshift sources suffer from magnification or demagnification due to weak gravitational lensing by large-scale structure. One consequence of this is that the distance-redshift relation, in wide use for cosmological tests, suffers lensing-induced scatter which can be quantified by the magnification probability distribution. Predicting this distribution generally requires a method for ray tracing through cosmological N-body simulations. However, standard methods tend to apply the multiple-thin-lens approximation. In an effort to quantify the accuracy of these methods, we develop an innovative code that performs ray tracing without the use of this approximation. The efficiency and accuracy of this computationally challenging approach can be improved by careful choices of numerical parameters; therefore, the results are analysed for the behaviour of the ray-tracing code in the vicinity of Schwarzschild and Navarro-Frenk-White lenses. Preliminary comparisons are drawn with the multiple-lens-plane ray-bundle method in the context of cosmological mass distributions for a source redshift of zs= 0.5. Research undertaken as part of the Commonwealth Cosmology Initiative (CCI: ), an international collaboration supported by the Australian Research Council (ARC).
Weak lensing with sizes, magnitudes and shapes
NASA Astrophysics Data System (ADS)
Alsing, Justin; Kirk, Donnacha; Heavens, Alan; Jaffe, Andrew H.
2015-09-01
Weak lensing can be observed through a number of effects on the images of distant galaxies; their shapes are sheared, sizes and fluxes (magnitudes) are magnified and positions on the sky are modified by the lensing field. Galaxy shapes probe the shear field whilst size, magnitude and number density probe the convergence field. Both contain cosmological information. In this paper, we are concerned with the magnification of sizes and magnitudes of individual galaxies as a probe of cosmic convergence. We develop a Bayesian approach for inferring the convergence field from measured sizes, magnitudes and redshifts and demonstrate that this inference requires detailed knowledge of the joint distribution of intrinsic sizes and magnitudes. We build a simple parametrized model for the size-magnitude distribution and estimate this distribution for CFHTLenS galaxies. In light of the measured distribution, we show that the typical dispersion on convergence estimation is 0.8, compared to 0.38 for shear. We discuss the possibility of physical systematics for magnification (similar to intrinsic alignments for shear) and compute the expected gains in the dark energy figure-of-merit (FoM) from combining magnification with shear for different scenarios regarding systematics: accounting for intrinsic alignments but no systematics for magnification, including magnification could improve the FoM by up to a factor of 2.5, whilst when accounting for physical systematics in both shear and magnification we anticipate a gain between 25 and 65 per cent. The fact that shear and magnification are subject to different systematics makes magnification an attractive complement to any cosmic shear analysis.
Weak lensing goes bananas: what flexion really measures
NASA Astrophysics Data System (ADS)
Schneider, P.; Er, X.
2008-07-01
In weak gravitational lensing, the image distortion caused by shear measures the projected tidal gravitational field of the deflecting mass distribution. To lowest order, the shear is proportional to the mean image ellipticity. If the image sizes are not small compared to the scale over which the shear varies, higher-order distortions occur, called flexion. For ordinary weak lensing, the observable quantity is not the shear, but the reduced shear, owing to the mass-sheet degeneracy. Likewise, the flexion itself is unobservable. Instead, higher-order image distortions measure the reduced flexion, i.e., derivatives of the reduced shear. We derive the corresponding lens equation in terms of the reduced flexion and calculate the resulting relation between brightness moments of source and image. Assuming an isotropic distribution of source orientations, estimates for the reduced shear and flexion are obtained and then tested with simulations. In particular, the presence of flexion affects the determination of the reduced shear. The results of these simulations yield the amount of bias of the estimators as a function of the shear and flexion. We point out and quantify a fundamental limitation of the flexion formalism in terms of the product of reduced flexion and source size. If this product increases above the derived threshold, multiple images of the source are formed locally, and the formalism breaks down. Finally, we show how a general (reduced) flexion field can be decomposed into its four components. Two of them are due to a shear field, carrying an E- and B-mode in general. The other two components do not correspond to a shear field, and they can also be split up into corresponding E- and B-modes.
Gravitational Lenses and the Structure and Evolution of Galaxies
NASA Technical Reports Server (NTRS)
Kockanek, Christopher; Oliversen, Ronald J. (Technical Monitor)
2002-01-01
This grant has supported papers which present a new direction in the theory and interpretation of gravitational lenses. During the second year we have focused more closely on the relationship of baryons and dark matter.
Cosmological constraints from Subaru weak lensing cluster counts
NASA Astrophysics Data System (ADS)
Hamana, Takashi; Sakurai, Junya; Koike, Michitaro; Miller, Lance
2015-06-01
We present results of weak lensing cluster counts obtained from 11-degree2 Subaru/SuprimeCam data. Although the area is much smaller than previous work dealing with weak lensing peak statistics, the number density of galaxies usable for weak lensing analysis is about twice as large. The higher galaxy number density reduces the noise in the weak lensing mass maps, and thus increases the signal-to-noise ratio (S/N) of peaks of the lensing signal due to massive clusters. This enables us to construct a weak lensing selected cluster sample by adopting a high threshold S/N, such that the contamination rate due to false signals is small. We find six peaks with S/N > 5. For all the peaks, previously identified clusters of galaxies are matched within a separation of 1', demonstrating good correspondence between the peaks and clusters of galaxies. We evaluate the statistical error in the weak lensing cluster counts using mock weak lensing data generated from full-sky ray-tracing simulations, and find Npeak = 6 3.1 in an effective area of 9.0 degree2. We compare the measured weak lensing cluster counts with the theoretical model prediction based on halo models and place the constraint on the ?m-?8 plane which is found to be consistent with currently standard ?CDM models. It is demonstrated that the weak lensing cluster counts can place a unique constraint on the ?8-c0 plane, where c0 is the normalization of the dark matter halo mass-concentration relationship. Finally we discuss prospects for ongoing/future wide field optical galaxy surveys.
What is Gravitational Lensing?(LBNL Summer Lecture Series)
Alexie, Leauthaud; Reiko, Nakajima [Berkeley Center for Cosmological Physics, Berkely, California, United States
2010-01-08
July 28, 2009 Berkeley Lab summer lecture: Gravitational lensing is explained by Einstein's general theory of relativity: galaxies and clusters of galaxies, which are very massive objects, act on spacetime by causing it to become curved. Alexie Leauthaud and Reiko Nakajima, astrophysicists with the Berkeley Center for Cosmological Physics, will discuss how scientists use gravitational lensing to investigate the nature of dark energy and dark matter in the universe.
What is Gravitational Lensing? (LBNL Summer Lecture Series)
Leauthaud, Alexie; Nakajima, Reiko
2009-07-28
Summer Lecture Series 2009: Gravitational lensing is explained by Einstein's general theory of relativity: galaxies and clusters of galaxies, which are very massive objects, act on spacetime by causing it to become curved. Alexie Leauthaud and Reiko Nakajima, astrophysicists with the Berkeley Center for Cosmological Physics, will discuss how scientists use gravitational lensing to investigate the nature of dark energy and dark matter in the universe.
What is Gravitational Lensing? (LBNL Summer Lecture Series)
Leauthaud, Alexie; Nakajima, Reiko [Berkeley Center for Cosmological Physics
2011-04-28
Summer Lecture Series 2009: Gravitational lensing is explained by Einstein's general theory of relativity: galaxies and clusters of galaxies, which are very massive objects, act on spacetime by causing it to become curved. Alexie Leauthaud and Reiko Nakajima, astrophysicists with the Berkeley Center for Cosmological Physics, will discuss how scientists use gravitational lensing to investigate the nature of dark energy and dark matter in the universe.
Early Weak Lensing Results From The Dark Energy Survey
NASA Astrophysics Data System (ADS)
Maccrann, Niall; Dark Energy Survey Collaboration
2016-01-01
I present the early weak lensing results, including cosmological constraints, from the Dark Energy Survey (DES). Although only 3% of the final survey, DES Science Verification data already constituted a competitive weak lensing dataset, and the thoroughly tested shear catalogs allowed a number of interesting science analyses including cosmology from cosmic shear, mass mapping, combining lensing with galaxy clustering and combining with CMB lensing. I will summarize the main results of these analyses, discuss common systematic effects which need to be addressed to take advantage of the greater statistical power of main survey data, and outline some of improvements at various stages of the analysis pipeline that aim to do this.
NASA Astrophysics Data System (ADS)
Cao, Zhoujian; Li, Li-Fang; Wang, Yan
2014-09-01
The gravitational lensing effect is important to the detection of electromagnetic signals in astrophysics. The gravitational wave lensing effect has also been found significant to gravitational wave detection in the past decade. Recent analysis shows that the lensing events for advanced detectors could be quite plausible. The black holes in our Milky Way Galaxy may play the role of lens objects. These facts motivate us to study the lensing effects on gravitational wave signals for advanced detectors. Taking advanced LIGO and Einstein Telescope for examples, we investigate the lensing effects on the parameter extraction of gravitational wave signals. Using the Markov chain Monte Carlo simulation together with matched filtering methods, we find that the lensing effect for a lens object with small mass is negligible. But when the mass of the lens object increases to larger than 1000M⊙ the lensing effect becomes important. Using the template without lensing corrections would result in loss of signal detections. In contrast if we consider templates with lensing effects, the lensed signal may provide much information about the lens black hole. These facts may give us a new way to determine the parameters of the lensing object. For example, this kind of signal may also help us estimate the mass and the distance of the supermassive black hole hosted at the center of our Galaxy.
Magnification relations in gravitational lensing via multidimensional residue integrals
Dalal, Neal; Rabin, Jeffrey M.
2001-04-01
We investigate the so-called magnification relations of gravitational lensing models. We show that multidimensional residue integrals provide a simple explanation for the existence of these relations, and an effective method of computation. We illustrate the method with several examples, thereby deriving new magnification relations for galaxy lens models and microlensing (point mass lensing).
Gravitational lensing by clusters of galaxies - Constraining the mass distribution
NASA Technical Reports Server (NTRS)
Miralda-Escude, Jordi
1991-01-01
The possibility of placing constraints on the mass distribution of a cluster of galaxies by analyzing the cluster's gravitational lensing effect on the images of more distant galaxies is investigated theoretically in the limit of weak distortion. The steps in the proposed analysis are examined in detail, and it is concluded that detectable distortion can be produced by clusters with line-of-sight velocity dispersions of over 500 km/sec. Hence it should be possible to determine (1) the cluster center position (with accuracy equal to the mean separation of the background galaxies), (2) the cluster-potential quadrupole moment (to within about 20 percent of the total potential if velocity dispersion is 1000 km/sec), and (3) the power law for the outer-cluster density profile (if enough background galaxies in the surrounding region are observed).
Influence of the cosmological constant on gravitational lensing in small systems
Sereno, Mauro
2008-02-15
The cosmological constant {lambda} affects gravitational lensing phenomena. The contribution of {lambda} to the observable angular positions of multiple images and to their amplification and time delay is here computed through a study of the weak deflection limit of the equations of motion in the Schwarzschild-de Sitter metric. Because of {lambda} the unresolved images are slightly demagnified, the radius of the Einstein ring decreases, and the time delay increases. The effect is however negligible for near lenses. In the case of a null cosmological constant, we provide some updated results on lensing by a Schwarzschild black hole.
Combining weak-lensing tomography and spectroscopic redshift surveys
Cai, Yan -Chuan; Bernstein, Gary
2012-05-11
Redshift space distortion (RSD) is a powerful way of measuring the growth of structure and testing General Relativity, but it is limited by cosmic variance and the degeneracy between galaxy bias b and the growth rate factor f. The cross-correlation of lensing shear with the galaxy density field can in principle measure b in a manner free from cosmic variance limits, breaking the f-b degeneracy and allowing inference of the matter power spectrum from the galaxy survey. We analyze the growth constraints from a realistic tomographic weak lensing photo-z survey combined with a spectroscopic galaxy redshift survey over the samemore » sky area. For sky coverage fsky = 0.5, analysis of the transverse modes measures b to 2-3% accuracy per Δz = 0.1 bin at z < 1 when ~10 galaxies arcmin–2 are measured in the lensing survey and all halos with M > Mmin = 1013h–1M⊙ have spectra. For the gravitational growth parameter parameter γ (f = Ωγm), combining the lensing information with RSD analysis of non-transverse modes yields accuracy σ(γ) ≈ 0.01. Adding lensing information to the RSD survey improves \\sigma(\\gamma) by an amount equivalent to a 3x (10x) increase in RSD survey area when the spectroscopic survey extends down to halo mass 1013.5 (1014) h–1 M⊙. We also find that the σ(γ) of overlapping surveys is equivalent to that of surveys 1.5-2 times larger if they are separated on the sky. This gain is greatest when the spectroscopic mass threshold is 1013 -1014 h–1 M⊙, similar to LRG surveys. The gain of overlapping surveys is reduced for very deep or very shallow spectroscopic surveys, but any practical surveys are more powerful when overlapped than when separated. As a result, the gain of overlapped surveys is larger in the case when the primordial power spectrum normalization is uncertain by > 0.5%.« less
Combining weak-lensing tomography and spectroscopic redshift surveys
Cai, Yan -Chuan; Bernstein, Gary
2012-05-11
Redshift space distortion (RSD) is a powerful way of measuring the growth of structure and testing General Relativity, but it is limited by cosmic variance and the degeneracy between galaxy bias b and the growth rate factor f. The cross-correlation of lensing shear with the galaxy density field can in principle measure b in a manner free from cosmic variance limits, breaking the f-b degeneracy and allowing inference of the matter power spectrum from the galaxy survey. We analyze the growth constraints from a realistic tomographic weak lensing photo-z survey combined with a spectroscopic galaxy redshift survey over the same sky area. For sky coverage f_{sky} = 0.5, analysis of the transverse modes measures b to 2-3% accuracy per Δz = 0.1 bin at z < 1 when ~10 galaxies arcmin^{–2} are measured in the lensing survey and all halos with M > M_{min} = 10^{13}h^{–1}M_{⊙} have spectra. For the gravitational growth parameter parameter γ (f = Ω^{γ}_{m}), combining the lensing information with RSD analysis of non-transverse modes yields accuracy σ(γ) ≈ 0.01. Adding lensing information to the RSD survey improves \\sigma(\\gamma) by an amount equivalent to a 3x (10x) increase in RSD survey area when the spectroscopic survey extends down to halo mass 10^{13.5} (10^{14}) h^{–1} M_{⊙}. We also find that the σ(γ) of overlapping surveys is equivalent to that of surveys 1.5-2 times larger if they are separated on the sky. This gain is greatest when the spectroscopic mass threshold is 10^{13} -10^{14} h^{–1} M_{⊙}, similar to LRG surveys. The gain of overlapping surveys is reduced for very deep or very shallow spectroscopic surveys, but any practical surveys are more powerful when overlapped than when separated. As a result, the gain of overlapped surveys is larger in the case when the primordial power spectrum normalization is uncertain by > 0.5%.
Gravitational Lenses and the Structure and Evolution of Galaxies
NASA Technical Reports Server (NTRS)
Kochanek, Christopher
2003-01-01
The grant has supported the completion of 16 papers and 4 conference proceedings to date. During the first year of the project we completed five papers, each of which represents a new direction in the theory and interpretation of gravitational lenses. In the first paper, "The Importance of Einstein Rings", we developed the first theory for the formation and structure of the Einstein rings formed by lensing extended sources like the host galaxies of quasar and radio sources. We applied the theory to three lenses with lensed host galaxies. For the time delay lens PG 1115+080 we found that the structure of the Einstein ring ruled out models of the gravitational potential which permitted a large Hubble constant (70 km/s Mpc). In the second paper, :Cusped Mass Models Of Gravitational Lenses", we introduced a new class of lens models where the central density is characterized by a cusp ( rho proportional to tau(sup -gamma), 1 less than gamma less than 2) as in most modern models and theories of galaxies rather than a finite core radius. In the third paper, "Global Probes of the Impact of Baryons on Dark Matter Halos", we made the first globally consistent models for the separation distribution of gravitational lenses including both galaxy and cluster lenses. We show that the key physics for the origin of the sharp separation cutoff in the separation distribution near 3 arc sec is the effect of the cooling baryons in galaxies on the density structure of the system.
Strong Gravitational Lensing in a Brane-World Black Hole
NASA Astrophysics Data System (ADS)
Li, GuoPing; Cao, Biao; Feng, Zhongwen; Zu, Xiaotao
2015-09-01
Adopting the strong field limit approach, we investigated the strong gravitational lensing in a Brane-World black hole, which means that the strong field limit coefficients and the deflection angle in this gravitational field are obtained. With this result, it can be said with certainly that the strong gravitational lensing is related to the metric of gravitational fields closely, the cosmology parameter ? and the dark matter parameter ? come from the Brane-World black hole exerts a great influence on it. Comparing with the Schwarzschild-AdS spacetime and the Schwarzschild-XCMD spacetime, the parameters ?, ? of black holes have the similar effects on the gravitational lensing. In some way, we infer that the real gravitational fields in our universe can be described by this metric, so the results of the strong gravitational lensing in this spacetime will be more reasonable for us to observe. Finally, it has to be noticed that the influence which the parameters ?, ? exerted on the main observable quantities of this gravitational field is discussed.
Constraints on cosmological models from strong gravitational lensing systems
Cao, Shuo; Pan, Yu; Zhu, Zong-Hong; Biesiada, Marek; Godlowski, Wlodzimierz E-mail: panyu@cqupt.edu.cn E-mail: godlowski@uni.opole.pl
2012-03-01
Strong lensing has developed into an important astrophysical tool for probing both cosmology and galaxies (their structure, formation, and evolution). Using the gravitational lensing theory and cluster mass distribution model, we try to collect a relatively complete observational data concerning the Hubble constant independent ratio between two angular diameter distances D{sub ds}/D{sub s} from various large systematic gravitational lens surveys and lensing by galaxy clusters combined with X-ray observations, and check the possibility to use it in the future as complementary to other cosmological probes. On one hand, strongly gravitationally lensed quasar-galaxy systems create such a new opportunity by combining stellar kinematics (central velocity dispersion measurements) with lensing geometry (Einstein radius determination from position of images). We apply such a method to a combined gravitational lens data set including 70 data points from Sloan Lens ACS (SLACS) and Lens Structure and Dynamics survey (LSD). On the other hand, a new sample of 10 lensing galaxy clusters with redshifts ranging from 0.1 to 0.6 carefully selected from strong gravitational lensing systems with both X-ray satellite observations and optical giant luminous arcs, is also used to constrain three dark energy models (ΛCDM, constant w and CPL) under a flat universe assumption. For the full sample (n = 80) and the restricted sample (n = 46) including 36 two-image lenses and 10 strong lensing arcs, we obtain relatively good fitting values of basic cosmological parameters, which generally agree with the results already known in the literature. This results encourages further development of this method and its use on larger samples obtained in the future.
Constraints on cosmological models from strong gravitational lensing systems
NASA Astrophysics Data System (ADS)
Cao, Shuo; Pan, Yu; Biesiada, Marek; Godlowski, Wlodzimierz; Zhu, Zong-Hong
2012-03-01
Strong lensing has developed into an important astrophysical tool for probing both cosmology and galaxies (their structure, formation, and evolution). Using the gravitational lensing theory and cluster mass distribution model, we try to collect a relatively complete observational data concerning the Hubble constant independent ratio between two angular diameter distances Dds/Ds from various large systematic gravitational lens surveys and lensing by galaxy clusters combined with X-ray observations, and check the possibility to use it in the future as complementary to other cosmological probes. On one hand, strongly gravitationally lensed quasar-galaxy systems create such a new opportunity by combining stellar kinematics (central velocity dispersion measurements) with lensing geometry (Einstein radius determination from position of images). We apply such a method to a combined gravitational lens data set including 70 data points from Sloan Lens ACS (SLACS) and Lens Structure and Dynamics survey (LSD). On the other hand, a new sample of 10 lensing galaxy clusters with redshifts ranging from 0.1 to 0.6 carefully selected from strong gravitational lensing systems with both X-ray satellite observations and optical giant luminous arcs, is also used to constrain three dark energy models (ΛCDM, constant w and CPL) under a flat universe assumption. For the full sample (n = 80) and the restricted sample (n = 46) including 36 two-image lenses and 10 strong lensing arcs, we obtain relatively good fitting values of basic cosmological parameters, which generally agree with the results already known in the literature. This results encourages further development of this method and its use on larger samples obtained in the future.
Gravitational lensing by black holes: The case of Sgr A*
Bozza, V.
2014-01-14
The strong gravitational fields created by black holes dramatically affect the propagation of photons by bending their trajectories. Gravitational lensing thus stands as the main source of information on the space-time structure in such extreme regimes. We will review the theory and phenomenology of gravitational lensing by black holes, with the generation of higher order images and giant caustics by rotating black holes. We will then focus on Sgr A*, the black hole at the center of the Milky Way, for which next-to-come technology will be able to reach resolutions of the order of the Schwarzschild radius and ultimately test the existence of an event horizon.
Wardlow, Julie L.; Cooray, Asantha; De Bernardis, Francesco; Calanog, J.; Amblard, A.; Arumugam, V.; Aussel, H.; Bethermin, M.; Blundell, R.; Bussmann, R. S.; Bock, J.; Bridge, C.; Carpenter, J. M.; Boselli, A.; Buat, V.; Burgarella, D.; Cabrera-Lavers, A.; Castro-Rodriguez, N.; Casey, C. M.; and others
2013-01-01
We present a list of 13 candidate gravitationally lensed submillimeter galaxies (SMGs) from 95 deg{sup 2} of the Herschel Multi-tiered Extragalactic Survey, a surface density of 0.14 {+-} 0.04 deg{sup -2}. The selected sources have 500 {mu}m flux densities (S {sub 500}) greater than 100 mJy. Gravitational lensing is confirmed by follow-up observations in 9 of the 13 systems (70%), and the lensing status of the four remaining sources is undetermined. We also present a supplementary sample of 29 (0.31 {+-} 0.06 deg{sup -2}) gravitationally lensed SMG candidates with S {sub 500} = 80-100 mJy, which are expected to contain a higher fraction of interlopers than the primary candidates. The number counts of the candidate lensed galaxies are consistent with a simple statistical model of the lensing rate, which uses a foreground matter distribution, the intrinsic SMG number counts, and an assumed SMG redshift distribution. The model predicts that 32%-74% of our S {sub 500} {>=} 100 mJy candidates are strongly gravitationally lensed ({mu} {>=} 2), with the brightest sources being the most robust; this is consistent with the observational data. Our statistical model also predicts that, on average, lensed galaxies with S {sub 500} = 100 mJy are magnified by factors of {approx}9, with apparently brighter galaxies having progressively higher average magnification, due to the shape of the intrinsic number counts. 65% of the sources are expected to have intrinsic 500 {mu}m flux densities less than 30 mJy. Thus, samples of strongly gravitationally lensed SMGs, such as those presented here, probe below the nominal Herschel detection limit at 500 {mu}m. They are good targets for the detailed study of the physical conditions in distant dusty, star-forming galaxies, due to the lensing magnification, which can lead to spatial resolutions of {approx}0.''01 in the source plane.
Data mining for gravitationally lensed quasars
NASA Astrophysics Data System (ADS)
Agnello, Adriano; Kelly, Brandon C.; Treu, Tommaso; Marshall, Philip J.
2015-04-01
Gravitationally lensed quasars are brighter than their unlensed counterparts and produce images with distinctive morphological signatures. Past searches and target-selection algorithms, in particular the Sloan Quasar Lens Search (SQLS), have relied on basic morphological criteria, which were applied to samples of bright, spectroscopically confirmed quasars. The SQLS techniques are not sufficient for searching into new surveys (e.g. DES, PS1, LSST), because spectroscopic information is not readily available and the large data volume requires higher purity in target/candidate selection. We carry out a systematic exploration of machine-learning techniques and demonstrate that a two-step strategy can be highly effective. In the first step, we use catalogue-level information (griz+WISE magnitudes, second moments) to pre-select targets, using artificial neural networks. The accepted targets are then inspected with pixel-by-pixel pattern recognition algorithms (gradient-boosted trees), to form a final set of candidates. The results from this procedure can be used to further refine the simpler SQLS algorithms, with a twofold (or threefold) gain in purity and the same (or 80 per cent) completeness at target-selection stage, or a purity of 70 per cent and a completeness of 60 per cent after the candidate-selection step. Simpler photometric searches in griz+WISE based on colour cuts would provide samples with 7 per cent purity or less. Our technique is extremely fast, as a list of candidates can be obtained from a Stage III experiment (e.g. DES catalogue/data base) in a few CPU hours. The techniques are easily extendable to Stage IV experiments like LSST with the addition of time domain information.
Three gravitationally lensed supernovae behind clash galaxy clusters
Patel, Brandon; McCully, Curtis; Jha, Saurabh W.; Holoien, Thomas W.-S.; Rodney, Steven A.; Jones, David O.; Graur, Or; Riess, Adam G.; Merten, Julian; Zitrin, Adi; Matheson, Thomas; Sako, Masao; Postman, Marc; Coe, Dan; Bradley, Larry; Bartelmann, Matthias; Balestra, Italo; Benítez, Narciso; Bouwens, Rychard; Broadhurst, Tom; and others
2014-05-01
We report observations of three gravitationally lensed supernovae (SNe) in the Cluster Lensing And Supernova survey with Hubble (CLASH) Multi-Cycle Treasury program. These objects, SN CLO12Car (z = 1.28), SN CLN12Did (z = 0.85), and SN CLA11Tib (z = 1.14), are located behind three different clusters, MACSJ1720.2+3536 (z = 0.391), RXJ1532.9+3021 (z = 0.345), and A383 (z = 0.187), respectively. Each SN was detected in Hubble Space Telescope optical and infrared images. Based on photometric classification, we find that SNe CLO12Car and CLN12Did are likely to be Type Ia supernovae (SNe Ia), while the classification of SN CLA11Tib is inconclusive. Using multi-color light-curve fits to determine a standardized SN Ia luminosity distance, we infer that SN CLO12Car was ∼1.0 ± 0.2 mag brighter than field SNe Ia at a similar redshift and ascribe this to gravitational lens magnification. Similarly, SN CLN12Did is ∼0.2 ± 0.2 mag brighter than field SNe Ia. We derive independent estimates of the predicted magnification from CLASH strong+weak-lensing maps of the clusters (in magnitude units, 2.5 log{sub 10}μ): 0.83 ± 0.16 mag for SN CLO12Car, 0.28 ± 0.08 mag for SN CLN12Did, and 0.43 ± 0.11 mag for SN CLA11Tib. The two SNe Ia provide a new test of the cluster lens model predictions: we find that the magnifications based on the SN Ia brightness and those predicted by the lens maps are consistent. Our results herald the promise of future observations of samples of cluster-lensed SNe Ia (from the ground or space) to help illuminate the dark-matter distribution in clusters of galaxies, through the direct determination of absolute magnifications.
Is There a Quad Problem Among Pptical Gravitational Lenses?
Oguri, Masamune
2007-06-06
Most of optical gravitational lenses recently discovered in the Sloan Digital Sky Survey Quasar Lens Search (SQLS) have two-images rather than four images, in marked contrast to radio lenses for which the fraction of four-image lenses (quad fraction) is quite high. We revisit the quad fraction among optical lenses by taking the selection function of the SQLS into account. We find that the current observed quad fraction in the SQLS is indeed lower than, but consistent with, the prediction of our theoretical model. The low quad fraction among optical lenses, together with the high quad fraction among radio lenses, implies that the quasar optical luminosity function has a relatively shallow faint end slope.
Kirk, D.; et al.
2015-12-14
We measure the cross-correlation between weak lensing of galaxy images and of the cosmic microwave background (CMB). The effects of gravitational lensing on different sources will be correlated if the lensing is caused by the same mass fluctuations. We use galaxy shape measurements from 139 deg$^{2}$ of the Dark Energy Survey (DES) Science Verification data and overlapping CMB lensing from the South Pole Telescope (SPT) and Planck. The DES source galaxies have a median redshift of $z_{\\rm med} {\\sim} 0.7$, while the CMB lensing kernel is broad and peaks at $z{\\sim}2$. The resulting cross-correlation is maximally sensitive to mass fluctuations at $z{\\sim}0.44$. Assuming the Planck 2015 best-fit cosmology, the amplitude of the DES$\\times$SPT cross-power is found to be $A = 0.88 \\pm 0.30$ and that from DES$\\times$Planck to be $A = 0.86 \\pm 0.39$, where $A=1$ corresponds to the theoretical prediction. These are consistent with the expected signal and correspond to significances of $2.9 \\sigma$ and $2.2 \\sigma$ respectively. We demonstrate that our results are robust to a number of important systematic effects including the shear measurement method, estimator choice, photometric redshift uncertainty and CMB lensing systematics. Significant intrinsic alignment of galaxy shapes would increase the cross-correlation signal inferred from the data; we calculate a value of $A = 1.08 \\pm 0.36$ for DES$\\times$SPT when we correct the observations with a simple IA model. With three measurements of this cross-correlation now existing in the literature, there is not yet reliable evidence for any deviation from the expected LCDM level of cross-correlation, given the size of the statistical uncertainties and the significant impact of systematic errors, particularly IAs. We provide forecasts for the expected signal-to-noise of the combination of the five-year DES survey and SPT-3G.
On the probability of magnification by cosmologically distributed gravitational lenses
NASA Technical Reports Server (NTRS)
Pei, Yichuan C.
1993-01-01
An analytical method for calculating the statistical properties of source magnification caused by gravitational lenses randomly distributed throughout the universe is presented. Two lenses are considered at different redshifts to show that such an assumption is a statistically adequate approximation. The derived general formulas are applied to point-mass lenses with both point and extended sources. Analytical results of the magnification probability for point sources are accurate to within 10 percent in comparison with the available numerical simulations to moderate redshifts of less than about 2. In terms of the flux conservation, the results are accurate to within 18 percent at a redshift of 6 with respect to the Dyer-Roeder model of a clumpy universe. It is concluded that the present formulas are adequate for statistical studies of magnification by random gravitational lenses on cosmological scales.
CFHTLenS tomographic weak lensing: quantifying accurate redshift distributions
NASA Astrophysics Data System (ADS)
Benjamin, Jonathan; Van Waerbeke, Ludovic; Heymans, Catherine; Kilbinger, Martin; Erben, Thomas; Hildebrandt, Hendrik; Hoekstra, Henk; Kitching, Thomas D.; Mellier, Yannick; Miller, Lance; Rowe, Barnaby; Schrabback, Tim; Simpson, Fergus; Coupon, Jean; Fu, Liping; Harnois-Draps, Joachim; Hudson, Michael J.; Kuijken, Konrad; Semboloni, Elisabetta; Vafaei, Sanaz; Velander, Malin
2013-05-01
The Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) comprises deep multicolour (u*g'r'i'z') photometry spanning 154 deg2, with accurate photometric redshifts and shape measurements. We demonstrate that the redshift probability distribution function summed over galaxies provides an accurate representation of the galaxy redshift distribution accounting for random and catastrophic errors for galaxies with best-fitting photometric redshifts zp < 1.3. We present cosmological constraints using tomographic weak gravitational lensing by large-scale structure. We use two broad redshift bins 0.5 < zp ? 0.85 and 0.85 < zp ? 1.3 free of intrinsic alignment contamination, and measure the shear correlation function on angular scales in the range 1-40 arcmin. We show that the problematic redshift scaling of the shear signal, found in previous Canada-France-Hawaii Telescope Legacy Survey data analyses, does not affect the CFHTLenS data. For a flat ? cold dark matter model and a fixed matter density ?m = 0.27, we find the normalization of the matter power spectrum ?8 = 0.771 0.041. When combined with cosmic microwave background data (Wilkinson Microwave Anisotropy Probe 7-year results), baryon acoustic oscillation data (BOSS) and a prior on the Hubble constant from the Hubble Space Telescope distance ladder, we find that CFHTLenS improves the precision of the fully marginalized parameter estimates by an average factor of 1.5-2. Combining our results with the above cosmological probes, we find ?m = 0.2762 0.0074 and ?8 = 0.802 0.013.
GREAT3: The Third Gravitational Lensing Accuracy Testing Challenge
NASA Astrophysics Data System (ADS)
Simet, Melanie; Mandelbaum, R.; Rowe, B.; Great3 Collaboration
2014-01-01
We describe the ongoing weak lensing community data challenge, GREAT3, and the associated open-source image simulation software, GalSim. The GREAT3 challenge tests the impact on weak lensing measurements of (a) realistic galaxy morphologies, (b) realistic uncertainty in the point-spread function estimation, and (c) the need to combine multiple exposures when estimating the galaxy shape. It includes simulated ground- and space-based data. The tests of realistic galaxy morphologies rely on a training set of galaxies from the Hubble Space Telescope, a subset of which has been publicly released for community use, with the remainder to be released at the end of the challenge. We describe some technical considerations for generating the challenge data and for testing weak lensing measurements with the next generation of weak lensing surveys, such as DES, HSC, KIDS, and Pan-STARRS.
Gravitational Lenses and the Structure and Evolution of Galaxies
NASA Technical Reports Server (NTRS)
Oliversen, Ronald J. (Technical Monitor); Kochanek, Christopher
2004-01-01
During the first year of the project we completed five papers, each of which represents a new direction in the theory and interpretation of gravitational lenses. In the first paper, The Importance of Einstein Rings, we developed the first theory for the formation and structure of the Einstein rings formed by lensing extended sources like the host galaxies of quasar and radio sources. In the second paper, Cusped Mass Models Of Gravitational Lenses, we introduced a new class of lens models. In the third paper, Global Probes of the Impact of Baryons on Dark Matter Halos, we made the first globally consistent models for the separation distribution of gravitational lenses including both galaxy and cluster lenses. The last two papers explore the properties of two lenses in detail. During the second year we have focused more closely on the relationship of baryons and dark matter. In the third year we have been further examining the relationship between baryons and dark matter. In the present year we extended our statistical analysis of lens mass distributions using a self-similar model for the halo mass distribution as compared to the luminous galaxy.
Massey, Richard; Hoekstra, Henk; Kitching, Thomas; Rhodes, Jason; Cropper, Mark; Amiaux, Jerome; Harvey, David; Mellier, Yannick; Meneghetti, Massimo; Miller, Lance; Paulin-Henriksson, Stephane; Pires, Sandrine; Scaramella, Roberto; Schrabback, Tim
2012-12-13
The first half of this paper explores the origin of systematic biases in the measurement of weak gravitational lensing. Compared to previous work, we expand the investigation of point spread function instability and fold in for the first time the effects of non-idealities in electronic imaging detectors and imperfect galaxy shape measurement algorithms. In addition, these now explain the additive A(ℓ) and multiplicative M(ℓ) systematics typically reported in current lensing measurements. We find that overall performance is driven by a product of a telescope/camera's absolute performance, and our knowledge about its performance.
Constraining the mass-concentration relation through weak lensing peak function
Mainini, R.; Romano, A. E-mail: anna.romano@oar.inaf.it
2014-08-01
Halo masses and concentrations have been studied extensively, by means of N-body simulations as well as observationally, during the last decade. Nevertheless, the exact form of the mass-concentration relation is still widely debated. One of the most promising method to estimate masses and concentrations relies on gravitational lensing from massive halos. Here we investigate the impact of the mass-concentration relation on halo peak abundance in weak lensing shear maps relying on the aperture mass method for peak detections. After providing a prescription to take into account the concentration dispersion (always neglected in previous works) in peak number counts predictions, we assess their power to constrain the mass-concentration relation by means of Fisher matrix technique. We find that, when combined with different cosmological probes, peak statistics information from near-future weak lensing surveys provides an interesting and complementary alternative method to lessen the long standing controversy about the mass-concentration relation.
Substructure in the Hubble Frontier Fields clusters from weak lensing flexion measurements
NASA Astrophysics Data System (ADS)
Rexroth, Markus
2015-08-01
Flexion is the second order weak gravitational lensing effect which is responsible for the arclike appearance of lensed sources. Its strong signal in the intermediate regime and the orthogonality to the shear field make flexion an ideal complement to today's strong and weak lensing measurements. Furthermore, its high sensitivity to local density peaks makes it a great tool for detecting substructure and increasing the resolution of mass maps. The strength of the Hubble Frontier Fields clusters and the high quality of the data make these objects a prime target for flexion measurements. We present an automated measurement pipeline and substructure constraints from its application to the clusters MACSJ0416.1-2403 and Abell 2744.
Polarization as an indicator of intrinsic alignment in radio weak lensing
NASA Astrophysics Data System (ADS)
Brown, Michael L.; Battye, Richard A.
2011-01-01
We propose a new technique for weak gravitational lensing in the radio band making use of polarization information. Since the orientation of a galaxys polarized emission is both unaffected by lensing and is related to the galaxys intrinsic orientation, it effectively provides information on the unlensed galaxy position angle. We derive a new weak-lensing estimator, which exploits this effect and makes full use of both the observed galaxy shapes and the estimates of the intrinsic position angles as provided by polarization. Our method has the potential both to reduce the effects of shot noise and to reduce to negligible levels, in a model-independent way, all effects of intrinsic galaxy alignments. We test our technique on simulated weak-lensing skies, including an intrinsic alignment contaminant consistent with recent observations, in three overlapping redshift bins. Adopting a standard weak-lensing analysis and ignoring intrinsic alignments results in biases of 5-10 per cent in the recovered power spectra and cosmological parameters. Applying our new estimator to one-tenth the number of galaxies used for the standard case, we recover both power spectra and the input cosmology with similar precision and with negligible residual bias. This remains true even in the presence of a substantial (astrophysical) scatter in the relationship between the observed orientation of the polarized emission and the intrinsic orientation. Assuming a reasonable polarization fraction for star-forming galaxies, and no cosmological conspiracy in the relationship between polarization direction and intrinsic morphology, our estimator should prove a valuable tool for weak-lensing analyses of forthcoming radio surveys, in particular, deep wide-field surveys with e-MERLIN, MeerKAT and ASKAP, and ultimately, definitive radio lensing surveys with the SKA.
Gravitational lensing shear by an exotic lens object with negative convergence or negative mass
NASA Astrophysics Data System (ADS)
Izumi, Koji; Hagiwara, Chisaki; Nakajima, Koki; Kitamura, Takao; Asada, Hideki
2013-07-01
Gravitational lens models with negative convergence (surface mass density projected onto the lens plane) inspired by modified gravity theories, exotic matter, and energy have been recently discussed in such a way that a static and spherically symmetric modified spacetime metric depends on the inverse distance to the power of positive n (n=1 for Schwarzschild metric, n=2 for Ellis wormhole) in the weak-field approximation [T. Kitamura, K. Nakajima, and H. Asada, Phys. Rev. D 87, 027501 (2013)], and it has been shown that demagnification of images could occur for n>1 lens models associated with exotic matter (and energy), though they cause the gravitational pull on light rays. The present paper considers gravitational lensing shear by the demagnifying lens models and other models such as negative-mass compact objects causing the gravitational repulsion on light rays like a concave lens. It is shown that images by the lens models for the gravitational pull are tangentially elongated, whereas those by the repulsive ones are radially distorted. This feature of lensed image shapes may be used for searching (or constraining) localized exotic matter or energy with gravitational lensing surveys. It is suggested also that an underdense region such as a cosmic void might produce radially elongated images of background galaxies rather than tangential ones.
Weak Lensing PSF Correction of Wide-field CCD Mosaic Images (SULI Paper)
Cevallos, Marissa; /Caltech /SLAC
2006-01-04
Gravitational lensing provides some of the most compelling evidence for the existence of dark matter. Dark matter on galaxy cluster scales can be mapped due to its weak gravitational lensing effect: a cluster mass distribution can be inferred from the net distortion of many thousands of faint background galaxies that it induces. Because atmospheric aberration and defects in the detector distort the apparent shape of celestial objects, it is of great importance to characterize accurately the point spread function (PSF) across an image. In this research, the PSF is studied in images from the Canada-France-Hawaii Telescope (CFHT), whose camera is divided into 12 CCD chips. Traditional weak lensing methodology involves averaging the PSF across the entire image: in this work we investigate the effects of measuring the PSF in each chip independently. This chip-by-chip analysis was found to reduce the strength of the correlation between star and galaxy shapes, and predicted more strongly the presence of known galaxy clusters in mass maps. These results suggest correcting the CFHT PSF on an individual chip basis significantly improves the accuracy of detecting weak lensing.
Scaling the universe: Gravitational lenses and the Hubble constant
Myers, Steven T.
1999-01-01
Gravitational lenses, besides being interesting in their own right, have been demonstrated to be suitable as “gravitational standard rulers” for the measurement of the rate of expansion of the Universe (Ho), as well as to constrain the values of the cosmological parameters such as Ωo and Λo that control the evolution of the volume of the Universe with cosmic time. PMID:10200245
Strong lensing of gravitational waves as seen by LISA.
Sereno, M; Sesana, A; Bleuler, A; Jetzer, Ph; Volonteri, M; Begelman, M C
2010-12-17
We discuss strong gravitational lensing of gravitational waves from the merging of massive black hole binaries in the context of the LISA mission. Detection of multiple events would provide invaluable information on competing theories of gravity, evolution and formation of structures and, possibly, constraints on H0 and other cosmological parameters. Most of the optical depth for lensing is provided by intervening massive galactic halos, for which wave optics effects are negligible. Probabilities to observe multiple events are sizable for a broad range of formation histories. For the most optimistic models, up to ? 4 multiple events with a signal to noise ratio ? 8 are expected in a 5-year mission. Chances are significant even for conservative models with either light (? 60%) or heavy (? 40%) seeds. Because of lensing amplification, some intrinsically too faint signals are brought over threshold (? 2 per year). PMID:21231571
Reverberation Mapping of a Gravitationally-lensed Quasar
NASA Astrophysics Data System (ADS)
Denney, Kelly D.; Courbin, Frederic; Kochanek, Christopher S.; MacLeod, Chelsea L.; Meylan, Georges; Morgan, Christopher W.; Mosquera, Ana; Moustakas, Leonidas; Onken, Christopher A.; Peterson, Bradley M.; Sluse, Dominique
2014-02-01
We propose a continuation of the program we began in 2013B to perform reverberation mapping on a gravitationally lensed quasar. Gravitationally lensed quasars are already rich test beds for studying cosmology, black hole accretion physics, dark matter, and galaxy properties. Here, we will expand their use by spectroscopically monitoring the CIV quasar emission line with GMOS to measure the broad line region size and black hole mass of the z=1.7 lensed quasar HE0435-1223. The success of this program has significant implications for studies of quasar physics, galaxy evolution at high redshift, and further studies of cosmology, and it is possible with only a modest addition (<2.5 nights) of Gemini time in 2014A.
The effect of weak lensing on distance estimates from supernovae
Smith, Mathew; Maartens, Roy; Bacon, David J.; Nichol, Robert C.; Campbell, Heather; D'Andrea, Chris B.; Clarkson, Chris; Bassett, Bruce A.; Cinabro, David; Finley, David A.; Frieman, Joshua A.; Galbany, Lluis; Garnavich, Peter M.; Olmstead, Matthew D.; Schneider, Donald P.; Shapiro, Charles; Sollerman, Jesper
2014-01-01
Using a sample of 608 Type Ia supernovae from the SDSS-II and BOSS surveys, combined with a sample of foreground galaxies from SDSS-II, we estimate the weak lensing convergence for each supernova line of sight. We find that the correlation between this measurement and the Hubble residuals is consistent with the prediction from lensing (at a significance of 1.7σ). Strong correlations are also found between the residuals and supernova nuisance parameters after a linear correction is applied. When these other correlations are taken into account, the lensing signal is detected at 1.4σ. We show, for the first time, that distance estimates from supernovae can be improved when lensing is incorporated, by including a new parameter in the SALT2 methodology for determining distance moduli. The recovered value of the new parameter is consistent with the lensing prediction. Using cosmic microwave background data from WMAP7, H {sub 0} data from Hubble Space Telescope and Sloan Digital Sky Survey (SDSS) Baryon acoustic oscillations measurements, we find the best-fit value of the new lensing parameter and show that the central values and uncertainties on Ω {sub m} and w are unaffected. The lensing of supernovae, while only seen at marginal significance in this low-redshift sample, will be of vital importance for the next generation of surveys, such as DES and LSST, which will be systematics-dominated.
Resolved Spectroscopy of Gravitationally Lensed Galaxies at z~=2
NASA Astrophysics Data System (ADS)
Jones, Tucker
2015-02-01
Spatially resolved spectroscopy is even more powerful when combined with magnification by gravitational lensing. I discuss observations of lensed galaxies at z~=2 with spatial resolution reaching 100 parsecs. Near-IR integral field spectroscopy reveals the kinematics, distribution and physical properties of star forming regions, and gas-phase metallicity gradients. Roughly two thirds of observed galaxies are isolated systems with coherent velocity fields, large velocity dispersion, multiple giant star-forming regions, and negative gas-phase metallicity gradients, suggestive of inside-out growth in gravitationally unstable disks. The remainder are undergoing mergers and have shallower metallicity gradients, indicating mixing of the interstellar gas via gravitational interaction. The metallicity gradients in isolated galaxies are consistent with simulations using standard feedback prescriptions, whereas simulations with enhanced feedback predict shallower gradients. These measurements therefore constrain the growth of galaxies from mergers and star formation as well as the regulatory feedback.
General requirements on matter power spectrum predictions for cosmology with weak lensing tomography
Hearin, Andrew P.; Zentner, Andrew R.; Ma, Zhaoming E-mail: zentner@pitt.edu
2012-04-01
Forthcoming projects such as DES, LSST, WFIRST, and Euclid aim to measure weak lensing shear correlations with unprecedented precision, constraining the dark energy equation of state at the percent level. Reliance on photometrically-determined redshifts constitutes a major source of uncertainty for these surveys. Additionally, interpreting the weak lensing signal requires a detailed understanding of the nonlinear physics of gravitational collapse. We present a new analysis of the stringent calibration requirements for weak lensing analyses of future imaging surveys that addresses both photo-z uncertainty and errors in the calibration of the matter power spectrum. We find that when photo-z uncertainty is taken into account the requirements on the level of precision in the prediction for the matter power spectrum are more stringent than previously thought. Including degree-scale galaxy clustering statistics in a joint analysis with weak lensing not only strengthens the survey's constraining power by ∼ 20%, but can also have a profound impact on the calibration demands, decreasing the degradation in dark energy constraints with matter power spectrum uncertainty by a factor of 2-5. Similarly, using galaxy clustering information significantly relaxes the demands on photo-z calibration. We compare these calibration requirements to the contemporary state-of-the-art in photometric redshift estimation and predictions of the power spectrum and suggest strategies to utilize forthcoming data optimally.
Weak Gravitational Field and Casimir Energy
NASA Astrophysics Data System (ADS)
Tanhayi, M. R.; Pirmoradian, R.
2016-02-01
In this paper we consider the effect of a weak gravitation field on the Casimir energy. Under a weak perturbation of a metric, we first obtain the linear energy-momentum tensor of a scalar field in a generic background and then the corrected energy of a scalar filed which satisfies the Dirichlet boundary condition is calculated up to first order of the metric perturbation. We show that our results coincide to the previous related works e.g., the Casimir effect when studied in Fermi coordinates.
Galaxy cluster center detection methods with weak lensing
NASA Astrophysics Data System (ADS)
Simet, Melanie
The precise location of galaxy cluster centers is a persistent problem in weak lensing mass estimates and in interpretations of clusters in a cosmological context. In this work, we test methods of centroid determination from weak lensing data and examine the effects of such self-calibration on the measured masses. Drawing on lensing data from the Sloan Digital Sky Survey Stripe 82, a 275 square degree region of coadded data in the Southern Galactic Cap, together with a catalog of MaxBCG clusters, we show that halo substructure as well as shape noise and stochasticity in galaxy positions limit the precision of such a self-calibration (in the context of Stripe 82, to ˜ 500 h-1 kpc or larger) and bias the mass estimates around these points to a level that is likely unacceptable for the purposes of making cosmological measurements. We also project the usefulness of this technique in future surveys.
Testing gravity with halo density profiles observed through gravitational lensing
Narikawa, Tatsuya; Yamamoto, Kazuhiro E-mail: kazuhiro@hiroshima-u.ac.jp
2012-05-01
We present a new test of the modified gravity endowed with the Vainshtein mechanism with the density profile of a galaxy cluster halo observed through gravitational lensing. A scalar degree of freedom in the galileon modified gravity is screened by the Vainshtein mechanism to recover Newtonian gravity in high-density regions, however it might not be completely hidden on the outer side of a cluster of galaxies. Then the modified gravity might yield an observational signature in a surface mass density of a cluster of galaxies measured through gravitational lensing, since the scalar field could contribute to the lensing potential. We investigate how the transition in the Vainshtein mechanism affects the surface mass density observed through gravitational lensing, assuming that the density profile of a cluster of galaxies follows the original Navarro-Frenk-White (NFW) profile, the generalized NFW profile and the Einasto profile. We compare the theoretical predictions with observational results of the surface mass density reported recently by other researchers. We obtain constraints on the amplitude and the typical scale of the transition in the Vainshtein mechanism in a subclass of the generalized galileon model.
Cosmic equation of state from strong gravitational lensing systems
NASA Astrophysics Data System (ADS)
Biesiada, Marek; Pirkowska, Aleksandra; Malec, Beata
2010-08-01
The accelerating expansion of the Universe is a great challenge for both physics and cosmology. In light of lacking the convincing theoretical explanation, an effective description of this phenomenon in terms of a cosmic equation of state turns out useful. The strength of modern cosmology lies in consistency across independent, often unrelated pieces of evidence. Therefore, every alternative method of restricting the cosmic equation of state is important. Strongly gravitationally lensed quasar-galaxy systems create such a new opportunity by combining stellar kinematics (central velocity dispersion measurements) with lensing geometry (Einstein radius determination from position of images). In this paper we apply such a method to a combined data sets from Sloan Lens ACS and Lens Structure and Dynamics surveys of gravitational lenses. As a result we obtain the cosmic equation of state parameters, which generally agree with results already known in the literature. This demonstrates that the method can be further used on larger samples obtained in the future. Independently noticed systematic deviation between fits done on standard candles and standard rulers is revealed in our findings. We also identify an important selection effect crucial to our method associated with the geometric configuration of the lensing system along the line of sight, which may have consequences for sample construction from the future lensing surveys.
Cosmic variance of the galaxy cluster weak lensing signal
NASA Astrophysics Data System (ADS)
Gruen, D.; Seitz, S.; Becker, M. R.; Friedrich, O.; Mana, A.
2015-06-01
Intrinsic variations of the projected density profiles of clusters of galaxies at fixed mass are a source of uncertainty for cluster weak lensing. We present a semi-analytical model to account for this effect, based on a combination of variations in halo concentration, ellipticity and orientation, and the presence of correlated haloes. We calibrate the parameters of our model at the 10 per cent level to match the empirical cosmic variance of cluster profiles at M_{200m}? 10^{14}ldots 10^{15} h^{-1}{ M_{?}}, z = 0.250.5 in a cosmological simulation. We show that weak lensing measurements of clusters significantly underestimate mass uncertainties if intrinsic profile variations are ignored, and that our model can be used to provide correct mass likelihoods. Effects on the achievable accuracy of weak lensing cluster mass measurements are particularly strong for the most massive clusters and deep observations (with ?20 per cent uncertainty from cosmic variance alone at M_{200m}? 10^{15} h^{-1}{ M_{?}} and z = 0.25), but significant also under typical ground-based conditions. We show that neglecting intrinsic profile variations leads to biases in the mass-observable relation constrained with weak lensing, both for intrinsic scatter and overall scale (the latter at the 15 per cent level). These biases are in excess of the statistical errors of upcoming surveys and can be avoided if the cosmic variance of cluster profiles is accounted for.
Shear and Ellipticity in Gravitational Lenses
NASA Astrophysics Data System (ADS)
Keeton, C. R.; Kochanek, C. S.; Seljak, U.
1997-06-01
Galaxies modeled as singular isothermal ellipsoids with an axis ratio distribution similar to the observed axis ratio distribution of E and S0 galaxies are statistically consistent with both the observed numbers of two-image and four-image lenses and the inferred ellipticities of individual lenses. However, no four-image lens is well fitted by the model (typical ?2/Ndof ~ 20), the axis ratio of the model can be significantly different from that of the observed lens galaxy, and the major axes of the model and the galaxy may be slightly misaligned. We found that models with a second, independent, external shear axis could fit the data well (typical ?2/Ndof ~ 1), while adding the same number of extra parameters to the radial mass distribution does not produce such a dramatic improvement in the fit. An independent shear axis can be produced by misalignments between the luminous galaxy and its dark matter halo, or by external shear perturbations due to galaxies and clusters correlated with the primary lens or along the line of sight. We estimate that the external shear perturbations have no significant effect on the expected numbers of two-image and four-image lenses but that they can be important perturbations in individual lens models. However, the amplitudes of the external shears required to produce good fits are larger than our estimates for typical external shear perturbations (10%-15% shear instead of 1%-3%), suggesting that the origin of the extra angular structure must be intrinsic to the primary lens galaxy in most cases.
Modified gravity: the CMB, weak lensing and general parameterisations
Thomas, Shaun A.; Appleby, Stephen A.; Weller, Jochen E-mail: stephen.appleby@ph.tum.de
2011-03-01
We examine general physical parameterisations for viable gravitational models in the f(R) framework. This is related to the mass of an additional scalar field, called the scalaron, that is introduced by the theories. Using a simple parameterisation for the scalaron mass M(a) we show there is an exact correspondence between the model and popular parameterisations of the modified Poisson equation μ(a,k) and the ratio of the Newtonian potentials η(a,k). We argue that although f(R) models are well described by the general [μ(a,k),η(a,k)] parameterization, specific functional forms of μ,η in the literature do not accurately represent f(R) behaviour, specifically at low redshift. We subsequently construct an improved description for the scalaron mass (and therefore μ(a,k) and η(a,k)) which captures their essential features and has benefits derived from a more physical origin. We study the scalaron's observational signatures and show the modification to the background Friedmann equation and CMB power spectrum to be small. We also investigate its effects in the linear and non linear matter power spectrum-where the signatures are evident-thus giving particular importance to weak lensing as a probe of these models. Using this new form, we demonstrate how the next generation Euclid survey will constrain these theories and its complementarity to current solar system tests. In the most optimistic case Euclid, together with a Planck prior, can constrain a fiducial scalaron mass M{sub 0} = 9.4 × 10{sup −30}eV at the ∼ 20% level. However, the decay rate of the scalaron mass, with fiducial value ν = 1.5, can be constrained to ∼ 3% uncertainty.
Reducing systematic error in weak lensing cluster surveys
Utsumi, Yousuke; Miyazaki, Satoshi; Hamana, Takashi; Geller, Margaret J.; Kurtz, Michael J.; Fabricant, Daniel G.; Dell'Antonio, Ian P.; Oguri, Masamune
2014-05-10
Weak lensing provides an important route toward collecting samples of clusters of galaxies selected by mass. Subtle systematic errors in image reduction can compromise the power of this technique. We use the B-mode signal to quantify this systematic error and to test methods for reducing this error. We show that two procedures are efficient in suppressing systematic error in the B-mode: (1) refinement of the mosaic CCD warping procedure to conform to absolute celestial coordinates and (2) truncation of the smoothing procedure on a scale of 10'. Application of these procedures reduces the systematic error to 20% of its original amplitude. We provide an analytic expression for the distribution of the highest peaks in noise maps that can be used to estimate the fraction of false peaks in the weak-lensing ?-signal-to-noise ratio (S/N) maps as a function of the detection threshold. Based on this analysis, we select a threshold S/N = 4.56 for identifying an uncontaminated set of weak-lensing peaks in two test fields covering a total area of ?3 deg{sup 2}. Taken together these fields contain seven peaks above the threshold. Among these, six are probable systems of galaxies and one is a superposition. We confirm the reliability of these peaks with dense redshift surveys, X-ray, and imaging observations. The systematic error reduction procedures we apply are general and can be applied to future large-area weak-lensing surveys. Our high-peak analysis suggests that with an S/N threshold of 4.5, there should be only 2.7 spurious weak-lensing peaks even in an area of 1000 deg{sup 2}, where we expect ?2000 peaks based on our Subaru fields.
Reducing Systematic Error in Weak Lensing Cluster Surveys
NASA Astrophysics Data System (ADS)
Utsumi, Yousuke; Miyazaki, Satoshi; Geller, Margaret J.; Dell'Antonio, Ian P.; Oguri, Masamune; Kurtz, Michael J.; Hamana, Takashi; Fabricant, Daniel G.
2014-05-01
Weak lensing provides an important route toward collecting samples of clusters of galaxies selected by mass. Subtle systematic errors in image reduction can compromise the power of this technique. We use the B-mode signal to quantify this systematic error and to test methods for reducing this error. We show that two procedures are efficient in suppressing systematic error in the B-mode: (1) refinement of the mosaic CCD warping procedure to conform to absolute celestial coordinates and (2) truncation of the smoothing procedure on a scale of 10'. Application of these procedures reduces the systematic error to 20% of its original amplitude. We provide an analytic expression for the distribution of the highest peaks in noise maps that can be used to estimate the fraction of false peaks in the weak-lensing ?-signal-to-noise ratio (S/N) maps as a function of the detection threshold. Based on this analysis, we select a threshold S/N = 4.56 for identifying an uncontaminated set of weak-lensing peaks in two test fields covering a total area of ~3 deg2. Taken together these fields contain seven peaks above the threshold. Among these, six are probable systems of galaxies and one is a superposition. We confirm the reliability of these peaks with dense redshift surveys, X-ray, and imaging observations. The systematic error reduction procedures we apply are general and can be applied to future large-area weak-lensing surveys. Our high-peak analysis suggests that with an S/N threshold of 4.5, there should be only 2.7 spurious weak-lensing peaks even in an area of 1000 deg2, where we expect ~2000 peaks based on our Subaru fields. Based in part on data collected at Subaru Telescope and obtained from the SMOKA, which is operated by the Astronomy Data Center, National Astronomical Observatory of Japan.
Gravitational Lensing by Dark Matter Halos with Nonuniversal Density Profiles
NASA Astrophysics Data System (ADS)
Zhang, Tong-Jie
2004-02-01
The statistics of gravitational lensing can provide us with a very powerful probe of the mass distribution of matter in the universe. By comparing predicted strong lensing probabilities with observations, we can test the mass distribution of dark matter halos, in particular, the inner density slope. In this Letter, unlike previous work that directly models the density profiles of dark matter halos semianalytically, we generalize the density profiles of dark matter halos from high-resolution N-body simulations by means of generalized Navarro-Frenk-White (GNFW) models of three populations with slopes, ?, of about -1.5, -1.3, and -1.1 for galaxies, groups, and clusters, respectively. This approach is an alternative and independent way to examine the slopes of mass-density profiles of halos. We present calculations of lensing probabilities using these GNFW profiles for three populations in various spatially flat cosmological models with a cosmological constant ?. We show that the compound model of density profiles does not match well with the observed lensing probabilities derived from the Jodrell-Bank VLA Astrometric Survey data in combination with the Cosmic Lens All-Sky Survey data. Together with the previous work on lensing probability, our results suggest that a singular isothermal sphere mass model of less than about 1013 h-1 Msolar can predict strong lensing probabilities that are consistent with observations of small splitting angles.
Gravitational lensing by a non-Schwarzschild black hole in a plasma
NASA Astrophysics Data System (ADS)
Hakimov, Abdullo; Atamurotov, Farruh
2016-03-01
We study gravitational lensing in the vicinity of a massive object described by non-Schwarzschild geometry surrounded by a homogeneous plasma. The expression for the deflection angle in a non-Schwarzschild space-time in the weak field regime in the presence of plasma have been derived. It has been shown that the obtained deflection angle depends on (i) the frequency of the electromagnetic wave, due to the dispersion properties of the plasma; (ii) the gravitational mass M; and (iii) deformation parameter ɛ of the gravitational lens. Moreover, the influence of deformation parameter of the gravitational lens and plasma frequency on the magnification of brightness of the source star has been studied in the case of microlensing.
Precision photometric redshift calibration for galaxy-galaxy weak lensing
NASA Astrophysics Data System (ADS)
Mandelbaum, R.; Seljak, U.; Hirata, C. M.; Bardelli, S.; Bolzonella, M.; Bongiorno, A.; Carollo, M.; Contini, T.; Cunha, C. E.; Garilli, B.; Iovino, A.; Kampczyk, P.; Kneib, J.-P.; Knobel, C.; Koo, D. C.; Lamareille, F.; Le Fvre, O.; Le Borgne, J.-F.; Lilly, S. J.; Maier, C.; Mainieri, V.; Mignoli, M.; Newman, J. A.; Oesch, P. A.; Perez-Montero, E.; Ricciardelli, E.; Scodeggio, M.; Silverman, J.; Tasca, L.
2008-05-01
Accurate photometric redshifts are among the key requirements for precision weak lensing measurements. Both the large size of the Sloan Digital Sky Survey (SDSS) and the existence of large spectroscopic redshift samples that are flux-limited beyond its depth have made it the optimal data source for developing methods to properly calibrate photometric redshifts for lensing. Here, we focus on galaxy-galaxy lensing in a survey with spectroscopic lens redshifts, as in the SDSS. We develop statistics that quantify the effect of source redshift errors on the lensing calibration and on the weighting scheme, and show how they can be used in the presence of redshift failure and sampling variance. We then demonstrate their use with 2838 source galaxies with spectroscopy from DEEP2 and zCOSMOS, evaluating several public photometric redshift algorithms, in two cases including a full p(z) for each object, and find lensing calibration biases as low as <1 per cent (due to fortuitous cancellation of two types of bias) or as high as 20 per cent for methods in active use (despite the small mean photoz bias of these algorithms). Our work demonstrates that lensing-specific statistics must be used to reliably calibrate the lensing signal, due to asymmetric effects of (frequently non-Gaussian) photoz errors. We also demonstrate that large-scale structure (LSS) can strongly impact the photoz calibration and its error estimation, due to a correlation between the LSS and the photoz errors, and argue that at least two independent degree-scale spectroscopic samples are needed to suppress its effects. Given the size of our spectroscopic sample, we can reduce the galaxy-galaxy lensing calibration error well below current SDSS statistical errors. Based in part on observations undertaken at the European Southern Observatory (ESO) Very Large Telescope (VLT) under Large Programme 175.A-0839. E-mail: rmandelb@ias.edu (RM); seljak@itp.uzh.ch (US) Hubble Fellow.
PROBING PRIMORDIAL NON-GAUSSIANITY WITH WEAK-LENSING MINKOWSKI FUNCTIONALS
Shirasaki, Masato; Yoshida, Naoki; Nishimichi, Takahiro; Hamana, Takashi
2012-11-20
We study the cosmological information contained in the Minkowski functionals (MFs) of weak gravitational lensing convergence maps. We show that the MFs provide strong constraints on the local-type primordial non-Gaussianity parameter f {sub NL}. We run a set of cosmological N-body simulations and perform ray-tracing simulations of weak lensing to generate 100 independent convergence maps of a 25 deg{sup 2} field of view for f {sub NL} = -100, 0 and 100. We perform a Fisher analysis to study the degeneracy among other cosmological parameters such as the dark energy equation of state parameter w and the fluctuation amplitude {sigma}{sub 8}. We use fully nonlinear covariance matrices evaluated from 1000 ray-tracing simulations. For upcoming wide-field observations such as those from the Subaru Hyper Suprime-Cam survey with a proposed survey area of 1500 deg{sup 2}, the primordial non-Gaussianity can be constrained with a level of f {sub NL} {approx} 80 and w {approx} 0.036 by weak-lensing MFs. If simply scaled by the effective survey area, a 20,000 deg{sup 2} lensing survey using the Large Synoptic Survey Telescope will yield constraints of f {sub NL} {approx} 25 and w {approx} 0.013. We show that these constraints can be further improved by a tomographic method using source galaxies in multiple redshift bins.
Gravitational lenses in generalized Einstein-aether theory: The bullet cluster
Dai, D.-C.; Matsuo, Reijiro; Starkman, Glenn
2008-11-15
We study the lensing properties of an asymmetric mass distribution and vector field in generalized Einstein-aether (GEA) theory. As vector-field fluctuations are responsible in GEA for seeding baryonic structure formation, vector-field concentrations can exist independently of baryonic matter. Such concentrations would not be expected to be tied to baryonic matter except gravitationally, and so, like dark matter halos, would become separated from baryonic matter in interacting systems such as the bullet cluster. These vector-field concentrations cause metric deviations that affect weak lensing. Therefore, the distribution of weak lensing deviates from that which would be inferred from the luminous mass distribution, in a way that numerical calculations demonstrate can be consistent with observations. This suggests that MOND-inspired theories can reproduce weak lensing observations, but makes clear the price: the existence of a coherent large-scale fluctuation of a field(s) weakly tied to the baryonic matter, not completely dissimilar to a dark matter halo.
A search for closely spaced gravitational lenses
Crampton, D.; Mcclure, R.D.; Fletcher, J.M.; Hutchings, J.B. National Research Council of Canada, Herzberg Institute of Astrophysics, Ottawa )
1989-10-01
A new image-stabilizing camera was used to search for closely spaced images of a sample of 25 intrinsically luminous quasars with z greater than 1.6 and m smaller than 19. Observations of seven similarly selected quasars with the regular CCD camera in good seeing conditions are also reported. Of the 32 quasars, seven are gravitational lens candidates. Two of these have subarcsecond separations. Additional information on all these candidates is required. 22 refs.
NASA Astrophysics Data System (ADS)
Chen, Bin; Kantowski, R.; Dai, X.
2014-01-01
We have developed an accurate gravitational lens theory for an inhomogeneity embedded in an otherwise homogeneous universe, which to the lowest order is applicable to any mass distribution. We derive the Fermat potential for a spherically symmetric lens embedded in a FLRW cosmology and use it to investigate the late-time integrated Sachs-Wolfe effect (ISW) caused by individual large scale inhomogeneities, in particular, cosmic voids. We present a simple analytical expression for the CMB temperature fluctuation across such a lens as the derivative of the lens Fermat potential. Our formalism is applicable to both linear and nonlinear density evolution scenarios, to arbitrarily large density contrasts, and to all open and closed background cosmologies. Our results are particularly useful for modeling ISW effects extracted through stacking large numbers of cosmic voids and clusters (that is, the aperture photometry method). For structures co-expanding with the background cosmology, i.e., for time-independent density contrasts, we find that the gravitational lensing time delay alone can produce fluctuations of the order of seen in recent observations by WMAP and Planck. We revisit the possibility of explaining the non-Gaussian cold spot on the south hemisphere via the Rees-Sciama effect of a large cosmic void using constraints obtained from the most recent void catalogs and our new void-lensing formalism, and compare it with other explanations such as a collapsing cosmic texture. We also study the remapping of primordial CMB anisotropies, the weak-lensing shear, and magnification caused by void lensing.
Catastrophic photometric redshift errors: weak-lensing survey requirements
NASA Astrophysics Data System (ADS)
Bernstein, Gary; Huterer, Dragan
2010-01-01
We study the sensitivity of weak-lensing surveys to the effects of catastrophic redshift errors - cases where the true redshift is mis-estimated by a significant amount. To compute the biases in cosmological parameters, we adopt an efficient linearized analysis where the redshift errors are directly related to shifts in the weak-lensing convergence power spectra. We estimate the number Nspec of unbiased spectroscopic redshifts needed to determine the catastrophic error rate well enough that biases in cosmological parameters are below statistical errors of weak-lensing tomography. While the straightforward estimate of Nspec is ~106, we find that using only the photometric redshifts with z <~ 2.5 leads to a drastic reduction in Nspec to ~30000 while negligibly increasing statistical errors in dark-energy parameters. Therefore, the size of the spectroscopic survey needed to control catastrophic errors is similar to that previously deemed necessary to constrain the core of the zs-zp distribution. We also study the efficacy of the recent proposal to measure redshift errors by cross-correlation between the photo-z and spectroscopic samples. We find that this method requires ~10 per cent a priori knowledge of the bias and stochasticity of the outlier population, and is also easily confounded by lensing magnification bias. The cross-correlation method is therefore unlikely to supplant the need for a complete spectroscopic-redshift survey of the source population.
Catastrophic photometric redshift errors: Weak-lensing survey requirements
Bernstein, Gary; Huterer, Dragan
2010-01-11
We study the sensitivity of weak lensing surveys to the effects of catastrophic redshift errors - cases where the true redshift is misestimated by a significant amount. To compute the biases in cosmological parameters, we adopt an efficient linearized analysis where the redshift errors are directly related to shifts in the weak lensing convergence power spectra. We estimate the number Nspec of unbiased spectroscopic redshifts needed to determine the catastrophic error rate well enough that biases in cosmological parameters are below statistical errors of weak lensing tomography. While the straightforward estimate of Nspec is ~106 we find that using onlymore » the photometric redshifts with z ≤ 2.5 leads to a drastic reduction in Nspec to ~ 30,000 while negligibly increasing statistical errors in dark energy parameters. Therefore, the size of spectroscopic survey needed to control catastrophic errors is similar to that previously deemed necessary to constrain the core of the zs – zp distribution. We also study the efficacy of the recent proposal to measure redshift errors by cross-correlation between the photo-z and spectroscopic samples. We find that this method requires ~ 10% a priori knowledge of the bias and stochasticity of the outlier population, and is also easily confounded by lensing magnification bias. In conclusion, the cross-correlation method is therefore unlikely to supplant the need for a complete spectroscopic redshift survey of the source population.« less
A new weak lensing shear analysis method using ellipticity defined by 0th order moments
NASA Astrophysics Data System (ADS)
Okura, Yuki; Futamase, Toshifumi
2015-04-01
We developed a new method that uses ellipticity defined by 0th order moments (0th-ellipticity) for weak gravitational lensing shear analysis. Although there is a strong correlation between the ellipticity calculated using this approach and the usual ellipticity defined by the 2nd order moment, the ellipticity calculated here has a higher signal-to-noise ratio because it is weighted to the central region of the image. These results were confirmed using data for Abell 1689 from the Subaru telescope. For shear analysis, we adopted the ellipticity of re-smeared artificial image method for point spread function correction, and we tested the precision of this 0th-ellipticity with simple simulation, then we obtained the same level of precision with the results of ellipticity defined by quadrupole moments. Thus, we can expect that weak lensing analysis using 0 shear will be improved in proportion to the statistical error.
Galaxy masses in large surveys: Connecting luminous and dark matter with weak lensing and kinematics
NASA Astrophysics Data System (ADS)
Reyes, Reinabelle
2011-01-01
Galaxy masses are difficult to determine because light traces stars and gas in a non-trivial way, and does not trace dark matter, which extends well beyond the luminous regions of galaxies. In this thesis, I use the most direct probes of dark matter available---weak gravitational lensing and galaxy kinematics---to trace the total mass in galaxies (and galaxy clusters) in large surveys. In particular, I use the large, homogeneous dataset from the Sloan Digital Sky Survey (SDSS), which provides spectroscopic redshifts for a large sample of galaxies at z ? 0.2 and imaging data to a depth of r < 22. By combining complementary probes, I am able to obtain robust observational constraints that cannot be obtained from any single technique alone. First, I use weak lensing of galaxy clusters to derive an optimal optical tracer of cluster mass, which was found to be a combination of cluster richness and the luminosity of the brightest cluster galaxy. Next, I combine weak lensing of luminous red galaxies with redshift distortions and clustering measurements to derive a robust probe of gravity on cosmological scales. Finally, I combine weak lensing with the kinematics of disk galaxies to constrain the total mass profile over several orders of magnitude. I derive a minimal-scatter relation between disk velocity and stellar mass (also known as the Tully-Fisher relation) that can be used, by construction, on a similarly-selected lens sample. Then, I combine this relation with halo mass measurements from weak lensing to place constraints on the ratio of the optical to virial velocities, as well as the ratio of halo to stellar masses, both as a function of stellar mass. These results will serve as inputs to and constraints on disk galaxy formation models, which will be explored in future work.
Strong gravitational lensing in non-commutative wormholes
NASA Astrophysics Data System (ADS)
Sharif, M.; Iftikhar, Sehrish
2015-05-01
This paper is devoted to study gravitational lensing of static spherically symmetric non-commutative wormholes in galactic halo region. We formulate the field equations with anisotropic matter using particlelike source of gravitation in the form of Lorentzian distribution. We explore energy conditions and equilibrium condition of the wormhole model using generalized Tolman-Oppenheimmer-Volkov equation. To investigate position of wormhole, we evaluate angle of deflection in the strong field limit through numerical approach. It is found that the angle of deflection diverges for the photon radius.
Higher-order gravitational lensing reconstruction using Feynman diagrams
Jenkins, Elizabeth E.; Manohar, Aneesh V.; Yadav, Amit P.S.; Waalewijn, Wouter J. E-mail: amanohar@ucsd.edu E-mail: ayadav@physics.ucsd.edu
2014-09-01
We develop a method for calculating the correlation structure of the Cosmic Microwave Background (CMB) using Feynman diagrams, when the CMB has been modified by gravitational lensing, Faraday rotation, patchy reionization, or other distorting effects. This method is used to calculate the bias of the Hu-Okamoto quadratic estimator in reconstructing the lensing power spectrum up to O (φ{sup 4}) in the lensing potential φ. We consider both the diagonal noise TT TT, EB EB, etc. and, for the first time, the off-diagonal noise TT TE, TB EB, etc. The previously noted large O (φ{sup 4}) term in the second order noise is identified to come from a particular class of diagrams. It can be significantly reduced by a reorganization of the φ expansion. These improved estimators have almost no bias for the off-diagonal case involving only one B component of the CMB, such as EE EB.
Resolving high energy emission of jets using strong gravitational lensing
NASA Astrophysics Data System (ADS)
Barnacka, Anna
2014-11-01
Chandra observations of M87 in 2004 uncovered an outburst originating in distant knot along the jet hundreds of parsecs from the core. This discovery challenges our understanding of the origin of high energy flares. Current technology is inadequate to resolve jets at distances greater than M87, or observed at higher energies. We propose to use gravitationally lensed jets to investigate the structure of more distant sources. Photons emitted at different sites cross the lens plane at different distances, thus magnification ratios and time delays differ between the mirage images. Monitoring of flares from lensed jets reveals the origin of the emission. With detectors like Chandra, lensed systems are a tool for resolving the structure of the jets and for investigating their cosmic evolution.
Higher-order gravitational lensing reconstruction using Feynman diagrams
NASA Astrophysics Data System (ADS)
Jenkins, Elizabeth E.; Manohar, Aneesh V.; Waalewijn, Wouter J.; Yadav, Amit P. S.
2014-09-01
We develop a method for calculating the correlation structure of the Cosmic Microwave Background (CMB) using Feynman diagrams, when the CMB has been modified by gravitational lensing, Faraday rotation, patchy reionization, or other distorting effects. This method is used to calculate the bias of the Hu-Okamoto quadratic estimator in reconstructing the lensing power spectrum up to Script O (phi4) in the lensing potential phi. We consider both the diagonal noise TT TT, EB EB, etc. and, for the first time, the off-diagonal noise TT TE, TB EB, etc. The previously noted large Script O (phi4) term in the second order noise is identified to come from a particular class of diagrams. It can be significantly reduced by a reorganization of the phi expansion. These improved estimators have almost no bias for the off-diagonal case involving only one B component of the CMB, such as EE EB.
Hubble Frontier Fields : ``A New Era for Gravitational Lensing''
NASA Astrophysics Data System (ADS)
Jauzac, Mathilde; Eckert, Dominique; Jullo, Eric; Richard, Johan; Ebeling, Harald; Kneib, Jean-Paul; Limousin, Marceau; Atek, Hakim; Natarajan, Priyamvada; Rexroth, Markus
2015-08-01
The Hubble Frontier Fields (HFF) initiative constitutes the largest commitment ever of HST time to the exploration of the distant Universe via gravitational lensing by massive galaxy clusters.I will present the new gravitational lensing pictures of the first HFF complex clusters. We have demonstrated that we are now able to `weight’ these clusters' cores down to the percent level precision (recently published works), serving our quest for the high-redshift Universe.However, while the depth of these dataset makes these clusters amazing Cosmic Telescopes, it also enables us to get an unprecedented understanding of the cluster physics.Therefore, presenting the case of MACSJ0416 and Abell 2744, I will demonstrate the importance of such high-quality data to analyse the merging/dynamical history of the cluster itself while comparing dark matter, light and gas distributions.
Yoo, Jaiyul
2009-01-15
We present a coherent theoretical framework for computing gravitational lensing effects and redshift-space distortions in an inhomogeneous universe and investigate their impacts on galaxy two-point statistics. Adopting the linearized Friedmann-Lemaitre-Robertson-Walker metric, we derive the gravitational lensing and the generalized Sachs-Wolfe effects that include the weak lensing distortion, magnification, and time delay effects, and the redshift-space distortion, Sachs-Wolfe, and integrated Sachs-Wolfe effects, respectively. Based on this framework, we first compute their effects on observed source fluctuations, separating them as two physically distinct origins: the volume effect that involves the change of volume and is always present in galaxy two-point statistics, and the source effect that depends on the intrinsic properties of source populations. Then we identify several terms that are ignored in the standard method, and we compute the observed galaxy two-point statistics, an ensemble average of all the combinations of the intrinsic source fluctuations and the additional contributions from the gravitational lensing and the generalized Sachs-Wolfe effects. This unified treatment of galaxy two-point statistics clarifies the relation of the gravitational lensing and the generalized Sachs-Wolfe effects to the metric perturbations and the underlying matter fluctuations. For near-future dark energy surveys, we compute additional contributions to the observed galaxy two-point statistics and analyze their impact on the anisotropic structure. Thorough theoretical modeling of galaxy two-point statistics would be not only necessary to analyze precision measurements from upcoming dark energy surveys, but also provide further discriminatory power in understanding the underlying physical mechanisms.
NASA Astrophysics Data System (ADS)
Israel, H.; Erben, T.; Reiprich, T. H.; Vikhlinin, A.; Sarazin, C. L.; Schneider, P.
2012-10-01
Context. Evolution in the mass function of galaxy clusters sensitively traces both the expansion history of the Universe and cosmological structure formation. Robust cluster mass determinations are a key ingredient for a reliable measurement of this evolution, especially at high redshift. Weak gravitational lensing is a promising tool for, on average, unbiased mass estimates. Aims: This weak lensing project aims at measuring reliable weak lensing masses for a complete X-ray selected sample of 36 high redshift (0.35 < z < 0.9) clusters. The goal of this paper is to demonstrate the robustness of the methodology against commonly encountered problems, including pure instrumental effects, the presence of bright (8-9 mag) stars close to the cluster centre, ground based measurements of high-z (z ~0.8) clusters, and the presence of massive unrelated structures along the line-sight. Methods: We select a subsample of seven clusters observed with MMT/MegaCam. Instrumental effects are checked in detail by cross-comparison with an archival CFHT/MegaCam observation. We derive mass estimates for seven clusters by modelling the tangential shear with an NFW profile, in two cases with multiple components to account for projected structures in the line-of-sight. Results: We firmly detect lensing signals from all seven clusters at more than 3.5? and determine their masses, ranging from 1014 M? to 1015 M?, despite the presence of nearby bright stars. We retrieve the lensing signal of more than one cluster in the CL 1701+6414 field, while apparently observing CL 1701+6414 through a massive foreground filament. We also find a multi-peaked shear signal in CL 1641+4001. Shear structures measured in the MMT and CFHT images of CL 1701+6414 are highly correlated. Conclusions: We confirm the capability of MMT/MegaCam to infer weak lensing masses from high-z clusters, demonstrated by the high level of consistency between MMT and CFHT results for CL 1701+6414. This shows that, when a sophisticated analysis is applied, instrumental effects are well under control. Observations reported here were obtained at the MMT Observatory, a joint facility of the Smithsonian Institution and the University of Arizona.Appendices are available in electronic form at http://www.aanda.orgReduced and coadded MMT image files are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A79
Measurement and calibration of noise bias in weak lensing galaxy shape estimation
NASA Astrophysics Data System (ADS)
Kacprzak, Tomasz; Zuntz, Joe; Rowe, Barnaby; Bridle, Sarah; Refregier, Alexandre; Amara, Adam; Voigt, Lisa; Hirsch, Michael
2012-12-01
Weak gravitational lensing has the potential to constrain cosmological parameters to high precision. However, as shown by the Shear Testing Programmes and Gravitational lensing Accuracy Testing challenges, measuring galaxy shears is a non-trivial task: various methods introduce different systematic biases which have to be accounted for. We investigate how pixel noise on the image affects the bias on shear estimates from a maximum likelihood forward model-fitting approach using a sum of co-elliptical Srsic profiles, in complement to the theoretical approach of an associated paper. We evaluate the bias using a simple but realistic galaxy model and find that the effects of noise alone can cause biases of the order of 1-10 per cent on measured shears, which is significant for current and future lensing surveys. We evaluate a simulation-based calibration method to create a bias model as a function of galaxy properties and observing conditions. This model is then used to correct the simulated measurements. We demonstrate that, for the simple case in which the correct range of galaxy models is used in the fit, the calibration method can reduce noise bias to the level required for estimating cosmic shear in upcoming lensing surveys.
Time delays for eleven gravitationally lensed quasars revisited
NASA Astrophysics Data System (ADS)
Eulaers, E.; Magain, P.
2011-12-01
Aims: We test the robustness of published time delays for 11 lensed quasars by using two techniques to measure time shifts in their light curves. Methods: We chose to use two fundamentally different techniques to determine time delays in gravitationally lensed quasars: a method based on fitting a numerical model and another one derived from the minimum dispersion method introduced by Pelt and collaborators. To analyse our sample in a homogeneous way and avoid bias caused by the choice of the method used, we apply both methods to 11 different lensed systems for which delays have been published: JVAS B0218+357, SBS 0909+523, RX J0911+0551, FBQS J0951+2635, HE 1104-1805, PG 1115+080, JVAS B1422+231, SBS 1520+530, CLASS B1600+434, CLASS B1608+656, and HE 2149-2745 Results: Time delays for three double lenses, JVAS B0218+357, HE 1104-1805, and CLASS B1600+434, as well as the quadruply lensed quasar CLASS B1608+656 are confirmed within the error bars. We correct the delay for SBS 1520+530. For PG 1115+080 and RX J0911+0551, the existence of a second solution on top of the published delay is revealed. The time delays in four systems, SBS 0909+523, FBQS J0951+2635, JVAS B1422+231, and HE 2149-2745 prove to be less reliable than previously claimed. Conclusions: If we wish to derive an estimate of H0 based on time delays in gravitationally lensed quasars, we need to obtain more robust light curves for most of these systems in order to achieve a higher accuracy and robustness on the time delays.
Optical Gravitational Lensing Experiment - Database of 1992 results
NASA Astrophysics Data System (ADS)
Szymanski, M.; Udalski, A.
1993-04-01
Description and technical details of the data bases constructed for handling a huge amount of data from the Optical Gravitational Lensing Experiment (OGLE) are presented. The described software allows easy and fast retrieving photometric data of any from about 10 exp 6 stars observed during the 1992 OGLE observing season (6.5 GBytes of raw data, about 1.3 x 10 exp 8 photometric measurements).
Strong gravitational lensing with Gauss-Bonnet correction
Sadeghi, J.; Vaez, H. E-mail: h.vaez@umz.ac.ir
2014-06-01
In this paper we investigate the strong gravitational lensing in a five dimensional background with Gauss-Bonnet gravity, so that in 4-dimensions the Gauss-Bonnet correction disappears. By considering the logarithmic term for deflection angle, we obtain the deflection angle α-circumflex and corresponding parameters ā and b-bar . Finally, we estimate some properties of relativistic images such as θ{sub ∞}, s and r{sub m}.
NASA Astrophysics Data System (ADS)
Shirasaki, Masato; Yoshida, Naoki
2014-05-01
The measurement of cosmic shear using weak gravitational lensing is a challenging task that involves a number of complicated procedures. We study in detail the systematic errors in the measurement of weak-lensing Minkowski Functionals (MFs). Specifically, we focus on systematics associated with galaxy shape measurements, photometric redshift errors, and shear calibration correction. We first generate mock weak-lensing catalogs that directly incorporate the actual observational characteristics of the Canada-France-Hawaii Lensing Survey (CFHTLenS). We then perform a Fisher analysis using the large set of mock catalogs for various cosmological models. We find that the statistical error associated with the observational effects degrades the cosmological parameter constraints by a factor of a few. The Subaru Hyper Suprime-Cam (HSC) survey with a sky coverage of ~1400 deg2 will constrain the dark energy equation of the state parameter with an error of ?w 0 ~ 0.25 by the lensing MFs alone, but biases induced by the systematics can be comparable to the 1? error. We conclude that the lensing MFs are powerful statistics beyond the two-point statistics only if well-calibrated measurement of both the redshifts and the shapes of source galaxies is performed. Finally, we analyze the CFHTLenS data to explore the ability of the MFs to break degeneracies between a few cosmological parameters. Using a combined analysis of the MFs and the shear correlation function, we derive the matter density \\Omega _m0 = 0.256+/- ^{0.054}_{0.046}.
Non-linear relativistic contributions to the cosmological weak-lensing convergence
Andrianomena, Sambatra; Clarkson, Chris; Patel, Prina; Umeh, Obinna; Uzan, Jean-Philippe E-mail: chris.clarkson@gmail.com E-mail: umeobinna@gmail.com
2014-06-01
Relativistic contributions to the dynamics of structure formation come in a variety of forms, and can potentially give corrections to the standard picture on typical scales of 100 Mpc. These corrections cannot be obtained by Newtonian numerical simulations, so it is important to accurately estimate the magnitude of these relativistic effects. Density fluctuations couple to produce a background of gravitational waves, which is larger than any primordial background. A similar interaction produces a much larger spectrum of vector modes which represent the frame-dragging rotation of spacetime. These can change the metric at the percent level in the concordance model at scales below the equality scale. Vector modes modify the lensing of background galaxies by large-scale structure. This gives in principle the exciting possibility of measuring relativistic frame dragging effects on cosmological scales. The effects of the non-linear tensor and vector modes on the cosmic convergence are computed and compared to first-order lensing contributions from density fluctuations, Doppler lensing, and smaller Sachs-Wolfe effects. The lensing from gravitational waves is negligible so we concentrate on the vector modes. We show the relative importance of this for future surveys such as Euclid and SKA. We find that these non-linear effects only marginally affect the overall weak lensing signal so they can safely be neglected in most analyses, though are still much larger than the linear Sachs-Wolfe terms. The second-order vector contribution can dominate the first-order Doppler lensing term at moderate redshifts and are actually more important for survey geometries like the SKA.
Gravitational Lensing Size Scales for Quasars
NASA Astrophysics Data System (ADS)
Chartas, G.; Kochanek, C.; Dai, X.; Morgan, C.; Blackburne, J.; Chen, B.; Mosquera, A.; MacLeod, C.
2015-07-01
We review results from our monitoring observations of several lensed quasars performed in the optical, UV, and X-ray bands. Modeling of the multi-wavelength light curves provides constraints on the extent of the optical, UV and X-ray emission regions. One of the important results of our analysis is that the optical sizes as inferred from the microlesning analysis are significantly larger than those predicted by the theoretical-thin-disk estimate. In a few cases we also constrain the slope of the size-wavelength relation. Our size constraints of the soft and hard X-ray emission regions of quasars indicate that in some objects of our sample the hard emission region is more compact than the soft and in others the soft emission region is smaller. This difference may be the result of the relative strengths of the disk-reflected (harder and extended) versus corona-direct (softer and compact) components in the quasars of our sample. Finally, we present the analysis of several strong microlensing events where we detect an evolution of the relativistic Fe line profile as the magnification caustic traverses the accretion disk. These caustic crossings are used to provide independent estimates of the size of Fe K emission region.
The HST Frontier Fields: Gravitational Lensing Models Release
NASA Astrophysics Data System (ADS)
Coe, Dan A.; Lotz, J.; Natarajan, P.; Richard, J.; Zitrin, A.; Kneib, J.; Ebeling, H.; Sharon, K.; Johnson, T.; Limousin, M.; Bradac, M.; Hoag, A.; Cain, B.; Merten, J.; Williams, L. L.; Sebesta, K.; Meneghetti, M.; Koekemoer, A. M.; Barker, E. A.
2014-01-01
The Hubble Frontier Fields (HFF) is a Director's Discretionary Time (DDT) program to deeply observe up to six massive strong-lensing galaxy clusters and six "blank" fields in parallel. These complementary observations will yield magnified and direct images of some of the most distant galaxies yet observed. The strongly lensed images will be our deepest views of our universe to date. Interpretation of some (but not all) observed properties of the strongly lensed galaxies requires gravitational lens modeling. In order to maximize the value of this public dataset to the extragalactic community, STScI commissioned five teams funded by NASA to derive the best possible lens models from existing data. After coordinating to share observational constraints, including measured redshifts of strongly lensed galaxies, the teams independently derived lens models using robust, established methodologies. STScI released these models to the community in October before HFF observations of the first cluster, Abell 2744. Here we describe these models as well as a web tool which allows users to extract magnification estimates with uncertainties from all models for any galaxy strongly lensed by a HFF cluster. Inputs are the galaxy's coordinates (RA and Dec), redshift, and (optionally) observed radius. We also discuss ongoing work to study lens model uncertainties by modeling simulated clusters.
The Weak Lensing Signal and the Clustering of BOSS Galaxies. I. Measurements
NASA Astrophysics Data System (ADS)
Miyatake, Hironao; More, Surhud; Mandelbaum, Rachel; Takada, Masahiro; Spergel, David N.; Kneib, Jean-Paul; Schneider, Donald P.; Brinkmann, J.; Brownstein, Joel R.
2015-06-01
A joint analysis of the clustering of galaxies and their weak gravitational lensing signal is well-suited to simultaneously constrain the galaxy-halo connection as well as the cosmological parameters by breaking the degeneracy between galaxy bias and the amplitude of clustering signal. In a series of two papers, we perform such an analysis at the highest redshift (z 0.53) in the literature using CMASS galaxies in the Sloan Digital Sky Survey-III Baryon Oscillation Spectroscopic Survey Eleventh Data Release (BOSS DR11) catalog spanning 8300 deg2. In this paper, we present details of the clustering and weak lensing measurements of these galaxies. We define a subsample of 400,916 CMASS galaxies based on their redshifts and stellar-mass estimates so that the galaxies constitute an approximately volume-limited and similar population over the redshift range 0.47?slant z?slant 0.59. We obtain a signal-to-noise ratio (S/N) ? 56 for the galaxy clustering measurement. We also explore the redshift and stellar-mass dependence of the clustering signal. For the weak lensing measurement, we use existing deeper imaging data from the Canada-France-Hawaii Telescope Legacy Survey with publicly available shape and photometric redshift catalogs from CFHTLenS, but only in a 105 deg2 area that overlaps with BOSS. This restricts the lensing measurement to only 5084 CMASS galaxies. After careful systematic tests, we find a highly significant detection of the CMASS weak lensing signal, with total S/N ? 26. These measurements form the basis of the halo occupation distribution and cosmology analysis presented in More et al. (Paper II).
Gravitational Lensing Statistics in Universes Dominated by Dark Energy
NASA Astrophysics Data System (ADS)
Kuhlen, Michael; Keeton, Charles R.; Madau, Piero
2004-01-01
The distribution of image separations in multiply imaged gravitational lens systems can simultaneously constrain the core structure of dark matter halos and cosmological parameters. We study lens statistics in flat, low-density universes with different equations of state w=pQ/?Q for the dark energy component. The fact that dark energy modifies the distance-redshift relation and the mass function of dark matter halos leads to changes in the lensing optical depth as a function of image separation ??. Those effects must, however, be distinguished from effects associated with the structure of dark matter halos. Baryonic cooling causes galaxy-mass halos to have different central density profiles than group- and cluster-mass halos, which causes the distribution of normal arcsecond-scale lenses to differ from the distribution of ``wide-separation'' (??>~4'') lenses. Fortunately, the various parameters related to cosmology and halo structure have very different effects on the overall image separation distribution: (1) the abundance of wide-separation lenses is extremely sensitive (by orders of magnitude) to the distribution of ``concentration'' parameters for massive halos modeled with the Navarro-Frenk-White profile, (2) the transition between normal and wide-separation lenses depends mainly on the mass scale where baryonic cooling ceases to be efficient, and (3) dark energy has effects at all image separation scales. While current lens samples cannot usefully constrain all of the parameters, ongoing and future imaging surveys should discover hundreds or thousands of lenses and make it possible to disentangle the various effects and constrain all of the parameters simultaneously. Incidentally, we mention that for the sake of discovering lensed quasars, survey area is more valuable than depth.
NASA Astrophysics Data System (ADS)
Miller, L.; Heymans, C.; Kitching, T. D.; van Waerbeke, L.; Erben, T.; Hildebrandt, H.; Hoekstra, H.; Mellier, Y.; Rowe, B. T. P.; Coupon, J.; Dietrich, J. P.; Fu, L.; Harnois-Déraps, J.; Hudson, M. J.; Kilbinger, M.; Kuijken, K.; Schrabback, T.; Semboloni, E.; Vafaei, S.; Velander, M.
2013-03-01
A likelihood-based method for measuring weak gravitational lensing shear in deep galaxy surveys is described and applied to the Canada-France-Hawaii Telescope (CFHT) Lensing Survey (CFHTLenS). CFHTLenS comprises 154 deg2 of multi-colour optical data from the CFHT Legacy Survey, with lensing measurements being made in the i' band to a depth i'AB < 24.7, for galaxies with signal-to-noise ratio νSN ≳ 10. The method is based on the lensfit algorithm described in earlier papers, but here we describe a full analysis pipeline that takes into account the properties of real surveys. The method creates pixel-based models of the varying point spread function (PSF) in individual image exposures. It fits PSF-convolved two-component (disc plus bulge) models to measure the ellipticity of each galaxy, with Bayesian marginalization over model nuisance parameters of galaxy position, size, brightness and bulge fraction. The method allows optimal joint measurement of multiple, dithered image exposures, taking into account imaging distortion and the alignment of the multiple measurements. We discuss the effects of noise bias on the likelihood distribution of galaxy ellipticity. Two sets of image simulations that mirror the observed properties of CFHTLenS have been created to establish the method's accuracy and to derive an empirical correction for the effects of noise bias.
The DES Science Verification Weak Lensing Shear Catalogs
Jarvis, M.
2015-07-20
We present weak lensing shear catalogs for 139 square degrees of data taken during the Science Verification (SV) time for the new Dark Energy Camera (DECam) being used for the Dark Energy Survey (DES). We describe our object selection, point spread function estimation and shear measurement procedures using two independent shear pipelines, IM3SHAPE and NGMIX, which produce catalogs of 2.12 million and 3.44 million galaxies respectively. We also detail a set of null tests for the shear measurements and find that they pass the requirements for systematic errors at the level necessary for weak lensing science applications using the SV data. Furthermore, we discuss some of the planned algorithmic improvements that will be necessary to produce sufficiently accurate shear catalogs for the full 5-year DES, which is expected to cover 5000 square degrees.
The statistics of gravitational lenses. III - Astrophysical consequences of quasar lensing
NASA Technical Reports Server (NTRS)
Ostriker, J. P.; Vietri, M.
1986-01-01
The method of Schmidt and Green (1983) for calculating the luminosity function of quasars is combined with gravitational-lensing theory to compute expected properties of lensed systems. Multiple quasar images produced by galaxies are of order 0.001 of the observed quasars, with the numbers over the whole sky calculated to be (0.86, 120, 1600) to limiting B magnitudes of (16, 19, 22). The amount of 'false evolution' is small except for an interesting subset of apparently bright, large-redshift objects for which minilensing by starlike objects may be important. Some of the BL Lac objects may be in this category, with the galaxy identified as the parent object really a foreground object within which stars have lensed a background optically violent variable quasar.
Direct Shear Mapping: Prospects for Weak Lensing Studies of Individual Galaxy-Galaxy Lensing Systems
NASA Astrophysics Data System (ADS)
de Burgh-Day, C. O.; Taylor, E. N.; Webster, R. L.; Hopkins, A. M.
2015-11-01
Using both a theoretical and an empirical approach, we have investigated the frequency of low redshift galaxy-galaxy lensing systems in which the signature of 3D weak lensing might be directly detectable. We find good agreement between these two approaches. Using data from the Galaxy and Mass Assembly redshift survey we estimate the frequency of detectable weak lensing at low redshift. We find that below a redshift of z ~ 0.6, the probability of a galaxy being weakly lensed by ? ? 0.02 is ~ 0.01. We have also investigated the feasibility of measuring the scatter in the M * - Mh relation using shear statistics. We estimate that for a shear measurement error of ?? = 0.02 (consistent with the sensitivity of the Direct Shear Mapping technique), with a sample of ~50,000 spatially and spectrally resolved galaxies, the scatter in the M * - Mh relation could be measured. While there are currently no existing IFU surveys of this size, there are upcoming surveys that will provide this data (e.g The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), surveys with Hector, and the Square Kilometre Array (SKA)).
TESTING THE DARK ENERGY WITH GRAVITATIONAL LENSING STATISTICS
Cao Shuo; Zhu Zonghong; Covone, Giovanni
2012-08-10
We study the redshift distribution of two samples of early-type gravitational lenses, extracted from a larger collection of 122 systems, to constrain the cosmological constant in the {Lambda}CDM model and the parameters of a set of alternative dark energy models (XCDM, Dvali-Gabadadze-Porrati, and Ricci dark energy models), in a spatially flat universe. The likelihood is maximized for {Omega}{sub {Lambda}} = 0.70 {+-} 0.09 when considering the sample excluding the Sloan Lens ACS systems (known to be biased toward large image-separation lenses) and no-evolution, and {Omega}{sub {Lambda}} = 0.81 {+-} 0.05 when limiting to gravitational lenses with image separation {Delta}{theta} > 2'' and no-evolution. In both cases, results accounting for galaxy evolution are consistent within 1{sigma}. The present test supports the accelerated expansion, by excluding the null hypothesis (i.e., {Omega}{sub {Lambda}} = 0) at more than 4{sigma}, regardless of the chosen sample and assumptions on the galaxy evolution. A comparison between competitive world models is performed by means of the Bayesian information criterion. This shows that the simplest cosmological constant model-that has only one free parameter-is still preferred by the available data on the redshift distribution of gravitational lenses. We perform an analysis of the possible systematic effects, finding that the systematic errors due to sample incompleteness, galaxy evolution, and model uncertainties approximately equal the statistical errors, with present-day data. We find that the largest sources of systemic errors are the dynamical normalization and the high-velocity cutoff factor, followed by the faint-end slope of the velocity dispersion function.
Biesiada, Marek; Ding, Xuheng; Zhu, Zong-Hong; Piórkowska, Aleksandra E-mail: dingxuheng@mail.bnu.edu.cn E-mail: zhuzh@bnu.edu.cn
2014-10-01
Gravitational wave (GW) experiments are entering their advanced stage which should soon open a new observational window on the Universe. Looking into this future, the Einstein Telescope (ET) was designed to have a fantastic sensitivity improving significantly over the advanced GW detectors. One of the most important astrophysical GW sources supposed to be detected by the ET in large numbers are double compact objects (DCO) and some of such events should be gravitationally lensed by intervening galaxies. We explore the prospects of observing gravitationally lensed inspiral DCO events in the ET. This analysis is a significant extension of our previous paper [1]. We are using the intrinsic merger rates of the whole class of DCO (NS-NS,BH-NS,BH-BH) located at different redshifts as calculated by [2] by using StarTrack population synthesis evolutionary code. We discuss in details predictions from each evolutionary scenario. Our general conclusion is that ET would register about 50–100 strongly lensed inspiral events per year. Only the scenario in which nascent BHs receive strong kick gives the predictions of a few events per year. Such lensed events would be dominated by the BH-BH merging binary systems. Our results suggest that during a few years of successful operation ET will provide a considerable catalog of strongly lensed events.
NASA Astrophysics Data System (ADS)
Biesiada, Marek; Ding, Xuheng; Piórkowska, Aleksandra; Zhu, Zong-Hong
2014-10-01
Gravitational wave (GW) experiments are entering their advanced stage which should soon open a new observational window on the Universe. Looking into this future, the Einstein Telescope (ET) was designed to have a fantastic sensitivity improving significantly over the advanced GW detectors. One of the most important astrophysical GW sources supposed to be detected by the ET in large numbers are double compact objects (DCO) and some of such events should be gravitationally lensed by intervening galaxies. We explore the prospects of observing gravitationally lensed inspiral DCO events in the ET. This analysis is a significant extension of our previous paper [1]. We are using the intrinsic merger rates of the whole class of DCO (NS-NS,BH-NS,BH-BH) located at different redshifts as calculated by [2] by using StarTrack population synthesis evolutionary code. We discuss in details predictions from each evolutionary scenario. Our general conclusion is that ET would register about 50-100 strongly lensed inspiral events per year. Only the scenario in which nascent BHs receive strong kick gives the predictions of a few events per year. Such lensed events would be dominated by the BH-BH merging binary systems. Our results suggest that during a few years of successful operation ET will provide a considerable catalog of strongly lensed events.
Optimizing weak lensing mass estimates for cluster profile uncertainty
Gruen, D.; Bernstein, G. M.; Lam, T. Y.; Seitz, S.
2011-09-11
Weak lensing measurements of cluster masses are necessary for calibrating mass-observable relations (MORs) to investigate the growth of structure and the properties of dark energy. However, the measured cluster shear signal varies at fixed mass M_{200m }due to inherent ellipticity of background galaxies, intervening structures along the line of sight, and variations in the cluster structure due to scatter in concentrations, asphericity and substructure. We use N-body simulated halos to derive and evaluate a weak lensing circular aperture mass measurement M_{ap} that minimizes the mass estimate variance <(M_{ap} - M_{200m})^{2}> in the presence of all these forms of variability. Depending on halo mass and observational conditions, the resulting mass estimator improves on M_{ap} filters optimized for circular NFW-profile clusters in the presence of uncorrelated large scale structure (LSS) about as much as the latter improve on an estimator that only minimizes the influence of shape noise. Optimizing for uncorrelated LSS while ignoring the variation of internal cluster structure puts too much weight on the profile near the cores of halos, and under some circumstances can even be worse than not accounting for LSS at all. As a result, we discuss the impact of variability in cluster structure and correlated structures on the design and performance of weak lensing surveys intended to calibrate cluster MORs.
Optimizing weak lensing mass estimates for cluster profile uncertainty
Gruen, D.; Bernstein, G. M.; Lam, T. Y.; Seitz, S.
2011-09-11
Weak lensing measurements of cluster masses are necessary for calibrating mass-observable relations (MORs) to investigate the growth of structure and the properties of dark energy. However, the measured cluster shear signal varies at fixed mass M200m due to inherent ellipticity of background galaxies, intervening structures along the line of sight, and variations in the cluster structure due to scatter in concentrations, asphericity and substructure. We use N-body simulated halos to derive and evaluate a weak lensing circular aperture mass measurement Map that minimizes the mass estimate variance <(Map - M200m)2> in the presence of all these forms of variability. Dependingmore » on halo mass and observational conditions, the resulting mass estimator improves on Map filters optimized for circular NFW-profile clusters in the presence of uncorrelated large scale structure (LSS) about as much as the latter improve on an estimator that only minimizes the influence of shape noise. Optimizing for uncorrelated LSS while ignoring the variation of internal cluster structure puts too much weight on the profile near the cores of halos, and under some circumstances can even be worse than not accounting for LSS at all. As a result, we discuss the impact of variability in cluster structure and correlated structures on the design and performance of weak lensing surveys intended to calibrate cluster MORs.« less
How gravitational lensing helps ?-ray photons avoid ? ? absorption
Barnacka, Anna; Bttcher, Markus; Sushch, Iurii E-mail: Markus.Bottcher@nwu.ac.za
2014-08-01
We investigate potential ? ? absorption of ?-ray emission from blazars arising from inhomogeneities along the line of sight, beyond the diffuse Extragalactic Background Light (EBL). As plausible sources of excess ? ? opacity, we consider (1) foreground galaxies, including cases in which this configuration leads to strong gravitational lensing, (2) individual stars within these foreground galaxies, and (3) individual stars within our own galaxy, which may act as lenses for microlensing events. We found that intervening galaxies close to the line of sight are unlikely to lead to significant excess ? ? absorption. This opens up the prospect of detecting lensed gamma-ray blazars at energies above 10 GeV with their gamma-ray spectra effectively only affected by the EBL. The most luminous stars located either in intervening galaxies or in our galaxy provide an environment in which these gamma-rays could, in principle, be significantly absorbed. However, despite a large microlensing probability due to stars located in intervening galaxies, ?-rays avoid absorption by being deflected by the gravitational potentials of such intervening stars to projected distances ({sup i}mpact parameters{sup )} where the resulting ? ? opacities are negligible. Thus, neither of the intervening excess photon fields considered here, provide a substantial source of excess ? ? opacity beyond the EBL, even in the case of very close alignments between the background blazar and a foreground star or galaxy.
Galactic Internet made possible by star gravitational lensing
NASA Astrophysics Data System (ADS)
Maccone, Claudio
2013-02-01
In this paper we study how to create a radio bridge between the Sun and any other star made up by both the gravitational lenses of the Sun and that star. The alignment for this radio bridge to work is very strict, but the power-saving is enormous, due to the huge contributions of the two stars' lenses to the overall antenna gain of the system. In particular, we study in detail: The Sun-Alpha Centauri A radio bridge. The Sun-Barnard's star radio bridge. The Sun-Sirius A radio bridge. The radio bridge between the Sun and any Sun-like star located in the Galactic Bulge. The radio bridge between the Sun and a similar Sun-like star located inside the Andromeda galaxy (M31). Finally, we find the information channel capacity for each of the above radio bridges, putting thus a physical constraint to the maximum information transfer that will be enabled even by exploiting the stars as gravitational lenses. The conclusion is that a Galactic Internet is indeed physically possible. May be the Galactic Internet already is in existence, and was created long ago by civilizations more advanced than ours. But the potential for creating such a system has only recently been realized by Humans.
Using Strong Gravitational Lensing to Identify Fossil Group Progenitors
NASA Astrophysics Data System (ADS)
Johnson, Lucas; Irwin, Jimmy; White, Raymond Edwin
2016-01-01
Fossil galaxy systems are thought to be the end result of group evolution, as galaxies experiencing dynamical friction sink to the center of the group potential and merge into a single elliptical that dominates the rest of the members in both mass and luminosity. However, two alternate formation mechanisms are possible: a group merger scenario where two smaller group BGG's merge into one large elliptical which then promotes the final group to fossil status or the group being initially "born that way." The group merger mechanism could explain why some fossils exhibit cool cores while others do not, as gas cooling timescales are significantly longer than galaxy merging timescales. Most fossil systems discovered lie within z<0.2, which begs the question: what did these systems look like in the past, and which formation process did they undergo? Such progenitors are expected to be systems with imminent or ongoing major mergers that will transition into fossil status before z=0. The group merger scenario (particularly along the line-of-sight), or even simply the dominance of the fossil BGG, suggests a highly concentrated system ideal for strong gravitational lensing. Strong lensing events also preferentially pick out merging systems which makes this an ideal selection criteria for our study. We use the CASSOWARY survey of strong lensing events as our sample with the goal of determining if lensing systems have a predisposition of being fossil systems or progenitors. We present a catalog of fossil progenitor candidates from the CASSOWARY survey with redshifts ranging from 0.1
Probing Dark Energy with Weak Lensing with LSST
NASA Astrophysics Data System (ADS)
Dell'Antonio, Ian P.; Wittman, D.; Jain, B.; Bosch, J.; Clowe, D.; Jarvis, M.; Jee, M.; Tyson, J.; Zhan, H.; LSST Weak Lensing Science Collaboration
2011-01-01
LSST will measure the shape, magnitude, and colors of more than 3x109 galaxies over 20,000 square degrees. These data will be used in several complementary ways to measure the properties of dark energy. Reconstruction of the shear power spectrum on linear and non-linear scales l /< 2000, and of the cross-correlation of shear measured in different photometric redshift bins, provides a constraint on the evolution of dark energy that is complementary to the purely geometric measures provided by Supernovae and BAO. Combining weak lensing and BAO measurements breaks degeneracies and results in tighter constraints on dark energy than each method can provide individually. Cross-correlation of the shear and galaxy number density signal within redshift shells minimizes the sensitivity to photo-z errors. Measurements of the shear bispectrum constrain dark energy and allow an independent test of theories of gravity. In addition to the galaxy shape correlations, LSST will detect 50,000 shear peaks with significance greater than 4?, and 10,000 securely detected clusters of galaxies with line-of-sight velocity dispersions greater than 700 km/s. These allow independent constraints on the dark energy signature in the growth of structure. Tomographic study of the shear of background galaxies as a function of redshift allows the a geometric test of dark energy to be extracted from the weak lensing data. Finally, lensing signatures beyond the shear (magnification and flexion) will be accessible with LSST with unprecedented statistical power. The ability of LSST to extract the dark energy signal will depend on the accuracy with which the stellar PSF can be determined, and on the unbiased reconstruction of object shapes from long sequences of exposures in which the objects are detected at low significance. We discuss the prospects for cosmological constraints from weak lensing studies with LSST.
Catastrophic photometric redshift errors: Weak-lensing survey requirements
Bernstein, Gary; Huterer, Dragan
2010-01-11
We study the sensitivity of weak lensing surveys to the effects of catastrophic redshift errors - cases where the true redshift is misestimated by a significant amount. To compute the biases in cosmological parameters, we adopt an efficient linearized analysis where the redshift errors are directly related to shifts in the weak lensing convergence power spectra. We estimate the number N_{spec} of unbiased spectroscopic redshifts needed to determine the catastrophic error rate well enough that biases in cosmological parameters are below statistical errors of weak lensing tomography. While the straightforward estimate of N_{spec} is ~10^{6} we find that using only the photometric redshifts with z ≤ 2.5 leads to a drastic reduction in N_{spec} to ~ 30,000 while negligibly increasing statistical errors in dark energy parameters. Therefore, the size of spectroscopic survey needed to control catastrophic errors is similar to that previously deemed necessary to constrain the core of the z_{s} – z_{p} distribution. We also study the efficacy of the recent proposal to measure redshift errors by cross-correlation between the photo-z and spectroscopic samples. We find that this method requires ~ 10% a priori knowledge of the bias and stochasticity of the outlier population, and is also easily confounded by lensing magnification bias. In conclusion, the cross-correlation method is therefore unlikely to supplant the need for a complete spectroscopic redshift survey of the source population.
Statistical uncertainties and systematic errors in weak lensing mass estimates of galaxy clusters
NASA Astrophysics Data System (ADS)
Khlinger, F.; Hoekstra, H.; Eriksen, M.
2015-11-01
Upcoming and ongoing large area weak lensing surveys will also discover large samples of galaxy clusters. Accurate and precise masses of galaxy clusters are of major importance for cosmology, for example, in establishing well-calibrated observational halo mass functions for comparison with cosmological predictions. We investigate the level of statistical uncertainties and sources of systematic errors expected for weak lensing mass estimates. Future surveys that will cover large areas on the sky, such as Euclid or LSST and to lesser extent DES, will provide the largest weak lensing cluster samples with the lowest level of statistical noise regarding ensembles of galaxy clusters. However, the expected low level of statistical uncertainties requires us to scrutinize various sources of systematic errors. In particular, we investigate the bias due to cluster member galaxies which are erroneously treated as background source galaxies due to wrongly assigned photometric redshifts. We find that this effect is significant when referring to stacks of galaxy clusters. Finally, we study the bias due to miscentring, i.e. the displacement between any observationally defined cluster centre and the true minimum of its gravitational potential. The impact of this bias might be significant with respect to the statistical uncertainties. However, complementary future missions such as eROSITA will allow us to define stringent priors on miscentring parameters which will mitigate this bias significantly.
Weak lensing by galaxy troughs in DES Science Verification data
Gruen, D.; Friedrich, O.; Amara, A.; Bacon, D.; Bonnett, C.; Hartley, W.; Jain, B.; M. Jarvis; Kavprzak, T.; Krause, E.; et al
2015-11-29
In this study, we measure the weak lensing shear around galaxy troughs, i.e. the radial alignment of background galaxies relative to underdensities in projections of the foreground galaxy field over a wide range of redshift in Science Verification data from the Dark Energy Survey. Our detection of the shear signal is highly significant (10σ–15σ for the smallest angular scales) for troughs with the redshift range z ϵ [0.2, 0.5] of the projected galaxy field and angular diameters of 10 arcmin…1°. These measurements probe the connection between the galaxy, matter density, and convergence fields. By assuming galaxies are biased tracers ofmore » the matter density with Poissonian noise, we find agreement of our measurements with predictions in a fiducial Λ cold dark matter model. The prediction for the lensing signal on large trough scales is virtually independent of the details of the underlying model for the connection of galaxies and matter. Our comparison of the shear around troughs with that around cylinders with large galaxy counts is consistent with a symmetry between galaxy and matter over- and underdensities. In addition, we measure the two-point angular correlation of troughs with galaxies which, in contrast to the lensing signal, is sensitive to galaxy bias on all scales. The lensing signal of troughs and their clustering with galaxies is therefore a promising probe of the statistical properties of matter underdensities and their connection to the galaxy field.« less
Weak lensing by galaxy troughs in DES Science Verification data
Gruen, D.; Friedrich, O.; Amara, A.; Bacon, D.; Bonnett, C.; Hartley, W.; Jain, B.; M. Jarvis; Kavprzak, T.; Krause, E.; Mana, A.; Rozo, E.; Rykoff, E. S.; Seitz, S.; Sheldon, E.; Troxel, M. A.; Vikram, V.; Abbott, T. M. C.; Abdalla, F. B.; Allam, S.; Armstrong, R.; Banerji, M.; Bauer, A. H.; Becker, M. R.; Benoit-Levy, A.; Bernstein, G. M.; Bernstein, R. A.; Bertin, E.; Bridle, S. L.; Brooks, D.; Buckley-Geer, E.; Burke, D. L.; Capozzi, D.; Rosell, A. Carnero; Carretero, J.; Crocce, M.; Cunha, C. E.; D'Andrea, C. B.; da Costa, L. N.; DePoy, D. L.; Desai, S.; Diehl, H. T.; Dietrich, J. P.; Doel, P.; Eifler, T. F.; Neto, A. Fausti; Fernandez, E.; Flaugher, B.; Fosalba, P.; Frieman, J.; Gerdes, D. W.; Gruendl, R. A.; Gutierrez, G.; Honscheid, K.; James, D. J.; Kuehn, K.; Kuropatkin, N.; Lahav, O.; Li, T. S.; Lima, M.; Maia, M. A. G.; March, M.; Martini, P.; Melchior, P.; Miller, C. J.; Miguel, R.; Mohr, J. J.; Nord, B.; Orgando, R.; Plazas, A. A.; Reil, K.; Romer, A. K.; Roodman, A.; Sako, M.; Sanchez, E.; Scarpine, V.; Schubnell, M.; Sevilla-Noarbe, I.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thaler, J.; Thomas, D.; Walker, A. R.; Wechsler, R. H.; Weller, J.; Zhang, Y.; Zuntz, J.
2015-11-29
In this study, we measure the weak lensing shear around galaxy troughs, i.e. the radial alignment of background galaxies relative to underdensities in projections of the foreground galaxy field over a wide range of redshift in Science Verification data from the Dark Energy Survey. Our detection of the shear signal is highly significant (10σ–15σ for the smallest angular scales) for troughs with the redshift range z ϵ [0.2, 0.5] of the projected galaxy field and angular diameters of 10 arcmin…1°. These measurements probe the connection between the galaxy, matter density, and convergence fields. By assuming galaxies are biased tracers of the matter density with Poissonian noise, we find agreement of our measurements with predictions in a fiducial Λ cold dark matter model. The prediction for the lensing signal on large trough scales is virtually independent of the details of the underlying model for the connection of galaxies and matter. Our comparison of the shear around troughs with that around cylinders with large galaxy counts is consistent with a symmetry between galaxy and matter over- and underdensities. In addition, we measure the two-point angular correlation of troughs with galaxies which, in contrast to the lensing signal, is sensitive to galaxy bias on all scales. The lensing signal of troughs and their clustering with galaxies is therefore a promising probe of the statistical properties of matter underdensities and their connection to the galaxy field.
Weak lensing by galaxy troughs in DES Science Verification data
NASA Astrophysics Data System (ADS)
Gruen, D.; Friedrich, O.; Amara, A.; Bacon, D.; Bonnett, C.; Hartley, W.; Jain, B.; Jarvis, M.; Kacprzak, T.; Krause, E.; Mana, A.; Rozo, E.; Rykoff, E. S.; Seitz, S.; Sheldon, E.; Troxel, M. A.; Vikram, V.; Abbott, T. M. C.; Abdalla, F. B.; Allam, S.; Armstrong, R.; Banerji, M.; Bauer, A. H.; Becker, M. R.; Benoit-Lévy, A.; Bernstein, G. M.; Bernstein, R. A.; Bertin, E.; Bridle, S. L.; Brooks, D.; Buckley-Geer, E.; Burke, D. L.; Capozzi, D.; Carnero Rosell, A.; Carrasco Kind, M.; Carretero, J.; Crocce, M.; Cunha, C. E.; D'Andrea, C. B.; da Costa, L. N.; DePoy, D. L.; Desai, S.; Diehl, H. T.; Dietrich, J. P.; Doel, P.; Eifler, T. F.; Neto, A. Fausti; Fernandez, E.; Flaugher, B.; Fosalba, P.; Frieman, J.; Gerdes, D. W.; Gruendl, R. A.; Gutierrez, G.; Honscheid, K.; James, D. J.; Kuehn, K.; Kuropatkin, N.; Lahav, O.; Li, T. S.; Lima, M.; Maia, M. A. G.; March, M.; Martini, P.; Melchior, P.; Miller, C. J.; Miquel, R.; Mohr, J. J.; Nord, B.; Ogando, R.; Plazas, A. A.; Reil, K.; Romer, A. K.; Roodman, A.; Sako, M.; Sanchez, E.; Scarpine, V.; Schubnell, M.; Sevilla-Noarbe, I.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thaler, J.; Thomas, D.; Walker, A. R.; Wechsler, R. H.; Weller, J.; Zhang, Y.; Zuntz, J.
2016-01-01
We measure the weak lensing shear around galaxy troughs, i.e. the radial alignment of background galaxies relative to underdensities in projections of the foreground galaxy field over a wide range of redshift in Science Verification data from the Dark Energy Survey. Our detection of the shear signal is highly significant (10σ-15σ for the smallest angular scales) for troughs with the redshift range z ∈ [0.2, 0.5] of the projected galaxy field and angular diameters of 10 arcmin…1°. These measurements probe the connection between the galaxy, matter density, and convergence fields. By assuming galaxies are biased tracers of the matter density with Poissonian noise, we find agreement of our measurements with predictions in a fiducial Λ cold dark matter model. The prediction for the lensing signal on large trough scales is virtually independent of the details of the underlying model for the connection of galaxies and matter. Our comparison of the shear around troughs with that around cylinders with large galaxy counts is consistent with a symmetry between galaxy and matter over- and underdensities. In addition, we measure the two-point angular correlation of troughs with galaxies which, in contrast to the lensing signal, is sensitive to galaxy bias on all scales. The lensing signal of troughs and their clustering with galaxies is therefore a promising probe of the statistical properties of matter underdensities and their connection to the galaxy field.
Weak Lensing by Galaxy Troughs in DES Science Verification Data
Gruen, D.
2015-09-29
We measure the weak lensing shear around galaxy troughs, i.e. the radial alignment of background galaxies relative to underdensities in projections of the foreground galaxy field over a wide range of redshift in Science Verification data from the Dark Energy Survey. Our detection of the shear signal is highly significant (10?15? for the smallest angular scales) for troughs with the redshift range z ? [0.2, 0.5] of the projected galaxy field and angular diameters of 10 arcmin1. These measurements probe the connection between the galaxy, matter density, and convergence fields. By assuming galaxies are biased tracers of the matter density with Poissonian noise, we find agreement of our measurements with predictions in a fiducial ? cold dark matter model. Furthermore, the prediction for the lensing signal on large trough scales is virtually independent of the details of the underlying model for the connection of galaxies and matter. Our comparison of the shear around troughs with that around cylinders with large galaxy counts is consistent with a symmetry between galaxy and matter over- and underdensities. In addition, we measure the two-point angular correlation of troughs with galaxies which, in contrast to the lensing signal, is sensitive to galaxy bias on all scales. Finally, the lensing signal of troughs and their clustering with galaxies is therefore a promising probe of the statistical properties of matter underdensities and their connection to the galaxy field.
Weak Lensing by Galaxy Troughs in DES Science Verification Data
Gruen, D.
2015-09-29
We measure the weak lensing shear around galaxy troughs, i.e. the radial alignment of background galaxies relative to underdensities in projections of the foreground galaxy field over a wide range of redshift in Science Verification data from the Dark Energy Survey. Our detection of the shear signal is highly significant (10?15? for the smallest angular scales) for troughs with the redshift range z ? [0.2, 0.5] of the projected galaxy field and angular diameters of 10 arcmin1. These measurements probe the connection between the galaxy, matter density, and convergence fields. By assuming galaxies are biased tracers of the matter densitymorewith Poissonian noise, we find agreement of our measurements with predictions in a fiducial ? cold dark matter model. Furthermore, the prediction for the lensing signal on large trough scales is virtually independent of the details of the underlying model for the connection of galaxies and matter. Our comparison of the shear around troughs with that around cylinders with large galaxy counts is consistent with a symmetry between galaxy and matter over- and underdensities. In addition, we measure the two-point angular correlation of troughs with galaxies which, in contrast to the lensing signal, is sensitive to galaxy bias on all scales. Finally, the lensing signal of troughs and their clustering with galaxies is therefore a promising probe of the statistical properties of matter underdensities and their connection to the galaxy field.less
Gravitational lensing analysis of the Kilo-Degree Survey
NASA Astrophysics Data System (ADS)
Kuijken, Konrad; Heymans, Catherine; Hildebrandt, Hendrik; Nakajima, Reiko; Erben, Thomas; de Jong, Jelte T. A.; Viola, Massimo; Choi, Ami; Hoekstra, Henk; Miller, Lance; van Uitert, Edo; Amon, Alexandra; Blake, Chris; Brouwer, Margot; Buddendiek, Axel; Conti, Ian Fenech; Eriksen, Martin; Grado, Aniello; Harnois-Déraps, Joachim; Helmich, Ewout; Herbonnet, Ricardo; Irisarri, Nancy; Kitching, Thomas; Klaes, Dominik; La Barbera, Francesco; Napolitano, Nicola; Radovich, Mario; Schneider, Peter; Sifón, Cristóbal; Sikkema, Gert; Simon, Patrick; Tudorica, Alexandru; Valentijn, Edwin; Verdoes Kleijn, Gijs; van Waerbeke, Ludovic
2015-12-01
The Kilo-Degree Survey (KiDS) is a multi-band imaging survey designed for cosmological studies from weak lensing and photometric redshifts. It uses the European Southern Observatory VLT Survey Telescope with its wide-field camera OmegaCAM. KiDS images are taken in four filters similar to the Sloan Digital Sky Survey ugri bands. The best seeing time is reserved for deep r-band observations. The median 5σ limiting AB magnitude is 24.9 and the median seeing is below 0.7 arcsec. Initial KiDS observations have concentrated on the Galaxy and Mass Assembly (GAMA) regions near the celestial equator, where extensive, highly complete redshift catalogues are available. A total of 109 survey tiles, 1 square degree each, form the basis of the first set of lensing analyses of halo properties of GAMA galaxies. Nine galaxies per square arcminute enter the lensing analysis, for an effective inverse shear variance of 69 arcmin-2. Accounting for the shape measurement weight, the median redshift of the sources is 0.53. KiDS data processing follows two parallel tracks, one optimized for weak lensing measurement and one for accurate matched-aperture photometry (for photometric redshifts). This technical paper describes the lensing and photometric redshift measurements (including a detailed description of the Gaussian aperture and photometry pipeline), summarizes the data quality and presents extensive tests for systematic errors that might affect the lensing analyses. We also provide first demonstrations of the suitability of the data for cosmological measurements, and describe our blinding procedure for preventing confirmation bias in the scientific analyses. The KiDS catalogues presented in this paper are released to the community through http://kids.strw.leidenuniv.nl.
SPITZER IMAGING OF HERSCHEL-ATLAS GRAVITATIONALLY LENSED SUBMILLIMETER SOURCES
Hopwood, R.; Negrello, M.; Wardlow, J.; Cooray, A.; Khostovan, A. A.; Kim, S.; Barton, E.; Da Cunha, E.; Cooke, J.; Burgarella, D.; Aretxaga, I.; Auld, R.; Baes, M.; Bertoldi, F.; Bonfield, D. G.; Blundell, R.; Buttiglione, S.; Cava, A.; Dannerbauer, H.
2011-02-10
We present physical properties of two submillimeter selected gravitationally lensed sources, identified in the Herschel Astrophysical Terahertz Large Area Survey. These submillimeter galaxies (SMGs) have flux densities >100 mJy at 500 {mu}m, but are not visible in existing optical imaging. We fit light profiles to each component of the lensing systems in Spitzer IRAC 3.6 and 4.5 {mu}m data and successfully disentangle the foreground lens from the background source in each case, providing important constraints on the spectral energy distributions (SEDs) of the background SMG at rest-frame optical-near-infrared wavelengths. The SED fits show that these two SMGs have high dust obscuration with A{sub V} {approx} 4-5 and star formation rates of {approx}100 M{sub sun} yr{sup -1}. They have low gas fractions and low dynamical masses compared with 850 {mu}m selected galaxies.
Weak lensing survey of galaxy clusters in the CFHTLS Deep
NASA Astrophysics Data System (ADS)
Gavazzi, R.; Soucail, G.
2007-02-01
Aims: We present a weak lensing search of galaxy clusters in the 4 deg2 of the CFHT Legacy Survey Deep. This work aims at building a mass-selected sample of clusters with well controlled selection effects. This present survey is a preliminary step toward a full implementation in the forthcoming 170 deg2 of the CFHTLS Wide survey. Methods: We use the deep i' band images observed under subarcsecond seeing conditions to perform weak lensing mass reconstructions and to identify high convergence peaks. Thanks to the availability of deep u^*g'r'i'z' exposures, sources are selected from their photometric redshifts in the weak lensing analysis. We also use lensing tomography to derive an estimate of the lens redshift. After considering the raw statistics of peaks we check whether they can be associated to a clear optical counterpart or to published X-ray selected clusters. Results: Among the 14 peaks found above a signal-to-noise detection threshold ?=3.5, nine are secure detections with estimated redshift 0.1? z_l?0.7 and a velocity dispersion 450??_v? 700 {km s}-1. This low mass range is accessible thanks to the high density of background sources. Considering the intersection between the shear-selected clusters and XMM-LSS X-ray clusters in the D1 field, we observe that the ICM gas in these low-mass clusters (T_X1{-}2 keV) is not hotter than the temperature inferred from shear, this trend being different for published massive clusters. A more extended weak lensing survey, with higher statistics of mass structures will be a promising way to bypass several of the problems related to standard detection methods based on the complex physics of baryons. Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This work is based in part on data products produced at TERAPIX and the Canadian Astronomy Data Centre as part of the Canada-France-Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNRS.
Quasar Structure from Microlensing in Gravitationally Lensed Quasars
NASA Astrophysics Data System (ADS)
Morgan, Christopher W.
2007-12-01
I investigate microlensing in gravitationally lensed quasars and discuss the use of its signal to probe quasar structure on small angular scales. I describe our lensed quasar optical monitoring program and RETROCAM, the optical camera I built for the 2.4m Hiltner telescope to monitor lensed quasars. I use the microlensing variability observed in 11 gravitationally lensed quasars to show that the accretion disk size at 2500 is related to the black hole mass by log(R2500/cm) = (15.700.16) + (0.640.18)log(MBH/109M?). This scaling is consistent with the expectation from thin disk theory (R ? MBH2/3), but it implies that black holes radiate with relatively low efficiency, log(?) = -1.540.36 + log(L/LE) where ?=L/(Mdotc2). With one exception, these sizes are larger by a factor of 4 than the size needed to produce the observed 0.8m quasar flux by thermal radiation from a thin disk with the same T ? R-3/4 temperature profile. More sophisticated disk models are clearly required, particularly as our continuing observations improve the precision of the measurements and yield estimates of the scaling with wavelength and accretion rate. This research made extensive use of a Beowulf computer cluster obtained through the Cluster Ohio program of the Ohio Supercomputer Center. Support for program HST-GO-9744 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS-5-26666.
A comparison of cosmological models using strong gravitational lensing galaxies
Melia, Fulvio; Wei, Jun-Jie; Wu, Xue-Feng E-mail: jjwei@pmo.ac.cn E-mail: fmelia@email.arizona.edu E-mail: xfwu@pmo.ac.cn
2015-01-01
Strongly gravitationally lensed quasar-galaxy systems allow us to compare competing cosmologies as long as one can be reasonably sure of the mass distribution within the intervening lens. In this paper, we assemble a catalog of 69 such systems from the Sloan Lens ACS and Lens Structure and Dynamics surveys suitable for this analysis, and carry out a one-on-one comparison between the standard model, ?CDM, and the R{sub h}=ct universe, which has thus far been favored by the application of model selection tools to other kinds of data. We find that both models account for the lens observations quite well, though the precision of these measurements does not appear to be good enough to favor one model over the other. Part of the reason is the so-called bulge-halo conspiracy that, on average, results in a baryonic velocity dispersion within a fraction of the optical effective radius virtually identical to that expected for the whole luminous-dark matter distribution modeled as a singular isothermal ellipsoid, though with some scatter among individual sources. Future work can greatly improve the precision of these measurements by focusing on lensing systems with galaxies as close as possible to the background sources. Given the limitations of doing precision cosmological testing using the current sample, we also carry out Monte Carlo simulations based on the current lens measurements to estimate how large the source catalog would have to be in order to rule out either model at a ?99.7% confidence level. We find that if the real cosmology is ?CDM, a sample of ?200 strong gravitational lenses would be sufficient to rule out R{sub h}=ct at this level of accuracy, while ?300 strong gravitational lenses would be required to rule out ?CDM if the real universe were instead R{sub h}=ct. The difference in required sample size reflects the greater number of free parameters available to fit the data with ?CDM. We point out that, should the R{sub h}=ct universe eventually emerge as the correct cosmology, its lack of any free parameters for this kind of work will provide a remarkably powerful probe of the mass structure in lensing galaxies, and a means of better understanding the origin of the bulge-halo conspiracy.
A Comparison of Cosmological Models Using Strong Gravitational Lensing Galaxies
NASA Astrophysics Data System (ADS)
Melia, Fulvio; Wei, Jun-Jie; Wu, Xue-Feng
2015-01-01
Strongly gravitationally lensed quasar-galaxy systems allow us to compare competing cosmologies as long as one can be reasonably sure of the mass distribution within the intervening lens. In this paper, we assemble a catalog of 69 such systems from the Sloan Lens ACS and Lens Structure and Dynamics surveys suitable for this analysis, and carry out a one-on-one comparison between the standard model, ?CDM, and the {{R}h}=ct universe, which has thus far been favored by the application of model selection tools to other kinds of data. We find that both models account for the lens observations quite well, though the precision of these measurements does not appear to be good enough to favor one model over the other. Part of the reason is the so-called bulge-halo conspiracy that, on average, results in a baryonic velocity dispersion within a fraction of the optical effective radius virtually identical to that expected for the whole luminous-dark matter distribution modeled as a singular isothermal ellipsoid, though with some scatter among individual sources. Future work can greatly improve the precision of these measurements by focusing on lensing systems with galaxies as close as possible to the background sources. Given the limitations of doing precision cosmological testing using the current sample, we also carry out Monte Carlo simulations based on the current lens measurements to estimate how large the source catalog would have to be in order to rule out either model at a 99.7% confidence level. We find that if the real cosmology is ?CDM, a sample of 200 strong gravitational lenses would be sufficient to rule out {{R}h}=ct at this level of accuracy, while 300 strong gravitational lenses would be required to rule out ?CDM if the real universe were instead {{R}h}=ct. The difference in required sample size reflects the greater number of free parameters available to fit the data with ?CDM. We point out that, should the {{R}h}=ct universe eventually emerge as the correct cosmology, its lack of any free parameters for this kind of work will provide a remarkably powerful probe of the mass structure in lensing galaxies, and a means of better understanding the origin of the bulge-halo conspiracy.
Cold Dark Matter and Strong Gravitational Lensing: Concord or Conflict?
NASA Astrophysics Data System (ADS)
Keeton, Charles R.
2001-11-01
Using the number and sizes of observed gravitational lenses, I derive upper limits on the dark matter content of elliptical galaxies. On average, dark matter can account for no more than 33% of the total mass within one effective radius (Re) of elliptical galaxies or 40% of the mass within 2Re (95% confidence upper limits). I show that galaxies built from cold dark matter (CDM) mass distributions are too concentrated to comfortably satisfy these limits; a high-density (?M=1) CDM cosmology is ruled out at better than 95% confidence, while a low-density, flat cosmology is only marginally consistent with the lens data. Thus, lensing adds to the evidence from spiral galaxy dynamics that CDM mass distributions are too concentrated on kiloparsec scales to agree with real galaxies and extends the argument to elliptical galaxies. Lensing also provides a unique probe of the very inner regions of galaxies, because images are predicted to form near the centers of lens galaxies but are not observed. The lack of central images in deep maps of radio lenses places strong lower limits on the central densities of galaxies. The central densities of CDM galaxies are too low on ~10 pc scales. Supermassive black holes can help suppress central images, but they must lie well off the observed black hole-bulge mass correlation in order to satisfy current limits on central images. Self-interacting dark matter, or any other modification to regular cold dark matter, must simultaneously reduce the densities on kiloparsec scales and increase the densities on parsec scales in order to satisfy the unique constraints from lensing.
GRAVITATIONAL LENSING CORRECTIONS IN FLAT {Lambda}CDM COSMOLOGY
Kantowski, Ronald; Chen Bin; Dai Xinyu E-mail: Bin.Chen-1@ou.ed
2010-08-01
We compute the deflection angle to order (m/r {sub 0}){sup 2} and m/r{sub 0} x {Lambda}r {sup 2}{sub 0} for a light ray traveling in a flat {Lambda}CDM cosmology that encounters a completely condensed mass region. We use a Swiss cheese model for the inhomogeneities and find that the most significant correction to the Einstein angle occurs not because of the nonlinear terms but instead occurs because the condensed mass is embedded in a background cosmology. The Swiss cheese model predicts a decrease in the deflection angle of {approx}2% for weakly lensed galaxies behind the rich cluster A1689 and that the reduction can be as large as {approx}5% for similar rich clusters at z {approx} 1. Weak-lensing deflection angles caused by galaxies can likewise be reduced by as much as {approx}4%. We show that the lowest order correction in which {Lambda} appears is proportional to m/r{sub 0} x {radical}({Lambda}r{sub 0}{sup 2}) and could cause as much as a {approx}0.02% increase in the deflection angle for light that passes through a rich cluster. The lowest order nonlinear correction in the mass is proportional to m/r{sub 0}x{radical}(m/r{sub 0}) and can increase the deflection angle by {approx}0.005% for weak lensing by galaxies.
NASA Astrophysics Data System (ADS)
Applegate, D. E.; Mantz, A.; Allen, S. W.; der Linden, A. von; Morris, R. Glenn; Hilbert, S.; Kelly, Patrick L.; Burke, D. L.; Ebeling, H.; Rapetti, D. A.; Schmidt, R. W.
2016-04-01
This is the fourth in a series of papers studying the astrophysics and cosmology of massive, dynamically relaxed galaxy clusters. Here, we use measurements of weak gravitational lensing from the Weighing the Giants project to calibrate Chandra X-ray measurements of total mass that rely on the assumption of hydrostatic equilibrium. This comparison of X-ray and lensing masses measures the combined bias of X-ray hydrostatic masses from both astrophysical and instrumental sources. While we cannot disentangle the two sources of bias, only the combined bias is relevant for calibrating cosmological measurements using relaxed clusters. Assuming a fixed cosmology, and within a characteristic radius (r2500) determined from the X-ray data, we measure a lensing to X-ray mass ratio of 0.96 ± 9 per cent (stat) ± 9 per cent (sys). We find no significant trends of this ratio with mass, redshift or the morphological indicators used to select the sample. Our results imply that any departures from hydrostatic equilibrium at these radii are offset by calibration errors of comparable magnitude, with large departures of tens-of-percent unlikely. In addition, we find a mean concentration of the sample measured from lensing data of c_{200} = 3.0_{-1.8}^{+4.4}. Anticipated short-term improvements in lensing systematics, and a modest expansion of the relaxed lensing sample, can easily increase the measurement precision by 30-50 per cent, leading to similar improvements in cosmological constraints that employ X-ray hydrostatic mass estimates, such as on Ωm from the cluster gas mass fraction.
Simulating Gravity: Dark Matter and Gravitational Lensing in the Classroom
NASA Astrophysics Data System (ADS)
Ford, Jes; Stang, Jared; Anderson, Catherine
2015-12-01
Dark matter makes up most of the matter in the universe but very little of a standard introductory physics curriculum. Here we present our construction and use of a spandex sheet-style gravity simulator to qualitatively demonstrate two aspects of modern physics related to dark matter. First, we describe an activity in which students explore the dependence of orbital velocities on the central mass of a system, in a demonstration of how scientists first discovered dark matter. Second, we discuss the use of the gravity simulator as a visualization of gravitational lensing, a current astronomical technique for mapping dark matter in the sky. After providing the necessary background for the phenomena of interest, we describe our construction of the gravity simulator and detail our facilitation of these two activities. Together, these activities provide a conceptual visualization of gravitational phenomena related to indirect detection techniques for studying dark matter.
Weak-lensing statistics from the Coyote Universe
NASA Astrophysics Data System (ADS)
Eifler, Tim
2011-11-01
Analysing future weak-lensing data sets from KIDS, Dark Energy Survey (DES), LSST, Euclid and WFIRST requires precise predictions for the weak-lensing measures. In this paper, we present a weak-lensing prediction code based on the Coyote Universe emulator. The Coyote Universe emulator predicts the (non-linear) power spectrum of density fluctuations (P?) to high accuracy for k?[0.002; 3.4] h Mpc-1 within the redshift interval z?[0; 1]; outside this regime, we extend P? using a modified HALOFIT code. This pipeline is used to calculate various second-order cosmic shear statistics, e.g., shear power spectrum, shear-shear correlation function, ring statistics and Complete Orthogonal Set of EB-mode Integrals (COSEBIs), and we examine how the upper limit in k (and z), to which P? is known, impacts on these statistics. For example, we find that kmax 8 h Mpc-1 causes a bias in the shear power spectrum at ? 4000 that is comparable to the statistical errors (intrinsic shape noise and cosmic variance) of a DES-like survey, whereas for LSST-like errors kmax 15 h Mpc-1 is needed to limit the bias at ? 4000. For the most recently developed second-order shear statistics, the COSEBIs, we find that nine modes can be calculated accurately knowing P? to kmax= 10 h Mpc-1. The COSEBIs allow for an EB-mode decomposition using a shear-shear correlation function measured over a finite range, thereby avoiding any EB-mode mixing due to finite survey size. We perform a detailed study in a five-dimensional parameter space in order to examine whether all cosmological information is captured by these nine modes with the result that already 7-8 modes are sufficient.
A generalized method for measuring weak lensing magnification with weighted number counts
NASA Astrophysics Data System (ADS)
Gillis, Bryan R.; Taylor, Andy N.
2016-03-01
We present a derivation of a generalized optimally weighted estimator for the weak lensing magnification signal, including a calculation of errors. With this estimator, we present a local method for optimally estimating the local effects of magnification from weak gravitational lensing, using a comparison of number counts in an arbitrary region of space to the expected unmagnified number counts. We show that when equivalent lens and source samples are used, this estimator is simply related to the optimally weighted correlation function estimator used in past work and vice-versa, but this method has the benefits that it can calculate errors with significantly less computational time, that it can handle overlapping lens and source samples, and that it can easily be extended to mass-mapping. We present a proof-of-principle test of this method on data from the Canada-France-Hawaii Telescope Lensing Survey, showing that its calculated magnification signals agree with predictions from model fits to shear data. Finally, we investigate how magnification data can be used to supplement shear data in determining the best-fitting model mass profiles for galaxy dark matter haloes. We find that at redshifts greater than z ˜ 0.6, the inclusion of magnification can often significantly improve the constraints on the components of the mass profile which relate to galaxies' local environments relative to shear alone, and in high-redshift low- and medium-mass bins, it can have a higher signal-to-noise than the shear signal.
Relativistic weak lensing from a fully non-linear cosmological density field
NASA Astrophysics Data System (ADS)
Thomas, D. B.; Bruni, M.; Wands, D.
2015-09-01
In this paper we examine cosmological weak lensing on non-linear scales and show that there are Newtonian and relativistic contributions and that the latter can also be extracted from standard Newtonian simulations. We use the post-Friedmann formalism, a post-Newtonian type framework for cosmology, to derive the full weak-lensing deflection angle valid on non-linear scales for any metric theory of gravity. We show that the only contributing term that is quadratic in the first order deflection is the expected Born correction and lens-lens coupling term. We use this deflection angle to analyse the vector and tensor contributions to the E- and B- mode cosmic shear power spectra. In our approach, once the gravitational theory has been specified, the metric components are related to the matter content in a well-defined manner. Specifying General Relativity, we write down a complete set of equations for a GR+ΛCDM universe for computing all of the possible lensing terms from Newtonian N-body simulations. We illustrate this with the vector potential and show that, in a GR+ΛCDM universe, its contribution to the E-mode is negligible with respect to that of the conventional Newtonian scalar potential, even on non-linear scales. Thus, under the standard assumption that Newtonian N-body simulations give a good approximation of the matter dynamics, we show that the standard ray tracing approach gives a good description for a ΛCDM cosmology.
THE WEIGHT OF EMPTINESS: THE GRAVITATIONAL LENSING SIGNAL OF STACKED VOIDS
Krause, Elisabeth; Dore, Olivier; Chang, Tzu-Ching; Umetsu, Keiichi
2013-01-10
The upcoming new generation of spectroscopic galaxy redshift surveys will provide large samples of cosmic voids, large distinct, underdense structures in the universe. Combining these with future galaxy imaging surveys, we study the prospects of probing the underlying matter distribution in and around cosmic voids via the weak gravitational lensing effects of stacked voids, utilizing both shear and magnification information. The statistical precision is greatly improved by stacking a large number of voids along different lines of sight, even when taking into account the impact of inherent miscentering and projection effects. We show that Dark Energy Task Force Stage IV surveys, such as the Euclid satellite and the Large Synoptic Survey Telescope, should be able to detect the void lensing signal with sufficient precision from stacking abundant medium-sized voids, thus providing direct constraints on the matter density profile of voids independent of assumptions on galaxy bias.
Constraining cosmological parameters with observational data including weak lensing effects
NASA Astrophysics Data System (ADS)
Li, Hong; Liu, Jie; Xia, Jun-Qing; Sun, Lei; Fan, Zu-Hui; Tao, Charling; Tilquin, Andre; Zhang, Xinmin
2009-05-01
In this Letter, 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, such as the equation-of-state (EoS) of dark energy w, the density fluctuation amplitude ?, the total neutrino mass ?m and the parameters associated with the power spectrum of the primordial fluctuations. Our results show that the ?CDM model remains a good fit to all of these data. In a flat universe, we obtain a tight limit on the constant EoS of dark energy, w=-0.970.041 (1?). For the dynamical dark energy model with time evolving EoS parameterized as w(a)=w+w(1-a), we find that the best-fit values are w=-1.064 and w=0.375, implying the mildly preference of Quintom model whose EoS gets across the cosmological constant boundary during evolution. Regarding the total neutrino mass limit, we obtain the upper limit, ?m<0.471 eV (95% C.L.) within the framework of the flat ?CDM model. Due to the obvious degeneracies between the neutrino mass and the EoS of dark energy model, this upper limit will be relaxed by a factor of 2 in the framework of dynamical dark energy models. Assuming that the primordial fluctuations are adiabatic with a power law spectrum, within the ?CDM model, we find that the upper limit on the ratio of the tensor to scalar is r<0.35 (95% C.L.) and the inflationary models with the slope n?1 are excluded at more than 2? confidence level. In this Letter we pay particular attention to the contribution from the weak lensing data and find that the current weak lensing data do improve the constraints on matter density ?, ?, ?m, and the EoS of dark energy.
Gravitational lens equation for embedded lenses; magnification and ellipticity
Chen, B.; Kantowski, R.; Dai, X.
2011-10-15
We give the lens equation for light deflections caused by point mass condensations in an otherwise spatially homogeneous and flat universe. We assume the signal from a distant source is deflected by a single condensation before it reaches the observer. We call this deflector an embedded lens because the deflecting mass is part of the mean density. The embedded lens equation differs from the conventional lens equation because the deflector mass is not simply an addition to the cosmic mean. We prescribe an iteration scheme to solve this new lens equation and use it to compare our results with standard linear lensing theory. We also compute analytic expressions for the lowest order corrections to image amplifications and distortions caused by incorporating the lensing mass into the mean. We use these results to estimate the effect of embedding on strong lensing magnifications and ellipticities and find only small effects, <1%, contrary to what we have found for time delays and for weak lensing, {approx}5%.
X-RAY MONITORING OF GRAVITATIONAL LENSES WITH CHANDRA
Chen Bin; Dai Xinyu; Kochanek, Christopher S.; Blackburne, Jeffrey A.; Chartas, George; Morgan, Christopher W.
2012-08-10
We present Chandra monitoring data for six gravitationally lensed quasars: QJ 0158-4325, HE 0435-1223, SDSS 0924+0219, SDSS 1004+4112, HE 1104-1805, and Q 2237+0305. X-ray microlensing variability is detected in all six lenses with high confidence. We furthermore detect energy-dependent microlensing in HE 0435-1223, SDSS 0924+0219, SDSS 1004+4112, and Q 2237+0305. Through a detailed spectral analysis for each lens we find that simple power-law models plus Gaussian emission lines give good fits to the spectra. We detect intrinsic spectral variability in two epochs of Q 2237+0305, and differential absorption between images in QJ 0158-4325 and Q2237+0305. We also detect the Fe K{alpha} emission line in all six lenses, and the Ni XXVII K{alpha} line in two images of Q 2237+0305. The rest-frame equivalent widths of the Fe K{alpha} lines are measured to be 0.4-1.2 keV, significantly higher than those measured in typical active galactic nuclei of similar X-ray luminosities. This suggests that the Fe K{alpha} emission region is more compact or centrally concentrated than the continuum emission region.
Broad Iron Emission from Gravitationally Lensed Quasars Observed by Chandra
NASA Astrophysics Data System (ADS)
Walton, D. J.; Reynolds, M. T.; Miller, J. M.; Reis, R. C.; Stern, D.; Harrison, F. A.
2015-06-01
Recent work has demonstrated the potential of gravitationally lensed quasars to extend measurements of black hole spin out to high redshift with the current generation of X-ray observatories. Here we present an analysis of a large sample of 27 lensed quasars in the redshift range 1.0? z? 4.5 observed with Chandra, utilizing over 1.6 Ms of total observing time, focusing on the rest-frame iron K emission from these sources. Although the X-ray signal-to-noise ratio (S/N) currently available does not permit the detection of iron emission from the inner accretion disk in individual cases in our sample, we find significant structure in the stacked residuals. In addition to the narrow core, seen almost ubiquitously in local active galactic nuclei (AGNs), we find evidence for an additional underlying broad component from the inner accretion disk, with a clear red wing to the emission profile. Based on simulations, we find the detection of this broader component to be significant at greater than the 3? level. This implies that iron emission from the inner disk is relatively common in the population of lensed quasars, and in turn further demonstrates that, with additional observations, this population represents an opportunity to significantly extend the sample of AGN spin measurements out to high redshift.
Are some BL Lacs artefacts of gravitational lensing?
Ostriker, J P; Vietri, M
1990-03-01
WE suggested in 1985 that a significant fraction of BL Lacertae objects, a kind of lineless quasar, seen in nearby galaxies are in fact images, gravitationally lensed and substantially amplified by stars in the nearby galaxy, of background objects, optically violent variable (OVV) quasars at redshifts z > 1 (ref. 1). This hypothesis was made on the basis of certain general similarities between BL Lacs and O Ws, but for two recently observed BL Lacs(2,3) a strong case can be made that the accompanying elliptical galaxy is a foreground object. In addition, we argue that the distribution of BL Lac redshifts is hard to understand without gravitational lensing, unless we happen to be at a very local maximum of the spatial cosmic distribution of BL Lacs. Our analysis also indicates that the galaxies whose stars are likely to act as microlenses will be found in two peaks, one nearby, with redshift 0.05-0.10, and the other near the distant quasar. PMID:18278021
A gravitationally lensed water maser in the early Universe.
Impellizzeri, C M Violette; McKean, John P; Castangia, Paola; Roy, Alan L; Henkel, Christian; Brunthaler, Andreas; Wucknitz, Olaf
2008-12-18
Water masers are found in dense molecular clouds closely associated with supermassive black holes at the centres of active galaxies. On the basis of the understanding of the local water-maser luminosity function, it was expected that masers at intermediate and high redshifts would be extremely rare. However, galaxies at redshifts z > 2 might be quite different from those found locally, not least because of more frequent mergers and interaction events. Here we use gravitational lensing to search for masers at higher redshifts than would otherwise be possible, and find a water maser at redshift 2.64 in the dust- and gas-rich, gravitationally lensed type-1 quasar MG J0414+0534 (refs 6-13). The isotropic luminosity is 10,000 (, solar luminosity), which is twice that of the most powerful local water maser and half that of the most distant maser previously known. Using the locally determined luminosity function, the probability of finding a maser this luminous associated with any single active galaxy is 10(-6). The fact that we see such a maser in the first galaxy we observe must mean that the volume densities and luminosities of masers are higher at redshift 2.64. PMID:19092930
Gravitational lensing by self-dual black holes in loop quantum gravity
NASA Astrophysics Data System (ADS)
Sahu, Satyabrata; Lochan, Kinjalk; Narasimha, D.
2015-03-01
We study gravitational lensing by a recently proposed black hole solution in loop quantum gravity. We highlight the fact that the quantum gravity corrections to the Schwarzschild metric in this model evade the "mass suppression" effects (that the usual quantum gravity corrections are susceptible to) by virtue of one of the parameters in the model being dimensionless, which is unlike any other quantum gravity motivated parameter. Gravitational lensing in the strong and weak deflection regimes is studied, and a sample consistency relation is presented which could serve as a test of this model. We discuss that, though the consistency relation for this model is qualitatively similar to what would have been in Brans-Dicke, in general it can be a good discriminator between many alternative theories. Although the observational prospects do not seem to be very optimistic even for a galactic supermassive black hole case, time delay between relativistic images for a billion solar mass black holes in other galaxies might be within reach of future relativistic lensing observations.
Three Gravitational Lenses for the Price of One: Enhanced Strong Lensing Through Galaxy Clustering
Fassnacht, Chris D.; McKean, J.P.; Koopmans, L.V.E.; Treu, T.; Blandford, R.D.; Auger, M.W.; Jeltema, T.E.; Lubin, L.M.; Margoniner, V.E.; Wittman, D.; /UC, Davis /Kapteyn Astron. Inst., Groningen /UC, Santa Barbara /KIPAC, Menlo Park /Carnegie Inst. Observ.
2006-04-03
We report the serendipitous discovery of two strong gravitational lens candidates (ACS J160919+6532 and ACS J160910+6532) in deep images obtained with the Advanced Camera for Surveys on the Hubble Space Telescope, each less than 40'' from the previously known gravitational lens system CLASS B1608+656. The redshifts of both lens galaxies have been measured with Keck and Gemini: one is a member of a small galaxy group at z {approx} 0.63, which also includes the lensing galaxy in the B1608+656 system, and the second is a member of a foreground group at z {approx} 0.43. By measuring the effective radii and surface brightnesses of the two lens galaxies, we infer their velocity dispersions based on the passively evolving Fundamental Plane (FP) relation. Elliptical isothermal lens mass models are able to explain their image configurations within the lens hypothesis, with a velocity dispersion compatible with that estimated from the FP for a reasonable source-redshift range. Based on the large number of massive early-type galaxies in the field and the number-density of faint blue galaxies, the presence of two additional lens systems around CLASS B1608+656 is not unlikely in hindsight. Gravitational lens galaxies are predominantly early-type galaxies, which are clustered, and the lensed quasar host galaxies are also clustered. Therefore, obtaining deep high-resolution images of the fields around known strong lens systems is an excellent method of enhancing the probability of finding additional strong gravitational lens systems.
Mapping gravitational lensing of the CMB using local likelihoods
Anderes, Ethan; Knox, Lloyd; Engelen, Alexander van
2011-02-15
We present a new estimation method for mapping the gravitational lensing potential from observed CMB intensity and polarization fields. Our method uses Bayesian techniques to estimate the average curvature of the potential over small local regions. These local curvatures are then used to construct an estimate of a low pass filter of the gravitational potential. By utilizing Bayesian/likelihood methods one can easily overcome problems with missing and/or nonuniform pixels and problems with partial sky observations (E- and B-mode mixing, for example). Moreover, our methods are local in nature, which allow us to easily model spatially varying beams, and are highly parallelizable. We note that our estimates do not rely on the typical Taylor approximation which is used to construct estimates of the gravitational potential by Fourier coupling. We present our methodology with a flat sky simulation under nearly ideal experimental conditions with a noise level of 1 {mu}K-arcmin for the temperature field, {radical}(2) {mu}K-arcmin for the polarization fields, with an instrumental beam full width at half maximum (FWHM) of 0.25 arcmin.
A Bayesian Analysis of Regularised Source Inversions in Gravitational Lensing
Suyu, Sherry H.; Marshall, P.J.; Hobson, M.P.; Blandford, R.D.; /Caltech /KIPAC, Menlo Park
2006-01-25
Strong gravitational lens systems with extended sources are of special interest because they provide additional constraints on the models of the lens systems. To use a gravitational lens system for measuring the Hubble constant, one would need to determine the lens potential and the source intensity distribution simultaneously. A linear inversion method to reconstruct a pixellated source distribution of a given lens potential model was introduced by Warren and Dye. In the inversion process, a regularization on the source intensity is often needed to ensure a successful inversion with a faithful resulting source. In this paper, we use Bayesian analysis to determine the optimal regularization constant (strength of regularization) of a given form of regularization and to objectively choose the optimal form of regularization given a selection of regularizations. We consider and compare quantitatively three different forms of regularization previously described in the literature for source inversions in gravitational lensing: zeroth-order, gradient and curvature. We use simulated data with the exact lens potential to demonstrate the method. We find that the preferred form of regularization depends on the nature of the source distribution.
Weak lensing and modified gravity of cosmic structure
NASA Astrophysics Data System (ADS)
Clampitt, Joseph
We offer predictions of symmetron modified gravity in the neighborhood of realistic dark matter halos. The predictions for the fifth force (FF) are obtained by solving the nonlinear symmetron equation of motion in the spherical NFW approximation. We compare the three major known screening mechanisms: Vainshtein, Chameleon, and Symmetron around such dark matter sources, emphasizing the significant differences between them and highlighting observational tests which exploit these differences. In addition to halos, we investigate the behavior of the FF in voids in chameleon modified gravity models using the spherical collapse method. The FF can be many times larger than the Newtonian force. This is very different from the case in halos, where the FF is no more than 1/3 of gravity. Individual voids in chameleon models grow larger by ~10%. The number density is up to 2.5 times larger in chameleon models. This difference is about 10 times larger than that in the halo mass function. Turning to weak lensing data analysis, we search for the lensing signal of massive filaments between 220,000 pairs of Luminous Red Galaxies (LRGs) from the Sloan Digital Sky Survey. We use a nulling technique to remove the contribution of the LRG halos, resulting in a 10-sigma detection of the filament lensing signal. We compare the measurements with halo model predictions based on a calculation of 3-point halo-halo-mass correlations. Comparing the "thick" halo model filament to a "thin" string of halos, thick filaments larger than a Mpc in width are clearly preferred by the data. In addition to filaments, dark matter voids should exhibit a weak lensing signal. We find voids in the galaxy distribution using a novel algorithm, then perform a stacked shear measurement on 20,000 voids with radii between 15-40 Mpc/h and redshifts between 0.16-0.37. We detect the characteristic radial shear signal of voids with a statistical significance that exceeds 13-sigma. The mass profile corresponds to a fractional underdensity of about -0.4 inside the void radius and a slow approach to the mean density.
WEAK LENSING MEASUREMENT OF GALAXY CLUSTERS IN THE CFHTLS-WIDE SURVEY
Shan Huanyuan; Tao Charling; Kneib, Jean-Paul; Jauzac, Mathilde; Limousin, Marceau; Fan Zuhui; Massey, Richard; Rhodes, Jason; Thanjavur, Karun; McCracken, Henry J.
2012-03-20
We present the first weak gravitational lensing analysis of the completed Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). We study the 64 deg{sup 2} W1 field, the largest of the CFHTLS-Wide survey fields, and present the largest contiguous weak lensing convergence 'mass map' yet made. 2.66 million galaxy shapes are measured, using the Kaiser Squires and Broadhurst Method (KSB) pipeline verified against high-resolution Hubble Space Telescope imaging that covers part of the CFHTLS. Our i'-band measurements are also consistent with an analysis of independent r'-band imaging. The reconstructed lensing convergence map contains 301 peaks with signal-to-noise ratio {nu} > 3.5, consistent with predictions of a {Lambda}CDM model. Of these peaks, 126 lie within 3.'0 of a brightest central galaxy identified from multicolor optical imaging in an independent, red sequence survey. We also identify seven counterparts for massive clusters previously seen in X-ray emission within 6 deg{sup 2} XMM-LSS survey. With photometric redshift estimates for the source galaxies, we use a tomographic lensing method to fit the redshift and mass of each convergence peak. Matching these to the optical observations, we confirm 85 groups/clusters with {chi}{sup 2}{sub reduced} < 3.0, at a mean redshift (z{sub c} ) = 0.36 and velocity dispersion ({sigma}{sub c}) = 658.8 km s{sup -1}. Future surveys, such as DES, LSST, KDUST, and EUCLID, will be able to apply these techniques to map clusters in much larger volumes and thus tightly constrain cosmological models.
Shirasaki, Masato; Yoshida, Naoki
2014-05-01
The measurement of cosmic shear using weak gravitational lensing is a challenging task that involves a number of complicated procedures. We study in detail the systematic errors in the measurement of weak-lensing Minkowski Functionals (MFs). Specifically, we focus on systematics associated with galaxy shape measurements, photometric redshift errors, and shear calibration correction. We first generate mock weak-lensing catalogs that directly incorporate the actual observational characteristics of the Canada-France-Hawaii Lensing Survey (CFHTLenS). We then perform a Fisher analysis using the large set of mock catalogs for various cosmological models. We find that the statistical error associated with the observational effects degrades the cosmological parameter constraints by a factor of a few. The Subaru Hyper Suprime-Cam (HSC) survey with a sky coverage of ?1400 deg{sup 2} will constrain the dark energy equation of the state parameter with an error of ?w {sub 0} ? 0.25 by the lensing MFs alone, but biases induced by the systematics can be comparable to the 1? error. We conclude that the lensing MFs are powerful statistics beyond the two-point statistics only if well-calibrated measurement of both the redshifts and the shapes of source galaxies is performed. Finally, we analyze the CFHTLenS data to explore the ability of the MFs to break degeneracies between a few cosmological parameters. Using a combined analysis of the MFs and the shear correlation function, we derive the matter density ?{sub m0}=0.256{sub 0.046}{sup 0.054}.
Itoh, Yousuke; Futamase, Toshifumi; Hattori, Makoto
2009-08-15
Gravitational waves propagate along null geodesics like light rays in the geometrical optics approximation, and they may have a chance to suffer from gravitational lensing by intervening objects, as is the case for electromagnetic waves. Long wavelengths of gravitational waves and compactness of possible sources may enable us to extract information in the interference among the lensed images. We point out that the interference term contains information of relative transverse velocity of the source-lens-observer system, which may be obtained by possible future space-borne gravitational wave detectors such as BBO/DECIGO.
Gravitational Lensing of Distant Supernovae in Cold Dark Matter Universes
NASA Astrophysics Data System (ADS)
Porciani, Cristiano; Madau, Piero
2000-04-01
Ongoing searches for supernovae (SNe) at cosmological distances have recently started to provide large numbers of events with measured redshifts and apparent brightnesses. Compared to quasars or galaxies, Type Ia SNe represent a population of sources with well-known intrinsic properties and could be used to detect gravitational lensing even in the absence of multiple or highly distorted images. We investigate the lensing effect of background SNe due to mass condensations in three popular cold dark matter cosmologies (?CDM, OCDM, and SCDM) and compute lensing frequencies, rates of SN explosions, and distributions of arrival-time differences and image separations. If dark halos approximate singular isothermal spheres on galaxy scales and Navarro-Frenk-White profiles on group/cluster scales, and are distributed in mass according to the Press-Schechter theory, then about one of every 12 SNe at z~1 will be magnified by ?m>=0.1 mag (SCDM). The detection rate of SNe Ia with magnification ?m>=0.3 is estimated to be of the order of a few events yr-1 deg-2 at maximum B light and IAB<=25, 100 times smaller than the total rate expected at these magnitude levels. In the field, events magnified by more than 0.75 mag are 7 times less frequent; about one-fifth of them give rise to observable multiple images. While the time delay between the images is shorter than 3 days in ~25% of the cases (shorter than 30 days in 50%) (SCDM), a serious bias against the detection of small-separation events in ground-based surveys is caused by the luminosity of the foreground lensing galaxy. Because of the flat K-correction and wide luminosity function, Type II SNe dominate the number counts at IAB>25 and have the largest fraction of lensed objects. The optimal survey sensitivity for Type Ia SNe magnified by ?m>=0.75 mag is IAB~23. Magnification bias increases their incidence by a factor of 50 in samples with IAB<=22, dropping to a factor of 3.5 at 24 mag. At faint magnitudes, the enhancement is larger for SNe II.
Fitting formulae of the reduced-shear power spectrum for weak lensing
NASA Astrophysics Data System (ADS)
Kilbinger, M.
2010-09-01
Context. Weak gravitational lensing is a powerful probe of large-scale structure and cosmology. Most commonly, second-order correlations of observed galaxy ellipticities are expressed as a projection of the matter power spectrum, corresponding to the lowest-order approximation between the projected and the three-dimensional power spectrum. Aims: The dominant lensing-only contribution beyond the zero-order approximation is the reduced shear, which takes into account not only lensing-induced distortions but also the isotropic magnification of galaxy images. This involves an integral over the matter bispectrum. We provide a fast and general way to calculate this correction term. Methods: Using a model for the matter bispectrum, we fit elementary functions to the reduced-shear contribution and its derivatives with respect to cosmological parameters. The dependence on cosmology is encompassed in a Taylor-expansion around a fiducial model. Results: Within a region in parameter space comprising the WMAP7 68% error ellipsoid, the total reduced-shear power spectrum (shear plus fitted reduced-shear correction) is accurate to 1% (2%) for ? < 104 (? < 2 105). This corresponds to a factor of four reduction in the bias compared to the case where no correction is used. This precision is necessary to match the accuracy of current non-linear power spectrum predictions from numerical simulations. Conclusions: Appendix A is only available in electronic form at http://www.aanda.org
Gravitational Lensing Science with the Atacama Cosmology Telescope Polarization Survey
NASA Astrophysics Data System (ADS)
Van Englen, Alexander; Atacama Cosmology Telescope Team
2016-01-01
The gravitational lensing of the cosmic microwave background (CMB) has emerged as a new probe of precision cosmology. The Atacama Cosmology Telescope is currently undergoing its second year surveying the CMB sky at arcminute angular resolution. CMB maps obtained from this survey can be used to reconstruct the density of dark matter along the line of sight between us and the CMB last-scattering surface. These maps can be used both on their own and in cross-correlation with other probes of large scale structure to trace the history of structure growth in the Universe. In this talk I will summarize recent results from these analyses, highlighting constraints on the neutrino mass and dark energy as well as the history of star formation obtained from cross-correlation with maps of the cosmic infrared background.
Detection of gravitational lensing in the cosmic microwave background
Smith, Kendrick M.; Zahn, Oliver; Dore, Olivier
2007-08-15
Gravitational lensing of the cosmic microwave background (CMB), a long-standing prediction of the standard cosmological model, is ultimately expected to be an important source of cosmological information, but first detection has not been achieved to date. We report a 3.4{sigma} detection, by applying quadratic estimator techniques to all sky maps from the Wilkinson microwave anisotropy probe (WMAP) satellite, and correlating the result with radio galaxy counts from the NRAO VLA sky survey (NVSS). We present our methodology including a detailed discussion of potential contaminants. Our error estimates include systematic uncertainties from density gradients in NVSS, beam effects in WMAP, galactic microwave foregrounds, resolved and unresolved CMB point sources, and the thermal Sunyaev-Zel'dovich effect.
Probing dark matter halos with strong gravitational lensing
NASA Astrophysics Data System (ADS)
Ferreras, Ignacio
2015-08-01
Strong gravitational lensing over galaxy scales allows us to explore dark matter halos and their connection with the luminous component. In this talk we present recent work on a sample extracted from the SLACS dataset, where the spectroscopic information from SDSS allows us to study the effect of a non-universal initial mass function on the stellar mass-to-light ratio. In addition, by studying galaxies where the background source probes the central part of the lens, we can derive significant constraints on the properties of the dark matter halo. This is one of the few observational methods that can be used to contrast with the standard concentration-virial mass relationships proposed by numerical simulations.
Cosmological Parameter Survey Using the Gravitational Lensing Method
NASA Astrophysics Data System (ADS)
Premadi, Premana W.; Martel, Hugo; Matzner, Richard; Futamase, Toshifumi
Using a multiple-lens plane algorithm, we study light propagation in inhomogeneous universes for 43 different COBE-normalized Cold Dark Matter models, with various values of the density parameter Ω0, cosmological constant λ0, Hubble constant H0, and rms density fluctuation σ8. We performed a total of 3798 experiments, each experiment consisting of propagating a square beam of angular size 21.9'' × 21.9'' composed of 116 281 light rays from the observer up to redshift z = 3. These experiments provide statis-tics of the magnification, shear, and multiple imaging of distant sources. The results of these experiments might be compared with observations, and eventually help constrain the possible values of the cosmological parameters. Additionally, they provide insight into the gravitational lensing process and its complex relationship with the various cosmological parameters.
Seeing the Invisible Universe with Gravitational Lensing and SNAP
Bernstein, Gary
2005-11-03
Recent high-precision cosmological measurements provide solid evidence that normal matter comprises only 4% of the content of the Universe. The dominant substances are completely invisible and have never been detected in a laboratory: 23% in some 'dark matter' particles, and 73% in a form of 'dark energy' that is currently accelerating the expansion of the Universe. The dark matter and dark energy do, however, distort our view of the Universe behind them through gravitational lensing, just as the 'obscure glass' on the doors of a shower stall is designed to be transparent but produces a distorted view of its occupant. I will describe how present and future experiments such as the SNAP spacecraft can measure this very subtle distorting effect and use it to infer the properties of the dark matter and dark energy that dominate the Universe.
WEAK-LENSING PEAK FINDING: ESTIMATORS, FILTERS, AND BIASES
Schmidt, Fabian
2011-07-10
Large catalogs of shear-selected peaks have recently become a reality. In order to properly interpret the abundance and properties of these peaks, it is necessary to take into account the effects of the clustering of source galaxies, among themselves and with the lens. In addition, the preferred selection of magnified galaxies in a flux- and size-limited sample leads to fluctuations in the apparent source density that correlate with the lensing field. In this paper, we investigate these issues for two different choices of shear estimators that are commonly in use today: globally normalized and locally normalized estimators. While in principle equivalent, in practice these estimators respond differently to systematic effects such as magnification and cluster member dilution. Furthermore, we find that the answer to the question of which estimator is statistically superior depends on the specific shape of the filter employed for peak finding; suboptimal choices of the estimator+filter combination can result in a suppression of the number of high peaks by orders of magnitude. Magnification and size bias generally act to increase the signal-to-noise {nu} of shear peaks; for high peaks the boost can be as large as {Delta}{nu} {approx} 1-2. Due to the steepness of the peak abundance function, these boosts can result in a significant increase in the observed abundance of shear peaks. A companion paper investigates these same issues within the context of stacked weak-lensing mass estimates.
SPACE WARPS - I. Crowdsourcing the discovery of gravitational lenses
NASA Astrophysics Data System (ADS)
Marshall, Philip J.; Verma, Aprajita; More, Anupreeta; Davis, Christopher P.; More, Surhud; Kapadia, Amit; Parrish, Michael; Snyder, Chris; Wilcox, Julianne; Baeten, Elisabeth; Macmillan, Christine; Cornen, Claude; Baumer, Michael; Simpson, Edwin; Lintott, Chris J.; Miller, David; Paget, Edward; Simpson, Robert; Smith, Arfon M.; Küng, Rafael; Saha, Prasenjit; Collett, Thomas E.
2016-01-01
We describe SPACE WARPS, a novel gravitational lens discovery service that yields samples of high purity and completeness through crowdsourced visual inspection. Carefully produced colour composite images are displayed to volunteers via a web-based classification interface, which records their estimates of the positions of candidate lensed features. Images of simulated lenses, as well as real images which lack lenses, are inserted into the image stream at random intervals; this training set is used to give the volunteers instantaneous feedback on their performance, as well as to calibrate a model of the system that provides dynamical updates to the probability that a classified image contains a lens. Low-probability systems are retired from the site periodically, concentrating the sample towards a set of lens candidates. Having divided 160 deg2 of Canada-France-Hawaii Telescope Legacy Survey imaging into some 430 000 overlapping 82 by 82 arcsec tiles and displaying them on the site, we were joined by around 37 000 volunteers who contributed 11 million image classifications over the course of eight months. This stage 1 search reduced the sample to 3381 images containing candidates; these were then refined in stage 2 to yield a sample that we expect to be over 90 per cent complete and 30 per cent pure, based on our analysis of the volunteers performance on training images. We comment on the scalability of the SPACE WARPS system to the wide field survey era, based on our projection that searches of 105 images could be performed by a crowd of 105 volunteers in 6 d.
Measuring angular diameter distances of strong gravitational lenses
NASA Astrophysics Data System (ADS)
Jee, I.; Komatsu, E.; Suyu, S. H.
2015-11-01
The distance-redshift relation plays a fundamental role in constraining cosmological models. In this paper, we show that measurements of positions and time delays of strongly lensed images of a background galaxy, as well as those of the velocity dispersion and mass profile of a lens galaxy, can be combined to extract the angular diameter distance of the lens galaxy. Physically, as the velocity dispersion and the time delay give a gravitational potential (GM/r) and a mass (GM) of the lens, respectively, dividing them gives a physical size (r) of the lens. Comparing the physical size with the image positions of a lensed galaxy gives the angular diameter distance to the lens. A mismatch between the exact locations at which these measurements are made can be corrected by measuring a local slope of the mass profile. We expand on the original idea put forward by Paraficz and Hjorth, who analyzed singular isothermal lenses, by allowing for an arbitrary slope of a power-law spherical mass density profile, an external convergence, and an anisotropic velocity dispersion. We find that the effect of external convergence cancels out when dividing the time delays and velocity dispersion measurements. We derive a formula for the uncertainty in the angular diameter distance in terms of the uncertainties in the observables. As an application, we use two existing strong lens systems, B1608+656 (zL=0.6304) and RXJ1131-1231 (zL=0.295), to show that the uncertainty in the inferred angular diameter distances is dominated by that in the velocity dispersion, ?2, and its anisotropy. We find that the current data on these systems should yield about 16% uncertainty in DA per object. This improves to 13% when we measure ?2 at the so-called sweet-spot radius. Achieving 7% is possible if we can determine ?2 with 5% precision.
The impact of cosmic variance on simulating weak lensing surveys
NASA Astrophysics Data System (ADS)
Kannawadi, Arun; Mandelbaum, Rachel; Lackner, Claire
2015-06-01
Upcoming weak lensing surveys will survey large cosmological volumes to measure the growth of cosmological structure with time and thereby constrain dark energy. One major systematic uncertainty in this process is the calibration of the weak lensing shape distortions, or shears. Most upcoming surveys plan to test several aspects of their shear estimation algorithms using sophisticated image simulations that include realistic galaxy populations based on high-resolution data from the Hubble Space Telescope (HST). However, existing data sets from the HST cover very small cosmological volumes, so cosmic variance could cause the galaxy populations in them to be atypical. A narrow redshift slice from such surveys could be dominated by a single large overdensity or underdensity. In that case, the morphology-density relation could alter the local galaxy populations and yield an incorrect calibration of shear estimates as a function of redshift. We directly test this scenario using the COSMOS survey, the largest-area HST survey to date, and show how the statistical distributions of galaxy shapes and morphological parameters (e.g. Sérsic n) are influenced by redshift-dependent cosmic variance. The typical variation in rms ellipticity due to environmental effects is 5 per cent (absolute, not relative) for redshift bins of width Δz = 0.05, which could result in uncertain shear calibration at the 1 per cent level. We conclude that the cosmic variance effects are large enough to exceed the systematic error budget of future surveys, but can be mitigated with careful choice of training data set and sufficiently large redshift binning.
EFFECTIVE MODELS FOR STATISTICAL STUDIES OF GALAXY-SCALE GRAVITATIONAL LENSING
Lapi, A.; Negrello, M.; Gonzalez-Nuevo, J.; Cai, Z.-Y.; De Zotti, G.; Danese, L.
2012-08-10
We have worked out simple analytical formulae that accurately approximate the relationship between the position of the source with respect to the lens center and the amplification of the images, hence the lens cross section, for realistic lens profiles. We find that, for essentially the full range of parameters either observationally determined or yielded by numerical simulations, the combination of dark matter and star distribution can be very well described, for lens radii relevant to strong lensing, by a simple power law whose slope is very weakly dependent on the parameters characterizing the global matter surface density profile and close to isothermal in agreement with direct estimates for individual lens galaxies. Our simple treatment allows an easy insight into the role of the different ingredients that determine the lens cross section and the distribution of gravitational amplifications. They also ease the reconstruction of the lens mass distribution from the observed images and, vice versa, allow a fast application of ray-tracing techniques to model the effect of lensing on a variety of source structures. The maximum amplification depends primarily on the source size. Amplifications larger than Almost-Equal-To 20 are indicative of compact source sizes at high-z, in agreement with expectations if galaxies formed most of their stars during the dissipative collapse of cold gas. Our formalism has allowed us to reproduce the counts of strongly lensed galaxies found in the H-ATLAS Science Demonstration Phase field. While our analysis is focused on spherical lenses, we also discuss the effect of ellipticity and the case of late-type lenses (showing why they are much less common, even though late-type galaxies are more numerous). Furthermore, we discuss the effect of a cluster halo surrounding the early-type lens and of a supermassive black hole at its center.
OBSERVING GRAVITATIONAL LENSING EFFECTS BY Sgr A* WITH GRAVITY
Bozza, V.; Mancini, L. E-mail: mancini@mpia-hd.mpg.de
2012-07-01
The massive black hole Sgr A* at the Galactic center is surrounded by a cluster of stars orbiting around it. Light from these stars is bent by the gravitational field of the black hole, giving rise to several phenomena: astrometric displacement of the primary image, the creation of a secondary image that may shift the centroid of Sgr A*, and magnification effects on both images. The soon-to-be second-generation Very Large Telescope Interferometer instrument GRAVITY will perform observations in the near-infrared of the Galactic center at unprecedented resolution, opening the possibility of observing such effects. Here we investigate the observability limits for GRAVITY of gravitational lensing effects on the S-stars in the parameter space 1[D{sub LS}, {gamma}, K], where D{sub LS} is the distance between the lens and the source, {gamma} is the alignment angle of the source, and K is the source's apparent magnitude in the K band. The easiest effect to observe in future years is the astrometric displacement of primary images. In particular, the shift of the star S17 from its Keplerian orbit will be detected as soon as GRAVITY becomes operative. For exceptional configurations, it will be possible to detect effects related to the spin of the black hole or post-Newtonian orders in the deflection.
Gravitational lensing: a unique probe of dark matter and dark energy
Ellis, Richard S.
2010-01-01
I review the development of gravitational lensing as a powerful tool of the observational cosmologist. After the historic eclipse expedition organized by Arthur Eddington and Frank Dyson, the subject lay observationally dormant for 60 years. However, subsequent progress has been astonishingly rapid, especially in the past decade, so that gravitational lensing now holds the key to unravelling the two most profound mysteries of our Universe—the nature and distribution of dark matter, and the origin of the puzzling cosmic acceleration first identified in the late 1990s. In this non-specialist review, I focus on the unusual history and achievements of gravitational lensing and its future observational prospects. PMID:20123743
Gravitational lensing: a unique probe of dark matter and dark energy.
Ellis, Richard S
2010-03-13
I review the development of gravitational lensing as a powerful tool of the observational cosmologist. After the historic eclipse expedition organized by Arthur Eddington and Frank Dyson, the subject lay observationally dormant for 60 years. However, subsequent progress has been astonishingly rapid, especially in the past decade, so that gravitational lensing now holds the key to unravelling the two most profound mysteries of our Universe-the nature and distribution of dark matter, and the origin of the puzzling cosmic acceleration first identified in the late 1990s. In this non-specialist review, I focus on the unusual history and achievements of gravitational lensing and its future observational prospects. PMID:20123743
The impact of correlated noise on galaxy shape estimation for weak lensing
NASA Astrophysics Data System (ADS)
Gurvich, Alex; Mandelbaum, Rachel
2016-04-01
The robust estimation of the tiny distortions (shears) of galaxy shapes caused by weak gravitational lensing in the presence of much larger shape distortions due to the point spread function (PSF) has been widely investigated. One major problem is that most galaxy shape measurement methods are subject to bias due to pixel noise in the images (`noise bias'). Noise bias is usually characterized using uncorrelated noise fields; however, real images typically have low-level noise correlations due to galaxies below the detection threshold, and some types of image processing can induce further noise correlations. We investigate the effective detection significance and its impact on noise bias in the presence of correlated noise for one method of galaxy shape estimation. For a fixed noise variance, the biases in galaxy shape estimates can differ substantially for uncorrelated versus correlated noise. However, use of an estimate of detection significance that accounts for the noise correlations can almost entirely remove these differences, leading to consistent values of noise bias as a function of detection significance for correlated and uncorrelated noise. We confirm the robustness of this finding to properties of the galaxy, the PSF, and the noise field, and quantify the impact of anisotropy in the noise correlations. Our results highlight the importance of understanding the pixel noise model and its impact on detection significances when correcting for noise bias on weak lensing.
Gravitational radiation and gravitational lensing as a source of electromagnetic bursts
NASA Astrophysics Data System (ADS)
McBreen, B.; Metcalfe, L.
1988-03-01
What causes gamma-ray bursts has long been a puzzle to theoreticians. Here the authors propose that fluctuations in the position of a compact source originating in a stochastic background of gravitational waves cause the source to pass back and forth across the high-intensification caustics of an intervening galactic lens. The intensified images cross the Solar System with superluminal speed and give rise to gamma-ray bursts (GRBs). The features of this model are (1) the GRB is a result of a lensing phenomenon and not a sudden power surge in a compact source; (2) the directions to the sources obtained with the light-travel-time method are incorrect; (3) the spectral features arise from high-angular-resolution scans across accretion disks around Kerr black holes; and (4) the lensed sources are probably BL Lac objects.
NASA Astrophysics Data System (ADS)
Troxel, Michael A.
Gravitational lensing has been identified as a critical cosmological tool in studying the evolution of large scale structure in the universe as well as the nature of dark matter and dark energy. One of the primary physical systematics of weak lensing due to large scale structure (cosmic shear) is the intrinsic alignment (IA) of galaxies, which poses a barrier to precision weak lensing measurements. Methods for identifying and removing its effects on cosmological information are key to the success of weak lensing survey science goals. We have expanded model-independent techniques to isolate and remove the IA contamination from the lensing signal. These self-calibration techniques take advantage of complementary survey information to self-calibrate the lensing signal, which along with unique lensing and IA geometry and separation dependencies, allow us to reconstruct the IA correlations at the level of the spectrum and bispectrum. We have demonstrated that the self-calibration approach can reduce the IA bias over most relevant scale and redshift ranges by up to a factor of 10 or more. This could reduce a potential 10-20% bias in some cosmological information down to the 1-2% level. The self-calibration techniques have the added benefit of preserving the IA signal, which itself provides additional information that can be used in studying the formation and evolution of large scale structure in the universe. We have also identified a new source of intrinsic alignment contamination in cross-correlations with cosmic microwave background lensing and proposed a method to calibrate it, and we explored the potential of future surveys to measure directly various 2- and 3-point intrinsic alignment correlations. Finally, we have investigated the use of exact anisotropic and inhomogeneous models in general relativity for large- and small-scale structures in the universe, developing the frameworks necessary to analyze gravitational lensing in such models, and have compared them to observations, identifying potential sources of bias. We have found, for example, that ignoring substructure level anisotropies in structures could bias the lensing convergence, shear, and kinematic mass estimates by up to 10% or more. We conclude by presenting a numerical code package for calculations in such exact anisotropic and inhomogeneous models.
NASA Astrophysics Data System (ADS)
Egami, Eiichi; Rawle, Timothy; Cava, Antonio; Clement, Benjamin; Dessauges-Zavadsky, Miroslava; Ebeling, Harald; Kneib, Jean-Paul; Perez-Gonzalez, Pablo; Richard, Johan; Rujopakarn, Wiphu; Schaerer, Daniel; Walth, Gregory
2015-10-01
Using the Herschel Space Observatory, our team has been conducting a large survey of the fields of massive galaxy clusters, 'The Herschel Lensing Survey (HLS)' (PI: Egami; 419 hours). The main scientific goal is to penetrate the confusion limit of Herschel by taking advantage of the strong gravitational lensing power of these massive clusters and study the population of low-luminosity and/or high-redshift dusty star-forming galaxies that are beyond the reach of field Herschel surveys. In the course of this survey, we have obtained deep PACS (100/160 um) and SPIRE (250/350/500 um) images for 54 clusters (HLS-deep) as well as shallower (but nearly confusion-limited) SPIRE images for 527 clusters (HLS-snapshot). The goal of this proposal is to obtain shallow (500 sec/band) 3.6/4.5 um images of 266 cluster fields that have been observed by the HLS-snapshot survey but do not have any corresponding IRAC data. The HLS-snapshot SPIRE images are deep enough to detect a large number of sources in the target cluster fields, many of which are distant star-forming galaxies lensed by the foreground clusters, and the large sample size of HLS-snapshot promises a great potential for making exciting discoveries. Yet, these Herschel images would be of limited use if we could not identify the counterparts of the Herschel sources accurately and efficiently. The proposed IRAC snapshot program will greatly enhance the utility of these Herschel data, and will feed powerful gound observing facilities like ALMA and NOEMA with interesting targets to follow up.
NASA Astrophysics Data System (ADS)
Troxel, Michael A.; Ishak-Boushaki, M. B.
2014-01-01
Gravitational lensing has been identified as a critical tool in studying the evolution of large scale structure in the universe, as well as shedding light on the nature and influence of dark matter and dark energy. One of the primary systematic biases in weak lensing due to large scale structure (or cosmic shear) is the intrinsic alignment (IA) of galaxies, which poses a barrier to precision weak lensing measurements. Methods for identifying and removing its effects on cosmological information are key to the success of current and planned lensing surveys. We have expanded model-independent techniques to indirectly isolate and remove the IA contamination from the lensing signal. These self-calibration techniques take advantage of complimentary survey information to self-calibrate the lensing signal, which along with the unique lensing and IA geometry and separation dependencies, allow us to reconstruct the various IA correlations at the level of the spectrum and bispectrum. For cross-correlations, we have demonstrated that the self-calibration approach can reduce the IA bias over most relevant scale and redshift ranges by up to a factor of 10 or more. In the case of auto-correlations, we have demonstrated the feasibility of implementing the self-calibration for conservative estimates of photo-z accuracy in planned surveys. This could reduce a potential 10-20% bias in some cosmological information down to the 1-2% level. In both cases, the self-calibration has the added benefit of preserving the IA signal, that itself provides additional information which can be used in studying the formation and evolution of large scale structure in the universe. We have also investigated some impacts on kinematic and lensing information derived from the use of exact relativistic models for structures and cosmology with some level of anisotropies. We have found, for example, that ignoring substructure level anisotropies in structures could bias mass estimates by up to 10%.
The Effect of Environment on Shear in Strong Gravitational Lenses
NASA Astrophysics Data System (ADS)
Wong, Kenneth C.; Keeton, C. R.; Williams, K. A.; Momcheva, I. G.; Zabludoff, A. I.
2010-05-01
Using new photometric and spectroscopic data in the fields of nine strong gravitational lenses that lie in galaxy groups, we analyze the effects of both the local group environment and line-of-sight structures on the lens potential. We derive the shear directly from measurements of the lens environment, independent of the shear obtained from lens modeling. We account for possible tidal stripping of the group galaxies by allowing the fraction of total mass apportioned to the group dark matter halo and the individual group galaxies to vary freely. The environment produces an average shear of γ = 0.14 ± 0.04, significant enough to affect quantities derived from lens observables. However, the direction and magnitude of the shears derived from the environment does not match those obtained via lens modeling in three of the six 4-image systems where we have calculated model shears. The source of this disagreement is not clear, implying that the assumptions inherent in both the environment and lens model approaches must be reconsidered. If only the local group environment of the lens is included, the average shear is γ = 0.08 ± 0.03, indicating that line-of-sight contributions to the lens potential are not negligible. We isolate the effects of various theoretical and observational uncertainties on our results. Of those uncertainties, scatter in the Faber-Jackson relation dominates, boosting the scatter in the shear components γc and γs by as much as 0.04. Error in the group centroid position has a large effect on lenses near the centers of their respective groups, resulting in an offset in γc or γs of as much as 0.06. Future surveys of lens environments should prioritize spectroscopic sampling of both the local lens environment and objects along the line of sight, particularly bright (I < 21.5) objects projected within 2' of the lens.
Weak lensing analysis of MS 1008-1224 with the VLT
NASA Astrophysics Data System (ADS)
Athreya, R. M.; Mellier, Y.; van Waerbeke, L.; Pell, R.; Fort, B.; Dantel-Fort, M.
2002-03-01
We present a gravitational lensing analysis of the cluster of galaxies MS 1008-1224 (z=0.31), based on very deep observations obtained using the VLT with FORS1 and ISAAC during the science verification phase. Two different mass reconstruction algorithms were applied to the B-, V-, R- and I-band data to obtain similar projected mass distributions in all the bands. The FORS1 (BVRI) and ISAAC (JK) data were combined to determine the photometric redshift distribution of galaxies within the ISAAC field and to estimate the mass. We inferred from weak shear a minimum mass of 2.3 x 1014 h-1 Msun on large scales (within ~ 700 h-1 kpc, diameter) which agrees well with the X-ray mass mass estimate. The Mass-to-light ratios are also in excellent agreement. The observed mass profile is consistent with Pseudo-Isothermal Sphere models as well as a Navarro, Frenk and White model. In the inner regions the lensing mass is about twice as high as the X-ray mass which supports the long-held view that complex physical processes occuring in the innermost parts of lensing-clusters are mainly responsible for the X-ray-lensing mass discrepancy. We found that the central part of the cluster comprises two mass peaks whose center of mass is located 10-20 arcsec north of the cD galaxy. A similar offset between the cD and the peak of the X-ray distribution has been reported before. The optical, X-ray and the mass distributions show that MS 1008-1224 is composed of several subsystems which are probably undergoing a merger. It is likely that the gas is not in equilibrium in the innermost regions which vitiates the X-ray mass estimate there. We discovered that MS 1008-1224 shows a remarkable case of cluster-cluster lensing. The photometric redshifts show an excess of galaxies located 30 arcsec south-west of the cD galaxy at a redshift of ~ 0.9. This distant cluster is therefore also lensed by MS 1008-1224, which, if confirmed with spectroscopic data, would make this the first known case of magnification of a distant cluster by another one. Based on observations obtained at the Very Large Telescope at Cerro Paranal operated by the European Southern Observatory.
NASA Astrophysics Data System (ADS)
Fox, G.; Soucail, G.; Pointecouteau, E.; Arnaud, M.; Limousin, M.; Pratt, G. W.
2012-10-01
The total mass of clusters of galaxies is a key parameter for studing massive halos. It relates to numerous gravitational and baryonic processes at play in the framework of large-scale structure formation, thus rendering its determination both important and challenging. From a sample of the 11 X-ray bright clusters selected from the EXCPRES sample, we investigate the optical and X-ray properties of clusters with respect to their total mass derived from weak gravitational lensing. From multicolor, wide-field imaging obtained with MegaCam at CFHT, we derive the shear profile of each individual cluster of galaxies. We carefully investigate all systematic sources related to the weak lensing mass determination. The weak lensing masses are then compared to the X-ray masses obtained from the analysis of XMM-Newton observations assuming hydrostatic equilibrium. We find good agreement between the two mass proxies although a few outliers with either perturbed morphology or poor quality data prevent deriving robust mass estimates. The weak lensing mass is also correlated with the optical richness and the total optical luminosity, as well as with the X-ray luminosity, to provide scaling relations within the redshift range 0.4 < z < 0.6. These relations are in good agreement with previous works at lower redshifts. For the LX - M relation we combine our sample with two other cluster and group samples from the literature, thus covering two decades in mass and X-ray luminosity, with a regular and coherent correlation between the two physical quantities. Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii.
Correcting the z 8 Galaxy Luminosity Function for Gravitational Lensing Magnification Bias
NASA Astrophysics Data System (ADS)
Mason, Charlotte A.; Treu, Tommaso; Schmidt, Kasper B.; Collett, Thomas E.; Trenti, Michele; Marshall, Philip J.; Barone-Nugent, Robert; Bradley, Larry D.; Stiavelli, Massimo; Wyithe, Stuart
2015-05-01
We present a Bayesian framework to account for the magnification bias from both strong and weak gravitational lensing in estimates of high-redshift galaxy luminosity functions (LFs). We illustrate our method by estimating the z 8 UV LF using a sample of 97 Y-band dropouts (Lyman break galaxies) found in the Brightest of Reionizing Galaxies (BoRG) survey and from the literature. We find the LF is well described by a Schechter function with characteristic magnitude of {{M}\\star }=-19.85-0.35+0.30, faint-end slope of ? =-1.72-0.29+0.30, and number density of {{log }10}{{{\\Psi }}\\star }(Mp{{c}-3})=-3.00-0.31+0.23. These parameters are consistent within the uncertainties with those inferred from the same sample without accounting for the magnification bias, demonstrating that the effect is small for current surveys at z 8, and cannot account for the apparent overdensity of bright galaxies compared to a Schechter function found recently by Bowler et al. and Finkelstein et al. We estimate that the probability of finding a strongly lensed z 8 source in our sample is in the range 3-15% depending on limiting magnitude. We identify one strongly lensed candidate and three cases of intermediate lensing in BoRG (estimated magnification ? > 1.4) in addition to the previously known candidate group-scale strong lens. Using a range of theoretical LFs we conclude that magnification bias will dominate wide field surveyssuch as those planned for the Euclid and WFIRST missionsespecially at z > 10. Magnification bias will need to be accounted for in order to derive accurate estimates of high-redshift LFs in these surveys and to distinguish between galaxy formation models.
Bayesian constraints on dark matter halo properties using gravitationally lensed supernovae
NASA Astrophysics Data System (ADS)
Karpenka, N. V.; March, M. C.; Feroz, F.; Hobson, M. P.
2013-08-01
A hierarchical Bayesian method is applied to the analysis of Type Ia supernovae (SNIa) observations to constrain the properties of the dark matter haloes of galaxies along the SNIa lines of sight via their gravitational lensing effect. The full joint posterior distribution of the dark matter halo parameters is explored using the nested sampling algorithm MULTINEST, which also efficiently calculates the Bayesian evidence, thereby facilitating robust model comparison. We first demonstrate the capabilities of the method by applying it to realistic simulated SNIa data, based on the real 3-year data release from the Supernova Legacy Survey (SNLS3). Assuming typical values for the parameters in a truncated singular isothermal sphere (SIS) halo model, we find that a catalogue analogous to the existing SNLS3 data set is typically incapable of detecting the lensing signal, but a catalogue containing approximately three times as many SNIa can produce robust and accurate parameter constraints and lead to a clear preference for the SIS halo model over a model that assumes no lensing. In the analysis of the real SNLS3 data, contrary to previous studies, we obtain only a very marginal detection of a lensing signal and weak constraints on the halo parameters for the truncated SIS model, although these constraints are tighter than those typically obtained from equivalent simulated SNIa data sets. This difference is driven by a preferred value of ? ? 1 in the assumed scaling law ? ? L? between velocity dispersion and luminosity, which is somewhat higher than the canonical values of ? = 1/4 and ? = 1/3 for early and late-type galaxies, respectively.
Fingerprinting dark energy. II. Weak lensing and galaxy clustering tests
Sapone, Domenico; Amendola, Luca
2010-11-15
The characterization of dark energy is a central task of cosmology. To go beyond a cosmological constant, we need to introduce at least an equation of state and a sound speed and consider observational tests that involve perturbations. If dark energy is not completely homogeneous on observable scales, then the Poisson equation is modified and dark matter clustering is directly affected. One can then search for observational effects of dark energy clustering using dark matter as a probe. In this paper we exploit an analytical approximate solution of the perturbation equations in a general dark energy cosmology to analyze the performance of next-decade large-scale surveys in constraining equation of state and sound speed. We find that tomographic weak lensing and galaxy redshift surveys can constrain the sound speed of the dark energy only if the latter is small, of the order of c{sub s} < or approx. 0.01 (in units of c). For larger sound speeds the error grows to 100% and more. We conclude that large-scale structure observations contain very little information about the perturbations in canonical scalar field models with a sound speed of unity. Nevertheless, they are able to detect the presence of cold dark energy, i.e. a dark energy with nonrelativistic speed of sound.
Weber's gravitational force as static weak field approximation
NASA Astrophysics Data System (ADS)
Tiandho, Yuant
2016-02-01
Weber's gravitational force (WGF) is one of gravitational model that can accommodate a non-static system because it depends not only on the distance but also on the velocity and the acceleration. Unlike Newton's law of gravitation, WGF can predict the anomalous of Mercury and gravitational bending of light near massive object very well. Then, some researchers use WGF as an alternative model of gravitation and propose a new mechanics theory namely the relational mechanics theory. However, currently we have known that the theory of general relativity which proposed by Einstein can explain gravity with very accurate. Through the static weak field approximation for the non-relativistic object, we also have known that the theory of general relativity will reduce to Newton's law of gravity. In this work, we expand the static weak field approximation that compatible with relativistic object and we obtain a force equation which correspond to WGF. Therefore, WGF is more precise than Newton's gravitational law. The static-weak gravitational field that we used is a solution of the Einstein's equation in the vacuum that satisfy the linear field approximation. The expression of WGF with ξ = 1 and satisfy the requirement of energy conservation are obtained after resolving the geodesic equation. By this result, we can conclude that WGF can be derived from the general relativity.
NASA Astrophysics Data System (ADS)
Hojjati, Alireza; McCarthy, Ian G.; Harnois-Deraps, Joachim; Ma, Yin-Zhe; Van Waerbeke, Ludovic; Hinshaw, Gary; Le Brun, Amandine M. C.
2015-10-01
We use the cosmo-OWLS suite of cosmological hydrodynamical simulations, which includes different galactic feedback models, to predict the cross-correlation signal between weak gravitational lensing and the thermal Sunyaev-Zeldovich (tSZ) y-parameter. The predictions are compared to the recent detection reported by van Waerbeke and collaborators. The simulations reproduce the weak lensing-tSZ cross-correlation, ξyκ(θ), well. The uncertainty arising from different possible feedback models appears to be important on small scales only (0θ lesssim 1 arcmin), while the amplitude of the correlation on all scales is sensitive to cosmological parameters that control the growth rate of structure (such as σ8, Ωm and Ωb). This study confirms our previous claim (in Ma et al.) that a significant proportion of the signal originates from the diffuse gas component in low-mass (Mhalo lesssim 1014 Msolar) clusters as well as from the region beyond the virial radius. We estimate that approximately 20% of the detected signal comes from low-mass clusters, which corresponds to about 30% of the baryon density of the Universe. The simulations also suggest that more than half of the baryons in the Universe are in the form of diffuse gas outside halos (gtrsim 5 times the virial radius) which is not hot or dense enough to produce a significant tSZ signal or be observed by X-ray experiments. Finally, we show that future high-resolution tSZ-lensing cross-correlation observations will serve as a powerful tool for discriminating between different galactic feedback models.
Cosmic superstring gravitational lensing phenomena: Predictions for networks of (p,q) strings
Shlaer, Benjamin; Wyman, Mark
2005-12-15
The unique, conical space-time created by cosmic strings brings about distinctive gravitational lensing phenomena. The variety of these distinctive phenomena is increased when the strings have nontrivial mutual interactions. In particular, when strings bind and create junctions, rather than intercommute, the resulting configurations can lead to novel gravitational lensing patterns. In this brief note, we use exact solutions to characterize these phenomena, the detection of which would be strong evidence for the existence of complex cosmic string networks of the kind predicted by string theory-motivated cosmic string models. We also correct some common errors in the lensing phenomenology of straight cosmic strings.
Weak-lensing mass estimates of galaxy groups and the line-of-sight contamination
NASA Astrophysics Data System (ADS)
Spinelli, P. F.; Seitz, S.; Lerchster, M.; Brimioulle, F.; Finoguenov, A.
2012-02-01
Weak lensing is an important technique to determine the masses of galaxy groups. However, the distortion imprint on the shape of the background galaxies is not only affected by the gravitational field of the main group, but also affected by all the mass content along the line of sight. Using COSMOS shear mock data, we study the shear profile around 165 groups and investigate the level at which the neighbouring groups can enhance or suppress the shear signal from the main halo. The mock data are based on Canada-France-Hawaii Telescope and Subaru observations, which are used to obtain the photometric redshifts of galaxies in the field and a realistic galaxy density, given by the weak-lensing distortion analysis of the observed data. We further use information on the galaxy groups (having a median mass and redshift of M200= 3.1 × 1013 M⊙ and z = 0.68, respectively) from the COSMOS X-ray catalogue of extended sources. The expected gravitational shear field of these groups is calculated assuming that the haloes are described by Navarro-Frenk-White density profiles, and the total shear is computed by summing the shear over all the lenses. We conclude that, on average, the signal-to-noise ratio for a detection of the main halo is affected by ? with respect to the signal-to-noise ratio the same halo would have if it was isolated in the sky. Groups with neighbours that are close in projected distance (≲1 arcmin) are the most affected, but haloes located at larger angular distances also cause a measurable shear signal. These (angular) distant groups can be interpreted as uncorrelated large-scale structure. The average bias in the mass-excess estimate of individual groups that is introduced by the external haloes is zero with an rms of ˜6-72 per cent, depending on the aperture size used. One way to eliminate this bias is by stacking the density profile of several groups. The shear signal introduced by large-scale structure acts as an external source of noise. The averaged uncertainty introduced is ? per component for an aperture size of θ˜ 5 arcmin, which corresponds to ˜1.8 per cent of the one-component intrinsic ellipticity value. This large-scale structure noise error becomes equal to intrinsic ellipticity noise if there are measurements for ˜3000 galaxies within a certain aperture, a number that is already achieved by current deep surveys such as COSMOS and therefore that should not be ignored.
NASA Astrophysics Data System (ADS)
Chen, Songbai; Jing, Jiliang
2015-10-01
We have investigated the strong gravitational lensing for the photons coupled to Weyl tensor in a Schwarzschild black hole spacetime. We find that in the four-dimensional black hole spacetime the equation of motion of the photons depends not only on the coupling between photon and Weyl tensor, but also on the polarization direction of the photons. It is quite different from that in the case of the usual photon without coupling to Weyl tensor in which the equation of motion is independent of the polarization of the photon. Moreover, we find that the coupling and the polarization direction modify the properties of the photon sphere, the deflection angle, the coefficients in strong field lensing, and the observational gravitational lensing variables. Combining with the supermassive central object in our Galaxy, we estimated three observables in the strong gravitational lensing for the photons coupled to Weyl tensor.
Impact of Atmospheric Chromatic Effects on Weak Lensing Measurements
NASA Astrophysics Data System (ADS)
Meyers, Joshua E.; Burchat, Patricia R.
2015-07-01
Current and future imaging surveys will measure cosmic shear with statistical precision that demands a deeper understanding of potential systematic biases in galaxy shape measurements than has been achieved to date. We use analytic and computational techniques to study the impact on shape measurements of two atmospheric chromatic effects for ground-based surveys such as the Dark Energy Survey and the Large Synoptic Survey Telescope (LSST): (1) atmospheric differential chromatic refraction and (2) wavelength dependence of seeing. We investigate the effects of using the point-spread function (PSF) measured with stars to determine the shapes of galaxies that have different spectral energy distributions than the stars. We find that both chromatic effects lead to significant biases in galaxy shape measurements for current and future surveys, if not corrected. Using simulated galaxy images, we find a form of chromatic model bias that arises when fitting a galaxy image with a model that has been convolved with a stellar, instead of galactic, PSF. We show that both forms of atmospheric chromatic biases can be predicted (and corrected) with minimal model bias by applying an ordered set of perturbative PSF-level corrections based on machine-learning techniques applied to six-band photometry. Catalog-level corrections do not address the model bias. We conclude that achieving the ultimate precision for weak lensing from current and future ground-based imaging surveys requires a detailed understanding of the wavelength dependence of the PSF from the atmosphere, and from other sources such as optics and sensors. The source code for this analysis is available at https://github.com/DarkEnergyScienceCollaboration/chroma.
THE IMPACT OF CORRELATED PROJECTIONS ON WEAK LENSING CLUSTER COUNTS
Marian, Laura; Smith, Robert E.; Bernstein, Gary M.
2010-01-20
Large-scale structure projections are an obstacle in converting the shear signal of clusters detected in weak-lensing maps into virial masses. However, this step is not necessary for constraining cosmology with the shear-peak abundance, if we are able to predict its amplitude. We generate a large ensemble of N-body simulations spanning four cosmological models, with total volume V{sub tot} approx 1(h {sup -1} Gpc){sup 3} per model. Variations to the matter density parameter and amplitude of fluctuations are considered. We measure the abundance of peaks in the mass density projected in approx100 h {sup -1} Mpc slabs to determine the impact of structures spatially correlated with the simulation clusters, identified by the three-dimensional (3D) friends-of-friends (FoF) algorithm. The halo model shows that the choice of the smoothing filter for the density field is important in reducing the contribution of correlated projections to individual halo masses. Such contributions are less than 2% in the case of the optimal, compensated filter used throughout this analysis. We measure the change in the mass of peaks when projected in slabs of various thicknesses. Peaks in slabs of 26 h {sup -1} Mpc and 102 h {sup -1} Mpc suffer an average mass change of less than 2% compared to their mass in slabs of 51 h {sup -1} Mpc. We then explore the cosmology dependence of the projected-peak mass function, and find that, for a wide range of slab thicknesses (< 500 h {sup -1} Mpc), it scales with cosmology in exactly the same way as the 3D FoF mass function and the Sheth-Tormen (ST) formula. This extends the earlier result of Marian et al. Finally, we show that for all cosmological models considered, the low and intermediate mass bins of the peak abundance can be described using a modified ST functional form to within 10%-20% accuracy.
Gravitational anomaly and Hawking radiation near a weakly isolated horizon
Wu Xiaoning; Huang Chaoguang; Sun Jiarui
2008-06-15
Based on the idea of the work by Wilczek and his collaborators, we consider the gravitational anomaly near a weakly isolated horizon. We find that there exists a universal choice of tortoise coordinate for any weakly isolated horizon. Under this coordinate, the leading behavior of a quite arbitrary scalar field near a horizon is a 2-dimensional chiral scalar field. This means we can extend the idea of Wilczek and his collaborators to more general cases and show the relation between gravitational anomaly and Hawking radiation is a universal property of a black hole horizon.
Gravitational anomaly and Hawking radiation near a weakly isolated horizon
NASA Astrophysics Data System (ADS)
Wu, Xiaoning; Huang, Chao-Guang; Sun, Jia-Rui
2008-06-01
Based on the idea of the work by Wilczek and his collaborators, we consider the gravitational anomaly near a weakly isolated horizon. We find that there exists a universal choice of tortoise coordinate for any weakly isolated horizon. Under this coordinate, the leading behavior of a quite arbitrary scalar field near a horizon is a 2-dimensional chiral scalar field. This means we can extend the idea of Wilczek and his collaborators to more general cases and show the relation between gravitational anomaly and Hawking radiation is a universal property of a black hole horizon.
Seeing in the Dark: Weak Lensing from the Sloan Digital Sky Survey
NASA Astrophysics Data System (ADS)
Huff, Eric Michael
Statistical weak lensing by large-scale structure { cosmic shear { is a promising cosmological tool, which has motivated the design of several large upcoming astronomical surveys. This Thesis presents a measurement of cosmic shear using coadded Sloan Digital Sky Survey (SDSS) imaging in 168 square degrees of the equatorial region, with r < 23:5 and i < 22:5, a source number density of 2.2 per arcmin2 and median redshift of zmed = 0.52. These coadds were generated using a new rounding kernel method that was intended to minimize systematic errors in the lensing measurement due to coherent PSF anisotropies that are otherwise prevalent in the SDSS imaging data. Measurements of cosmic shear out to angular separations of 2 degrees are presented, along with systematics tests of the catalog generation and shear measurement steps that demonstrate that these results are dominated by statistical rather than systematic errors. Assuming a cosmological model corresponding to WMAP7 (Komatsu et al., 2011) and allowing only the amplitude of matter fluctuations sigma8 to vary, the best-t value of the amplitude of matter fluctuations is sigma 8=0.636+0.109-0.154 (1sigma); without systematic errors this would be sigma8=0.636+0.099 -0.137 (1sigma). Assuming a flat ? CDM model, the combined constraints with WMAP7 are sigma8=0.784+0.028 -0.026 (1sigma). The 2sigma error range is 14 percent smaller than WMAP7 alone. Aside from the intrinsic value of such cosmological constraints from the growth of structure, some important lessons are identified for upcoming surveys that may face similar issues when combining multi-epoch data to measure cosmic shear. Motivated by the challenges faced in the cosmic shear measurement, two new lensing probes are suggested for increasing the available weak lensing signal. Both use galaxy scaling relations to control for scatter in lensing observables. The first employs a version of the well-known fundamental plane relation for early type galaxies. This modified "photometric fundamental plane" replaces velocity dispersions with photometric galaxy properties, thus obviating the need for spectroscopic data. We present the first detection of magnification using this method by applying it to photometric catalogs from the Sloan Digital Sky Survey. This analysis shows that the derived magnification signal is comparable to that available from conventional methods using gravitational shear. We suppress the dominant sources of systematic error and discuss modest improvements that may allow this method to equal or even surpass the signal-to-noise achievable with shear. Moreover, some of the dominant sources of systematic error are substantially different from those of shear-based techniques. The second outlines an idea for using the optical Tully-Fisher relation to dramatically improve the signal-to-noise and systematic error control for shear measurements. The expected error properties and potential advantages of such a measurement are proposed, and a pilot study is suggested in order to test the viability of Tully-Fisher weak lensing in the context of the forthcoming generation of large spectroscopic surveys.
The Effect of Environment on Shear in Strong Gravitational Lenses
NASA Astrophysics Data System (ADS)
Wong, Kenneth C.; Keeton, Charles R.; Williams, Kurtis A.; Momcheva, Ivelina G.; Zabludoff, Ann I.
2011-01-01
Using new photometric and spectroscopic data in the fields of nine strong gravitational lenses that lie in galaxy groups, we analyze the effects of both the local group environment and line-of-sight (LOS) galaxies on the lens potential. We use Monte Carlo simulations to derive the shear directly from measurements of the complex lens environment, providing the first detailed independent check of the shear obtained from lens modeling. We account for possible tidal stripping of the group galaxies by varying the fraction of total mass apportioned between the group dark matter halo and individual group galaxies. The environment produces an average shear of γ = 0.08 (ranging from 0.02 to 0.17), significant enough to affect quantities derived from lens observables. However, the direction and magnitude of the shears do not match those obtained from lens modeling in three of the six four-image systems in our sample (B1422, RXJ1131, and WFI2033). The source of this disagreement is not clear, implying that the assumptions inherent in both the environment and lens model approaches must be reconsidered. If only the local group environment of the lens is included, the average shear is γ = 0.05 (ranging from 0.01 to 0.14), indicating that LOS contributions to the lens potential are not negligible. We isolate the effects of various theoretical and observational uncertainties on our results. Of those uncertainties, the scatter in the Faber-Jackson relation and error in the group centroid position dominate. Future surveys of lens environments should prioritize spectroscopic sampling of both the local lens environment and objects along the LOS, particularly those bright (I< 21.5) galaxies projected within 5' of the lens. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.
Gravitational Thermodynamics for Interstellar Gas and Weakly Degenerate Quantum Gas
NASA Astrophysics Data System (ADS)
Zhu, Ding Yu; Shen, Jian Qi
2016-03-01
The temperature distribution of an ideal gas in gravitational fields has been identified as a longstanding problem in thermodynamics and statistical physics. According to the principle of entropy increase (i.e., the principle of maximum entropy), we apply a variational principle to the thermodynamical entropy functional of an ideal gas and establish a relationship between temperature gradient and gravitational field strength. As an illustrative example, the temperature and density distributions of an ideal gas in two simple but typical gravitational fields (i.e., a uniform gravitational field and an inverse-square gravitational field) are considered on the basis of entropic and hydrostatic equilibrium conditions. The effect of temperature inhomogeneity in gravitational fields is also addressed for a weakly degenerate quantum gas (e.g., Fermi and Bose gas). The present gravitational thermodynamics of a gas would have potential applications in quantum fluids, e.g., Bose–Einstein condensates in Earth’s gravitational field and the temperature fluctuation spectrum in cosmic microwave background radiation.
NASA Astrophysics Data System (ADS)
Sereno, Mauro; Veropalumbo, Alfonso; Marulli, Federico; Covone, Giovanni; Moscardini, Lauro; Cimatti, Andrea
2015-06-01
The joint analysis of clustering and stacked gravitational lensing of galaxy clusters in large surveys can constrain the formation and evolution of structures and the cosmological parameters. On scales outside a few virial radii, the halo bias, b, is linear and the lensing signal is dominated by the correlated distribution of matter around galaxy clusters. We discuss a method to measure the power spectrum amplitude ?8 and b based on a minimal modelling. We considered a sample of 120 000 clusters photometrically selected from the Sloan Digital Sky Survey in the redshift range 0.1 < z < 0.6. The autocorrelation was studied through the two-point function of a subsample of 70 000 clusters; the matter-halo correlation was derived from the weak lensing signal of the subsample of 1200 clusters with Canada-France-Hawaii Telescope Lensing Survey data. We obtained a direct measurement of b, which increases with mass in agreement with predictions of the ? cold dark matter paradigm. Assuming ?M = 0.3, we found ?8 = 0.79 0.16. We used the same clusters for measuring both lensing and clustering and the estimate of ?8 did require neither the mass-richness relation, nor the knowledge of the selection function, nor the modelling of b. With an additional theoretical prior on the bias, we obtained ?8 = 0.75 0.08.
UP TO 100,000 RELIABLE STRONG GRAVITATIONAL LENSES IN FUTURE DARK ENERGY EXPERIMENTS
Serjeant, S.
2014-09-20
The Euclid space telescope will observe ∼10{sup 5} strong galaxy-galaxy gravitational lens events in its wide field imaging survey over around half the sky, but identifying the gravitational lenses from their observed morphologies requires solving the difficult problem of reliably separating the lensed sources from contaminant populations, such as tidal tails, as well as presenting challenges for spectroscopic follow-up redshift campaigns. Here I present alternative selection techniques for strong gravitational lenses in both Euclid and the Square Kilometre Array, exploiting the strong magnification bias present in the steep end of the Hα luminosity function and the H I mass function. Around 10{sup 3} strong lensing events are detectable with this method in the Euclid wide survey. While only ∼1% of the total haul of Euclid lenses, this sample has ∼100% reliability, known source redshifts, high signal-to-noise, and a magnification-based selection independent of assumptions of lens morphology. With the proposed Square Kilometre Array dark energy survey, the numbers of reliable strong gravitational lenses with source redshifts can reach 10{sup 5}.
Interaction of Dirac and Majorana neutrinos with weak gravitational fields
Menon, A.; Thalapillil, Arun M.
2008-12-01
In this paper the interaction of high energy neutrinos with weak gravitational fields is briefly explored. The form of the graviton-neutrino vertex is motivated from Lorentz and gauge invariance and the nonrelativistic interpretations of the neutrino-gravitational form factors are obtained. We comment on the renormalization conditions, the preservation of the weak equivalence principle and the definition of the neutrino mass radius. We associate the neutrino-gravitational form factors with specific angular momentum states. Based on Feynman diagrams, spin-statistics, CP invariance and symmetries of the angular momentum states in the graviton-neutrino vertex, we deduce differences between the Majorana and Dirac cases. It is then proved that in spite of the theoretical differences between the two cases, as far as experiments are considered, they would be virtually indistinguishable for any space-time geometry satisfying the weak-field condition. We then calculate the transition gravitational form factors for the neutrino by evaluating the relevant Feynman diagrams at 1-loop and estimate a neutrino transition mass radius. The form factor is seen to depend on the momentum transfer very weakly. It is also seen that the neutrino transition mass radius is smaller than the typical neutrino charge radius by a couple of orders of magnitude.
Adrián-Martínez, S.; Ardid, M.; Bou-Cabo, M.; André, M.; Anton, G.; Aubert, J.-J.; Bertin, V.; Brunner, J.; Busto, J.; Basa, S.; Biagi, S.; Capone, A.; Caramete, L.; and others
2014-11-01
This paper proposes to exploit gravitational lensing effects to improve the sensitivity of neutrino telescopes to the intrinsic neutrino emission of distant blazar populations. This strategy is illustrated with a search for cosmic neutrinos in the direction of four distant and gravitationally lensed Flat-Spectrum Radio Quasars. The magnification factor is estimated for each system assuming a singular isothermal profile for the lens. Based on data collected from 2007 to 2012 by the ANTARES neutrino telescope, the strongest constraint is obtained from the lensed quasar B0218+357, providing a limit on the total neutrino luminosity of this source of 1.08× 10{sup 46} erg s{sup -1}. This limit is about one order of magnitude lower than those previously obtained in the ANTARES standard point source searches with non-lensed Flat-Spectrum Radio Quasars.
PMN J1838-3427: A New Gravitationally Lensed Quasar
NASA Astrophysics Data System (ADS)
Winn, Joshua N.; Hewitt, Jacqueline N.; Schechter, Paul L.; Dressler, Alan; Falco, E. E.; Impey, C. D.; Kochanek, C. S.; Lehár, J.; Lovell, J. E. J.; McLeod, B. A.; Morgan, Nicholas D.; Muñoz, J. A.; Rix, H.-W.; Ruiz, Maria Teresa
2000-12-01
We report the discovery of a new double-image quasar that was found during a search for gravitational lenses in the southern sky. Radio source PMN J1838-3427 is composed of two flat-spectrum components with separation 1.0", flux density ratio 14:1, and matching spectral indices in VLA and VLBA images. Ground-based BRI images show the optical counterpart (total I=18.6) is also double, with the same separation and position angle as the radio components. An HST/WFPC2 image reveals the lens galaxy. The optical flux ratio (27:1) is higher than the radio value, probably because of differential extinction of the components by the lens galaxy. An optical spectrum of the bright component contains quasar emission lines at z=2.78 and several absorption features, including prominent Lyα absorption. The lens galaxy redshift could not be measured, but it is estimated to be z=0.36+/-0.08. The image configuration is consistent with the simplest plausible models for the lens potential. The flat radio spectrum and observed variability of PMN J1838-3427 suggest that the time delay between flux variations of the components is measurable and could thus provide an independent measurement of H0. Based on observations using the Very Large Array (VLA) and Very Long Baseline Array (VLBA) of the National Radio Astronomy Observatory (NRAO), the NASA/ESA Hubble Space Telescope (HST), the 3.6 m telescope of the European Southern Observatory (ESO) at La Silla, the du Pont telescope at Las Campanas Observatory (LCO), and the Australia Telescope Compact Array (ATCA). The NRAO is a facility of the National Science Foundation (NSF) operated under cooperative agreement by Associated Universities for Research in Astronomy, Inc., (AURA). The HST data were obtained from the Space Telescope Science Institute, which is operated by AURA under NASA contract NAS 5-26555. ATCA is part of the Australia Telescope which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO.
NASA Astrophysics Data System (ADS)
Hilbert, Stefan; Gair, Jonathan R.; King, Lindsay J.
2011-04-01
Gravitational lensing induces significant errors in the measured distances to high-redshift standard candles and standard sirens such as Type Ia supernovae, gamma-ray bursts and merging supermassive black hole binaries. There will therefore be a significant benefit from correcting for the lensing error by using independent and accurate estimates of the lensing magnification. Here, we investigate how accurately the magnification can be inferred from convergence maps reconstructed from galaxy shear and flexion data. We employ ray-tracing through the Millennium Simulation (MS) to simulate lensing observations in large fields, and perform a weak-lensing reconstruction on the simulated fields. We identify optimal ways to filter the reconstructed convergence maps and to convert them to magnification maps, and analyse the resulting relation between the estimated and true magnification for sources at redshifts zS= 1 to 5. We find that a deep shear survey with 100 galaxies arcmin-2 can help to reduce the lensing-induced distance errors for standard candles/sirens at redshifts zS? 1.5 (zS? 5) on average by 20 per cent (10 per cent), whereas a futuristic survey with shear and flexion estimates from 500 galaxies arcmin-2 yields much larger reductions of 50 per cent (35 per cent). For redshifts zS? 3, a further improvement by 5 per cent can be achieved, if the individual redshifts of the galaxies are used in the reconstruction. Moreover, the reconstruction allows one to identify regions for which the convergence is low, and in which an error reduction by up to 75 per cent can be achieved. Such strongly reduced magnification uncertainties will greatly improve the value of high-redshift standard candles/sirens as cosmological probes.
The effective number density of galaxies for weak lensing measurements in the LSST project
NASA Astrophysics Data System (ADS)
Chang, C.; Jarvis, M.; Jain, B.; Kahn, S. M.; Kirkby, D.; Connolly, A.; Krughoff, S.; Peng, E.-H.; Peterson, J. R.
2013-09-01
Future weak lensing surveys potentially hold the highest statistical power for constraining cosmological parameters compared to other cosmological probes. The statistical power of a weak lensing survey is determined by the sky coverage, the inverse of the noise in shear measurements and the galaxy number density. The combination of the latter two factors is often expressed in terms of neff - the `effective number density of galaxies used for weak lensing measurements'. In this work, we estimate neff for the Large Synoptic Survey Telescope (LSST) project, the most powerful ground-based lensing survey planned for the next two decades. We investigate how the following factors affect the resulting neff of the survey with detailed simulations: (1) survey time, (2) shear measurement algorithm, (3) algorithm for combining multiple exposures, (4) inclusion of data from multiple filter bands, (5) redshift distribution of the galaxies and (6) masking and blending. For the first time, we quantify in a general weak lensing analysis pipeline the sensitivity of neff to the above factors. We find that with current weak lensing algorithms, expected distributions of observing parameters, and all lensing data (r and i band, covering 18 000 degree2 of sky) for LSST, neff ? 37 arcmin-2 before considering blending and masking, neff ? 31 arcmin-2 when rejecting seriously blended galaxies and neff ? 26 arcmin-2 when considering an additional 15 per cent loss of galaxies due to masking. With future improvements in weak lensing algorithms, these values could be expected to increase by up to 20 per cent. Throughout the paper, we also stress the ways in which neff depends on our ability to understand and control systematic effects in the measurements.
Republication of: Quantum theory of weak gravitational fields
NASA Astrophysics Data System (ADS)
Bronstein, Matvei
2012-01-01
This is an English translation of a paper by Matvei Bronstein, first published in German in 1936 in a long-extinct Soviet journal, in which he presented the first attempt at quantizing a weak (linearized) gravitational field, rather modern in its approach. The paper has been selected by the Editors of General Relativity and Gravitation for re-publication in the Golden Oldies series of the journal. This republication is accompanied by an editorial note written by Stanley Deser and Alexei Starobinsky, and Bronstein's brief biography written by Stanley Deser.
SDSS J094604.90+183541.8: A GRAVITATIONALLY LENSED QUASAR AT z = 4.8
McGreer, Ian D.; Fan Xiaohui; Bian Fuyan; Farnsworth, Kara; Hall, Patrick B.; Inada, Naohisa; Oguri, Masamune; Strauss, Michael A.; Schneider, Donald P.
2010-08-15
We report the discovery of a gravitationally lensed quasar identified serendipitously in the Sloan Digital Sky Survey (SDSS). The object, SDSS J094604.90+183541.8, was initially targeted for spectroscopy as a luminous red galaxy, but the SDSS spectrum has the features of both a z = 0.388 galaxy and a z = 4.8 quasar. We have obtained additional imaging that resolves the system into two quasar images separated by 3.''06 and a bright galaxy that is strongly blended with one of the quasar images. We confirm spectroscopically that the two quasar images represent a single-lensed source at z = 4.8 with a total magnification of 3.2, and we derive a model for the lensing galaxy. This is the highest redshift lensed quasar currently known. We examine the issues surrounding the selection of such an unusual object from existing data and briefly discuss implications for lensed quasar surveys.
NASA Astrophysics Data System (ADS)
Spitzer, Isaac; Quimby, Robert
2016-01-01
Strongly lensed quasars can be used to study the Hubble constant and the lens mass by measuring time delay and image separation. These objects can require years of data to confirm however, so using data from preexisting surveys could greatly reduce the amount of time required to study them. We attempt to use Palomar Transient Factory survey data to detect variability in strongly lensed quasars and to measure time delays between the quasar images. We test our procedure using known gravitationally lensed quasars with measured time delays.
NASA Astrophysics Data System (ADS)
Biernaux, J.; Magain, P.; Sluse, D.; Chantry, V.
2016-01-01
Context. The luminosity profiles of galaxies acting as strong gravitational lenses can be tricky to study. Indeed, strong gravitational lensing images display several lensed components, both point-like and diffuse, around the lensing galaxy. Those objects limit the study of the galaxy luminosity to its inner parts. Therefore, the usual fitting methods perform rather badly on such images. Previous studies of strong lenses luminosity profiles using software such as GALFIT or IMFITFITS and various PSF-determining methods have resulted in somewhat discrepant results. Aims: The present work aims at investigating the causes of those discrepancies, as well as at designing more robust techniques for studying the morphology of early-type lensing galaxies with the ability to subtract a lensed signal from their luminosity profiles. Methods: We design a new method to independently measure each shape parameter, namely, the position angle, ellipticity, and half-light radius of the galaxy. Our half-light radius measurement method is based on an innovative scheme for computing isophotes that is well suited to measuring the morphological properties of gravititational lensing galaxies. Its robustness regarding various specific aspects of gravitational lensing image processing is analysed and tested against GALFIT. It is then applied to a sample of systems from the CASTLES database. Results: Simulations show that, when restricted to small, inner parts of the lensing galaxy, the technique presented here is more trustworthy than GALFIT. It gives more robust results than GALFIT, which shows instabilities regarding the fitting region, the value of the Sérsic index, and the signal-to-noise ratio. It is therefore better suited than GALFIT for gravitational lensing galaxies. It is also able to study lensing galaxies that are not much larger than the PSF. New values for the half-light radius of the objects in our sample are presented and compared to previous works. Table 6 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/585/A84
Discovery of a new component in the gravitationally lensed quasar 0957 + 561
NASA Technical Reports Server (NTRS)
Jones, C.; Stern, C.; Falco, E.; Forman, W.; David, L.; Shapiro, I.; Fabian, A. C.
1993-01-01
X-ray observations of the gravitationally lensed quasar 0957 + 561 with the Einstein Observatory High Resolution Imager indicate the presence of a new component in the system. The significantly greater X-ray intensity of image A compared with image B and the extended X-ray emission can be interpreted as the gravitational lensing of a quasi-circular X-ray emitting region into a partial Einstein ring. It is suggested that the observed X-ray emission is produced by a strong cooling flow which could arise were 0957 + 561 embedded in a group of cluster galaxies.
Detection of gravitational lenses and measurement of time delays from radiation fluctuations
NASA Astrophysics Data System (ADS)
Borra, Ermanno F.
1997-08-01
I suggest that measurements of intensity fluctuations caused by classical wave interactions can be used to find unresolved gravitational lenses and determine time delays of essentially arbitrary length among the images formed by a gravitational lens. No interferometry is needed, and the time delays can be measured by analysing the intensity signal alone. The technique works with lensed sources that have constant luminosities and is capable of measuring very long time delays. I suggest interferometric techniques, capable of measuring time delays of arbitrary length, that can be used to refine the measurements.
Strong gravitational lensing in a charged squashed Kaluza-Klein black hole
NASA Astrophysics Data System (ADS)
Sadeghi, J.; Banijamali, A.; Vaez, H.
2013-02-01
In this paper we investigate the strong gravitational lensing in a charged squashed Kaluza-Klein black hole. We suppose that the supermassive black hole in the galaxy center can be considered by a charged squashed Kaluza-Klein black hole and then we study the strong gravitational lensing theory and estimate the numerical values for parameters and observables of it. We explore the effects of the scale of extra dimension ? 0 and the charge of black hole ? q on these parameters and observables.
Gravitational lensing frequencies - Galaxy cross-sections and selection effects
NASA Technical Reports Server (NTRS)
Fukugita, Masataka; Turner, Edwin L.
1991-01-01
Four issues - (1) the best currently available data on the galaxy velocity-dispersion distribution, (2) the effects of finite core radii potential ellipticity on lensing cross sections, (3) the predicted distribution of lens image separations compared to observational angular resolutions, and (4) the preferential inclusion of lens systems in flux limited samples - are considered in order to facilitate more realistic predictions of multiple image galaxy-quasar lensing frequencies. It is found that (1) the SIS lensing parameter F equals 0.047 +/-0.019 with almost 90 percent contributed by E and S0 galaxies, (2) observed E and S0 core radii are remarkably small, yielding a factor of less than about 2 reduction in total lensing cross sections, (3) 50 percent of galaxy-quasar lenses have image separations greater than about 1.3 arcsec, and (4) amplification bias factors are large and must be carefully taken into account. It is concluded that flat universe models excessively dominated by the cosmological constant are not favored by the small observed galaxy-quasar lensing rate.
Comparing Dense Galaxy Cluster Redshift Surveys with Weak-lensing Maps
NASA Astrophysics Data System (ADS)
Hwang, Ho Seong; Geller, Margaret J.; Diaferio, Antonaldo; Rines, Kenneth J.; Zahid, H. Jabran
2014-12-01
We use dense redshift surveys of nine galaxy clusters at z ~ 0.2 to compare the galaxy distribution in each system with the projected matter distribution from weak lensing. By combining 2087 new MMT/Hectospec redshifts and the data in the literature, we construct spectroscopic samples within the region of weak-lensing maps of high (70%-89%) and uniform completeness. With these dense redshift surveys, we construct galaxy number density maps using several galaxy subsamples. The shape of the main cluster concentration in the weak-lensing maps is similar to the global morphology of the number density maps based on cluster members alone, mainly dominated by red members. We cross-correlate the galaxy number density maps with the weak-lensing maps. The cross-correlation signal when we include foreground and background galaxies at 0.5z cl < z < 2z cl is 10%-23% larger than for cluster members alone at the cluster virial radius. The excess can be as high as 30% depending on the cluster. Cross-correlating the galaxy number density and weak-lensing maps suggests that superimposed structures close to the cluster in redshift space contribute more significantly to the excess cross-correlation signal than unrelated large-scale structure along the line of sight. Interestingly, the weak-lensing mass profiles are not well constrained for the clusters with the largest cross-correlation signal excesses (>20% for A383, A689, and A750). The fractional excess in the cross-correlation signal including foreground and background structures could be a useful proxy for assessing the reliability of weak-lensing cluster mass estimates.
COMPARING DENSE GALAXY CLUSTER REDSHIFT SURVEYS WITH WEAK-LENSING MAPS
Hwang, Ho Seong; Geller, Margaret J.; Zahid, H. Jabran; Diaferio, Antonaldo; Rines, Kenneth J. E-mail: mgeller@cfa.harvard.edu E-mail: diaferio@ph.unito.it
2014-12-20
We use dense redshift surveys of nine galaxy clusters at z ∼ 0.2 to compare the galaxy distribution in each system with the projected matter distribution from weak lensing. By combining 2087 new MMT/Hectospec redshifts and the data in the literature, we construct spectroscopic samples within the region of weak-lensing maps of high (70%-89%) and uniform completeness. With these dense redshift surveys, we construct galaxy number density maps using several galaxy subsamples. The shape of the main cluster concentration in the weak-lensing maps is similar to the global morphology of the number density maps based on cluster members alone, mainly dominated by red members. We cross-correlate the galaxy number density maps with the weak-lensing maps. The cross-correlation signal when we include foreground and background galaxies at 0.5z {sub cl} < z < 2z {sub cl} is 10%-23% larger than for cluster members alone at the cluster virial radius. The excess can be as high as 30% depending on the cluster. Cross-correlating the galaxy number density and weak-lensing maps suggests that superimposed structures close to the cluster in redshift space contribute more significantly to the excess cross-correlation signal than unrelated large-scale structure along the line of sight. Interestingly, the weak-lensing mass profiles are not well constrained for the clusters with the largest cross-correlation signal excesses (>20% for A383, A689, and A750). The fractional excess in the cross-correlation signal including foreground and background structures could be a useful proxy for assessing the reliability of weak-lensing cluster mass estimates.
Probing cosmology with weak lensing selected clusters. II. Dark energy and f(R) gravity models
NASA Astrophysics Data System (ADS)
Shirasaki, Masato; Hamana, Takashi; Yoshida, Naoki
2016-02-01
Ongoing and future wide-field galaxy surveys can be used to locate a number of clusters of galaxies with cosmic shear measurement alone. We study constraints on cosmological models using statistics of weak lensing selected galaxy clusters. We extend our previous theoretical framework to model the statistical properties of clusters in variants of cosmological models as well as in the standard ΛCDM model. Weak lensing selection of clusters does not rely on conventional assumptions such as the relation between luminosity and mass and/or hydrostatic equilibrium, but a number of observational effects compromise robust identification. We use a large set of realistic mock weak lensing catalogs as well as analytic models to perform a Fisher analysis and make a forecast for constraining two competing cosmological models, the wCDM model and f(R) model proposed by Hu and Sawicki (2007, Phys. Rev. D, 76, 064004), with our lensing statistics. We show that weak lensing selected clusters are excellent probes of cosmology when combined with cosmic shear power spectrum even in the presence of galaxy shape noise and masked regions. With the information from weak lensing selected clusters, the precision of cosmological parameter estimates can be improved by a factor of ˜1.6 and ˜8 for the wCDM model and f(R) model, respectively. The Hyper Suprime-Cam survey with sky coverage of 1250 degrees squared can constrain the equation of state of dark energy w0 with a level of Δw0 ˜ 0.1. It can also constrain the additional scalar degree of freedom in the f(R) model with a level of |fR0| ˜ 5 × 10-6, when constraints from cosmic microwave background measurements are incorporated. Future weak lensing surveys with sky coverage of 20000 degrees squared will place tighter constraints on w0 and |fR0| even without cosmic microwave background measurements.
Probing cosmology with weak lensing selected clusters. II. Dark energy and f(R) gravity models
NASA Astrophysics Data System (ADS)
Shirasaki, Masato; Hamana, Takashi; Yoshida, Naoki
2015-10-01
Ongoing and future wide-field galaxy surveys can be used to locate a number of clusters of galaxies with cosmic shear measurement alone. We study constraints on cosmological models using statistics of weak lensing selected galaxy clusters. We extend our previous theoretical framework to model the statistical properties of clusters in variants of cosmological models as well as in the standard ?CDM model. Weak lensing selection of clusters does not rely on conventional assumptions such as the relation between luminosity and mass and/or hydrostatic equilibrium, but a number of observational effects compromise robust identification. We use a large set of realistic mock weak lensing catalogs as well as analytic models to perform a Fisher analysis and make a forecast for constraining two competing cosmological models, the wCDM model and f(R) model proposed by Hu and Sawicki (2007, Phys. Rev. D, 76, 064004), with our lensing statistics. We show that weak lensing selected clusters are excellent probes of cosmology when combined with cosmic shear power spectrum even in the presence of galaxy shape noise and masked regions. With the information from weak lensing selected clusters, the precision of cosmological parameter estimates can be improved by a factor of 1.6 and 8 for the wCDM model and f(R) model, respectively. The Hyper Suprime-Cam survey with sky coverage of 1250 degrees squared can constrain the equation of state of dark energy w0 with a level of ?w0 0.1. It can also constrain the additional scalar degree of freedom in the f(R) model with a level of |fR0| 5 10-6, when constraints from cosmic microwave background measurements are incorporated. Future weak lensing surveys with sky coverage of 20000 degrees squared will place tighter constraints on w0 and |fR0| even without cosmic microwave background measurements.
A weak lensing comparability study of galaxy mergers that host AGNs
NASA Astrophysics Data System (ADS)
Harvey, D.; Courbin, F.
2015-07-01
We compared the total mass density profiles of three different types of galaxies using weak gravitational lensing: (i) 29 galaxies that host quasars at bar{z}˜ 0.32 that are in a post-starburst quasar (PSQ) phase with high star formation indicating recent merger activity, (ii) 22 large elliptical galaxies from the Sloan Lens ACS Survey (SLACS) sample that do not host a quasar at bar{z}˜ 0.23, and (iii) 17 galaxies that host moderately luminous quasars at bar{z}˜ 0.36 powered by disc instabilities, but with no intense star formation. In an initial test we found no evidence for a connection between the merger state of a galaxy and the profile of the halo, with the PSQ profile comparable to that of the other two samples and consistent with the Leauthaud et al. study of moderately luminous quasars in Cosmic Evolution Survey (COSMOS). Given the compatibility of the two quasar samples, we combined these and found no evidence for any connection between black hole activity and the dark matter halo. All three mass profiles remained compatible with isothermality given the present data.
INTERPOLATING MASKED WEAK-LENSING SIGNAL WITH KARHUNEN-LOEVE ANALYSIS
VanderPlas, J. T.; Connolly, A. J.; Jain, B.; Jarvis, M.
2012-01-10
We explore the utility of Karhunen-Loeve (KL) analysis in solving practical problems in the analysis of gravitational shear surveys. Shear catalogs from large-field weak-lensing surveys will be subject to many systematic limitations, notably incomplete coverage and pixel-level masking due to foreground sources. We develop a method to use two-dimensional KL eigenmodes of shear to interpolate noisy shear measurements across masked regions. We explore the results of this method with simulated shear catalogs, using statistics of high-convergence regions in the resulting map. We find that the KL procedure not only minimizes the bias due to masked regions in the field, it also reduces spurious peak counts from shape noise by a factor of {approx}3 in the cosmologically sensitive regime. This indicates that KL reconstructions of masked shear are not only useful for creating robust convergence maps from masked shear catalogs, but also offer promise of improved parameter constraints within studies of shear peak statistics.
Rozo, Eduardo; Wu, Hao-Yi; Schmidt, Fabian; /Caltech
2011-11-04
When extracting the weak lensing shear signal, one may employ either locally normalized or globally normalized shear estimators. The former is the standard approach when estimating cluster masses, while the latter is the more common method among peak finding efforts. While both approaches have identical signal-to-noise in the weak lensing limit, it is possible that higher order corrections or systematic considerations make one estimator preferable over the other. In this paper, we consider the efficacy of both estimators within the context of stacked weak lensing mass estimation in the Dark Energy Survey (DES). We find that the two estimators have nearly identical statistical precision, even after including higher order corrections, but that these corrections must be incorporated into the analysis to avoid observationally relevant biases in the recovered masses. We also demonstrate that finite bin-width effects may be significant if not properly accounted for, and that the two estimators exhibit different systematics, particularly with respect to contamination of the source catalog by foreground galaxies. Thus, the two estimators may be employed as a systematic cross-check of each other. Stacked weak lensing in the DES should allow for the mean mass of galaxy clusters to be calibrated to {approx}2% precision (statistical only), which can improve the figure of merit of the DES cluster abundance experiment by a factor of {approx}3 relative to the self-calibration expectation. A companion paper investigates how the two types of estimators considered here impact weak lensing peak finding efforts.
Probing cosmology with weak lensing selected clusters - I. Halo approach and all-sky simulations
NASA Astrophysics Data System (ADS)
Shirasaki, Masato; Hamana, Takashi; Yoshida, Naoki
2015-11-01
We explore a variety of statistics of clusters selected with cosmic shear measurement by utilizing both analytic models and large numerical simulations. We first develop a halo model to predict the abundance and the clustering of weak lensing selected clusters. Observational effects such as galaxy shape noise are included in our model. We then generate realistic mock weak lensing catalogues to test the accuracy of our analytic model. To this end, we perform full-sky ray-tracing simulations that allow us to have multiple realizations of a large continuous area. We model the masked regions on the sky using the actual positions of bright stars, and generate 200 mock weak lensing catalogues with sky coverage of ˜1000 deg2. We show that our theoretical model agrees well with the ensemble average of statistics and their covariances calculated directly from the mock catalogues. With a typical selection threshold, ignoring shape noise correction causes overestimation of the clustering of weak lensing selected clusters with a level of about 10 per cent, and shape noise correction boosts the cluster abundance by a factor of a few. We calculate the cross-covariances using the halo model with accounting for the effective reduction of the survey area due to masks. The covariance of the cosmic shear auto power spectrum is affected by the mode-coupling effect that originates from sky masking. Our model and the results can be readily used for cosmological analysis with ongoing and future weak lensing surveys.
CLASH: Weak-lensing shear-and-magnification analysis of 20 galaxy clusters
Umetsu, Keiichi; Czakon, Nicole; Medezinski, Elinor; Lemze, Doron; Ford, Holland; Nonino, Mario; Balestra, Italo; Biviano, Andrea; Merten, Julian; Postman, Marc; Koekemoer, Anton; Meneghetti, Massimo; Donahue, Megan; Molino, Alberto; Benítez, Narciso; Seitz, Stella; Gruen, Daniel; Broadhurst, Tom; Grillo, Claudio; Melchior, Peter; and others
2014-11-10
We present a joint shear-and-magnification weak-lensing analysis of a sample of 16 X-ray-regular and 4 high-magnification galaxy clusters at 0.19 ≲ z ≲ 0.69 selected from the Cluster Lensing And Supernova survey with Hubble (CLASH). Our analysis uses wide-field multi-color imaging, taken primarily with Suprime-Cam on the Subaru Telescope. From a stacked-shear-only analysis of the X-ray-selected subsample, we detect the ensemble-averaged lensing signal with a total signal-to-noise ratio of ≅ 25 in the radial range of 200-3500 kpc h {sup –1}, providing integrated constraints on the halo profile shape and concentration-mass relation. The stacked tangential-shear signal is well described by a family of standard density profiles predicted for dark-matter-dominated halos in gravitational equilibrium, namely, the Navarro-Frenk-White (NFW), truncated variants of NFW, and Einasto models. For the NFW model, we measure a mean concentration of c{sub 200c}=4.01{sub −0.32}{sup +0.35} at an effective halo mass of M{sub 200c}=1.34{sub −0.09}{sup +0.10}×10{sup 15} M{sub ⊙}. We show that this is in excellent agreement with Λ cold dark matter (ΛCDM) predictions when the CLASH X-ray selection function and projection effects are taken into account. The best-fit Einasto shape parameter is α{sub E}=0.191{sub −0.068}{sup +0.071}, which is consistent with the NFW-equivalent Einasto parameter of ∼0.18. We reconstruct projected mass density profiles of all CLASH clusters from a joint likelihood analysis of shear-and-magnification data and measure cluster masses at several characteristic radii assuming an NFW density profile. We also derive an ensemble-averaged total projected mass profile of the X-ray-selected subsample by stacking their individual mass profiles. The stacked total mass profile, constrained by the shear+magnification data, is shown to be consistent with our shear-based halo-model predictions, including the effects of surrounding large-scale structure as a two-halo term, establishing further consistency in the context of the ΛCDM model.
Weak- and strong-lensing analyses of the triaxial matter distribution of Abell 1689
NASA Astrophysics Data System (ADS)
Sereno, Mauro; Umetsu, Keiichi
2011-10-01
Haloes formed in the standard ? cold dark matter framework should follow a universal mass density profile and fit a well-defined mass-concentration relation. Lensing analyses of clusters with a large Einstein radius seem to contradict this scenario, with the massive cluster Abell 1689 being often claimed as a notable example of a highly over-concentrated halo. Shape and orientation biases in lensing studies might be on the basis of this disagreement between theory and observations. We developed a method for a full three-dimensional analysis of strong- and weak-lensing data. Surface density maps estimated from lensing are deprojected to infer the actual triaxial structure of the cluster, whose mass distribution is approximated as an ellipsoidal Navarro-Frenk-White halo with arbitrary orientation. Inversion is performed under competing a priori assumptions, integrated in the method, thanks to Bayesian statistics. We applied the method to Abell 1689. Whatever the considered priors on shape and orientation, both weak- and strong-lensing analyses found the halo to be slightly over-concentrated but still consistent with theoretical predictions. We found some evidence for a mildly-triaxial lens (minor-to-major-axis ratio 0.5 0.2) with the major-axis orientated along the line of sight. Exploiting priors from N-body simulations, we found mass M200= (1.3 0.4) 1015 M? and concentration c200= 10 3 for the weak-lensing analysis of Subaru data, M200= (1.7 0.3) 1015 M? and c200= 6.1 0.9 for the strong-lensing analysis of multiple-image systems, and M200= (1.3 0.2) 1015 M? and c200= 7.3 0.8 for the combined weak- plus strong-lensing analysis. Based in part on data collected at the Subaru Telescope, which is operated by the National Astronomical Society of Japan.
Kernel regression estimates of time delays between gravitationally lensed fluxes
NASA Astrophysics Data System (ADS)
Otaibi, Sultanah AL; Tiňo, Peter; Cuevas-Tello, Juan C.; Mandel, Ilya; Raychaudhury, Somak
2016-03-01
Strongly lensed variable quasars can serve as precise cosmological probes, provided that time delays between the image fluxes can be accurately measured. A number of methods have been proposed to address this problem. In this paper, we explore in detail a new approach based on kernel regression estimates, which is able to estimate a single time delay given several datasets for the same quasar. We develop realistic artificial data sets in order to carry out controlled experiments to test of performance of this new approach. We also test our method on real data from strongly lensed quasar Q0957+561 and compare our estimates against existing results.
Testing the MOND Paradigm of Modified Dynamics with Galaxy-Galaxy Gravitational Lensing
NASA Astrophysics Data System (ADS)
Milgrom, Mordehai
2013-07-01
The MOND paradigm of modified dynamics predicts that the asymptotic gravitational potential of an isolated, bounded (baryonic) mass, M, is ϕ(r)=(MGa0)1/2ln(r). Relativistic MOND theories predict that the lensing effects of M are dictated by ϕ(r) as general-relativity lensing is dictated by the Newtonian potential. Thus MOND predicts that the asymptotic Newtonian potential deduced from galaxy-galaxy gravitational lensing will have (1) a logarithmic r dependence, and (2) a normalization (parametrized standardly as 2σ2) that depends only on M: σ=(MGa0/4)1/4. I compare these predictions with recent results of galaxy-galaxy lensing, and find agreement on all counts. For the “blue”-lenses subsample (“spiral” galaxies) MOND reproduces the observations well with an r'-band M/Lr'˜(1-3)(M/L)⊙, and for “red” lenses (“elliptical” galaxies) with M/Lr'˜(3-6)(M/L)⊙, both consistent with baryons only. In contradistinction, Newtonian analysis requires, typically, M/Lr'˜130(M/L)⊙, bespeaking a mass discrepancy of a factor ˜40. Compared with the staple, rotation-curve tests, MOND is here tested in a wider population of galaxies, through a different phenomenon, using relativistic test objects, and is probed to several-times-lower accelerations-as low as a few percent of a0.
Testing the MOND paradigm of modified dynamics with galaxy-galaxy gravitational lensing.
Milgrom, Mordehai
2013-07-26
The MOND paradigm of modified dynamics predicts that the asymptotic gravitational potential of an isolated, bounded (baryonic) mass, M, is ?(r)=(MGa0)1/2ln(r). Relativistic MOND theories predict that the lensing effects of M are dictated by ?(r) as general-relativity lensing is dictated by the Newtonian potential. Thus MOND predicts that the asymptotic Newtonian potential deduced from galaxy-galaxy gravitational lensing will have (1) a logarithmic r dependence, and (2) a normalization (parametrized standardly as 2?2) that depends only on M: ?=(MGa0/4)1/4. I compare these predictions with recent results of galaxy-galaxy lensing, and find agreement on all counts. For the blue-lenses subsample (spiral galaxies) MOND reproduces the observations well with an r?-band M/Lr??(13)(M/L)?, and for red lenses (elliptical galaxies) with M/Lr??(36)(M/L)?, both consistent with baryons only. In contradistinction, Newtonian analysis requires, typically, M/Lr??130(M/L)?, bespeaking a mass discrepancy of a factor ?40. Compared with the staple, rotation-curve tests, MOND is here tested in a wider population of galaxies, through a different phenomenon, using relativistic test objects, and is probed to several-times-lower accelerationsas low as a few percent of a0. PMID:23931350
NASA Astrophysics Data System (ADS)
Ding, Xuheng; Biesiada, Marek; Zhu, Zong-Hong
2015-12-01
With a fantastic sensitivity improving significantly over the advanced GW detectors, Einstein Telescope (ET) will be able to observe hundreds of thousand inspiralling double compact objects per year. By virtue of gravitational lensing effect, intrinsically unobservable faint sources can be observed by ET due to the magnification by intervening galaxies. We explore the possibility of observing such faint sources amplified by strong gravitational lensing. Following our previous work, we use the merger rates of DCO (NS-NS,BH-NS,BH-BH systems) as calculated by Dominik et al.(2013). It turns out that tens to hundreds of such (lensed) extra events will be registered by ET. This will strongly broaden the ET's distance reach for signals from such coalescences to the redshift range z = 2 - 8. However, with respect to the full inspiral event catalog this magnification bias is at the level of 0.001 and should not affect much cosmological inferences.
Weak-lensing B-modes as a probe of the isotropy of the universe
NASA Astrophysics Data System (ADS)
Pereira, Thiago S.; Pitrou, Cyril; Uzan, Jean-Philippe
2016-01-01
Aims: We use the angular power spectrum of B-modes of the weak-lensing shear as a tool for constraining late-time deviations of spatial isotropy in our Universe. Methods: We used the formalism of weak lensing in arbitrary spacetimes. Results: We find that off-diagonal correlations must exist between E-modes, B-modes, and convergence of the weak-lensing field, which allow one to reconstruct the eigendirections of anisotropic expansion. Focusing on future surveys, such as Euclid and the Square Kilometer Array (SKA), we find that observations can constrain the geometrical shear in units of the Hubble rate at the percent level or better. These observations offer a new and powerful method to probe our cosmological model, however, the power of this new technique still requires further investigations and a full analysis of signal-to-noise ratio.
A DETECTION OF WEAK-LENSING MAGNIFICATION USING GALAXY SIZES AND MAGNITUDES
Schmidt, Fabian; Rhodes, Jason; Leauthaud, Alexie; Tanaka, Masayuki; Massey, Richard; George, Matthew R.; Koekemoer, Anton M.; Finoguenov, Alexis
2012-01-10
Weak lensing is commonly measured using shear through galaxy ellipticities or using the effect of magnification bias on galaxy number densities. Here, we report on the first detection of weak-lensing magnification with a new, independent technique using the distribution of galaxy sizes and magnitudes. These data come for free in galaxy surveys designed for measuring shear. We present the magnification estimator and apply it to an X-ray-selected sample of galaxy groups in the COSMOS Hubble Space Telescope survey. The measurement of the projected surface density {Sigma}(r) is consistent with the shear measurements within the uncertainties and has roughly 40% of the signal to noise of the latter. We discuss systematic issues and challenges to realizing the potential of this new probe of weak lensing.
The Mass Of The Coma Cluster From Weak Lensing In The Sloan Digital Sky Survey
Kubo, Jeffrey M.; Stebbins, Albert; Annis, James; Dell'Antonio, Ian P.; Lin, Huan; Khiabanian, Hossein; Frieman, Joshua A.
2007-09-01
We present a weak lensing analysis of the Coma Cluster using the Sloan Digital Sky Survey (SDSS) Data Release Five. Complete imaging of a {approx} 200 square degree region is used to measure the tangential shear of this cluster. The shear is fit to an NFW model and we find a virial radius of r{sub 200} = 1.99{sup +0.21}{sub -0.22}h{sup -1}Mpc which corresponds to a virial mass of M{sub 200} = 1.88{sup +0.65}{sub -0.56} x 10{sup 15}h{sup -1}M{circle_dot}. We additionally compare our weak lensing measurement to the virial mass derived using dynamical techniques, and find they are in agreement. This is the lowest redshift, largest angle weak lensing measurement of an individual cluster to date.
THE EINSTEIN CROSS: CONSTRAINT ON DARK MATTER FROM STELLAR DYNAMICS AND GRAVITATIONAL LENSING
Van de Ven, Glenn; Falcon-Barroso, Jesus; Cappellari, Michele; Miller, Bryan W.; De Zeeuw, P. Tim
2010-08-20
We present two-dimensional line-of-sight stellar kinematics of the lens galaxy in the Einstein Cross, obtained with the GEMINI 8 m telescope, using the GMOS integral-field spectrograph. The stellar kinematics extend to a radius of 4'' (with 0.''2 spaxels), covering about two-thirds of the effective (or half-light) radius R{sub e} {approx_equal} 6'' of this early-type spiral galaxy at redshift z{sub l} {approx_equal} 0.04, of which the bulge is lensing a background quasar at redshift z{sub s} {approx_equal} 1.7. The velocity map shows regular rotation up to {approx}100 km s{sup -1} around the minor axis of the bulge, consistent with axisymmetry. The velocity dispersion map shows a weak gradient increasing toward a central (R < 1'') value of {sigma}{sub 0} = 170 {+-} 9 km s{sup -1}. We deproject the observed surface brightness from Hubble Space Telescope imaging to obtain a realistic luminosity density of the lens galaxy, which in turn is used to build axisymmetric dynamical models that fit the observed kinematic maps. We also construct a gravitational lens model that accurately fits the positions and relative fluxes of the four quasar images. We combine these independent constraints from stellar dynamics and gravitational lensing to study the total mass distribution in the inner parts of the lens galaxy. We find that the resulting luminous and total mass distribution are nearly identical around the Einstein radius R{sub E} = 0.''89, with a slope that is close to isothermal, but which becomes shallower toward the center if indeed mass follows light. The dynamical model fits to the observed kinematic maps result in a total mass-to-light ratio Y{sub dyn} = 3.7 {+-} 0.5 Y{sub sun,I} (in the I band). This is consistent with the Einstein mass M{sub E} = 1.54 x 10{sup 10} M {sub sun} divided by the (projected) luminosity within R{sub E} , which yields a total mass-to-light ratio of Y {sub E} = 3.4 Y{sub sun,I}, with an error of at most a few percent. We estimate from stellar population model fits to colors of the lens galaxy a stellar mass-to-light ratio Y{sub *} from 2.8 to 4.1 Y{sub sun,I}. Although a constant dark matter fraction of 20% is not excluded, dark matter may play no significant role in the bulge of this {approx}L {sub *} early-type spiral galaxy.
NASA Astrophysics Data System (ADS)
Sato, Masanori; Nishimichi, Takahiro
2013-06-01
We study how well the Gaussian approximation is valid for computing the covariance matrices of the convergence power and bispectrum in weak gravitational lensing analyses. We focus on its impact on the cosmological parameter estimations by comparing the results with and without non-Gaussian error contribution in the covariance matrix. We numerically derive the covariance matrix as well as the cosmology dependence of the spectra from a large set of N-body simulations performed for various cosmologies and carry out Fisher matrix forecasts for tomographic weak lensing surveys with three source redshifts. After showing the consistency of the power and bispectra measured from our simulations with the state-of-the-art fitting formulas, we investigate the covariance matrix assuming a typical ongoing survey across 1500deg2 with the mean source number density of 30arcmin-2 at the mean redshift zs=1.0. Although the shape noise contributes a significant fraction to the total error budget and it mitigates the impact of the non-Gaussian error for this source number density, we find that the non-Gaussian error degrades the cumulative signal-to-noise ratio up to the maximum multipole of 2000 by a factor of about 2 (3) in the power (bi-) spectrum analysis. Its impact on the final cosmological parameter forecast with 6 parameters can be as large as 15% in the size of the one-dimensional statistical error. This can be a problem in future wide and deep weak lensing surveys for precision cosmology. We also show how much the dark energy figure of merit is affected by the non-Gaussian error contribution and demonstrate an optimal survey design with a fixed observational time.
NASA Astrophysics Data System (ADS)
Harris, Edward G.
1991-05-01
Starting from the equations of general relativity, equations similar to those of electromagnetic theory are derived. It is assumed that the particles are slowly moving (v?c), and the gravitational field is sufficiently weak that nonlinear terms in Einstein's field equations can be neglected. For static fields, the analogy to electrostatics and magnetostatics is very close. Results are compared with those of a previous derivation by Braginsky, Caves, and Thorne [Phys. Rev. D 15, 2047-2068 (1977)]. These results lead to very simple derivations of the Lense-Thirring precession [Phys. Z. 19, 156-163 (1918)] and the spin-curvature force of Papepetrou [Proc. R. Soc. London Ser. A 209, 248-258 (1951)] and Pirani [Acta Phys. Pol. 15, 389-405 (1956)].
NASA Astrophysics Data System (ADS)
Corianò, Claudio; Rose, Luigi Delle; Maglio, Matteo Maria; Serino, Mirko
2015-01-01
We investigate the semiclassical approach to the lensing of photons in a spherically symmetric gravitational background, starting from Born level and include in our analysis the radiative corrections obtained from the electroweak theory for the graviton/photon/photon vertex. In this approach, the cross section is related to the angular variation of the impact parameter ( b), which is then solved for b as a function of the angle of deflection, and measured in horizon units ( b h ≡ b/(2 GM)). Exact numerical solutions for the angular deflection are presented. The numerical analysis shows that perturbation theory in a weak background agrees with the classical Einstein formula for the deflection already at distances of the order of 20 horizon units (˜20 b h ) and it is optimal in the description both of very strong and weak lensings. We show that the electroweak corrections to the cross section are sizeable, becoming very significant for high energy gamma rays. Our analysis covers in energy most of the photon spectrum, from the cosmic microwave background up to very high energy gamma rays, and scatterings with any value of the photon impact parameter. We also study the helicity-flip photon amplitude, which is of O( α 2) in the weak coupling α, and its massless fermion limit, which involves the exchange of a conformal anomaly pole. The corresponding cross section is proportional to the Born level result and brings to a simple renormalization of Einsten's formula.
THREE-DIMENSIONAL RECONSTRUCTION OF THE DENSITY FIELD: AN SVD APPROACH TO WEAK-LENSING TOMOGRAPHY
VanderPlas, J. T.; Connolly, A. J.; Jain, B.; Jarvis, M.
2011-02-01
We present a new method for constructing three-dimensional mass maps from gravitational lensing shear data. We solve the lensing inversion problem using truncation of singular values (within the context of generalized least-squares estimation) without a priori assumptions about the statistical nature of the signal. This singular value framework allows a quantitative comparison between different filtering methods: we evaluate our method beside the previously explored Wiener-filter approaches. Our method yields near-optimal angular resolution of the lensing reconstruction and allows cluster sized halos to be de-blended robustly. It allows for mass reconstructions which are two to three orders of magnitude faster than the Wiener-filter approach; in particular, we estimate that an all-sky reconstruction with arcminute resolution could be performed on a timescale of hours. We find however that linear, non-parametric reconstructions have a fundamental limitation in the resolution achieved in the redshift direction.
Retro gravitational lensing for Sgr A* with Radiastron
NASA Astrophysics Data System (ADS)
Zakharov, A. F.; Nucita, A. A.; de Paolis, F.; Ingrosso, G.
2005-03-01
Recently Holz & Wheeler (2002) have considered a very attractive possibility to detect retro-MACHOs, i.e. retro-images of the Sun by a Schwarzschild black hole. We analyze the case of a Kerr black hole with an arbitrary spin for some selected positions of a distant observer with respect to the equatorial plane of a Kerr black hole. We discuss glories (mirages) formed near rapidly rotating Kerr black hole horizons and propose a procedure to measure masses and rotation parameters by analyzing these forms of mirages. In some sense, that is a manifestation of gravitational lens effect in the strong gravitational field near the black hole horizon and a generalization of the retro-gravitational lens phenomenon. We also propose to use future radio interferometer Radioastron facilities to measure shapes of mirages (glories) and to evaluate the black hole spin as a function of the position angle of a distant observer.
Constraining the minimum luminosity of high redshift galaxies through gravitational lensing
NASA Astrophysics Data System (ADS)
Mashian, Natalie; Loeb, Abraham
2013-12-01
We simulate the effects of gravitational lensing on the source count of high redshift galaxies as projected to be observed by the Hubble Frontier Fields program and the James Webb Space Telescope (JWST) in the near future. Taking the mass density profile of the lensing object to be the singular isothermal sphere (SIS) or the Navarro-Frenk-White (NFW) profile, we model a lens residing at a redshift of zL = 0.5 and explore the radial dependence of the resulting magnification bias and its variability with the velocity dispersion of the lens, the photometric sensitivity of the instrument, the redshift of the background source population, and the intrinsic maximum absolute magnitude (Mmax) of the sources. We find that gravitational lensing enhances the number of galaxies with redshifts zgtrsim 13 detected in the angular region ?E/2 <= ? <= 2?E (where ?E is the Einstein angle) by a factor of ~ 3 and 1.5 in the HUDF (df/d?0 ~ 9 nJy) and medium-deep JWST surveys (df/d?0 ~ 6 nJy). Furthermore, we find that even in cases where a negative magnification bias reduces the observed number count of background sources, the lensing effect improves the sensitivity of the count to the intrinsic faint-magnitude cut-off of the Schechter luminosity function. In a field centered on a strong lensing cluster, observations of zgtrsim 6 and zgtrsim 13 galaxies with JWST can be used to infer this cut-off magnitude for values as faint as Mmax ~ -14.4 and -16.1 mag (Lmin ? 2.5 1026 and 1.2 1027 erg s-1 Hz-1) respectively, within the range bracketed by existing theoretical models. Gravitational lensing may therefore offer an effective way of constraining the low-luminosity cut-off of high-redshift galaxies.
Bradac, Marusa; Clowe, Douglas; Gonzalez, Anthony H.; Marshall, Phil; Forman, William; Jones, Christine; Markevitch, Maxim; Randall, Scott; Schrabback, Tim; Zaritsky, Dennis; /KIPAC, Menlo Park /Bonn, Inst. Astrophys. /Arizona U., Astron. Dept. - Steward Observ. /Florida U. /Harvard-Smithsonian Ctr. Astrophys.
2006-09-27
The galaxy cluster 1E0657-56 (z = 0.296) is remarkably well-suited for addressing outstanding issues in both galaxy evolution and fundamental physics. We present a reconstruction of the mass distribution from both strong and weak gravitational lensing data. Multi-color, high-resolution HST ACS images allow detection of many more arc candidates than were previously known, especially around the subcluster. Using the known redshift of one of the multiply imaged systems, we determine the remaining source redshifts using the predictive power of the strong lens model. Combining this information with shape measurements of ''weakly'' lensed sources, we derive a high-resolution, absolutely-calibrated mass map, using no assumptions regarding the physical properties of the underlying cluster potential. This map provides the best available quantification of the total mass of the central part of the cluster. We also confirm the result from Clowe et al. (2004, 2006a) that the total mass does not trace the baryonic mass.
Complementarity of weak lensing and peculiar velocity measurements in testing general relativity
Song, Yong-Seon; Zhao Gongbo; Bacon, David; Koyama, Kazuya; Nichol, Robert C.; Pogosian, Levon
2011-10-15
We explore the complementarity of weak lensing and galaxy peculiar velocity measurements to better constrain modifications to General Relativity. We find no evidence for deviations from General Relativity on cosmological scales from a combination of peculiar velocity measurements (for Luminous Red Galaxies in the Sloan Digital Sky Survey) with weak lensing measurements (from the Canadian France Hawaii Telescope Legacy Survey). We provide a Fisher error forecast for a Euclid-like space-based survey including both lensing and peculiar velocity measurements and show that the expected constraints on modified gravity will be at least an order of magnitude better than with present data, i.e. we will obtain {approx_equal}5% errors on the modified gravity parametrization described here. We also present a model-independent method for constraining modified gravity parameters using tomographic peculiar velocity information, and apply this methodology to the present data set.
Equatorial gravitational lensing by accelerating and rotating black hole with NUT parameter
NASA Astrophysics Data System (ADS)
Sharif, M.; Iftikhar, Sehrish
2016-01-01
This paper is devoted to study equatorial gravitational lensing in accelerating and rotating black hole with a NUT parameter in the strong field limit. For this purpose, we first calculate null geodesic equation using the Hamilton-Jacobi separation method. We then numerically obtain deflection angle and deflection coefficients which depend on acceleration and spin parameter of the black hole. We also investigate observables in the strong field limit by taking the example of a black hole in the center of galaxy. It is concluded that acceleration parameter has a significant effect on the strong field lensing in the equatorial plane.
COSMOGRAIL: Measuring Time Delays of Gravitationally Lensed Quasars to Constrain Cosmology
NASA Astrophysics Data System (ADS)
Tewes, M.; Courbin, F.; Meylan, G.; Kochanek, C. S.; Eulaers, E.; Cantale, N.; Mosquera, A. M.; Asfandiyarov, I.; Magain, P.; van Winckel, H.; Sluse, D.; Keerthi, R. K. S.; Stalin, C. S.; Prabhu, T. P.; Saha, P.; Dye, S.
2012-12-01
COSMOGRAIL is a long-term programme for the photometric monitoring of gravitationally lensed quasars. It makes use of several medium-size telescopes to derive long and well-sampled light curves of lensed quasars, in order to measure the time delays between the quasar images. These delays directly relate to the Hubble constant H0, without any need for secondary distance calibrations. COSMOGRAIL was initiated in 2004, and has now secured almost a decade of data, resulting in cosmological constraints that are very complementary to other cosmological probes.
The Dust-to-Gas Ratio in the Damped Ly alpha Clouds Towards the Gravitationally Lensed QSO 0957+561
NASA Technical Reports Server (NTRS)
Zuo, Lin; Beaver, E. A.; Burbidge, E. Margaret; Cohen, Ross D.; Junkkarinen, Vesa T.; Lyons, R. W.
1997-01-01
We present HST/FOS spectra of the two bright images (A and B) of the gravitationally lensed QSO 0957+561 in the wavelength range 2200-3300 A. We find that the absorption system (Z(sub abs)) = 1.3911) near z(sub em) is a weak, damped Ly alpha system with strong Ly alpha absorption lines seen in both images. However, the H(I) column densities are different, with the line of sight to image A intersecting a larger column density. The continuum shapes of the two spectra differ in the sense that the flux level of image A increases more slowly toward shorter wavelengths than that of image B. We explain this as the result of differential reddening by dust grains in the damped Ly alpha absorber. A direct outcome of this explanation is a determination of the dust-to-gas ratio, k, in the damped Ly alpha system. We derive k = 0.55 + 0.18 for a simple 1/lambda extinction law and k = 0.31 + 0.10 for the Galactic extinction curve. For gravitationally lensed systems with damped Ly alpha absorbers, our method is a powerful tool for determining the values and dispersion of k, and the shapes of extinction curves, especially in the FUV and EUV regions. We compare our results with previous work.
SDSS J102111.02+491330.4: A Newly discovered gravitationally lensed quasar
Pindor, Bart; Eisenstein, Daniel J.; Gregg, Michael D.; Becker, Robert H.; Inada, Naohisa; Oguri, Masamune; Hall, Patrick B.; Johnston, David E.; Richards, Gordon T.; Schneider, Donald P.; Turner, Edwin L.; Brasi, Guido; Hinz, Philip M.; Kenworthy, Matthew A.; Miller, Doug; Barentine, J.C.; Brewington, Howard J.; Brinkmann, J.; Harvanek, Michael; Kleinman, S.J.; Krzesinski, Jurek; /Toronto U., Astron. Dept. /Arizona U., Astron. Dept. - Steward Observ. /UC, Davis /LLNL, Livermore /Tokyo U., Inst. Astron. /Tokyo U. /Princeton U. Observ. /York U., Canada /Penn State U., Astron. Astrophys. /Apache Point Observ. /Mt. Suhora Observ., Cracow /Fermilab /Chicago U., Astron. Astrophys. Ctr.
2005-09-01
We report follow-up observations of two gravitational lens candidates identified in the Sloan Digital Sky Survey (SDSS) dataset. We have confirmed that SDSS J102111.02+491330.4 is a previously unknown gravitationally lensed quasar. This lens system exhibits two images of a z = 1.72 quasar, with an image separation of 1.14'' {+-} 0.04''. Optical and near-IR imaging of the system reveals the presence of the lensing galaxy between the two quasar images. Observations of SDSS J112012.12+671116.0 indicate that it is more likely a binary quasar than a gravitational lens. This system has two quasars at a redshift of z = 1.49, with an angular separation of 1.49'' {+-} 0.02''. However, the two quasars have markedly different SEDs and no lens galaxy is apparent in optical and near-IR images of this system. We also present a list of 31 SDSS lens candidates which follow-up observations have confirmed are not gravitational lenses.
NASA Astrophysics Data System (ADS)
Liu, Xiangkun; Pan, Chuzhong; Li, Ran; Shan, Huanyuan; Wang, Qiao; Fu, Liping; Fan, Zuhui; Kneib, Jean-Paul; Leauthaud, Alexie; Van Waerbeke, Ludovic; Makler, Martin; Moraes, Bruno; Erben, Thomas; Charbonnier, Alde
2015-07-01
We derived constraints on cosmological parameters using weak lensing peak statistics measured on the 130 deg2 of the Canada-France-Hawaii Telescope Stripe 82 Survey. This analysis demonstrates the feasibility of using peak statistics in cosmological studies. For our measurements, we considered peaks with signal-to-noise ratio in the range of ? = [3, 6]. For a flat ? cold dark matter model with only (?m, ?8) as free parameters, we constrained the parameters of the following relation ?8 = ?8(?m/0.27)? to be ?8 = 0.82 0.03 and ? = 0.43 0.02. The ? value found is considerably smaller than the one measured in two-point and three-point cosmic shear correlation analyses, showing a significant complement of peak statistics to standard weak lensing cosmological studies. The derived constraints on (?m, ?8) are fully consistent with the ones from either WMAP9 or Planck. From the weak lensing peak abundances alone, we obtained marginalized mean values of ? _m=0.38^{+0.27}_{-0.24} and ?8 = 0.81 0.26. Finally, we also explored the potential of using weak lensing peak statistics to constrain the mass-concentration relation of dark matter haloes simultaneously with cosmological parameters.
Statistics of Gravitational Lensing by a Galaxy in Cluster or in Field
NASA Astrophysics Data System (ADS)
Yoon, So-Yoon; Park, Myeong-Gu
1996-10-01
To examine the effect of neighboring galaxies on the gravitational lensing statistics, we performed numerical simulations of lensing by many galaxies. The models consist of a galaxy in the rich cluster like Coma, or a galaxy surrounded by field galaxies in Omega_0=1 universe with Omega_gal=0.1, Omega_gal=0.3 or Omega_gal=1.0, where Omega_gal is the total mass in galaxies. Field galaxies either have the same mass or follow Schechter luminosity function and luminosity-velocity relation. Each lensing galaxy is assumed to be singular isothermal sphere (SIS) with finite cutoff radius. In most simulations, the lensing is mainly due to the single galaxy. But in Omega_gal=0.3 universe, one out of five simulations have `collective lensing' event in which more than two galaxies collectively produce multiple images. These cases cannot be incorporated into the simple `standard' lensing statistics calculations. In cases where `collective lensing' does not occur, distribution of image separation changes from delta function to bimodal distribution due to shear induced by the surrounding galaxies. The amount of spread in the distribution is from a few % up to about 50% of the mean image separation in case when the galaxy is in the Coma-like cluster or when the galaxy is in the field with Omega_gal=0.1 or Omega_gal=0.3. The mean of the image separation changes less than 5% compared with a single lens case. Cross section for multiple image lensing turns out to be relatively insensitive to the presence of the neighboring galaxies, changing less than 5% for Coma-like cluster and Omega_gal=0.1, 0.3 universe cases. So we conclude that Coma-like cluster or field galaxies whose total mass density Omega_gal < 0.3 do not significantly affect the probability of multiple image lensing if we exclude the `collective lensing' cases. However, the distribution of the image separations can be significantly affected especially if the `collective lensing' cases are included. Therefore, the effects of surrounding galaxies may not be negligible when statistics of lensing is used to deduce the cosmological informations.
Shadows (Mirages) Around Black Holes and Retro Gravitational Lensing
NASA Astrophysics Data System (ADS)
Zakharov, A. F.; Nucita, A. A.; Depaolis, F.; Ingrosso, G.
Recently Holz & Wheeler [1] considered a very attracting possibility to detect retro-MACHOs, i.e. retro-images of the Sun by a Schwarzschild black hole. In this paper we discuss glories (mirages) formed near rapidly rotating Kerr black hole horizons and propose a procedure to measure masses and rotation parameters analyzing these forms of mirages (a detailed description of the problem is given in [2]). In some sense that is a manifestation of gravitational lens effect in the strong gravitational field near black hole horizon and a generalization of the retro-gravitational lens phenomenon. We analyze the case of a Kerr black hole rotating at arbitrary speed for some selected positions of a distant observer with respect to the equatorial plane of a Kerr black hole. Some time ago Falcke, Melia & Agol [3] suggested to search shadows at the Galactic Center. In this paper we present the boundaries for shadows calculated numerically. We also propose to use future radio interferometer RADIOASTRON facilities to measure shapes of mirages (glories) and to evaluate the black hole spin as a function of the position angle of a distant observer.
De Putter, Roland; Doré, Olivier; Das, Sudeep
2014-01-10
Cross correlations between the galaxy number density in a lensing source sample and that in an overlapping spectroscopic sample can in principle be used to calibrate the lensing source redshift distribution. In this paper, we study in detail to what extent this cross-correlation method can mitigate the loss of cosmological information in upcoming weak lensing surveys (combined with a cosmic microwave background prior) due to lack of knowledge of the source distribution. We consider a scenario where photometric redshifts are available and find that, unless the photometric redshift distribution p(z {sub ph}|z) is calibrated very accurately a priori (bias and scatter known to ∼0.002 for, e.g., EUCLID), the additional constraint on p(z {sub ph}|z) from the cross-correlation technique to a large extent restores the cosmological information originally lost due to the uncertainty in dn/dz(z). Considering only the gain in photo-z accuracy and not the additional cosmological information, enhancements of the dark energy figure of merit of up to a factor of four (40) can be achieved for a SuMIRe-like (EUCLID-like) combination of lensing and redshift surveys, where SuMIRe stands for Subaru Measurement of Images and Redshifts). However, the success of the method is strongly sensitive to our knowledge of the galaxy bias evolution in the source sample and we find that a percent level bias prior is needed to optimize the gains from the cross-correlation method (i.e., to approach the cosmology constraints attainable if the bias was known exactly).
Confirmation of general relativity on large scales from weak lensing and galaxy velocities.
Reyes, Reinabelle; Mandelbaum, Rachel; Seljak, Uros; Baldauf, Tobias; Gunn, James E; Lombriser, Lucas; Smith, Robert E
2010-03-11
Although general relativity underlies modern cosmology, its applicability on cosmological length scales has yet to be stringently tested. Such a test has recently been proposed, using a quantity, E(G), that combines measures of large-scale gravitational lensing, galaxy clustering and structure growth rate. The combination is insensitive to 'galaxy bias' (the difference between the clustering of visible galaxies and invisible dark matter) and is thus robust to the uncertainty in this parameter. Modified theories of gravity generally predict values of E(G) different from the general relativistic prediction because, in these theories, the 'gravitational slip' (the difference between the two potentials that describe perturbations in the gravitational metric) is non-zero, which leads to changes in the growth of structure and the strength of the gravitational lensing effect. Here we report that E(G) = 0.39 +/- 0.06 on length scales of tens of megaparsecs, in agreement with the general relativistic prediction of E(G) approximately 0.4. The measured value excludes a model within the tensor-vector-scalar gravity theory, which modifies both Newtonian and Einstein gravity. However, the relatively large uncertainty still permits models within f(R) theory, which is an extension of general relativity. A fivefold decrease in uncertainty is needed to rule out these models. PMID:20220843
Planck 2013 results. XVII. Gravitational lensing by large-scale structure
NASA Astrophysics Data System (ADS)
Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Armitage-Caplan, C.; Arnaud, M.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Basak, S.; Battaner, E.; Benabed, K.; Benot, A.; Benoit-Lvy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bobin, J.; Bock, J. J.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Bridges, M.; Bucher, M.; Burigana, C.; Butler, R. C.; Cardoso, J.-F.; Catalano, A.; Challinor, A.; Chamballu, A.; Chiang, H. C.; Chiang, L.-Y.; Christensen, P. R.; Church, S.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Dchelette, T.; Delabrouille, J.; Delouis, J.-M.; Dsert, F.-X.; Dickinson, C.; Diego, J. M.; Dole, H.; Donzelli, S.; Dor, O.; Douspis, M.; Dunkley, J.; Dupac, X.; Efstathiou, G.; Enlin, T. A.; Eriksen, H. K.; Finelli, F.; Forni, O.; Frailis, M.; Franceschi, E.; Galeotta, S.; Ganga, K.; Giard, M.; Giardino, G.; Giraud-Hraud, Y.; Gonzlez-Nuevo, J.; Grski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Hansen, F. K.; Hanson, D.; Harrison, D.; Henrot-Versill, S.; Hernndez-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Ho, S.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hovest, W.; Huffenberger, K. M.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Keihnen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Knox, L.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lhteenmki, A.; Lamarre, J.-M.; Lasenby, A.; Laureijs, R. J.; Lavabre, A.; Lawrence, C. R.; Leahy, J. P.; Leonardi, R.; Len-Tavares, J.; Lesgourgues, J.; Lewis, A.; Liguori, M.; Lilje, P. B.; Linden-Vrnle, M.; Lpez-Caniego, M.; Lubin, P. M.; Macas-Prez, J. F.; Maffei, B.; Maino, D.; Mandolesi, N.; Mangilli, A.; Maris, M.; Marshall, D. J.; Martin, P. G.; Martnez-Gonzlez, E.; Masi, S.; Massardi, M.; Matarrese, S.; Matthai, F.; Mazzotta, P.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mitra, S.; Miville-Deschnes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Moss, A.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Nrgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Osborne, S.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Paoletti, D.; Partridge, B.; Pasian, F.; Patanchon, G.; Perdereau, O.; Perotto, L.; Perrotta, F.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Popa, L.; Poutanen, T.; Pratt, G. W.; Przeau, G.; Prunet, S.; Puget, J.-L.; Pullen, A. R.; Rachen, J. P.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Roudier, G.; Rowan-Robinson, M.; Rubio-Martn, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savini, G.; Scott, D.; Seiffert, M. D.; Shellard, E. P. S.; Smith, K.; Spencer, L. D.; Starck, J.-L.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sunyaev, R.; Sureau, F.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Tavagnacco, D.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Tuovinen, J.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Vittorio, N.; Wade, L. A.; Wandelt, B. D.; White, M.; White, S. D. M.; Yvon, D.; Zacchei, A.; Zonca, A.
2014-11-01
On the arcminute angular scales probed by Planck, the cosmic microwave background (CMB) anisotropies are gently perturbed by gravitational lensing. Here we present a detailed study of this effect, detecting lensing independently in the 100, 143, and 217 GHz frequency bands with an overall significance of greater than 25?. We use thetemperature-gradient correlations induced by lensing to reconstruct a (noisy) map of the CMB lensing potential, which provides an integrated measure of the mass distribution back to the CMB last-scattering surface. Our lensing potential map is significantly correlated with other tracers of mass, a fact which we demonstrate using several representative tracers of large-scale structure. We estimate the power spectrum of the lensing potential, finding generally good agreement with expectations from the best-fitting ?CDM model for the Planck temperature power spectrum, showing that this measurement at z = 1100 correctly predicts the properties of the lower-redshift, later-time structures which source the lensing potential. When combined with the temperature power spectrum, our measurement provides degeneracy-breaking power for parameter constraints; it improves CMB-alone constraints on curvature by a factor of two and also partly breaks the degeneracy between the amplitude of the primordial perturbation power spectrum and the optical depth to reionization, allowing a measurement of the optical depth to reionization which is independent of large-scale polarization data. Discarding scale information, our measurement corresponds to a 4% constraint on the amplitude of the lensing potential power spectrum, or a 2% constraint on the root-mean-squared amplitude of matter fluctuations at z ~ 2.
Cosmological constraints from strong gravitational lensing in clusters of galaxies.
Jullo, Eric; Natarajan, Priyamvada; Kneib, Jean-Paul; D'Aloisio, Anson; Limousin, Marceau; Richard, Johan; Schimd, Carlo
2010-08-20
Current efforts in observational cosmology are focused on characterizing the mass-energy content of the universe. We present results from a geometric test based on strong lensing in galaxy clusters. Based on Hubble Space Telescope images and extensive ground-based spectroscopic follow-up of the massive galaxy cluster Abell 1689, we used a parametric model to simultaneously constrain the cluster mass distribution and dark energy equation of state. Combining our cosmological constraints with those from x-ray clusters and the Wilkinson Microwave Anisotropy Probe 5-year data gives Omega(m) = 0.25 +/- 0.05 and w(x) = -0.97 +/- 0.07, which are consistent with results from other methods. Inclusion of our method with all other available techniques brings down the current 2sigma contours on the dark energy equation-of-state parameter w(x) by approximately 30%. PMID:20724628
Okabe, Nobuhiro; Futamase, Toshifumi; Kuroshima, Risa; Kajisawa, Masaru
2014-04-01
We present a 4 deg{sup 2} weak gravitational lensing survey of subhalos in the very nearby Coma cluster using the Subaru/Suprime-Cam. The large apparent size of cluster subhalos allows us to measure the mass of 32 subhalos detected in a model-independent manner, down to the order of 10{sup –3} of the virial mass of the cluster. Weak-lensing mass measurements of these shear-selected subhalos enable us to investigate subhalo properties and the correlation between subhalo masses and galaxy luminosities for the first time. The mean distortion profiles stacked over subhalos show a sharply truncated feature which is well-fitted by a Navarro-Frenk-White (NFW) mass model with the truncation radius, as expected due to tidal destruction by the main cluster. We also found that subhalo masses, truncation radii, and mass-to-light ratios decrease toward the cluster center. The subhalo mass function, dn/dln M {sub sub}, in the range of 2 orders of magnitude in mass, is well described by a single power law or a Schechter function. Best-fit power indices of 1.09{sub −0.32}{sup +0.42} for the former model and 0.99{sub −0.23}{sup +0.34} for the latter, are in remarkable agreement with slopes of ∼0.9-1.0 predicted by the cold dark matter paradigm. The tangential distortion signals in the radial range of 0.02-2 h {sup –1} Mpc from the cluster center show a complex structure which is well described by a composition of three mass components of subhalos, the NFW mass distribution as a smooth component of the main cluster, and a lensing model from a large scale structure behind the cluster. Although the lensing signals are 1 order of magnitude lower than those for clusters at z ∼ 0.2, the total signal-to-noise ratio, S/N = 13.3, is comparable, or higher, because the enormous number of background source galaxies compensates for the low lensing efficiency of the nearby cluster.
Gravitational lensing by a massive black hole at the Galactic center
NASA Technical Reports Server (NTRS)
Wardle, Mark; Yusef-Zadeh, Farhad
1992-01-01
The manifestations of gravitational lensing by a massive black hole at the Galactic center, with particular attention given to lensing of stars in the stellar cluster that lie behind Sgr A*, and of Sgr A east, a nonthermal extended radio source which is known with certainty to lie behind the Galactic center. Lensing of the stellar cluster produces a deficit of stellar images within 10 mas of the center, and a surplus between 30 and 300 mas. The results suggest that the proper motion of the stars will produce brightness variations of stellar images on a time scale of a few years or less. Both images of such a source should be visible, and will rise and fall in luminosity together.
The SDSS-III BOSS quasar lens survey: discovery of 13 gravitationally lensed quasars
NASA Astrophysics Data System (ADS)
More, Anupreeta; Oguri, Masamune; Kayo, Issha; Zinn, Joel; Strauss, Michael A.; Santiago, Basilio X.; Mosquera, Ana M.; Inada, Naohisa; Kochanek, Christopher S.; Rusu, Cristian E.; Brownstein, Joel R.; da Costa, Luiz N.; Kneib, Jean-Paul; Maia, Marcio A. G.; Quimby, Robert M.; Schneider, Donald P.; Streblyanska, Alina; York, Donald G.
2016-02-01
We report the discovery of 13 confirmed two-image quasar lenses from a systematic search for gravitationally lensed quasars in the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). We adopted a methodology similar to that used in the SDSS Quasar Lens Search (SQLS). In addition to the confirmed lenses, we report 11 quasar pairs with small angular separations ( ≲ 2 arcsec) confirmed from our spectroscopy, which are either projected pairs, physical binaries, or possibly quasar lens systems whose lens galaxies have not yet been detected. The newly discovered quasar lens system, SDSS J1452+4224 at zs ≈ 4.8 is one of the highest redshift multiply imaged quasars found to date. Furthermore, we have over 50 good lens candidates yet to be followed up. Owing to the heterogeneous selection of BOSS quasars, the lens sample presented here does not have a well-defined selection function.
Chen, Yun; Geng, Chao-Qiang; Cao, Shuo; Huang, Yu-Mei; Zhu, Zong-Hong E-mail: geng@phys.nthu.edu.tw E-mail: huangymei@gmail.com
2015-02-01
We constrain the scalar field dark energy model with an inverse power-law potential, i.e., V(?)??{sup ??} (?>0), from a set of recent cosmological observations by compiling an updated sample of Hubble parameter measurements including 30 independent data points. Our results show that the constraining power of the updated sample of H(z) data with the HST prior on H{sub 0} is stronger than those of the SCP Union2 and Union2.1 compilations. A recent sample of strong gravitational lensing systems is also adopted to confine the model even though the results are not significant. A joint analysis of the strong gravitational lensing data with the more restrictive updated Hubble parameter measurements and the Type Ia supernovae data from SCP Union2 indicates that the recent observations still can not distinguish whether dark energy is a time-independent cosmological constant or a time-varying dynamical component.
The snapshot survey - A search for gravitationally lensed quasars with the Hubble Space Telescope
NASA Technical Reports Server (NTRS)
Bahcall, J. N.; Maoz, D.; Doxsey, R.; Schneider, D. P.; Bahcall, N. A.; Lahav, O.; Yanny, B.
1992-01-01
The first results from the HST Non-Proprietary Snapshot Survey are presented in order to investigate new examples of multiply imaged quasars that are the result of gravitational lensing. None of the approximately 30 quasars observed at high spatial resolution show evidence of multiple imaging by gravitational lensing. These results are compared with lower resolution ground-based surveys and current theoretical predictions. Several engineering problems in the observatory's performance are addressed. It particular, the large telescope pointing errors and drift rates are found to be primarily the result of the lack of correction for stellar aberration when pointing and tracking are performed solely with gyroscopes. The implications for the possibly low intrinsic gyro drift rate on future observations are discussed.
Weak lensing calibrated M-T scaling relation of galaxy groups in the cosmos field
Kettula, K.; Finoguenov, A.; Massey, R.; Rhodes, J.; Hoekstra, H.; Taylor, J. E.; Spinelli, P. F.; Tanaka, M.; Ilbert, O.; Capak, P.; McCracken, H. J.; Koekemoer, A.
2013-11-20
The scaling between X-ray observables and mass for galaxy clusters and groups is instrumental for cluster-based cosmology and an important probe for the thermodynamics of the intracluster gas. We calibrate a scaling relation between the weak lensing mass and X-ray spectroscopic temperature for 10 galaxy groups in the COSMOS field, combined with 55 higher-mass clusters from the literature. The COSMOS data includes Hubble Space Telescope imaging and redshift measurements of 46 source galaxies per arcminute{sup 2}, enabling us to perform unique weak lensing measurements of low-mass systems. Our sample extends the mass range of the lensing calibrated M-T relation an order of magnitude lower than any previous study, resulting in a power-law slope of 1.48{sub ?0.09}{sup +0.13}. The slope is consistent with the self-similar model, predictions from simulations, and observations of clusters. However, X-ray observations relying on mass measurements derived under the assumption of hydrostatic equilibrium have indicated that masses at group scales are lower than expected. Both simulations and observations suggest that hydrostatic mass measurements can be biased low. Our external weak lensing masses provide the first observational support for hydrostatic mass bias at group level, showing an increasing bias with decreasing temperature and reaching a level of 30%-50% at 1 keV.
Joint cosmic microwave background and weak lensing analysis: constraints on cosmological parameters.
Contaldi, Carlo R; Hoekstra, Henk; Lewis, Antony
2003-06-01
We use cosmic microwave background (CMB) observations together with the red-sequence cluster survey weak lensing results to derive constraints on a range of cosmological parameters. This particular choice of observations is motivated by their robust physical interpretation and complementarity. Our combined analysis, including a weak nucleosynthesis constraint, yields accurate determinations of a number of parameters including the amplitude of fluctuations sigma(8)=0.89+/-0.05 and matter density Omega(m)=0.30+/-0.03. We also find a value for the Hubble parameter of H(0)=70+/-3 km s(-1) Mpc(-1), in good agreement with the Hubble Space Telescope key-project result. We conclude that the combination of CMB and weak lensing data provides some of the most powerful constraints available in cosmology today. PMID:12857304
NASA Astrophysics Data System (ADS)
Coe, Daniel Aaron
The goal of thesis is to help scientists resolve one of the great mysteries of our time: the nature of Dark Matter. Dark Matter is currently believed to make up over 80% of the material in our universe, yet we have so far inferred but a few of its basic properties. Here we study the Dark Matter surrounding a galaxy cluster, Abell 1689, via the most direct method currently available--gravitational lensing. Abell 1689 is a "strong" gravitational lens, meaning it produces multiple images of more distant galaxies. The observed positions of these images can be measured very precisely and act as a blueprint allowing us to reconstruct the Dark Matter distribution of the lens. Until now, such mass models of Abell 1689 have reproduced the observed multiple images well but with significant positional offsets. Using a new method we develop here, we obtain a new mass model which perfectly reproduces the observed positions of 168 knots identified within 135 multiple images of 42 galaxies. An important ingredient to our mass model is the accurate measurement of distances to the lensed galaxies via their photometric redshifts. Here we develop tools which improve the accuracy of these measurements based on our study of the Hubble Ultra Deep Field, the only image yet taken to comparable depth as the magnified regions of Abell 1689. We present results both for objects in the Hubble Ultra Deep Field and for galaxies gravitationally lensed by Abell 1689. As part of this thesis, we also provide reviews of Dark Matter and Gravitational Lensing, including a chapter devoted to the mass profiles of Dark Matter halos realized in simulations. The original work presented here was performed primarily by myself under the guidance of Narciso Benítez and Holland Ford as a member of the Advanced Camera for Surveys GTO Science Team at Johns Hopkins University and the Instituto de Astrofisica de Andalucfa. My advisors served on my thesis committee along with Rick White, Gabor Domokos, and Steve Zelditch.
Spectroscopic identification of 25 disk galaxy candidate gravitational lenses in the SDSS
NASA Astrophysics Data System (ADS)
Focardi, P.; Rossetti, E.
2015-09-01
Context. Galaxy-scale gravitational lenses are powerful tools, which can be used to address major astrophysical questions that are still open. They can be identified either through imaging or through spectroscopy, which is less efficient than imaging but offers the major advantage of having both source and deflector red shift previously measured at discovery. Spectroscopic identification requires huge data sets of high spectral quality, such as the SDSS, and has so far focused on early-type galaxies, as the most massive galaxies are found among them. Aims: We aimed to perform spectroscopic identification of disk galaxies acting as gravitational lenses. Methods: We have selected about 300 000 galaxy spectra with EW(Hα) ≤-10 Å from the SDSS DR 8. On these spectra, we ran our original code RES, which is a fast, reliable tool able to provide a red-shift measure and to identify discordant red-shift systems if present. We have required RES to identify only systems based on a minimum number of four emission lines. We have inspected all the (54) SDSS images of the double z systems identified by RES and discarded systems for which z duplicity could be easily ascribed to the presence of two distinct objects. The remaining 25 systems, for which double z is very likely to be due to the gravitational lensing phenomenon, constitute our sample. Results: For each gravitational lens candidate system, we provide SDSS identification and image emission lines detected by RES and activity classification, when derivable. The disky nature of our candidate lenses is confirmed by their images, stellar mass estimates, g - r rest-frame colours and occurrence of star burst phenomena.
A distortion of very-high-redshift galaxy number counts by gravitational lensing.
Wyithe, J Stuart B; Yan, Haojing; Windhorst, Rogier A; Mao, Shude
2011-01-13
The observed number counts of high-redshift galaxy candidates have been used to build up a statistical description of star-forming activity at redshift z???7, when galaxies reionized the Universe. Standard models predict that a high incidence of gravitational lensing will probably distort measurements of flux and number of these earliest galaxies. The raw probability of this happening has been estimated to be ?0.5 per cent (refs 11, 12), but can be larger owing to observational biases. Here we report that gravitational lensing is likely to dominate the observed properties of galaxies with redshifts of z???12, when the instrumental limiting magnitude is expected to be brighter than the characteristic magnitude of the galaxy sample. The number counts could be modified by an order of magnitude, with most galaxies being part of multiply imaged systems, located less than 1?arcsec from brighter foreground galaxies at z???2. This lens-induced association of high-redshift and foreground galaxies has perhaps already been observed among a sample of galaxy candidates identified at z???10.6. Future surveys will need to be designed to account for a significant gravitational lensing bias in high-redshift galaxy samples. PMID:21228870
Caustics of 1/rn binary gravitational lenses: from galactic haloes to exotic matter
NASA Astrophysics Data System (ADS)
Bozza, V.; Melchiorre, C.
2016-03-01
We investigate the caustic topologies for binary gravitational lenses made up of two objects whose gravitational potential declines as 1/rn. With n<1 this corresponds to power-law dust distributions like the singular isothermal sphere. The n>1 regime can be obtained with some violations of the energy conditions, one famous example being the Ellis wormhole. Gravitational lensing provides a natural arena to distinguish and identify such exotic objects in our Universe. We find that there are still three topologies for caustics as in the standard Schwarzschild binary lens, with the main novelty coming from the secondary caustics of the close topology, which become huge at higher n. After drawing caustics by numerical methods, we derive a large amount of analytical formulae in all limits that are useful to provide deeper insight in the mathematics of the problem. Our study is useful to better understand the phenomenology of galaxy lensing in clusters as well as the distinct signatures of exotic matter in complex systems.
Algorithms and Programs for Strong Gravitational Lensing In Kerr Space-time Including Polarization
NASA Astrophysics Data System (ADS)
Chen, Bin; Kantowski, Ronald; Dai, Xinyu; Baron, Eddie; Maddumage, Prasad
2015-05-01
Active galactic nuclei (AGNs) and quasars are important astrophysical objects to understand. Recently, microlensing observations have constrained the size of the quasar X-ray emission region to be of the order of 10 gravitational radii of the central supermassive black hole. For distances within a few gravitational radii, light paths are strongly bent by the strong gravity field of the central black hole. If the central black hole has nonzero angular momentum (spin), then a photon’s polarization plane will be rotated by the gravitational Faraday effect. The observed X-ray flux and polarization will then be influenced significantly by the strong gravity field near the source. Consequently, linear gravitational lensing theory is inadequate for such extreme circumstances. We present simple algorithms computing the strong lensing effects of Kerr black holes, including the effects on polarization. Our algorithms are realized in a program “KERTAP” in two versions: MATLAB and Python. The key ingredients of KERTAP are a graphic user interface, a backward ray-tracing algorithm, a polarization propagator dealing with gravitational Faraday rotation, and algorithms computing observables such as flux magnification and polarization angles. Our algorithms can be easily realized in other programming languages such as FORTRAN, C, and C++. The MATLAB version of KERTAP is parallelized using the MATLAB Parallel Computing Toolbox and the Distributed Computing Server. The Python code was sped up using Cython and supports full implementation of MPI using the “mpi4py” package. As an example, we investigate the inclination angle dependence of the observed polarization and the strong lensing magnification of AGN X-ray emission. We conclude that it is possible to perform complex numerical-relativity related computations using interpreted languages such as MATLAB and Python.
Gravitational lensing effects of vacuum strings - Exact solutions
NASA Technical Reports Server (NTRS)
Gott, J. R., III
1985-01-01
Exact interior and exterior solutions to Einstein's field equations are derived for vacuum strings. The exterior solution for a uniform density vacuum string corresponds to a conical space while the interior solution is that of a spherical cap. For Mu equals 0-1/4 the external metric is ds-squared = -dt-squared + dr-squared + (1-4 Mu)-squared r-squared dphi-squared + dz-squared, where Mu is the mass per unit length in the string in Planck masses per Planck length. A maximum mass per unit length for a string is 6.73 x 10 to the 27th g/cm. It is shown that strings cause temperature fluctuations in the cosmic microwave background and produce equal brightness double QSO images separated by up to several minutes of arc. Formulae for lensing probabilities, image splittings, and time delays are derived for strings in a realistic cosmological setting. String searches using ST, the VLA, and the COBE satellite are discussed.
SDSS J133401.39+331534.3: A NEW SUBARCSECOND GRAVITATIONALLY LENSED QUASAR
Rusu, Cristian E.; Iye, Masanori; Oguri, Masamune; Inada, Naohisa; Kayo, Issha; Hayano, Yutaka; Oya, Shin; Hattori, Masayuki; Saito, Yoshihiko; Ito, Meguru; Minowa, Yosuke; Pyo, Tae-Soo; Terada, Hiroshi; Takami, Hideki; Watanabe, Makoto
2011-09-01
The quasar SDSS J133401.39+331534.3 at z = 2.426 is found to be a two-image gravitationally lensed quasar with an image separation of 0.''833. The object is first identified as a lensed quasar candidate in the Sloan Digital Sky Survey Quasar Lens Search, and then confirmed as a lensed system from follow-up observations at the Subaru and University of Hawaii 2.2 m telescopes. We estimate the redshift of the lensing galaxy to be 0.557 based on absorption lines in the quasar spectra as well as the color of the galaxy. In particular, we observe the system with the Subaru Telescope AO188 adaptive optics with a laser guide star, in order to derive accurate astrometry, which well demonstrates the usefulness of the laser guide star adaptive optics imaging for studying strong lens systems. Our mass modeling with improved astrometry implies that a nearby bright galaxy {approx}4'' apart from the lensing galaxy is likely to affect the lens potential.
Model-free analysis of quadruply imaged gravitationally lensed systems and substructured galaxies
NASA Astrophysics Data System (ADS)
Woldesenbet, Addishiwot G.; Williams, Liliya L. R.
2015-11-01
Multiple image gravitational lens systems, and especially quads, are invaluable in determining the amount and distribution of mass in galaxies. This is usually done by mass modelling using parametric or free-form methods. An alternative way of extracting information about lens mass distribution is to use lensing degeneracies and invariants. Where applicable, they allow one to make conclusions about whole classes of lenses without model fitting. Here, we use approximate, but observationally useful invariants formed by the three relative polar angles of quad images around the lens centre to show that many smooth elliptical+shear lenses can reproduce the same set of quad image angles within observational error. This result allows us to show in a model-free way what the general class of smooth elliptical+shear lenses looks like in the three-dimensional (3D) space of image relative angles, and that this distribution does not match that of the observed quads. We conclude that, even though smooth elliptical+shear lenses can reproduce individual quads, they cannot reproduce the quad population. What is likely needed is substructure, with clump masses larger than those responsible for flux ratio anomalies in quads, or luminous or dark nearby perturber galaxies.
Gravitational Lensing of the Microwave Background in the 2500 Square Degree SPT Survey
NASA Astrophysics Data System (ADS)
Zahn, Oliver
2013-04-01
The South Pole Telescope (SPT) is a 10-meter microwave background telescope located at the geographic South Pole that completed a deep multi-band survey of 2,500 square degrees of the southern sky in Fall 2011. The high angular resolution and sensitivity enable a reconstruction of the matter potential integrated toward the last scattering surface, effectively weighing the Hubble volume. The inferred lensing potential power spectrum is a sensitive probe of cosmological structure growth and geometry beyond the temperature and polarization power spectra. I will present the results of our analysis using an optimal trispectrum estimator to achieve the highest signal-to-noise measurement of gravitational lensing of the CMB to date. Careful control of astrophysical and instrumental contaminants of the non-Gaussian signature of lensing allow us to place robust constraints on dark energy and the sum of the masses of neutrinos. I will also discuss how the correlation of our lensing maps with galaxy clustering surveys can yield novel astrophysical and cosmological information. The talk will conclude by previewing the potential of joint analyses of our lensing measurements with Planck satellite data, as well as of new data currently being collected by SPTpol.
Correcting High-Redshift Galaxy Luminosity Functions for Gravitational Lensing Magnification Bias
NASA Astrophysics Data System (ADS)
Mason, Charlotte; Treu, Tommaso; Borello Schmidt, Kasper; Collett, Thomas; Trenti, Michele; Marshall, Philip; Barone-Nugent, Robert; Bradley, Larry; Stiavelli, Massimo; Wyithe, Stuart
2015-08-01
We present a Bayesian framework to account for the magnification bias from strong, intermediate and weak gravitational lensing in estimates of high-redshift galaxy UV luminosity functions (LFs), which is expected to significantly modify the bright-end of the LF. We illustrate our method by estimating the z ~ 8 UV LF using a sample of 97 Y-band dropouts (Lyman-break galaxies) found in the Brightest of Reionizing Galaxies (BoRG) survey and from the HUDF. We find the LF is well described by a Schechter function with parameters consistent within the uncertainties of those inferred from the same sample without accounting for the magnification bias (Schmidt et al. 2014), demonstrating that the effect is small for current surveys at z ~ 8. Hence we find that magnification bias alone cannot account for the apparent overdensity of z ~ 7 bright galaxies compared to a Schechter function found recently by Bowler et al. (2014a,b) and Finkelstein et al. (2014). Using a range of theoretical LFs we conclude that magnification bias will dominate wide-field surveys - such as those planned for the Euclid and WFIRST missions - especially at z > 10. In order to derive accurate estimates of high-redshift LFs in these surveys and to distinguish between galaxy formation models it will be vital to account for the magnification bias. We show that magnification bias can be an additional tool to probe the high-redshift universe and demonstrate this via a physical model for the UV LF at z > 8.
Lens Statistics with Gravitationally Lensed yet Morphologically Regular Images
NASA Astrophysics Data System (ADS)
Morioka, Masayo; Futamase, Toshifumi
2015-06-01
GRAMORs are GRAvitationally highly magnified yet MORphologically regular images. An example of this phenomenon was discovered in the cluster MACS J1149.5+2223 in 2009. We investigate the lens statistics of GRAMORs in detail. Assuming a NFW profile for a sample of clusters, we calculate the expected number and redshift distribution of GRAMORs using parameters from COSMOS data for the number density of the background galaxy. A model with a cluster placed at z = 0.544 based on WMAP5 cosmology predicts the redshift of a GRAMOR at z? 1.49 which is close to the observed z = 1.4906. These results show that the expected number of GRAMORs is about two per cluster in the most likely case, and thus a large number of GRAMORs would be observed in a systematic survey. The probability distribution function of source redshift for GRAMORs depends strongly on dark energy and may be useful for constraining the nature of dark energy.
Bandara, Kaushala; Crampton, David; Peng, Chien; Simard, Luc
2013-11-01
We take advantage of the magnification in size and flux of a galaxy provided by gravitational lensing to analyze the properties of 62 strongly lensed galaxies from the Sloan Lens ACS (SLACS) Survey. The sample of lensed galaxies spans a redshift range of 0.20 ? z ? 1.20 with a median redshift of z = 0.61. We use the lens modeling code LENSFIT to derive the luminosities, sizes, and Srsic indices of the lensed galaxies. The measured properties of the lensed galaxies show a primarily compact, {sup d}isk{sup -}like population with the peaks of the size and Srsic index distributions corresponding to ?1.50 kpc and n ? 1, respectively. Comparison of the SLACS galaxies to a non-lensing, broadband imaging survey shows that a lensing survey allows us to probe a galaxy population that reaches ?2 mag fainter. Our analysis allows us to compare the (z) = 0.61 disk galaxy sample (n ? 2.5) to an unprecedented local galaxy sample of ?670, 000 SDSS galaxies at z ? 0.1; this analysis indicates that the evolution of the luminosity-size relation since z ? 1 may not be fully explained by a pure-size or pure-luminosity evolution but may instead require a combination of both. Our observations are also in agreement with recent numerical simulations of disk galaxies that show evidence of a mass-dependent evolution since z ? 1, where high-mass disk galaxies (M{sub *} > 10{sup 9} M{sub ?}) evolve more in size and low-mass disk galaxies (M{sub *} ? 10{sup 9} M{sub ?}) evolve more in luminosity.
A test of the Suyama-Yamaguchi inequality from weak lensing
NASA Astrophysics Data System (ADS)
Grassi, Alessandra; Heisenberg, Lavinia; Byrnes, Christian T.; Schfer, Bjrn Malte
2014-08-01
We investigate the weak lensing signature of primordial non-Gaussianities of the local type by constraining the magnitude of the weak convergence bi- and trispectra expected for the Euclid weak lensing survey. Starting from expressions for the weak convergence spectra, bispectra and trispectra, whose relative magnitudes we investigate as a function of scale, we compute their respective signal-to-noise ratios by relating the polyspectra's amplitude to their Gaussian covariance using a Monte Carlo technique for carrying out the configuration space integrations. In computing the Fisher matrix on the non-Gaussianity parameters fNL, gNL and ?NL with a very similar technique, we can derive pieces of Bayesian evidence for a violation of the Suyama-Yamaguchi (SY) relation ?NL ? (6fNL/5)2 as a function of the true fNL- and ?NL-values and show that the relation can be probed down to levels of fNL ? 102 and ?NL ? 105. In a related study, we derive analytical expressions for the probability density that the SY relation is exactly fulfilled, as required by models in which any one field generates the perturbations. We conclude with an outlook on the levels of non-Gaussianity that can be probed with tomographic lensing surveys.
Discreteness of space from GUP in a weak gravitational field
NASA Astrophysics Data System (ADS)
Deb, Soumen; Das, Saurya; Vagenas, Elias C.
2016-04-01
Quantum gravity effects modify the Heisenberg's uncertainty principle to a generalized uncertainty principle (GUP). Earlier work showed that the GUP-induced corrections to the Schrödinger equation, when applied to a non-relativistic particle in a one-dimensional box, led to the quantization of length. Similarly, corrections to the Klein-Gordon and the Dirac equations, gave rise to length, area and volume quantizations. These results suggest a fundamental granular structure of space. In this work, it is investigated how spacetime curvature and gravity might influence this discreteness of space. In particular, by adding a weak gravitational background field to the above three quantum equations, it is shown that quantization of lengths, areas and volumes continue to hold. However, it should be noted that the nature of this new quantization is quite complex and under proper limits, it reduces to cases without gravity. These results suggest that quantum gravity effects are universal.
Gravitational failure of sea cliffs in weakly lithified sediment
Hampton, M.A.
2002-01-01
Gravitational failure of sea cliffs eroded into weakly lithified sediment at several sites in California involves episodic stress-release fracturing and cantilevered block falls. The principal variables that influence the gravitational stability are tensional stresses generated during the release of horizontal confining stress and weakening of the sediment with increased saturation levels. Individual failures typically comprise less than a cubic meter of sediment, but large areas of a cliff face can be affected by sustained instability over a period of several days. Typically, only the outer meter or so of sediment is removed during a failure episode. In-place sediment saturation levels vary over time and space, generally being higher during the rainy season but moderate to high year-round. Laboratory direct-shear tests show that sediment cohesion decreases abruptly with increasing saturation level; the decrease is similar for all tested sediment if the cohesion is normalized by the maximum, dry-sediment cohesion. Large failures that extend over most or all of the height of the sea cliff are uncommon, but a few large wedge-shaped failures sometimes occur, as does separation of large blocks at sea cliff-gully intersections.
Extreme gravitational lensing in vicinity of Schwarzschild-de Sitter black holes
NASA Astrophysics Data System (ADS)
Bakala, Pavel; ?ermk, Petr; Hledk, Stanislav; Stuchlk, Zden?k; Truparov, Kamila
2007-12-01
We have developed a realistic, fully general relativistic computer code to simulate optical projection in a strong, spherically symmetric gravitational field. The standard theoretical analysis of optical projection for an observer in the vicinity of a Schwarzschild black hole is extended to black hole spacetimes with a repulsive cosmological constant, i.e, Schwarzschild-de Sitterspacetimes. Influence of the cosmological constant is investigated for static observers and observers radially free-falling from the static radius. Simulations include effects of the gravitational lensing, multiple images, Doppler and gravitational frequency shift, as well as the intensity amplification. The code generates images of the sky for the static observer and a movie simulations of the changing sky for the radially free-falling observer. Techniques of parallel programming are applied to get a high performance and a fast run of the BHC simulation code.
Weak lensing effects on the galaxy three-point correlation function
Schmidt, Fabian; Vallinotto, Alberto; Sefusatti, Emiliano; Dodelson, Scott
2008-08-15
We study the corrections to the galaxy three-point correlation function induced by weak lensing magnification due to the matter distribution along the line of sight. We consistently derive all the correction terms arising up to second order in perturbation theory and provide analytic expressions as well as order-of-magnitude estimates for their relative importance. The magnification contributions depend on the geometry of the projected triangle on the sky plane and scale with different powers of the number count slope and redshift of the galaxy sample considered. We evaluate all terms numerically and show that, depending on the triangle configuration as well as the galaxy sample considered, weak lensing can in general significantly contribute to and alter the three-point correlation function observed through galaxy and quasar catalogs.
NASA Astrophysics Data System (ADS)
Wilson, Michelle; Zabludoff, Ann I.; Wong, Kenneth C.; Keeton, Charles R.; French, Katheryn Decker; Momcheva, Ivelina G.; Williams, Kurtis A.
2016-01-01
Galaxy-scale strong gravitational lensing has long been used to measure cosmological parameters such as the Hubble constant as well as the dark matter properties of galaxy halos. Additional mass around the lens galaxy or projected in the line-of-sight affects the light bending and needs to be incorporated into lensing analyses. We present new results from a spectroscopic survey to characterize the environmental and line-of-sight mass for 28 galaxy-scale lens fields. We show how the external convergence, number of lensed images, and lensed image separation are altered by groups at the lens and along the sightline.
Ade, P A R; Akiba, Y; Anthony, A E; Arnold, K; Atlas, M; Barron, D; Boettger, D; Borrill, J; Borys, C; Chapman, S; Chinone, Y; Dobbs, M; Elleflot, T; Errard, J; Fabbian, G; Feng, C; Flanigan, D; Gilbert, A; Grainger, W; Halverson, N W; Hasegawa, M; Hattori, K; Hazumi, M; Holzapfel, W L; Hori, Y; Howard, J; Hyland, P; Inoue, Y; Jaehnig, G C; Jaffe, A; Keating, B; Kermish, Z; Keskitalo, R; Kisner, T; Le Jeune, M; Lee, A T; Leitch, E M; Linder, E; Lungu, M; Matsuda, F; Matsumura, T; Meng, X; Miller, N J; Morii, H; Moyerman, S; Myers, M J; Navaroli, M; Nishino, H; Paar, H; Peloton, J; Poletti, D; Quealy, E; Rebeiz, G; Reichardt, C L; Richards, P L; Ross, C; Rotermund, K; Schanning, I; Schenck, D E; Sherwin, B D; Shimizu, A; Shimmin, C; Shimon, M; Siritanasak, P; Smecher, G; Spieler, H; Stebor, N; Steinbach, B; Stompor, R; Suzuki, A; Takakura, S; Tikhomirov, A; Tomaru, T; Wilson, B; Yadav, A; Zahn, O
2014-04-01
We reconstruct the gravitational lensing convergence signal from cosmic microwave background (CMB) polarization data taken by the Polarbear experiment and cross-correlate it with cosmic infrared background maps from the Herschel satellite. From the cross spectra, we obtain evidence for gravitational lensing of the CMB polarization at a statistical significance of 4.0? and indication of the presence of a lensing B-mode signal at a significance of 2.3?. We demonstrate that our results are not biased by instrumental and astrophysical systematic errors by performing null tests, checks with simulated and real data, and analytical calculations. This measurement of polarization lensing, made via the robust cross-correlation channel, not only reinforces POLARBEAR auto-correlation measurements, but also represents one of the early steps towards establishing CMB polarization lensing as a powerful new probe of cosmology and astrophysics. PMID:24745402
Combined strong and weak lensing analysis of 28 clusters from the Sloan Giant Arcs Survey
NASA Astrophysics Data System (ADS)
Oguri, Masamune; Bayliss, Matthew B.; Dahle, Hkon; Sharon, Keren; Gladders, Michael D.; Natarajan, Priyamvada; Hennawi, Joseph F.; Koester, Benjamin P.
2012-03-01
We study the mass distribution of a sample of 28 galaxy clusters using strong and weak lensing observations. The clusters are selected via their strong lensing properties as part of the Sloan Giant Arcs Survey (SGAS) from the Sloan Digital Sky Survey (SDSS). Mass modelling of the strong lensing information from the giant arcs is combined with weak lensing measurements from deep Subaru/Suprime-cam images to primarily obtain robust constraints on the concentration parameter and the shape of the mass distribution. We find that the concentration cvir is a steep function of the mass, cvir?M-0.590.12vir, with the value roughly consistent with the lensing-bias-corrected theoretical expectation for high-mass (1015 h-1 M?) clusters. However, the observationally inferred concentration parameters appear to be much higher at lower masses (1014 h-1 M?), possibly a consequence of the modification to the inner density profiles provided by baryon cooling. The steep mass-concentration relation is also supported from direct stacking analysis of the tangential shear profiles. In addition, we explore the 2D shape of the projected mass distribution by stacking weak lensing shear maps of individual clusters with prior information on the position angle from strong lens modelling, and find significant evidence for a large mean ellipticity with the best-fitting value of
Weak Lensing Analysis of Massive Galaxy Cluster IDCS J1426.5+3508 at z=1.75
NASA Astrophysics Data System (ADS)
Mo, Wenli; Gonzalez, Anthony H.; Jee, Myungkook J.; Massey, Richard; Rhodes, Jason; Brodwin, Mark; Eisenhardt, Peter R.; Marrone, Daniel P.; Stanford, S. Adam; Zeimann, Gregory
2016-01-01
We present a weak lensing study of the galaxy cluster IDCS J1426.5+3508 at z=1.75, which is the highest redshift strong lensing cluster known and the most distant cluster for which a weak lensing analysis has been undertaken. Using F160W, F814W, and F606W observations with the Hubble Space Telescope, we detect tangential shear at 2? significance. Fitting a Navarro-Frenk-White mass profile to the shear with a theoretical median mass-concentration relation, we derive a mass consistent with previous mass estimates from the Sunyaev-Zel'dovich (SZ) effect, X-ray, and strong lensing. The cluster lies on the local SZ-weak lensing mass scaling relation observed at low redshift, indicative of minimal evolution in this relation.
IDCS J1426.5+3508: Weak Lensing Analysis of a Massive Galaxy Cluster at z = 1.75
NASA Astrophysics Data System (ADS)
Mo, Wenli; Gonzalez, Anthony; Jee, M. James; Massey, Richard; Rhodes, Jason; Brodwin, Mark; Eisenhardt, Peter; Marrone, Daniel P.; Stanford, S. A.; Zeimann, Gregory R.
2016-02-01
We present a weak lensing study of the galaxy cluster IDCS J1426.5+3508 at z = 1.75, which is the highest-redshift strong lensing cluster known and the most distant cluster for which a weak lensing analysis has been undertaken. Using F160W, F814W, and F606W observations with the Hubble Space Telescope, we detect tangential shear at 2σ significance. Fitting a Navarro–Frenk–White mass profile to the shear with a theoretical median mass-concentration relation, we derive a mass {M}200,{crit}={2.3}-1.4+2.1× {10}14 M⊙. This mass is consistent with previous mass estimates from the Sunyaev–Zel’dovich (SZ) effect, X-ray, and strong lensing. The cluster lies on the local SZ–weak lensing mass scaling relation observed at low redshift, indicative of minimal evolution in this relation.
Non-Gaussian forecasts of weak lensing with and without priors
NASA Astrophysics Data System (ADS)
Sellentin, Elena; Schäfer, Björn Malte
2016-02-01
Including priors into a data analysis can mask the information content of a given data set alone. However, since the information content of a data set is usually estimated with the Fisher matrix, priors are added to enforce an approximately Gaussian likelihood. Here, we estimate the information content of a Euclid-like weak lensing data set with and without priors. Without priors, the Fisher matrix for 2d-weak lensing includes unphysical values of Ωm and h. The Cramer-Rao inequality then does not need to apply. We find that the new DALI expansion and Monte Carlo Markov Chains agree well and predict the presence of a dark energy with high significance, whereas a Fisher forecast also allows decelerated expansion. We find that a 2d-weak lensing analysis provides a sharp lower limit on the Hubble constant of h > 0.4, even if the equation of state of dark energy is jointly estimated. This is not predicted by the Fisher matrix and usually masked in other works by a sharp prior on h. Additionally, we find that DALI estimates Figures of Merit in the presence of non-Gaussianities better than the Fisher matrix and demonstrate how DALI allows switching to a speedy Hamiltonian Monte Carlo sampling of a highly curved likelihood with acceptance rates of ≈0.5. This shows how quick forecasts can be upgraded to accurate forecasts whenever needed. Results were gained with the public code from DALI.
MEASURING PRIMORDIAL NON-GAUSSIANITY THROUGH WEAK-LENSING PEAK COUNTS
Marian, Laura; Hilbert, Stefan; Smith, Robert E.; Schneider, Peter; Desjacques, Vincent
2011-02-10
We explore the possibility of detecting primordial non-Gaussianity of the local type using weak-lensing peak counts. We measure the peak abundance in sets of simulated weak-lensing maps corresponding to three models f{sub NL} = 0, - 100, and 100. Using survey specifications similar to those of EUCLID and without assuming any knowledge of the lens and source redshifts, we find the peak functions of the non-Gaussian models with f{sub NL} = {+-}100 to differ by up to 15% from the Gaussian peak function at the high-mass end. For the assumed survey parameters, the probability of fitting an f{sub NL} = 0 peak function to the f{sub NL} = {+-}100 peak functions is less than 0.1%. Assuming the other cosmological parameters are known, f{sub NL} can be measured with an error {Delta}f{sub NL} {approx} 13. It is therefore possible that future weak-lensing surveys like EUCLID and LSST may detect primordial non-Gaussianity from the abundance of peak counts, and provide information complementary to that obtained from the cosmic microwave background.
Constraining the minimum luminosity of high redshift galaxies through gravitational lensing
Mashian, Natalie; Loeb, Abraham E-mail: aloeb@cfa.harvard.edu
2013-12-01
We simulate the effects of gravitational lensing on the source count of high redshift galaxies as projected to be observed by the Hubble Frontier Fields program and the James Webb Space Telescope (JWST) in the near future. Taking the mass density profile of the lensing object to be the singular isothermal sphere (SIS) or the Navarro-Frenk-White (NFW) profile, we model a lens residing at a redshift of z{sub L} = 0.5 and explore the radial dependence of the resulting magnification bias and its variability with the velocity dispersion of the lens, the photometric sensitivity of the instrument, the redshift of the background source population, and the intrinsic maximum absolute magnitude (M{sub max}) of the sources. We find that gravitational lensing enhances the number of galaxies with redshifts z?> 13 detected in the angular region ?{sub E}/2 ? ? ? 2?{sub E} (where ?{sub E} is the Einstein angle) by a factor of ? 3 and 1.5 in the HUDF (df/d?{sub 0} ? 9 nJy) and medium-deep JWST surveys (df/d?{sub 0} ? 6 nJy). Furthermore, we find that even in cases where a negative magnification bias reduces the observed number count of background sources, the lensing effect improves the sensitivity of the count to the intrinsic faint-magnitude cut-off of the Schechter luminosity function. In a field centered on a strong lensing cluster, observations of z?> 6 and z?> 13 galaxies with JWST can be used to infer this cut-off magnitude for values as faint as M{sub max} ? -14.4 and -16.1 mag (L{sub min} ? 2.5 10{sup 26} and 1.2 10{sup 27} erg s{sup ?1} Hz{sup ?1}) respectively, within the range bracketed by existing theoretical models. Gravitational lensing may therefore offer an effective way of constraining the low-luminosity cut-off of high-redshift galaxies.
STRONG GRAVITATIONAL LENSING BY THE SUPER-MASSIVE cD GALAXY IN ABELL 3827
Carrasco, E. R.; Gomez, P. L.; Lee, H.; Diaz, R.; Bergmann, M.; Turner, J. E. H.; Miller, B. W.; West, M. J.; Verdugo, T.
2010-06-01
We have discovered strong gravitational lensing features in the core of the nearby cluster Abell 3827 by analyzing Gemini South GMOS images. The most prominent strong lensing feature is a highly magnified, ring-shaped configuration of four images around the central cD galaxy. GMOS spectroscopic analysis puts this source at z {approx} 0.2. Located {approx}20'' away from the central galaxy is a secondary tangential arc feature which has been identified as a background galaxy with z {approx} 0.4. We have modeled the gravitational potential of the cluster core, taking into account the mass from the cluster, the brightest cluster galaxy (BCG), and other galaxies. We derive a total mass of (2.7 {+-} 0.4) x 10{sup 13} M {sub sun} within 37 h {sup -1} kpc. This mass is an order of magnitude larger than that derived from X-ray observations. The total mass derived from lensing data suggests that the BCG in this cluster is perhaps the most massive galaxy in the nearby universe.
CFHTLenS: weak lensing calibrated scaling relations for low-mass clusters of galaxies
NASA Astrophysics Data System (ADS)
Kettula, K.; Giodini, S.; van Uitert, E.; Hoekstra, H.; Finoguenov, A.; Lerchster, M.; Erben, T.; Heymans, C.; Hildebrandt, H.; Kitching, T. D.; Mahdavi, A.; Mellier, Y.; Miller, L.; Mirkazemi, M.; Van Waerbeke, L.; Coupon, J.; Egami, E.; Fu, L.; Hudson, M. J.; Kneib, J. P.; Kuijken, K.; McCracken, H. J.; Pereira, M. J.; Rowe, B.; Schrabback, T.; Tanaka, M.; Velander, M.
2015-08-01
We present weak lensing and X-ray analysis of 12 low-mass clusters from the Canada-France-Hawaii Telescope Lensing Survey and XMM-CFHTLS surveys. We combine these systems with high-mass systems from Canadian Cluster Comparison Project and low-mass systems from Cosmic Evolution Survey to obtain a sample of 70 systems, spanning over two orders of magnitude in mass. We measure core-excised LX-TX, M-LX and M-TX scaling relations and include corrections for observational biases. By providing fully bias-corrected relations, we give the current limitations for LX and TX as cluster mass proxies. We demonstrate that TX benefits from a significantly lower intrinsic scatter at fixed mass than LX. By studying the residuals of the bias-corrected relations, we show for the first time using weak lensing masses that galaxy groups seem more luminous and warmer for their mass than clusters. This implies a steepening of the M-LX and M-TX relations at low masses. We verify the inferred steepening using a different high-mass sample from the literature and show that variance between samples is the dominant effect leading to discrepant scaling relations. We divide our sample into subsamples of merging and relaxed systems, and find that mergers may have enhanced scatter in lensing measurements, most likely due to stronger triaxiality and more substructure. For the LX-TX relation, which is unaffected by lensing measurements, we find the opposite trend in scatter. We also explore the effects of X-ray cross-calibration and find that Chandra calibration leads to flatter LX-TX and M-TX relations than XMM-Newton.
PROBING THE INNER KILOPARSEC OF MASSIVE GALAXIES WITH STRONG GRAVITATIONAL LENSING
Hezaveh, Yashar D.; Marshall, Philip J.; Blandford, Roger D.
2015-01-30
We examine the prospects of detecting demagnified images of gravitational lenses in observations of strongly lensed millimeter-wave molecular emission lines with ALMA. We model the lensing galaxies as a superposition of a dark matter component, a stellar component, and a central super-massive black hole (SMBH) and assess the detectability of the central images for a range of relevant parameters (e.g., stellar core, black hole mass, and source size). We find that over a large range of plausible parameters, future deep observations of lensed molecular lines with ALMA should enable the detection of the central images at ≳3σ significance. We use a Fisher analysis to examine the constraints that could be placed on these parameters in various scenarios and find that for large stellar cores, both the core size and the mass of the central SMBHs can be accurately measured. We also study the prospects for detecting binary SMBHs with such observations and find that only under rare conditions and with very long integrations (∼40 hr) the masses of both SMBHs may be measured using the distortions of central images.
Dark matter halo properties of GAMA galaxy groups from 100 square degrees of KiDS weak lensing data
NASA Astrophysics Data System (ADS)
Viola, M.; Cacciato, M.; Brouwer, M.; Kuijken, K.; Hoekstra, H.; Norberg, P.; Robotham, A. S. G.; van Uitert, E.; Alpaslan, M.; Baldry, I. K.; Choi, A.; de Jong, J. T. A.; Driver, S. P.; Erben, T.; Grado, A.; Graham, Alister W.; Heymans, C.; Hildebrandt, H.; Hopkins, A. M.; Irisarri, N.; Joachimi, B.; Loveday, J.; Miller, L.; Nakajima, R.; Schneider, P.; Sifón, C.; Verdoes Kleijn, G.
2015-10-01
The Kilo-Degree Survey is an optical wide-field survey designed to map the matter distribution in the Universe using weak gravitational lensing. In this paper, we use these data to measure the density profiles and masses of a sample of ˜1400 spectroscopically identified galaxy groups and clusters from the Galaxy And Mass Assembly survey. We detect a highly significant signal (signal-to-noise-ratio ˜120), allowing us to study the properties of dark matter haloes over one and a half order of magnitude in mass, from M ˜ 1013-1014.5 h-1 M⊙. We interpret the results for various subsamples of groups using a halo model framework which accounts for the mis-centring of the brightest cluster galaxy (used as the tracer of the group centre) with respect to the centre of the group's dark matter halo. We find that the density profiles of the haloes are well described by an NFW profile with concentrations that agree with predictions from numerical simulations. In addition, we constrain scaling relations between the mass and a number of observable group properties. We find that the mass scales with the total r-band luminosity as a power law with slope 1.16 ± 0.13 (1σ) and with the group velocity dispersion as a power law with slope 1.89 ± 0.27 (1σ). Finally, we demonstrate the potential of weak lensing studies of groups to discriminate between models of baryonic feedback at group scales by comparing our results with the predictions from the Cosmo-OverWhelmingly Large Simulations project, ruling out models without AGN feedback.
NASA Astrophysics Data System (ADS)
High, F. W.; Hoekstra, H.; Leethochawalit, N.; de Haan, T.; Abramson, L.; Aird, K. A.; Armstrong, R.; Ashby, M. L. N.; Bautz, M.; Bayliss, M.; Bazin, G.; Benson, B. A.; Bleem, L. E.; Brodwin, M.; Carlstrom, J. E.; Chang, C. L.; Cho, H. M.; Clocchiatti, A.; Conroy, M.; Crawford, T. M.; Crites, A. T.; Desai, S.; Dobbs, M. A.; Dudley, J. P.; Foley, R. J.; Forman, W. R.; George, E. M.; Gladders, M. D.; Gonzalez, A. H.; Halverson, N. W.; Harrington, N. L.; Holder, G. P.; Holzapfel, W. L.; Hoover, S.; Hrubes, J. D.; Jones, C.; Joy, M.; Keisler, R.; Knox, L.; Lee, A. T.; Leitch, E. M.; Liu, J.; Lueker, M.; Luong-Van, D.; Mantz, A.; Marrone, D. P.; McDonald, M.; McMahon, J. J.; Mehl, J.; Meyer, S. S.; Mocanu, L.; Mohr, J. J.; Montroy, T. E.; Murray, S. S.; Natoli, T.; Nurgaliev, D.; Padin, S.; Plagge, T.; Pryke, C.; Reichardt, C. L.; Rest, A.; Ruel, J.; Ruhl, J. E.; Saliwanchik, B. R.; Saro, A.; Sayre, J. T.; Schaffer, K. K.; Shaw, L.; Schrabback, T.; Shirokoff, E.; Song, J.; Spieler, H. G.; Stalder, B.; Staniszewski, Z.; Stark, A. A.; Story, K.; Stubbs, C. W.; uhada, R.; Tokarz, S.; van Engelen, A.; Vanderlinde, K.; Vieira, J. D.; Vikhlinin, A.; Williamson, R.; Zahn, O.; Zenteno, A.
2012-10-01
We use weak gravitational lensing to measure the masses of five galaxy clusters selected from the South Pole Telescope (SPT) survey, with the primary goal of comparing these with the SPT Sunyaev-Zel'dovich (SZ) and X-ray-based mass estimates. The clusters span redshifts 0.28 < z < 0.43 and have masses M 500 > 2 1014 h -1 M ?, and three of the five clusters were discovered by the SPT survey. We observed the clusters in the g'r'i' passbands with the Megacam imager on the Magellan Clay 6.5 m telescope. We measure a mean ratio of weak-lensing (WL) aperture masses to inferred aperture masses from the SZ data, both within an aperture of R 500, SZ derived from the SZ mass, of 1.04 0.18. We measure a mean ratio of spherical WL masses evaluated at R 500, SZ to spherical SZ masses of 1.07 0.18, and a mean ratio of spherical WL masses evaluated at R 500, WL to spherical SZ masses of 1.10 0.24. We explore potential sources of systematic error in the mass comparisons and conclude that all are subdominant to the statistical uncertainty, with dominant terms being cluster concentration uncertainty and N-body simulation calibration bias. Expanding the sample of SPT clusters with WL observations has the potential to significantly improve the SPT cluster mass calibration and the resulting cosmological constraints from the SPT cluster survey. These are the first WL detections using Megacam on the Magellan Clay telescope.
NASA Astrophysics Data System (ADS)
Hagstotz, Steffen; Schäfer, Björn Malte; Merkel, Philipp M.
2015-11-01
Many weak-lensing calculations make use of the Born approximation where the light ray is approximated by a straight path. We examine the effect of Born-corrections for lensing of the cosmic microwave background (CMB) in an analytical approach by taking perturbative corrections to the geodesic into account. The resulting extra power in the lensing potential spectrum is comparable to the power generated by non-linear structure formation and affects especially the polarization spectra, leading to relative changes of the order of 10-3 for the E-mode spectrum and several per cent on all scales to the B-mode spectrum. In contrast, there is only little change of spectra involving the CMB temperature. Additionally, the corrections excite one more degree of freedom resulting in a deflection component which cannot be described as a gradient of the lensing potential as it is related to image rotation in lens-lens coupling. We estimate the magnitude of this effect on the CMB spectra and find it to be negligible.
Full-sky formulae for weak lensing power spectra from total angular momentum method
Yamauchi, Daisuke; Taruya, Atsushi; Namikawa, Toshiya E-mail: namikawa@yukawa.kyoto-u.ac.jp
2013-08-01
We systematically derive full-sky formulae for the weak lensing power spectra generated by scalar, vector and tensor perturbations from the total angular momentum (TAM) method. Based on both the geodesic and geodesic deviation equations, we first give the gauge-invariant expressions for the deflection angle and Jacobi map as observables of the CMB lensing and cosmic shear experiments. We then apply the TAM method, originally developed in the theoretical studies of CMB, to a systematic derivation of the angular power spectra. The TAM representation, which characterizes the total angular dependence of the spatial modes projected along a line-of-sight, can carry all the information of the lensing modes generated by scalar, vector, and tensor metric perturbations. This greatly simplifies the calculation, and we present a complete set of the full-sky formulae for angular power spectra in both the E-/B-mode cosmic shear and gradient-/curl-mode lensing potential of deflection angle. Based on the formulae, we give illustrative examples of non-vanishing B-mode cosmic shear and curl-mode of deflection angle in the presence of the vector and tensor perturbations, and explicitly compute the power spectra.
NASA Astrophysics Data System (ADS)
Ling, Chenxiaoji; Wang, Qiao; Li, Ran; Li, Baojiu; Wang, Jie; Gao, Liang
2015-09-01
We explore the Minkowski functionals (MFs) of weak lensing convergence map to distinguish between f (R ) gravity and the general relativity (GR). The mock weak lensing convergence maps are constructed with a set of high-resolution simulations assuming different gravity models. It is shown that the lensing MFs of f (R ) gravity can be considerably different from that of GR because of the environmentally dependent enhancement of structure formation. We also investigate the effect of lensing noise on our results, and find that it is likely to distinguish F5, F6, and GR gravity models with a galaxy survey of 3000 degree2 and with a background source number density of ng=30 arcmin-2 , comparable to an upcoming survey dark energy survey (DES).We also find that the f (R ) signal can be partially degenerate with the effect of changing cosmology, but combined use of other observations, such as the cosmic microwave background (CMB) data, can help break this degeneracy.
Infrared imaging of MG 0414 + 0534 - The red gravitational lens systems as lensed radio galaxies
NASA Technical Reports Server (NTRS)
Annis, James; Luppino, Gerard A.
1993-01-01
We present an IR image of the gravitational lens system MG 0414 + 0534, and IR photometry of PG 1115 + 080, H1413 + 117, and Q1429 - 008. The IR of MG 0414 + 0534 shows a morphology that is similar to the radio and optical morphologies. The object is bright (K-prime = 13.7) and extremely red (I-K-prime = 5.7). MG 0414 + 0534 thus becomes the second radio-selected lens system to have very red optical IR colors. When plotted on a color-magnitude diagram of objects from a radio survey, MG 0414 + 0534 and the other very red system, MG 1131 + 0456, lie near the locus of radio galaxies. We therefore suggest that these systems are lensed high-redshift radio galaxies. In general, lensed radio galaxies should be common among lens systems selected from radio surveys, since a high proportion of radio sources are radio galaxies.
NASA Astrophysics Data System (ADS)
Moustakas, Leonidas A.; Cyr-Racine, Francis-Yan; Keeton, Charles R.
2016-01-01
The properties of the dark matter particle or particles lead to different small scale halo populations, distributions, and evolution over cosmic time. We introduce a new method for characterizing the properties of substructure within galaxies through the power spectrum of potential fluctuations, and demonstrate how complete sets of multiwavelength imaging and time domain observations can be processed directly to infer all facets of the strong gravitational lensing components and source properties, including the dark matter substructure power spectrum constraints. We are able to take advantage of analysis parallels with cosmic background radiation techniques, and furthermore demonstrate how this technique, dubbed The Aspen Framework, reduces to the long-standing approach of working with reduced or derived observable quantities in lensing.
Strong field limit analysis of gravitational lensing in Kerr-Taub-NUT spacetime
Wei, Shao-Wen; Liu, Yu-Xiao; Fu, Chun-E; Yang, Ke E-mail: liuyx@lzu.edu.cn E-mail: yangke09@lzu.edu.cn
2012-10-01
In this paper, we study numerically the quasi-equatorial lensing by the stationary, axially-symmetric black hole in Kerr-Taub-NUT spacetime in the strong field limit. The deflection angle of light ray and other strong deflection limit coefficients are obtained numerically and they are found to be closely dependent on the NUT charge n and spin a. We also compute the magnification and the positions of the relativistic images. The caustics are studied and the results show that these caustics drift away from the optical axis, which is quite different from the Schwarzschild black hole case. Moreover, the intersections of the critical curves on the equatorial plane are obtained and it is shown that they increase with the NUT charge. These results show that there is a significant effect of the NUT charge on the strong gravitational lensing.
NASA Astrophysics Data System (ADS)
Niikura, Hiroko; Takada, Masahiro; Okabe, Nobuhiro; Martino, Rossella; Takahashi, Ryuichi
2015-10-01
We develop a novel method of measuring the lensing distortion profiles of clusters by stacking the "scaled" amplitudes of background galaxy ellipticities as a function of the "scaled" centric radius according to the Navarro-Frenk-White (NFW) prediction of each cluster, based on the assumption that the different clusters in a sample follow the universal NFW profile. First we demonstrate the feasibility of this method using both the analytical NFW model and simulated halos in a suite of high-resolution N-body simulations. We then apply, as a proof of concept, this method to the Subaru weak lensing data and the XMM/Chandra X-ray observables for a sample of 50 massive clusters in the redshift range 0.15 ? z ? 0.3, where their halo masses differ from each other by up to a factor of 10. To estimate the NFW parameters of each cluster, we use the halo mass proxy relation of X-ray observables, based on either the hydrostatic equilibrium or the gas mass, and then infer the halo concentration from the model scaling relation of halo concentration with halo mass. We evaluate the performance of the NFW scaling analysis by measuring the scatters of 50 cluster lensing profiles relative to the NFW predictions over a range of radii, 0.14 ? R/[h-1 Mpc] ? 2.8. We found 4-6 ?-level evidence of the universal NFW profile in 50 clusters, for both the X-ray halo mass proxy relations, although the gas mass appears to be a better proxy of the underlying true mass. By comparing the measurements with the simulations of cluster lensing profiles taking into account the statistical errors of intrinsic galaxy shapes in the Subaru data, we argue that additional halo mass errors or intrinsic scatters of ?(M500c)/M500c 0.2-0.3 could reconcile the difference between measurements and simulations. This method allows us to some extent to preserve characteristics of individual clusters in the statistical weak lensing analysis, thereby yielding a new means of exploiting the underlying genuine form of the halo mass profile and the halo mass proxy relations via weak lensing information, under the assumption of the existence of the universal profile.
The time delay in strong gravitational lensing with Gauss-Bonnet correction
Man, Jingyun; Cheng, Hongbo E-mail: hbcheng@ecust.edu.cn
2014-11-01
The time delay between two relativistic images in the strong gravitational lensing governed by Gauss-Bonnet gravity is studied. We make a complete analytical derivation of the expression of time delay in presence of Gauss-Bonnet coupling. With respect to Schwarzschild, the time delay decreases as a consequence of the shrinking of the photon sphere. As the coupling increases, the second term in the time delay expansion becomes more relevant. Thus time delay in strong limit encodes some new information about geometry in five-dimensional spacetime with Gauss-Bonnet correction.
NASA Astrophysics Data System (ADS)
Moustakas, Leonidas; Cyr-Racine, Francis-Yan; Keeton, Charles; Benson, Andrew
2015-08-01
The assembly of galactic halos is a direct consequence of the history of accumulation of dark matter, over all mass scales. Through time-domain observations of strong gravitational lenses, in combination with high-resolution static multi-wavelength images from space and from the ground, the spatial and mass function distribution of these dark matter subhalos may be mapped. We present the Bayesian Inference techniques by which the properties of dark matter structure can be mapped over cosmic time, including the best constraints determined to date, and place these in the context of theoretical and numerical expectations of the assembly of galactic halos under Cold and Warm Dark Matter scenarios.
Strong gravitational lensing across a dilaton anti-de Sitter black hole
Ghosh, Tanwi; SenGupta, Soumitra
2010-02-15
In this work we investigate the gravitational lensing effect in the strong field region around dilaton black holes in an anti-de Sitter space. We also analyze the dependence of the radius of the photon sphere and deflection angle on dilaton coupling and the cosmological constant in this black hole spacetime. Finally the values of minimum impact parameter, the separation between the first and the other images, as well as the ratio between the flux of the first image and the flux coming from all the other images are determined to characterize some possible distinct signatures of such black holes.
Strong gravitational lensing in a charged squashed Kaluza-Klein Gdel black hole
NASA Astrophysics Data System (ADS)
Sadeghi, J.; Naji, J.; Vaez, H.
2014-01-01
In this Letter we investigate the strong gravitational lansing in a charged squashed Kaluza-Klein Gdel black hole. The deflection angle is considered by the logarithmic term proposed by Bozza et al. Then we study the variation of deflection angle and its parameters abar and bbar. We suppose that the supermassive black hole in the galaxy center can be considered by a charged squashed Kaluza-Klein black hole in a Gdel background. Then by the relations between lensing parameters and observables, we estimate the observables for different values of charge, extra dimension and Gdel parameters.
A WEAK-LENSING AND NEAR-INFRARED STUDY OF A3192: DISASSEMBLING A RICHNESS CLASS 3 ABELL CLUSTER
Hamilton-Morris, Victoria; Smith, Graham P.; Haines, C. P.; Sanderson, A. J. R.; Edge, A. C.; Egami, E.; Marshall, P. J.; Targett, T. A. E-mail: gps@star.sr.bham.ac.uk
2012-04-01
We present a joint gravitational lensing and near-infrared study of the galaxy cluster Abell 3192 (A3192) that has been associated both with galaxies at z = 0.168 and with the X-ray luminous cluster RXC J0358.8-2955 (RXC J0358) at z = 0.425. Weak-lensing analysis of our Hubble Space Telescope snapshot observation with the Advanced Camera for Surveys detects two mass over-densities separated by {approx}2 arcmin, one adjacent to the optical position of A3192 (4.4{sigma} significance) and the other adjacent to the X-ray position of RXC J0358 (6.2{sigma} significance). These mass peaks coincide with peaks in the K-band luminosity density of galaxies with near-infrared colors consistent with the red sequence at z = 0.168 and z 0.425, respectively. Moreover, the Bayesian evidence of parameterized mass models that include two cluster/group-scale halos centered on the respective mass peaks exceeds that of single-halo models by a factor of {>=}10. The total projected mass of each galaxy system within 250 kpc of the respective peaks is M{sub WL}(z = 0.168) {approx_equal} 3 Multiplication-Sign 10{sup 13} M{sub Sun} and M{sub WL}(z = 0.425) {approx_equal} 1.2 Multiplication-Sign 10{sup 14} M{sub Sun }, both with total mass-to-light ratios of M{sub WL}/L{sub K} {approx_equal} 20 M{sub Sun }/L{sub Sun }. The original Abell cluster therefore comprises two independent galaxy systems-a foreground group at z = 0.168 and RXC J0358 at z = 0.425. Our results demonstrate the power of combining X-ray, near-infrared, and weak-lensing observations to select massive clusters, place those clusters and interloper galaxy systems along the line of sight, and measure their masses. This combination will be invaluable to robust interpretation of future high-redshift cluster surveys, including eROSITA.
Analyzing Star Formation Properties in Dusty Early Universe Galaxies Using Gravitational Lensing
NASA Astrophysics Data System (ADS)
Bradli, Jaclyn C.; Bussmann, R. Shane; Riechers, Dominik A.; Clements, David; Perez-Fournon, Ismael
2015-01-01
Strong gravitational lensing has recently become one of the most important tools for studying star formation properties in extremely high redshift galaxies. Dust-obscured star-forming galaxies found at far-infrared/sub-millimeter wavelengths are important in the assembly of stellar mass and the evolution of massive galaxies. We present Submillimeter Array (SMA) imaging of Lockman 102, a strongly lensed submillimeter galaxy at z=5.29, discovered by the Herschel Space Observatory. The system was observed at 250, 350, 500 and 1000 microns, corresponding to rest frame wavelengths of 40, 56, 80, and 159 microns respectively. The observations were targeted at the thermal dust emission and the [CII] interstellar medium cooling line. We report an estimated photometric redshift of ~1.9 for the lensing galaxy, making it possibly the most distant lens currently known. We use uvmcmcfit, a publicly available Markov Chain Monte Carlo software tool we have developed for interferometric data, to fit lens models to Lockman 102. The results obtained from uvmcmcfit suggest the lensed system is composed of a single lensing galaxy and two extended sources. We have strong constraints on an intrinsic flux density of Lockman 102 of 4.55 + 0.45 mJy magnified by a factor of 12.5 + 1.2. From a modified blackbody fit we compute an intrinsic far infrared luminosity of 5.5e12 L?.This implies a star formation rate of ~950 M? yr-1, making Lockman 102 an extremely active dusty galaxy. We also compare Lockman 102 to other dusty luminous starburst galaxies at similar redshift, HLS0918 (Rawle et al. 2014) and AzTEC-3 (Riechers et al. 2014a) and determine it is among the most luminous and active galaxies ~1 Gyr after the Big Bang. It is only with strong lensing that the SMA is able to undertake such a detailed study of a galaxy at this distance; the continued improvements from new facilities such as ALMA offer a promising future in observing even more distant lensed systems.
Low X-ray luminosity galaxy clusters - III. Weak lensing mass determination at 0.18 < z < 0.70
NASA Astrophysics Data System (ADS)
Gonzalez, Elizabeth Johana; Fox, Gael; Nilo Castelln, Jos Luis; Domnguez Romero, Mariano J.; Alonso, Mara Victoria; Garca Lambas, Diego; Moreschi, Osvaldo; Gallo, Emanuel
2015-09-01
This is the third of a series of papers of low X-ray luminosity galaxy clusters. In this work we present the weak lensing analysis of eight clusters, based on observations obtained with the Gemini Multi-Object Spectrograph in the g', r' and i' passbands. For this purpose, we have developed a pipeline for the lensing analysis of ground-based images and we have performed tests applied to simulated data. We have determined the masses of seven galaxy clusters, five of them measured for the first time. For the four clusters with availably spectroscopic data, we find a general agreement between the velocity dispersions obtained via weak lensing assuming a singular isothermal sphere profile, and those obtained from the redshift distribution of member galaxies. The correlation between our weak lensing mass determinations and the X-ray luminosities is suitably fitted by other observations of the M-LX relation and models.
A new model to predict weak-lensing peak counts. II. Parameter constraint strategies
NASA Astrophysics Data System (ADS)
Lin, Chieh-An; Kilbinger, Martin
2015-11-01
Context. Peak counts have been shown to be an excellent tool for extracting the non-Gaussian part of the weak lensing signal. Recently, we developed a fast stochastic forward model to predict weak-lensing peak counts. Our model is able to reconstruct the underlying distribution of observables for analysis. Aims: In this work, we explore and compare various strategies for constraining a parameter using our model, focusing on the matter density ?m and the density fluctuation amplitude ?8. Methods: First, we examine the impact from the cosmological dependency of covariances (CDC). Second, we perform the analysis with the copula likelihood, a technique that makes a weaker assumption than does the Gaussian likelihood. Third, direct, non-analytic parameter estimations are applied using the full information of the distribution. Fourth, we obtain constraints with approximate Bayesian computation (ABC), an efficient, robust, and likelihood-free algorithm based on accept-reject sampling. Results: We find that neglecting the CDC effect enlarges parameter contours by 22% and that the covariance-varying copula likelihood is a very good approximation to the true likelihood. The direct techniques work well in spite of noisier contours. Concerning ABC, the iterative process converges quickly to a posterior distribution that is in excellent agreement with results from our other analyses. The time cost for ABC is reduced by two orders of magnitude. Conclusions: The stochastic nature of our weak-lensing peak count model allows us to use various techniques that approach the true underlying probability distribution of observables, without making simplifying assumptions. Our work can be generalized to other observables where forward simulations provide samples of the underlying distribution.
SDSS J131339.98+515128.3: A new GravitationallyLensed Quasar Selected Based on Near-infrared Excess
Ofek, E.O.; Oguri, M.; Jackson, N.; Inada, N.; Kayo, I.
2007-09-28
We report the discovery of a new gravitationally lensed quasar, SDSS J131339.98+515128.3, at a redshift of 1:875 with an image separation of 1: 0024. The lensing galaxy is clearly detected in visible-light follow-up observations. We also identify three absorption-line doublets in the spectra of the lensed quasar images, from which we measure the lens redshift to be 0:194. Like several other known lenses, the lensed quasar images have different continuum slopes. This difference is probably the result of reddening and microlensing in the lensing galaxy. The lensed quasar was selected by correlating Sloan Digital Sky Survey (SDSS) spectroscopic quasars with Two Micron All Sky Survey (2MASS) sources and choosing quasars that show near-infrared (IR) excess. The near-IR excess can originate, for example, from the contribution of the lensing galaxy at near-IR wavelengths. We show that the near-IR excess technique is indeed an efficient method to identify lensed systems from a large sample of quasars.
ERIC Educational Resources Information Center
Turner, Edwin L.
1988-01-01
Describes cosmic flukes which offer a unique window on new information about the universe. Discusses the historical background, theory, and detection of this effect. Proposes the importance of information found by the examination of these phenomena. (CW)
Gravitational lensing limits on the cosmological constant in a flat universe
NASA Technical Reports Server (NTRS)
Turner, Edwin L.
1990-01-01
Inflationary cosmological theories predict, and some more general aesthetic criteria suggest, that the large-scale spatial curvature of the universe k should be accurately zero (i.e., flat), a condition which is satisfied when the universe's present mean density and the value of the cosmological constant Lambda have certain pairs of values. Available data on the frequency of multiple image-lensing of high-redshift quasars by galaxies suggest that the cosmological constant cannot make a dominant contribution to producing a flat universe. In particular, if the mean density of the universe is as small as the baryon density inferred from standard cosmic nucleosynthesis calculations or as determined from typical dynamical studies of galaxies and galaxy clusters, then a value of Lambda large enough to produce a k = 0 universe would result in a substantially higher frequency of multiple-image lensing of quasars than has been observed so far. Shortcomings of the available lens data and uncertainties concerning galaxy properties allow some possibility of escaping this conclusion, but systematic searches for a gravitational lenses and continuing investigations of galaxy mass distributions should soon provide decisive information. It is also noted that nonzero-curvature cosmological models can account for the observed frequency of galaxy-quasar lens systems and for a variety of other constraints.
Two New Gravitationally Lensed Double Quasars from theSloan Digital Sky Survey
Inada, Naohisa; Oguri, Masamune; Becker, Robert H.; White, Richard L.; Kayo, Issha; Kochanek, Christopher S.; Hall, Patrick B.; Schneider, Donald P.; York, Donald G.; Richards, Gordon T.; /Tokyo U., Inst. Astron. /KIPAC, Menlo Park /Princeton U. Observ. /LLNL, Livermore /UC, Davis /Baltimore, Space Telescope Sci. /Nagoya U. /Ohio State U., Dept. Astron. /York U., Canada /Penn State U., Astron. Astrophys. /Chicago U., Astron. Astrophys. Ctr. /Chicago U., EFI /Johns Hopkins U. /Drexel U.
2006-09-28
We report the discoveries of the two-image gravitationally lensed quasars, SDSS J0746+4403 and SDSS J1406+6126, selected from the Sloan Digital Sky Survey (SDSS). SDSS J0746+4403, which will be included in our lens sample for statistics and cosmology, has a source redshift of z{sub s} = 2.00, an estimated lens redshift of z{sub l} {approx} 0.3, and an image separation of 1.08''. SDSS J1406+6126 has a source redshift of z{sub s} = 2.13, a spectroscopically measured lens redshift of z{sub l} = 0.27, and an image separation of 1.98''. We find that the two quasar images of SDSS J1406+6126 have different intervening Mg II absorption strengths, which are suggestive of large variations of absorbers on kpc scales. The positions and fluxes of both the lensed quasar systems are easily reproduced by simple mass models with reasonable parameter values. These objects bring to 18 the number of lensed quasars that have been discovered from the SDSS data.
GRAVITATIONAL LENSING OF STARS ORBITING THE MASSIVE BLACK HOLE IN THE GALACTIC CENTER
Bozza, V.; Mancini, L. E-mail: lmancini@physics.unisa.it
2009-05-01
The existence of a massive black hole in the center of the Milky Way, coinciding with the radio source Sgr A*, is being established on more and more solid grounds. In principle, this black hole, acting as a gravitational lens, is able to bend the light emitted by stars moving within its neighborhood, eventually generating secondary images. Extending a previous analysis of the gravitational lensing phenomenology to a new set of 27 stars, whose orbits have been well determined by recent observations, we have calculated all the properties of their secondary images, including time and magnitude of their luminosity peaks and their angular distances from the central black hole. The best lensing candidate is represented by the star S6, since the magnitude of its secondary image at the peak reaches K = 20.8, with an angular separation of 0.3 mas from the central black hole, which is just at the borders of the resolution limit in the K band of incoming astronomical instruments.
Statistical Properties of Gravitational Lensing in Cosmological Models with Cosmological Constant
NASA Astrophysics Data System (ADS)
Lee, Hyun-A.; Park, Myeong-Gu
1994-10-01
To extend the work of Gott, Park, and Lee(1989), statistical properties of gravitational lensing in a wide variety of cosmological models involving non-zero cosmological constant is investigated, using the redshifts of both lens and source and observed angular separation of images for gravitational lens systems. We assume singular isothermal sphere as lensing galaxy in homogeneous and isotropic Friedmann-Lemaitre-Robertson-Walker universe, Schechter luminosity function, standard angular diameter distance formula and other galaxy parameters used in Fukugita and Turner(1991). To find the most adequate flat cosmological model and put a limit on the value of dimensionless cosmological constant lambda_o, the mean value of angular separation of images, probability distribution of angular separation and cumulative probability are calculated for given source and lens redshifts and compared with the observed values through several statistical methods. When there is no angular selection effect, models with highest value of lambda_o is preferred generally. When the angular selection effects are considered, the preferred model depends on the shape of selection functions and statistical methods; yet, models with large lambda_o are preferred in general. However, the present data cannot rule out any of the flat universe models with enough confidence. This approach can potentially select out best model. But at the moment, we need more data.
NASA Astrophysics Data System (ADS)
Raffaelli, Bernard
2016-02-01
We examine in a semiclassical framework the deflection function of strong gravitational lensing, for static and spherically symmetric black holes, endowed with a photon sphere. From a first-order WKB analysis near the maximum of the Regge-Wheeler potential, we extract the real phase shifts from the S-matrix elements and then we derive the associated semiclassical deflection function, characterized by a logarithmic divergent behavior. More precisely, using the complex angular momentum techniques, we show that the Regge poles and the associated greybody factor residues, for a massless scalar field theory, from which one can recover the black hole quasinormal complex frequencies as well as the fluctuations of the high energy absorption cross section, play naturally the role of critical parameters in the divergent behavior of the semiclassical deflection function. For very high frequencies, we finally recover the logarithmic part of the classical strong deflection limit, which clarifies analytically the fundamental link between quasinormal modes and strong gravitational lensing, suggested in recent works.
NASA Astrophysics Data System (ADS)
Linet, B.; Teyssandier, P.
2016-02-01
We present a complete analysis of the light rays within the linearized, weak-field approximation of a Schwarzschild-like metric describing the gravitational field of an isolated, spherically symmetric body. We prove in this context the existence of two time transfer functions and we obtain these functions in an exact closed-form. We are led to distinguish two regimes. In the first regime, the two time transfer functions correspond to rays which are confined in regions of spacetime where the weak-field approximation is valid. Such a regime occurs in gravitational lensing configurations with double images of a given source. We find the general expressions of the angular separation and the difference in light travel time between the two images. In the second regime, there exists only one time transfer function corresponding to a light ray remaining in a region of weak field. Performing a Taylor expansion of this function with respect to the gravitational constant, we obtain the Shapiro time delay completed by a series of so-called "enhanced terms." The enhanced terms beyond the third order are new.
Choi, J.-Y.; Shin, I.-G.; Park, S.-Y.; Han, C.; Gould, A.; Gaudi, B. S.; Henderson, C. B.; Sumi, T.; Udalski, A.; Beaulieu, J.-P.; Street, R.; Dominik, M.; Allen, W.; Almeida, L. A.; Christie, G. W.; Depoy, D. L.; Dong, S.; Drummond, J.; Gal-Yam, A.; Collaboration: muFUN Collaboration; MOA Collaboration; OGLE Collaboration; PLANET Collaboration; RoboNet Collaboration; MiNDSTEp Consortium; and others
2012-05-20
We present the analysis of the light curves of nine high-magnification single-lens gravitational microlensing events with lenses passing over source stars, including OGLE-2004-BLG-254, MOA-2007-BLG-176, MOA-2007-BLG-233/OGLE-2007-BLG-302, MOA-2009-BLG-174, MOA-2010-BLG-436, MOA-2011-BLG-093, MOA-2011-BLG-274, OGLE-2011-BLG-0990/MOA-2011-BLG-300, and OGLE-2011-BLG-1101/MOA-2011-BLG-325. For all of the events, we measure the linear limb-darkening coefficients of the surface brightness profile of source stars by measuring the deviation of the light curves near the peak affected by the finite-source effect. For seven events, we measure the Einstein radii and the lens-source relative proper motions. Among them, five events are found to have Einstein radii of less than 0.2 mas, making the lenses very low mass star or brown dwarf candidates. For MOA-2011-BLG-274, especially, the small Einstein radius of {theta}{sub E} {approx} 0.08 mas combined with the short timescale of t{sub E} {approx} 2.7 days suggests the possibility that the lens is a free-floating planet. For MOA-2009-BLG-174, we measure the lens parallax and thus uniquely determine the physical parameters of the lens. We also find that the measured lens mass of {approx}0.84 M{sub Sun} is consistent with that of a star blended with the source, suggesting that the blend is likely to be the lens. Although we did not find planetary signals for any of the events, we provide exclusion diagrams showing the confidence levels excluding the existence of a planet as a function of the separation and mass ratio.
Accurate weak lensing of standard candles. II. Measuring σ8 with supernovae
NASA Astrophysics Data System (ADS)
Quartin, Miguel; Marra, Valerio; Amendola, Luca
2014-01-01
Soon the number of type Ia supernova (SN) measurements should exceed 100 000. Understanding the effect of weak lensing by matter structures on the supernova brightness will then be more important than ever. Although SN lensing is usually seen as a source of systematic noise, we will show that it can be in fact turned into signal. More precisely, the non-Gaussianity introduced by lensing in the SN Hubble diagram dispersion depends rather sensitively on the amplitude σ8 of the matter power spectrum. By exploiting this relation, we are able to predict constraints on σ8 of 7% (3%) for a catalog of 100 000 (500 000) SNe of average magnitude error 0.12, without having to assume that such intrinsic dispersion and its redshift evolution are known a priori. The intrinsic dispersion has been assumed to be Gaussian; possible intrinsic non-Gaussianities in the data set (due to the SN themselves and/or to other transients) could be potentially dealt with by means of additional nuisance parameters describing higher moments of the intrinsic dispersion distribution function. This method is independent of and complementary to the standard methods based on cosmic microwave background, cosmic shear, or cluster abundance observables.
Gravitational, lensing, and stability properties of Bose-Einstein condensate dark matter halos
NASA Astrophysics Data System (ADS)
Harko, Tiberiu; Lobo, Francisco S. N.
2015-08-01
The possibility that dark matter, whose existence is inferred from the study of galactic rotation curves, and from the mass deficit in galaxy clusters, can be in the form of a Bose-Einstein condensate has been extensively investigated lately. In the present work, we consider a detailed analysis of the astrophysical properties of the Bose-Einstein condensate dark matter halos that could provide clear observational signatures that help discriminate between different dark matter models. In the Bose-Einstein condensation model, dark matter can be described as a nonrelativistic, gravitationally confined Newtonian gas, whose density and pressure are related by a polytropic equation of state with index n =1 . The mass and gravitational properties of the condensate halos are obtained in a systematic form, including the mean logarithmic slopes of the density and of the tangential velocity. The lensing properties of the condensate dark matter are investigated in detail. In particular, a general analytical formula for the surface density, an important quantity that defines the lensing properties of a dark matter halos, is obtained in the form of series expansions. This enables arbitrary-precision calculations of the surface mass density, deflection angle, deflection potential, and of the magnification factor, thus giving the possibility of the comparison of the predicted lensing properties of the condensate dark matter halos with observations. The stability properties of the condensate halos are also investigated by using the scalar and the tensor virial theorems, respectively, and the virial perturbation equation for condensate dark matter halos is derived. As an application of the scalar virial theorem, we consider the problem of the stability of a slowly rotating and slightly disturbed galactic dark matter halo. For such a halo, the oscillation frequencies and the stability conditions are obtained in the linear approximation.
NASA Astrophysics Data System (ADS)
Mandelbaum, Rachel; Hirata, Christopher M.; Ishak, Mustapha; Seljak, Uro; Brinkmann, Jonathan
2006-04-01
The power spectrum of weak lensing shear caused by large-scale structure is an emerging tool for precision cosmology, in particular for measuring the effects of dark energy on the growth of structure at low redshift. One potential source of systematic error is intrinsic alignments of ellipticities of neighbouring galaxies [the intrinsic ellipticity-intrinsic ellipticity (II) correlation] that could mimic the correlations due to lensing. A related possibility pointed out by Hirata & Seljak is correlation between the intrinsic ellipticities of galaxies and the density field responsible for gravitational lensing shear [the gravitational shear-intrinsic ellipticity (GI) correlation]. We present constraints on both the II and GI correlations using 265908 spectroscopic galaxies from the Sloan Digital Sky Survey (SDSS) and using galaxies as tracers of the mass in the case of the GI analysis. The availability of redshifts in the SDSS allows us to select galaxies at small radial separations, which both reduces noise in the intrinsic alignment measurement and suppresses galaxy-galaxy lensing (which otherwise swamps the GI correlation). While we find no detection of the II correlation, our results are none the less statistically consistent with recent detections found using the SuperCOSMOS survey. Extrapolation of these limits to cosmic shear surveys at z~ 1 suggests that the II correlation is unlikely to have been a significant source of error for current measurements of ?8 with ~10 per cent accuracy, but may still be an issue for future surveys with projected statistical errors below the 1 per cent level unless eliminated using photometric redshifts. In contrast, we have a clear detection of GI correlation in galaxies brighter than L* that persists to the largest scales probed (60h-1 Mpc) and with a sign predicted by theoretical models. This correlation could cause the existing lensing surveys at z~ 1 to underestimate the linear amplitude of fluctuations by as much as 20 per cent depending on the source sample used, while for surveys at z~ 0.5 the underestimation may reach 30 per cent. The GI contamination is dominated by the brightest galaxies, possibly due to the alignment of brightest cluster galaxies (BCGs) with the cluster ellipticity due to anisotropic infall along filaments, although other sources of contamination cannot be excluded at this point. We propose that cosmic shear surveys should consider rejection of BCGs from their source catalogues as a test for GI contamination. Future high-precision weak lensing surveys must develop methods to search for and remove this contamination if they are to achieve their promise.
Weak Lensing Calibrated M-T Scaling Relation of Galaxy Groups in the COSMOS Fieldsstarf
NASA Astrophysics Data System (ADS)
Kettula, K.; Finoguenov, A.; Massey, R.; Rhodes, J.; Hoekstra, H.; Taylor, J. E.; Spinelli, P. F.; Tanaka, M.; Ilbert, O.; Capak, P.; McCracken, H. J.; Koekemoer, A.
2013-11-01
The scaling between X-ray observables and mass for galaxy clusters and groups is instrumental for cluster-based cosmology and an important probe for the thermodynamics of the intracluster gas. We calibrate a scaling relation between the weak lensing mass and X-ray spectroscopic temperature for 10 galaxy groups in the COSMOS field, combined with 55 higher-mass clusters from the literature. The COSMOS data includes Hubble Space Telescope imaging and redshift measurements of 46 source galaxies per arcminute2, enabling us to perform unique weak lensing measurements of low-mass systems. Our sample extends the mass range of the lensing calibrated M-T relation an order of magnitude lower than any previous study, resulting in a power-law slope of 1.48^{+0.13}_{-0.09}. The slope is consistent with the self-similar model, predictions from simulations, and observations of clusters. However, X-ray observations relying on mass measurements derived under the assumption of hydrostatic equilibrium have indicated that masses at group scales are lower than expected. Both simulations and observations suggest that hydrostatic mass measurements can be biased low. Our external weak lensing masses provide the first observational support for hydrostatic mass bias at group level, showing an increasing bias with decreasing temperature and reaching a level of 30%-50% at 1 keV. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA Inc., under NASA contract NAS 5-26555. Also based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan; the XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA; the European Southern Observatory under Large Program 175.A-0839, Chile; Kitt Peak National Observatory, Cerro Tololo Inter-American Observatory, and the National Optical Astronomy Observatory, which are operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation; the National Radio Astronomy Observatory, which is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.; and the Canada-France-Hawaii Telescope (CFHT) with MegaPrime/MegaCam operated as a joint project by the CFHT Corporation, CEA/DAPNIA, the National Research Council of Canada, the Canadian Astronomy Data Centre, the Centre National de la Recherche Scientifique de France, TERAPIX, and the University of Hawaii.
Cosmic discordance: are Planck CMB and CFHTLenS weak lensing measurements out of tune?
NASA Astrophysics Data System (ADS)
MacCrann, Niall; Zuntz, Joe; Bridle, Sarah; Jain, Bhuvnesh; Becker, Matthew R.
2015-08-01
We examine the level of agreement between low-redshift weak lensing data and the cosmic microwave background using measurements from the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) and Planck+Wilkinson Microwave Anisotropy Probe (WMAP) polarization. We perform an independent analysis of the CFHTLenS six bin tomography results of Heymans et al. We extend their systematics treatment and find the cosmological constraints to be relatively robust to the choice of non-linear modelling, extension to the intrinsic alignment model and inclusion of baryons. We find that when marginalized in the Ωm-σ8 plane, the 95 per cent confidence contours of CFHTLenS and Planck+WMAP only just touch, but the discrepancy is less significant in the full six-dimensional parameter space of Λ cold dark matter (ΛCDM). Allowing a massive active neutrino or tensor modes does not significantly resolve the tension in the full n-dimensional parameter space. Our results differ from some in the literature because we use the full tomographic information in the weak lensing data and marginalize over systematics. We note that adding a sterile neutrino to ΛCDM brings the 2D marginalized contours into greater overlap, mainly due to the extra effective number of neutrino species, which we find to be 0.88 ± 0.43 (68 per cent) greater than standard on combining the data sets. We discuss why this is not a completely satisfactory resolution, leaving open the possibility of other new physics or observational systematics as contributing factors. We provide updated cosmology fitting functions for the CFHTLenS constraints and discuss the differences from ones used in the literature.
Impact of magnification and size bias on the weak lensing power spectrum and peak statistics
NASA Astrophysics Data System (ADS)
Liu, Jia; Haiman, Zoltán; Hui, Lam; Kratochvil, Jan M.; May, Morgan
2014-01-01
The weak lensing power spectrum is a powerful tool to probe cosmological parameters. Additionally, lensing peak counts contain cosmological information beyond the power spectrum. Both of these statistics can be affected by the preferential selection of source galaxies in patches of the sky with high magnification, as well as by the dilution in the source galaxy surface density in such regions. If not accounted for, these biases introduce systematic errors for cosmological measurements. Here we quantify these systematic errors, using convergence maps from a suite of ray-tracing N-body simulations. At the cutoff magnitude m of ongoing and planned major weak lensing surveys, the logarithmic slope of the cumulative number counts s ≡d log n(>m)/d log m is in the range 0.1≲s≲0.5. At s≈0.2, expected in the I band for Large Synoptic Survey Telescope, the inferred values of Ωm, w, and σ8 are biased by many σ (where σ denotes the marginalized error), and therefore the biases will need to be carefully modeled. We also find that the parameters are biased differently in the (Ωm, w , σ8) parameter space when the power spectrum and the peak counts are used. In particular, w derived from the power spectrum is less affected than w derived from peak counts, while the opposite is true for the best-constrained combination of σ8Ωmγ (with γ =0.62 from the power spectrum and γ=0.48 from peak counts). This suggests that the combination of the power spectrum and peak counts can help mitigate the impact of magnification and size biases.
Selecting background galaxies in weak-lensing analysis of galaxy clusters *
NASA Astrophysics Data System (ADS)
Formicola, I.; Radovich, M.; Meneghetti, M.; Mazzotta, P.; Grado, A.; Giocoli, C.
2016-03-01
In this paper we present a new method to select the faint, background galaxies used to derive the mass of galaxy clusters by weak lensing. The method is based on the simultaneous analysis of the shear signal, that should be consistent with zero for the foreground, unlensed galaxies, and of the colors of the galaxies: photometric data from the COSMic evOlution Survey (COSMOS) are used to train the color selection. In order to validate this methodology we test it against a set of state-of-the-art image simulations of mock galaxy clusters in different redshift [0.23 - 0.45] and mass [0.5 - 1.55 × 1015M⊙] ranges, mimicking medium-deep multicolor imaging observations (e.g. SUBARU, LBT). The performance of our method in terms of contamination by unlensed sources is comparable to a selection based on photometric redshifts, which however requires a good spectral coverage and is thus much more observationally demanding. The application of our method to simulations gives an average ratio between estimated and true masses of ˜0.98 ± 0.09. As a further test, we finally apply our method to real data, and compare our results with other weak lensing mass estimates in the literature: for this purpose we choose the cluster Abell 2219 (z = 0.228), for which multi-band (BVRi) data are publicly available.
Weak lensing effects in the measurement of the dark energy equation of state with LISA
Van Den Broeck, Chris; Trias, M.; Sintes, A. M.; Sathyaprakash, B. S.
2010-06-15
The Laser Interferometer Space Antenna's (LISA's) observation of supermassive binary black holes (SMBBH) could provide a new tool for precision cosmography. Inclusion of subdominant signal harmonics in the inspiral signal allows for high-accuracy sky localization, dramatically improving the chances of finding the host galaxy and obtaining its redshift. A SMBBH merger can potentially have component masses from a wide range (10{sup 5}-10{sup 8}M{sub {center_dot}}) over which parameter accuracies vary considerably. We perform an in-depth study in order to understand (i) what fraction of possible SMBBH mergers allow for sky localization, depending on the parameters of the source, and (ii) how accurately w can be measured when the host galaxy can be identified. We also investigate how accuracies on all parameters improve when a knowledge of the sky position can be folded into the estimation of errors. We find that w can be measured to within a few percent in most cases, if the only error in measuring the luminosity distance is due to LISA's instrumental noise and the confusion background from Galactic binaries. However, weak lensing-induced errors will severely degrade the accuracy with which w can be obtained, emphasizing that methods to mitigate weak lensing effects would be required to take advantage of LISA's full potential.
Okura, Yuki; Futamase, Toshifumi E-mail: tof@astr.tohoku.ac.jp
2013-07-01
This is the third paper on the improvement of systematic errors in weak lensing analysis using an elliptical weight function, referred to as E-HOLICs. In previous papers, we succeeded in avoiding errors that depend on the ellipticity of the background image. In this paper, we investigate the systematic error that depends on the signal-to-noise ratio of the background image. We find that the origin of this error is the random count noise that comes from the Poisson noise of sky counts. The random count noise makes additional moments and centroid shift error, and those first-order effects are canceled in averaging, but the second-order effects are not canceled. We derive the formulae that correct this systematic error due to the random count noise in measuring the moments and ellipticity of the background image. The correction formulae obtained are expressed as combinations of complex moments of the image, and thus can correct the systematic errors caused by each object. We test their validity using a simulated image and find that the systematic error becomes less than 1% in the measured ellipticity for objects with an IMCAT significance threshold of {nu} {approx} 11.7.
NASA Astrophysics Data System (ADS)
Bandara, H. M. Kaushala T.
2012-06-01
This dissertation presents a detailed analysis of the galaxy-scale strong gravitational lenses discovered by the Sloan Lens ACS (SLACS) survey, with the aim of providing new insight into the processes that affect the evolution of galaxies at intermediate and high redshift. First, we present evidence for a relationship between the supermassive black hole mass and the total gravitational mass of the host galaxy, by utilizing the fact that gravitational lensing allows us to accurately measure the inner mass density profile of early-type lens galaxies and their total masses within an aperture. These results confirm that the properties of the bulge component of early-type galaxies and the resulting supermassive black hole are fundamentally regulated by the properties of the dark matter halo. We then utilize the lensing magnification for a detailed study of the photometric properties (luminosity, size and shape) of SLACS background sources and determine the evolution of the disk galaxy luminosity-size relation since z 1. A comparison of the observed SLACS luminosity-size relation to theoretical simulations provides strong evidence for mass-dependent evolution of disk galaxies since z 1. Furthermore, a comparison of the SLACS luminosity-size relation to that of a non-lensing, broad-band imaging survey shows that one can probe a galaxy population that is 2 magnitudes deeper by utilizing the lensing magnification. We continue the detailed study of SLACS background sources by combining the lensing magnification with diffraction-limited integral field spectroscopy to derive two-dimensional kinematic, star formation rate and metallicity distributions of gravitationally lensed galaxies at z > 0.78. Integral field spectroscopic observations of the Halpha emission line properties of a SLACS source galaxy (SDSS J0252+0039), at z = 0.98, show that the lensing magnification and adaptive optics advantages can be effectively combined to derive spatially resolved kinematics and star formation rates of compact, sub-luminous galaxies. Finally, we summarize the results of this dissertation and discuss how the powerful advantages of strong gravitational lensing can be utilized to address various questions about galaxy evolution through upcoming surveys and new telescope facilities.
NASA Astrophysics Data System (ADS)
Ishak, Mustapha B.; Mandelbaum, R.; Hirata, C.; Seljak, U.; Brinkmann, J.
2006-06-01
The power spectrum of weak lensing shear caused by large-scale structure is an emerging tool for precision cosmology. Potential sources of systematic errors are i) intrinsic alignments of ellipticities (II correlation) and ii) correlation between the intrinsic ellipticities of galaxies and the density field responsible for gravitational lensing shear (GI correlation). We present constraints on both the II and GI correlations using 265 908 spectroscopic galaxies from the Sloan Digital Sky Survey (SDSS). We have a clear detection of GI correlation in galaxies brighter than L* that persists to the largest scales probed (60/h Mpc) and with a sign predicted by theoretical models. While we find no detection of the II correlation, our results are nonetheless statistically consistent with recent detections found using the SuperCOSMOS survey. The GI correlation could cause the existing lensing surveys at z 1 to underestimate the linear amplitude of fluctuations by as much as 20% depending on the source sample used, while for surveys at z 0.5 the underestimation may reach 30%. The GI contamination is dominated by the brightest galaxies, possibly due to the alignment of brightest cluster galaxies (BCGs) with the cluster ellipticity due to anisotropic infall along filaments, although other sources of contamination cannot be excluded at this point. We propose that cosmic shear surveys should consider rejection of BCGs from their source catalogs as a test for GI contamination. Future high precision weak lensing surveys must develop methods to search for and remove this contamination if they are to achieve their promise.
Gravitational lensing effects in a time-variable cosmological 'constant' cosmology
NASA Technical Reports Server (NTRS)
Ratra, Bharat; Quillen, Alice
1992-01-01
A scalar field phi with a potential V(phi) varies as phi exp -alpha(alpha is greater than 0) has an energy density, behaving like that of a time-variable cosmological 'constant', that redshifts less rapidly than the energy densities of radiation and matter, and so might contribute significantly to the present energy density. We compute, in this spatially flat cosmology, the gravitational lensing optical depth, and the expected lens redshift distribution for fixed source redshift. We find, for the values of alpha of about 4 and baryonic density parameter Omega of about 0.2 consistent with the classical cosmological tests, that the optical depth is significantly smaller than that in a constant-Lambda model with the same Omega. We also find that the redshift of the maximum of the lens distribution falls between that in the constant-Lambda model and that in the Einstein-de Sitter model.
Prediction of emission line fluxes of gravitationally lensed very high-z galaxies
NASA Astrophysics Data System (ADS)
Inoue, Akio; Shimizu, Ikkoh; Okamoto, Takashi; Yoshida, Naoki; Matsuo, Hiroshi; Tamura, Yoichi
2015-08-01
Spectroscopic confirmation of very high-z galaxy candidates is extremely valuable because this is a direct proof of the existence of galaxies in the early Universe and put a strong constraint on the structure formation theory to produce such galaxies during the limited age of the Universe. Before the completion of the cosmic reionization, hydrogen Ly-alpha emission line is hard to be observed and we need other emission lines to confirm the redshift of galaxies. By using a state-of-the-art cosmological hydrodynamics simulation of galaxy formation and evolution with an emission line model based on Cloudy, we predict the line fluxes of some gravitationally-lensed very high-z galaxy candidates. We also discuss their detectability with the current and future telescopes.
NASA Astrophysics Data System (ADS)
Cañameras, R.; Nesvadba, N. P. H.; Guery, D.; McKenzie, T.; König, S.; Petitpas, G.; Dole, H.; Frye, B.; Flores-Cacho, I.; Montier, L.; Negrello, M.; Beelen, A.; Boone, F.; Dicken, D.; Lagache, G.; Le Floc'h, E.; Altieri, B.; Béthermin, M.; Chary, R.; de Zotti, G.; Giard, M.; Kneissl, R.; Krips, M.; Malhotra, S.; Martinache, C.; Omont, A.; Pointecouteau, E.; Puget, J.-L.; Scott, D.; Soucail, G.; Valtchanov, I.; Welikala, N.; Yan, L.
2015-09-01
We present an analysis of CO spectroscopy and infrared-to-millimetre dust photometry of 11 exceptionally bright far-infrared (FIR) and sub-mm sources discovered through a combination of the Planck all-sky survey and follow-up Herschel-SPIRE imaging - "Planck's Dusty Gravitationally Enhanced subMillimetre Sources". Each source has a secure spectroscopic redshift z = 2.2-3.6 from multiple lines obtained through a blind redshift search with EMIR at the IRAM 30-m telescope. Interferometry was obtained at IRAM and the SMA, and along with optical/near-infrared imaging obtained at the CFHT and the VLT reveal morphologies consistent with strongly gravitationally lensed sources, including several giant arcs. Additional photometry was obtained with JCMT/SCUBA-2 and IRAM/GISMO at 850 μm and 2 mm, respectively. The SEDs of our sources peak near either the 350 μm or 500 μm bands of SPIRE with peak flux densities between 0.35 and 1.14 Jy. All objects are extremely bright isolated point sources in the 18'' beam of SPIREat 250 μm, with apparent FIR luminosities of up to 3 × 1014 L⊙ (not correcting for the lensing effect). Their morphologies, sizes, CO line widths, CO luminosities, dust temperatures, and FIR luminosities provide additional empirical evidence that these are amongst the brightest strongly gravitationally lensed high-redshift galaxies on the sub-mm sky. Our programme extends the successful wide-area searches for strongly gravitationally lensed high-redshift galaxies (carried out with the South Pole Telescope and Herschel) towards even brighter sources, which are so rare that their systematic identification requires a genuine all-sky survey like Planck. Six sources are above the ≃600 mJy 90% completeness limit of the Planck catalogue of compact sources (PCCS) at 545 and 857 GHz, which implies that these must literally be amongst the brightest high-redshift FIR and sub-mm sources on the extragalactic sky. We discuss their dust masses and temperatures, and use additional WISE 22-μm photometry and template fitting to rule out a significant contribution of AGN heating to the total infrared luminosity. Six sources are detected in FIRST at 1.4 GHz, and the others have sensitive upper limits. Four have flux densities brighter than expected from the local FIR-radio correlation, but in the range previously found for high-z sub-mm galaxies, one has a deficit of FIR emission, and 6 are consistent with the local correlation, although this includes 3 galaxies with upper limits. We attribute this to the turbulent interstellar medium of these galaxies, rather than the presence of radio AGN. The global dust-to-gas ratios and star-formation efficiencies of our sources are predominantly in the range expected from massive, metal-rich, intense, high-redshift starbursts. An extensive multi-wavelength follow-up programme is being carried out to further characterize these sources and the intense star formation within them. Based on observations collected with the Herschel and Planck satellites, IRAM, SMA, JCMT, CFHT, and the VLT.
Mask effects on cosmological studies with weak-lensing peak statistics
Liu, Xiangkun; Pan, Chuzhong; Fan, Zuhui; Wang, Qiao
2014-03-20
With numerical simulations, we analyze in detail how the bad data removal, i.e., the mask effect, can influence the peak statistics of the weak-lensing convergence field reconstructed from the shear measurement of background galaxies. It is found that high peak fractions are systematically enhanced because of the presence of masks; the larger the masked area is, the higher the enhancement is. In the case where the total masked area is about 13% of the survey area, the fraction of peaks with signal-to-noise ratio ν ≥ 3 is ∼11% of the total number of peaks, compared with ∼7% of the mask-free case in our considered cosmological model. This can have significant effects on cosmological studies with weak-lensing convergence peak statistics, inducing a large bias in the parameter constraints if the effects are not taken into account properly. Even for a survey area of 9 deg{sup 2}, the bias in (Ω {sub m}, σ{sub 8}) is already intolerably large and close to 3σ. It is noted that most of the affected peaks are close to the masked regions. Therefore, excluding peaks in those regions in the peak statistics can reduce the bias effect but at the expense of losing usable survey areas. Further investigations find that the enhancement of the number of high peaks around the masked regions can be largely attributed to the smaller number of galaxies usable in the weak-lensing convergence reconstruction, leading to higher noise than that of the areas away from the masks. We thus develop a model in which we exclude only those very large masks with radius larger than 3' but keep all the other masked regions in peak counting statistics. For the remaining part, we treat the areas close to and away from the masked regions separately with different noise levels. It is shown that this two-noise-level model can account for the mask effect on peak statistics very well, and the bias in cosmological parameters is significantly reduced if this model is applied in the parameter fitting.
Mask Effects on Cosmological Studies with Weak-lensing Peak Statistics
NASA Astrophysics Data System (ADS)
Liu, Xiangkun; Wang, Qiao; Pan, Chuzhong; Fan, Zuhui
2014-03-01
With numerical simulations, we analyze in detail how the bad data removal, i.e., the mask effect, can influence the peak statistics of the weak-lensing convergence field reconstructed from the shear measurement of background galaxies. It is found that high peak fractions are systematically enhanced because of the presence of masks; the larger the masked area is, the higher the enhancement is. In the case where the total masked area is about 13% of the survey area, the fraction of peaks with signal-to-noise ratio ν >= 3 is ~11% of the total number of peaks, compared with ~7% of the mask-free case in our considered cosmological model. This can have significant effects on cosmological studies with weak-lensing convergence peak statistics, inducing a large bias in the parameter constraints if the effects are not taken into account properly. Even for a survey area of 9 deg2, the bias in (Ω m , σ8) is already intolerably large and close to 3σ. It is noted that most of the affected peaks are close to the masked regions. Therefore, excluding peaks in those regions in the peak statistics can reduce the bias effect but at the expense of losing usable survey areas. Further investigations find that the enhancement of the number of high peaks around the masked regions can be largely attributed to the smaller number of galaxies usable in the weak-lensing convergence reconstruction, leading to higher noise than that of the areas away from the masks. We thus develop a model in which we exclude only those very large masks with radius larger than 3' but keep all the other masked regions in peak counting statistics. For the remaining part, we treat the areas close to and away from the masked regions separately with different noise levels. It is shown that this two-noise-level model can account for the mask effect on peak statistics very well, and the bias in cosmological parameters is significantly reduced if this model is applied in the parameter fitting.
Mediavilla, E.; Lopez, P.; Gonzalez-Morcillo, C.; Jimenez-Vicente, J.
2011-11-01
We derive an exact solution (in the form of a series expansion) to compute gravitational lensing magnification maps. It is based on the backward gravitational lens mapping of a partition of the image plane in polygonal cells (inverse polygon mapping, IPM), not including critical points (except perhaps at the cell boundaries). The zeroth-order term of the series expansion leads to the method described by Mediavilla et al. The first-order term is used to study the error induced by the truncation of the series at zeroth order, explaining the high accuracy of the IPM even at this low order of approximation. Interpreting the Inverse Ray Shooting (IRS) method in terms of IPM, we explain the previously reported N {sup -3/4} dependence of the IRS error with the number of collected rays per pixel. Cells intersected by critical curves (critical cells) transform to non-simply connected regions with topological pathologies like auto-overlapping or non-preservation of the boundary under the transformation. To define a non-critical partition, we use a linear approximation of the critical curve to divide each critical cell into two non-critical subcells. The optimal choice of the cell size depends basically on the curvature of the critical curves. For typical applications in which the pixel of the magnification map is a small fraction of the Einstein radius, a one-to-one relationship between the cell and pixel sizes in the absence of lensing guarantees both the consistence of the method and a very high accuracy. This prescription is simple but very conservative. We show that substantially larger cells can be used to obtain magnification maps with huge savings in computation time.
Berge, Joel; Refregier, Alexandre
2010-04-01
We compare the efficiency of weak-lensing-selected galaxy cluster counts and of the weak-lensing bispectrum at capturing non-Gaussian features in the dark matter distribution. We use the halo model to compute the weak-lensing power spectrum, the bispectrum, and the expected number of detected clusters, and derive constraints on cosmological parameters for a large, low systematic weak-lensing survey, by focusing on the OMEGA{sub m}-sigma{sub 8} plane and on the dark energy equation of state. We separate the power spectrum into the resolved and the unresolved parts of the data, the resolved part being defined as detected clusters, and the unresolved part as the rest of the field. We consider four kinds of clusters counts, taking into account different amount of information: signal-to-noise ratio peak counts, counts as a function of clusters' mass, counts as a function of clusters' redshift, and counts as a function of clusters' mass and redshift. We show that when combined with the power spectrum, those four kinds of counts provide similar constraints, thus allowing one to perform the most direct counts, signal-to-noise peak counts, and get percent level constraints on cosmological parameters. We show that the weak-lensing bispectrum gives constraints comparable to those given by the power spectrum and captures non-Gaussian features as well as cluster counts, its combination with the power spectrum giving errors on cosmological parameters that are similar to, if not marginally smaller than, those obtained when combining the power spectrum with cluster counts. We finally note that in order to reach its potential, the weak-lensing bispectrum must be computed using all triangle configurations, as equilateral triangles alone do not provide useful information. The appendices summarize the halo model, and the way the power spectrum and bispectrum are computed in this framework.
Self-calibration of photometric redshift scatter in weak-lensing surveys
Zhang, Pengjie; Pen, Ue -Li; Bernstein, Gary
2010-06-11
Photo-z errors, especially catastrophic errors, are a major uncertainty for precision weak lensing cosmology. We find that the shear-(galaxy number) density and density-density cross correlation measurements between photo-z bins, available from the same lensing surveys, contain valuable information for self-calibration of the scattering probabilities between the true-z and photo-z bins. The self-calibration technique we propose does not rely on cosmological priors nor parameterization of the photo-z probability distribution function, and preserves all of the cosmological information available from shear-shear measurement. We estimate the calibration accuracy through the Fisher matrix formalism. We find that, for advanced lensing surveys such as the planned stage IV surveys, the rate of photo-z outliers can be determined with statistical uncertainties of 0.01-1% for z < 2 galaxies. Among the several sources of calibration error that we identify and investigate, the galaxy distribution bias is likely the most dominant systematic error, whereby photo-z outliers have different redshift distributions and/or bias than non-outliers from the same bin. This bias affects all photo-z calibration techniques based on correlation measurements. As a result, galaxy bias variations of O(0.1) produce biases in photo-z outlier rates similar to the statistical errors of our method, so this galaxy distribution bias may bias the reconstructed scatters at several-σ level, but is unlikely to completely invalidate the self-calibration technique.
Self-calibration of photometric redshift scatter in weak-lensing surveys
Zhang, Pengjie; Pen, Ue -Li; Bernstein, Gary
2010-06-11
Photo-z errors, especially catastrophic errors, are a major uncertainty for precision weak lensing cosmology. We find that the shear-(galaxy number) density and density-density cross correlation measurements between photo-z bins, available from the same lensing surveys, contain valuable information for self-calibration of the scattering probabilities between the true-z and photo-z bins. The self-calibration technique we propose does not rely on cosmological priors nor parameterization of the photo-z probability distribution function, and preserves all of the cosmological information available from shear-shear measurement. We estimate the calibration accuracy through the Fisher matrix formalism. We find that, for advanced lensing surveys such as themore » planned stage IV surveys, the rate of photo-z outliers can be determined with statistical uncertainties of 0.01-1% for z < 2 galaxies. Among the several sources of calibration error that we identify and investigate, the galaxy distribution bias is likely the most dominant systematic error, whereby photo-z outliers have different redshift distributions and/or bias than non-outliers from the same bin. This bias affects all photo-z calibration techniques based on correlation measurements. As a result, galaxy bias variations of O(0.1) produce biases in photo-z outlier rates similar to the statistical errors of our method, so this galaxy distribution bias may bias the reconstructed scatters at several-σ level, but is unlikely to completely invalidate the self-calibration technique.« less
Impact of spurious shear on cosmological parameter estimates from weak lensing observables
Petri, Andrea; May, Morgan; Haiman, Zoltán; Kratochvil, Jan M.
2014-12-30
We research, residual errors in shear measurements, after corrections for instrument systematics and atmospheric effects, can impact cosmological parameters derived from weak lensing observations. Here we combine convergence maps from our suite of ray-tracing simulations with random realizations of spurious shear. This allows us to quantify the errors and biases of the triplet (Ωm,w,σ8) derived from the power spectrum (PS), as well as from three different sets of non-Gaussian statistics of the lensing convergence field: Minkowski functionals (MFs), low-order moments (LMs), and peak counts (PKs). Our main results are as follows: (i) We find an order of magnitude smaller biasesmore » from the PS than in previous work. (ii) The PS and LM yield biases much smaller than the morphological statistics (MF, PK). (iii) For strictly Gaussian spurious shear with integrated amplitude as low as its current estimate of σsys2 ≈ 10-7, biases from the PS and LM would be unimportant even for a survey with the statistical power of Large Synoptic Survey Telescope. However, we find that for surveys larger than ≈ 100 deg2, non-Gaussianity in the noise (not included in our analysis) will likely be important and must be quantified to assess the biases. (iv) The morphological statistics (MF, PK) introduce important biases even for Gaussian noise, which must be corrected in large surveys. The biases are in different directions in (Ωm,w,σ8) parameter space, allowing self-calibration by combining multiple statistics. Our results warrant follow-up studies with more extensive lensing simulations and more accurate spurious shear estimates.« less
Impact of spurious shear on cosmological parameter estimates from weak lensing observables
Petri, Andrea; May, Morgan; Haiman, Zoltán; Kratochvil, Jan M.
2014-12-30
We research, residual errors in shear measurements, after corrections for instrument systematics and atmospheric effects, can impact cosmological parameters derived from weak lensing observations. Here we combine convergence maps from our suite of ray-tracing simulations with random realizations of spurious shear. This allows us to quantify the errors and biases of the triplet (Ω_{m},w,σ_{8}) derived from the power spectrum (PS), as well as from three different sets of non-Gaussian statistics of the lensing convergence field: Minkowski functionals (MFs), low-order moments (LMs), and peak counts (PKs). Our main results are as follows: (i) We find an order of magnitude smaller biases from the PS than in previous work. (ii) The PS and LM yield biases much smaller than the morphological statistics (MF, PK). (iii) For strictly Gaussian spurious shear with integrated amplitude as low as its current estimate of σ_{sys}^{2} ≈ 10^{-7}, biases from the PS and LM would be unimportant even for a survey with the statistical power of Large Synoptic Survey Telescope. However, we find that for surveys larger than ≈ 100 deg^{2}, non-Gaussianity in the noise (not included in our analysis) will likely be important and must be quantified to assess the biases. (iv) The morphological statistics (MF, PK) introduce important biases even for Gaussian noise, which must be corrected in large surveys. The biases are in different directions in (Ωm,w,σ8) parameter space, allowing self-calibration by combining multiple statistics. Our results warrant follow-up studies with more extensive lensing simulations and more accurate spurious shear estimates.
Impact of spurious shear on cosmological parameter estimates from weak lensing observables
Petri, Andrea; May, Morgan; Haiman, Zoltn; Kratochvil, Jan M.
2014-12-30
We research, residual errors in shear measurements, after corrections for instrument systematics and atmospheric effects, can impact cosmological parameters derived from weak lensing observations. Here we combine convergence maps from our suite of ray-tracing simulations with random realizations of spurious shear. This allows us to quantify the errors and biases of the triplet (?_{m},w,?_{8}) derived from the power spectrum (PS), as well as from three different sets of non-Gaussian statistics of the lensing convergence field: Minkowski functionals (MFs), low-order moments (LMs), and peak counts (PKs). Our main results are as follows: (i) We find an order of magnitude smaller biases from the PS than in previous work. (ii) The PS and LM yield biases much smaller than the morphological statistics (MF, PK). (iii) For strictly Gaussian spurious shear with integrated amplitude as low as its current estimate of ?_{sys}^{2} ? 10^{-7}, biases from the PS and LM would be unimportant even for a survey with the statistical power of Large Synoptic Survey Telescope. However, we find that for surveys larger than ? 100 deg^{2}, non-Gaussianity in the noise (not included in our analysis) will likely be important and must be quantified to assess the biases. (iv) The morphological statistics (MF, PK) introduce important biases even for Gaussian noise, which must be corrected in large surveys. The biases are in different directions in (?m,w,?8) parameter space, allowing self-calibration by combining multiple statistics. Our results warrant follow-up studies with more extensive lensing simulations and more accurate spurious shear estimates.
A Sneak Peek at the JWST Era: Observing Galaxies Below the Hubble Limit with Gravitational Lensing
NASA Astrophysics Data System (ADS)
Livermore, Rachael C.
2016-01-01
The installation of WFC3 on the Hubble Space Telescope pushed the frontier of high-redshift galaxy studies to only 500 Myr after the Big Bang. However, observations in this epoch remain challenging and are limited to the brightest galaxies; the fainter sources believed to be responsible for reionizing the Universe remain beyond the grasp of Hubble. With gravitational lensing, however, we can benefit from the magnification of faint sources, which brings them within reach of today's telescopes. The Hubble Frontier Fields program is a deep survey of strongly lensing clusters observed in the optical and near-infrared. Unfortunately, detecting highly magnified, intrinsically faint galaxies in these fields has proved challenging due to the bright foregound cluster galaxies and intracluster light. We have developed a technique using wavelet decomposition to overcome these difficulties and detect galaxies at z~7 with intrinsic UV magnitudes as faint as MUV = -13. We present this method and the resulting luminosity functions, which support a steep faint-end slope extending out to the observational limits. Our method has uncovered hundreds of galaxies at z > 6 fainter than any that have been seen before, providing our first insight into the small galaxy population during the epoch of reionization and a preview of the capabilities of JWST.
Strong Gravitational Lensing as a Tool to Investigate the Structure of Jets at High Energies
NASA Astrophysics Data System (ADS)
Barnacka, Anna; Geller, Margaret J.; Dell'Antonio, Ian P.; Benbow, Wystan
2014-06-01
The components of blazar jets that emit radiation span a factor of 1010 in scale. The spatial structure of these emitting regions depends on the observed energy. Photons emitted at different sites cross the lens plane at different distances from the mass-weighted center of the lens. Thus there are differences in magnification ratios and time delays between the images of lensed blazars observed at different energies. When the lens structure and redshift are known from optical observations, these constraints can elucidate the structure of the source at high energies. At these energies, current technology is inadequate to resolve these sources, and the observed light curve is thus the sum of the images. Durations of ?-ray flares are short compared with typical time delays; thus both the magnification ratio and the time delay can be measured for the delayed counterparts. These measurements are a basis for localizing the emitting region along the jet. To demonstrate the power of strong gravitational lensing, we build a toy model based on the best studied and the nearest relativistic jet M87.
Gravitational lensing and the Sunyaev-Zel'dovich effect in the millimetre/submillimetre waveband
NASA Astrophysics Data System (ADS)
Blain, A. W.
1998-06-01
The intensity of the cosmic microwave background radiation in the fields of clusters of galaxies is modified by inverse Compton scattering in the hot intracluster gas - the Sunyaev-Zel'dovich (SZ) effect. The effect is expected to be most pronounced at a frequency of about 350GHz (a wavelength of about 800mum), and has been detected in the centimetre and millimetre wavebands. In the millimetre/submillimetre waveband, the gravitationally lensed images of distant dusty star-forming galaxies in the background of the cluster are predicted to dominate the appearance of clusters on scales of several arcsec, and could confuse observations of the SZ effect at frequencies greater than about 200GHz (wavelengths shorter than about 1.5mm). Recent observations by Smail, Ivison & Blain confirm that a significant population of confusing sources is present in this waveband. Previous estimates of source confusion in observations of the millimetre/submillimetre-wave SZ effect did not include the effects of lensing by the cluster, and so the accuracy of such measurements could be lower than expected. Source subtraction may be required in order to measure the SZ effect accurately, and a careful analysis of the results of an ensemble of SZ measurements could be used to impose limits to the form of evolution of distant dusty star-forming galaxies.
MULTIPOLE GRAVITATIONAL LENSING AND HIGH-ORDER PERTURBATIONS ON THE QUADRUPOLE LENS
Chu, Z.; Lin, W. P.; Li, G. L.; Kang, X. E-mail: linwp@shao.ac.cn
2013-03-10
An arbitrary surface mass density of the gravitational lens can be decomposed into multipole components. We simulate the ray tracing for the multipolar mass distribution of the generalized Singular Isothermal Sphere model based on deflection angles, which are analytically calculated. The magnification patterns in the source plane are then derived from an inverse shooting technique. As has been found, the caustics of odd mode lenses are composed of two overlapping layers for some lens models. When a point source traverses this kind of overlapping caustics, the image numbers change by {+-}4, rather than {+-}2. There are two kinds of caustic images. One is the critical curve and the other is the transition locus. It is found that the image number of the fold is exactly the average value of image numbers on two sides of the fold, while the image number of the cusp is equal to the smaller one. We also focus on the magnification patterns of the quadrupole (m = 2) lenses under the perturbations of m = 3, 4, and 5 mode components and found that one, two, and three butterfly or swallowtail singularities can be produced, respectively. With the increasing intensity of the high-order perturbations, the singularities grow up to bring sixfold image regions. If these perturbations are large enough to let two or three of the butterflies or swallowtails make contact, then eightfold or tenfold image regions can be produced as well. The possible astronomical applications are discussed.
Strong gravitational lensing as a tool to investigate the structure of jets at high energies
Barnacka, Anna; Geller, Margaret J.; Benbow, Wystan; Dell'antonio, Ian P.
2014-06-20
The components of blazar jets that emit radiation span a factor of 10{sup 10} in scale. The spatial structure of these emitting regions depends on the observed energy. Photons emitted at different sites cross the lens plane at different distances from the mass-weighted center of the lens. Thus there are differences in magnification ratios and time delays between the images of lensed blazars observed at different energies. When the lens structure and redshift are known from optical observations, these constraints can elucidate the structure of the source at high energies. At these energies, current technology is inadequate to resolve these sources, and the observed light curve is thus the sum of the images. Durations of γ-ray flares are short compared with typical time delays; thus both the magnification ratio and the time delay can be measured for the delayed counterparts. These measurements are a basis for localizing the emitting region along the jet. To demonstrate the power of strong gravitational lensing, we build a toy model based on the best studied and the nearest relativistic jet M87.
Weak lensing mass map and peak statistics in Canada-France-Hawaii Telescope Stripe 82 survey
NASA Astrophysics Data System (ADS)
Shan, Huan Yuan; Kneib, Jean-Paul; Comparat, Johan; Jullo, Eric; Charbonnier, Alde; Erben, Thomas; Makler, Martin; Moraes, Bruno; Van Waerbeke, Ludovic; Courbin, Frdric; Meylan, Georges; Tao, Charling; Taylor, James E.
2014-08-01
We present a weak lensing mass map covering 124 deg2 of the Canada-France-Hawaii Telescope Stripe 82 Survey (CS82). We study the statistics of rare peaks in the map, including peak abundance, the peak-peak correlation functions and the tangential-shear profiles around peaks. We find that the abundance of peaks detected in CS82 is consistent with predictions from a ? cold dark matter cosmological model, once noise effects are properly included. The correlation functions of peaks with different signal-to-noise ratio (SNR) are well described by power laws, and there is a clear cross-correlation between the Sloan Digital Sky Survey III/Constant Mass galaxies and high SNR peaks. The tangential-shear profiles around peaks increase with peak SNR. We fit analytical models to the tangential-shear profiles, including a projected singular isothermal sphere (SIS) model and a projected Navarro, Frenk & White (NFW) model, plus a two-halo term. For the high SNR peaks, the SIS model is rejected at 3?. The NFW model plus a two-halo term gives more acceptable fits to the data. Some peaks match the positions of optically detected clusters, while others are relatively dark. Comparing dark and matched peaks, we find a difference in lensing signal of a factor of 2, suggesting that about half of the dark peaks are false detections.
Comparison of weak lensing by NFW and Einasto halos and systematic errors
NASA Astrophysics Data System (ADS)
Sereno, Mauro; Fedeli, Cosimo; Moscardini, Lauro
2016-01-01
Recent N-body simulations have shown that Einasto radial profiles provide the most accurate description of dark matter halos. Predictions based on the traditional NFW functional form may fail to describe the structural properties of cosmic objects at the percent level required by precision cosmology. We computed the systematic errors expected for weak lensing analyses of clusters of galaxies if one wrongly models the lens density profile. Even though the NFW fits of observed tangential shear profiles can be excellent, viral masses and concentrations of very massive halos (gtrsim 1015Msolar/h) can be over- and underestimated by 0~ 1 per cent, respectively. Misfitting effects also steepen the observed mass-concentration relation, as observed in multi-wavelength observations of galaxy groups and clusters. Based on shear analyses, Einasto and NFW halos can be set apart either with deep observations of exceptionally massive structures (gtrsim 21015Msolar/h) or by stacking the shear profiles of thousands of group-sized lenses (gtrsim 1014Msolar/h).
Weak-lensing detection of intracluster filaments with ground-based data
NASA Astrophysics Data System (ADS)
Maturi, Matteo; Merten, Julian
2013-11-01
According to the current standard model of cosmology, matter in the Universe arranges itself along a network of filamentary structure. These filaments connect the main nodes of this so-called "cosmic web", which are clusters of galaxies. Although its large-scale distribution is clearly characterized by numerical simulations, constraining the dark-matter content of the cosmic web in reality turns out to be difficult. The natural method of choice is gravitational lensing. However, the direct detection and mapping of the elusive filament signal is challenging and in this work we present two methods that are specifically tailored to achieve this task. A linear matched filter aims at detecting the smooth mass-component of filaments and is optimized to perform a shear decomposition that follows the anisotropic component of the lensing signal. Filaments clearly inherit this property due to their morphology. At the same time, the contamination arising from the central massive cluster is controlled in a natural way. The filament 1σ detection is of about κ ~ 0.01 - 0.005 according to the filter's template width and length, enabling the detection of structures beyond reach with other approaches. The second, complementary method seeks to detect the clumpy component of filaments. The detection is determined by the number density of subclump identifications in an area enclosing the potential filament, as was found within the observed field with the filter approach. We tested both methods against mocked observations based on realistic N-body simulations of filamentary structure and proved the feasibility of detecting filaments with ground-based data.
Real space estimator for the weak lensing convergence from the CMB
Carvalho, C. S.; Moodley, K.
2010-06-15
We propose an estimator defined in real space for the reconstruction of the weak lensing potential due to the intervening large-scale structure from high resolution maps of the cosmic microwave background. This estimator was motivated as an alternative to the quadratic estimator in harmonic space to surpass the difficulties of the analysis of maps containing galactic cuts and point source excisions. Using maps synthesized by pixel remapping, we implement the estimator for two experiments, namely, one in the absence and one in the presence of detector noise, and compare the reconstruction of the convergence field with that obtained with the quadratic estimator defined in harmonic space. We find good agreement between the input and the reconstructed power spectra using the proposed real space estimator. We discuss interesting features of the real space estimator and future extensions of this work.
Bonnett, C.
2015-07-21
We present photometric redshift estimates for galaxies used in the weak lensing analysis of the Dark Energy Survey Science Verification (DES SV) data. Four model- or machine learning-based photometric redshift methods { annz2, bpz calibrated against BCC-U fig simulations, skynet, and tpz { are analysed. For training, calibration, and testing of these methods, we also construct a catalogue of spectroscopically confirmed galaxies matched against DES SV data. The performance of the methods is evalu-ated against the matched spectroscopic catalogue, focusing on metrics relevant for weak lensing analyses, with additional validation against COSMOS photo-zs. From the galaxies in the DES SV shear catalogue, which have mean redshift 0.72 ±0.01 over the range 0:3 < z < 1:3, we construct three tomographic bins with means of z = {0.45; 0.67,1.00g}. These bins each have systematic uncertainties δ_{z} ≲ 0.05 in the mean of the fiducial skynet photo-z n(z). We propagate the errors in the redshift distributions through to their impact on cosmological parameters estimated with cosmic shear, and find that they cause shifts in the value of σ_{8} of approx. 3%. This shift is within the one sigma statistical errors on σ8 for the DES SV shear catalog. We also found that further study of the potential impact of systematic differences on the critical surface density, Σ_{crit}, contained levels of bias safely less than the statistical power of DES SV data. We recommend a final Gaussian prior for the photo-z bias in the mean of n(z) of width 0:05 for each of the three tomographic bins, and show that this is a sufficient bias model for the corresponding cosmology analysis.
NASA Astrophysics Data System (ADS)
Neronov, A.; Vovk, Ie.
2016-01-01
We show that observation of the time-dependent effect of microlensing of relativistically broadened emission lines (such as e.g. the Fe K ? line in x rays) in strongly lensed quasars could provide data on celestial mechanics of circular orbits in the direct vicinity of the horizon of supermassive black holes. This information can be extracted from the observation of evolution of the red/blue edge of the magnified line just before and just after the period of crossing of the innermost stable circular orbit by the microlensing caustic. The functional form of this evolution is insensitive to numerous astrophysical parameters of the accreting black hole and of the microlensing caustics network system (as opposed to the evolution of the full line spectrum). Measurement of the temporal evolution of the red/blue edge could provide a precision measurement of the radial dependence of the gravitational redshift and of velocity of the circular orbits, down to the innermost stable circular orbit. These measurements could be used to discriminate between general relativity and alternative models of the relativistic gravity in which the dynamics of photons and massive bodies orbiting the gravitating center is different from that of the geodesics in the Schwarzschild or Kerr space-times.
STRIDES: Galaxy Evolution over Cosmic Time from new samples of Gravitationally Lensed Quasars
NASA Astrophysics Data System (ADS)
Agnello, Adriano; Treu, Tommaso
2015-08-01
When a quasar is gravitationally lensed by a galaxy, its multiple images show light-curves that are offset by awell defined time delay, which depends on the mass profile of the lens and on cosmological distances to the lens and the source. By measuring the time-delay and accurately modelling the deflector's mass profile, this provides one-step measurements of cosmological distances to objects at redshift $z\\sim1,$ whence the cosmological parameters (primarily $H_0$). One can turn this argument around and learn about galaxies instead, or even perform a joint (and less biased) inference. The joint modelling of the lens, the source structure and time-variability implies that the DM halos of lens galaxies at z~0.4-1 and the source properties of quasars and their hosts at z~1-2are inferred, besides information on cosmology that is complementary to other low-redshift probes such as SN Ia and BAO.A large (N~100) sample of lensed quasars will be transformative in this sense, as these systems are rare on the sky.I will describe our STRIDES[*] searches in the Dark Energy Survey, aiming at 120 previously unknown lensed quasars brighter than i=21. Candidates have been selected with a variety of data mining techniques and flagged for follow-up (on spectroscopy, high-resolution imaging and lightcurve variability), which will take place in the following months. I will also cover recent modelling development of already monitored lenses within our collaboration, including a sharp multi-band reconstruction of the sources and use of stellar kinematics to ensure unbiased uncertainties on the lens mass profiles.This will lead to: (i) percent-level uncertainties on cosmological parameters(ii) insight on the coevolution of quasars and their host galaxies throughout cosmic time, up to z~2(iii) a quantative description of dark matter density profiles and the substructure content in massive galaxies up to z~1.[*] strides.physics.ucsb.edu
Morokuma, Tomoki; Inada, Naohisa; Oguri, Masamune; Ichikawa, Shin-Ichi; Kawano, Yozo; Tokita, Kouichi; Kayo, Issha; Hall, Patrick B.; Kochanek, Christopher S.; Richards, Gordon T.; York, Donald G.; Schneider, Donald P.; /Tokyo U., Inst. Astron. /KIPAC, Menlo Park /Princeton U. /Tokyo, Astron. Observ. /Nagoya U. /York U., Canada /Ohio State U., Dept. Astron. /Johns Hopkins U. /Drexel U. /Chicago U., Astron. Astrophys. Ctr. /Chicago U., EFI /Penn State U., Astron. Astrophys.
2006-09-28
We report the discovery of the two-image gravitationally lensed quasar SDSS J133222.62+034739.9 (SDSS J1332+0347) with an image separation of {Delta}{theta} = 1.14''. This system consists of a source quasar at z{sub s} = 1.445 and a lens galaxy at z{sub l} = 0.191. The agreement of the luminosity, ellipticity and position angle of the lens galaxy with those expected from lens model confirms the lensing hypothesis.
The Jubilee ISW project - I. Simulated ISW and weak lensing maps and initial power spectra results
NASA Astrophysics Data System (ADS)
Watson, W. A.; Diego, J. M.; Gottlber, S.; Iliev, I. T.; Knebe, A.; Martnez-Gonzlez, E.; Yepes, G.; Barreiro, R. B.; Gonzlez-Nuevo, J.; Hotchkiss, S.; Marcos-Caballero, A.; Nadathur, S.; Vielva, P.
2014-02-01
We present initial results from the Jubilee Integrated Sachs-Wolfe (ISW) project, which models the expected ? cold dark matter ISW effect in the Jubilee simulation. The simulation volume is (6 h-1 Gpc)3, allowing power on very large scales to be incorporated into the calculation. Haloes are resolved down to a mass of 1.5 1012 h-1 M?, which allows us to derive a catalogue of mock Luminous Red Galaxies (LRGs) for cross-correlation analysis with the ISW signal. We find the ISW effect observed on a projected sky to grow stronger at late times with the evolution of the ISW power spectrum matching expectations from linear theory. Maps of the gravitational-lensing effect are calculated using the same potential as for the ISW. We calculate the redshift dependence of the ISW-LRG cross-correlation signal for a full-sky survey with no noise considerations. For ? < 30, the signal is strongest for lower redshift bins (z 0.2-0.5), whereas for ? > 30, the signal is best observed with surveys covering z 0.6-1.0.
A demonstration of position angle-only weak lensing shear estimators on the GREAT3 simulations
NASA Astrophysics Data System (ADS)
Whittaker, Lee; Brown, Michael L.; Battye, Richard A.
2015-12-01
We develop and apply the position angle-only shear estimator of Whittaker, Brown & Battye to realistic galaxy images. This is done by demonstrating the method on the simulations of the third GRavitational lEnsing Accuracy Testing (GREAT3) challenge, which include contributions from anisotropic point spread functions (PSFs). We measure the position angles of the galaxies using three distinct methods - the integrated light method, quadrupole moments of surface brightness, and using model-based ellipticity measurements provided by IM3SHAPE. A weighting scheme is adopted to address biases in the position angle measurements which arise in the presence of an anisotropic PSF. Biases on the shear estimates, due to measurement errors on the position angles and correlations between the measurement errors and the true position angles, are corrected for using simulated galaxy images and an iterative procedure. The properties of the simulations are estimated using the deep field images provided as part of the challenge. A method is developed to match the distributions of galaxy fluxes and half-light radii from the deep fields to the corresponding distributions in the field of interest. We recover angle-only shear estimates with a performance close to current well-established model and moments-based methods for all three angle measurement techniques. The Q-values for all three methods are found to be Q 400. The code is freely available online at http://www.jb.man.ac.uk/mbrown/angle_only_shear/.
NASA Technical Reports Server (NTRS)
Miyatake, Hironao; Nishizawa, Atsushi J.; Takada, Masahiro; Mandelbaum, Rachel; Mineo, Sogo; Aihara, Hiroaki; Spergel, David N.; Bickerton, Steven J.; Bond, J. Richard; Hajian, Amir; Hilton, Matt; Hincks, Adam D.; Hughes, John P.; Infante, Leopoldo; Lin, Yen-Ting; Lupton, Robert H.; Marriage, Tobias A.; Marsden, Danica; Menanteau, Felipe; Miyazaki, Satoshi; Moodley, Kavilan; Niemack, Michael D.; Oguri, Masamune; Price, Paul A.; Reese, Eric D.; Sifon, Cristobal; Wollack, Edward J.; Yasuda, Naoki
2012-01-01
We present a Subaru weak lensing measurement of ACT-CL J0022.2-0036, one of the most luminous, high-redshift (z = 0.81) Sunyaev-Zel'dovich (SZ) clusters discovered in the 268 sq deg equatorial region survey of the Atacama Cosmology Telescope that overlaps with SDSS Stripe 82 field. Ours is the first weak lensing study with Subaru at such high redshifts. For the weak lensing analysis using i'-band images, we use a model-fitting (Gauss-Laguerre shapelet) method to measure shapes of galaxy images, where we fit galaxy images in different exposures simultaneously to obtain best-fit ellipticities taking into account the different PSFs in each exposure. We also take into account the astrometric distortion effect on galaxy images by performing the model fitting in the world coordinate system. To select background galaxies behind the cluster at z = 0.81, we use photometric redshift (photo-z) estimates for every galaxy derived from the co-added images of multi-passband Br'I'z'Y, with PSF matching/homogenization. After a photo-z cut for background galaxy selection, we detect the tangential weak lensing distortion signal with a total signal-to-noise ratio of about 3.7. By fitting a Navarro-Frenk-White model to the measured shear profile, we find the cluster mass to be M(sub 200 rho(sub m)) = [7.5 (+3.2 / -2.8)(stat.)(+1.3/-0.6)(sys)] x 10(exp 14)(solar mass)/h. The weak lensing-derived mass is consistent with previous mass estimates based on the SZ observation, with assumptions of hydrostatic equilibrium and virial theorem, as well as with scaling relations between SZ signal and mass derived from weak lensing, X-ray, and velocity dispersion, within the measurement errors. We also show that the existence of ACT-CL J0022.2-0036 at z = 0.81 is consistent with the cluster abundance prediction of the lambda-dominated cold dark matter structure formation model. We thus demonstrate the capability of Subaru-type ground-based images for studying weak lensing of high-redshift clusters.
Properties of Weak Lensing Clusters Detected on Hyper Suprime-Cams 2.3 deg2 field
NASA Astrophysics Data System (ADS)
Miyazaki, Satoshi; Oguri, Masamune; Hamana, Takashi; Tanaka, Masayuki; Miller, Lance; Utsumi, Yousuke; Komiyama, Yutaka; Furusawa, Hisanori; Sakurai, Junya; Kawanomoto, Satoshi; Nakata, Fumiaki; Uraguchi, Fumihiro; Koike, Michitaro; Tomono, Daigo; Lupton, Robert; Gunn, James E.; Karoji, Hiroshi; Aihara, Hiroaki; Murayama, Hitoshi; Takada, Masahiro
2015-07-01
We present properties of moderately massive clusters of galaxies detected by the newly developed Hyper Suprime-Cam on the Subaru telescope using weak gravitational lensing. Eight peaks exceeding a signal-to-noise ratio (S/N) of 4.5 are identified on the convergence S/N map of a 2.3 deg2 field observed during the early commissioning phase of the camera. Multi-color photometric data are used to generate optically selected clusters using the Cluster finding algorithm based on the Multiband Identification of Red-sequence galaxies algorithm. The optical cluster positions were correlated with the peak positions from the convergence map. All eight significant peaks have optical counterparts. The velocity dispersion of clusters is evaluated by adopting the Singular Isothemal Sphere fit to the tangential shear profiles, yielding virial mass estimates, {M}{500c}, of the clusters which range from 2.7 1013 to 4.4 10 {}14 {M}? . The number of peaks is considerably larger than the average number expected from ?CDM cosmology but this is not extremely unlikely if one takes the large sample variance in the small field into account. We could, however, safely argue that the peak count strongly favors the recent Planck result suggesting a high {? }8 value of 0.83. The ratio of stellar mass to the dark matter halo mass shows a clear decline as the halo mass increases. If the gas mass fraction, fg, in halos is universal, as has been suggested in the literature, the observed baryon mass in stars and gas shows a possible deficit compared with the total baryon density estimated from the baryon oscillation peaks in anisotropy of the cosmic microwave background.
On the bias of the distance-redshift relation from gravitational lensing
NASA Astrophysics Data System (ADS)
Kaiser, Nick; Peacock, John A.
2016-02-01
A long-standing question in cosmology is whether gravitational lensing changes the distance-redshift relation D (z) or the mean flux density of sources. Interest in this has been rekindled by recent studies in non-linear relativistic perturbation theory that find biases in both the area of a surface of constant redshift and in the mean distance to this surface, with a fractional bias in both cases of the order of the mean squared convergence <κ2>. Any such area bias could alter cosmic microwave background (CMB) cosmology, and the corresponding bias in mean flux density could affect supernova cosmology. We show that the perturbation to the area of a surface of constant redshift is in reality much smaller, being of the order of the cumulative bending angle squared, or roughly a part-in-a-million effect. This validates the arguments of Weinberg that the mean magnification of sources is unity and of Kibble & Lieu that the mean direction-averaged inverse magnification is unity. It also validates the conventional treatment of CMB lensing. But the existence of a scatter in magnification will cause any non-linear function of these conserved quantities to be statistically biased. The fractional bias in such quantities is generally of order <κ2>, which is orders of magnitude larger than the area perturbation. Claims for large bias in area or flux density of sources appear to have resulted from misinterpretation of such effects: they do not represent a new non-Newtonian effect, nor do they invalidate standard cosmological analyses.
Frontier Fields: Subaru Weak-Lensing Analysis of the Merging Galaxy Cluster A2744
NASA Astrophysics Data System (ADS)
Medezinski, Elinor; Umetsu, Keiichi; Okabe, Nobuhiro; Nonino, Mario; Molnar, Sandor; Massey, Richard; Dupke, Renato; Merten, Julian
2016-01-01
We present a weak-lensing analysis of the merging Frontier Fields (FF) cluster Abell 2744 using new Subaru/Suprime-Cam imaging. The wide-field lensing mass distribution reveals this cluster is comprised of four distinct substructures. Simultaneously modeling the two-dimensional reduced shear field using a combination of a Navarro-Frenk-White (NFW) model for the main core and truncated NFW models for the subhalos, we determine their masses and locations. The total mass of the system is constrained as {M}200{{c}}=(2.06+/- 0.42) {10}15 {M}? . The most massive clump is the southern component with {M}200{{c}}=(7.7+/- 3.4) {10}14 {M}? , followed by the western substructure ({M}200{{c}}=(4.5+/- 2.0) {10}14 {M}? ) and two smaller substructures to the northeast ({M}200{{c}}=(2.8+/- 1.6) {10}14 {M}? ) and northwest ({M}200{{c}}=(1.9+/- 1.2) {10}14 {M}? ). The presence of the four substructures supports the picture of multiple mergers. Using a composite of hydrodynamical binary simulations we explain this complicated system without the need for a slingshot effect to produce the northwest X-ray interloper, as previously proposed. The locations of the substructures appear to be offset from both the gas ({87}-28+34 arcsec, 90% CL) and the galaxies ({72}-53+34 arcsec, 90% CL) in the case of the northwestern and western subhalos. To confirm or refute these findings, high resolution space-based observations extending beyond the current FF limited coverage to the west and northwestern area are essential. Based in part on data collected at the Subaru Telescope, which is operated by the National Astronomical Society of Japan.
Cosmology Constraints from the Weak Lensing Peak Counts and the Power Spectrum in CFHTLenS
Liu, Jia; May, Morgan; Petri, Andrea; Haiman, Zoltan; Hui, Lam; Kratochvil, Jan M.
2015-03-04
Lensing peaks have been proposed as a useful statistic, containing cosmological information from non-Gaussianities that is inaccessible from traditional two-point statistics such as the power spectrum or two-point correlation functions. Here we examine constraints on cosmological parameters from weak lensing peak counts, using the publicly available data from the 154 deg2 CFHTLenS survey. We utilize a new suite of ray-tracing N-body simulations on a grid of 91 cosmological models, covering broad ranges of the three parameters Ω_{m}, σ_{8}, and w, and replicating the galaxy sky positions, redshifts, and shape noise in the CFHTLenS observations. We then build an emulator that interpolates the power spectrum and the peak counts to an accuracy of ≤ 5%, and compute the likelihood in the three-dimensional parameter space (Ω_{m}, σ_{8}, w) from both observables. We find that constraints from peak counts are comparable to those from the power spectrum, and somewhat tighter when different smoothing scales are combined. Neither observable can constrain w without external data. When the power spectrum and peak counts are combined, the area of the error “banana” in the (Ω_{m}, σ_{8}) plane reduces by a factor of ≈ two, compared to using the power spectrum alone. For a flat Λ cold dark matter model, combining both statistics, we obtain the constraint σ_{8}(Ω_{m}/0.27)0.63 = 0.85^{+0.03}_{-0.03}.
NASA Astrophysics Data System (ADS)
Nishizawa, Atsushi J.; Takada, Masahiro; Hamana, Takashi; Furusawa, Hisanori
2010-08-01
We use a mock catalog of galaxies based on the COSMOS galaxy catalog, including information on photometric redshift (photo-z) and spectral energy distribution types of galaxies, in order to study how to define a galaxy subsample suitable for weak lensing tomography feasible with optical (and near-IR) multi-band data. Since most useful cosmological information arises from the sample variance limited regime for upcoming lensing surveys, a suitable subsample can be obtained by discarding a large fraction of galaxies that have less reliable photo-z estimations. We develop a method to efficiently identify photo-z outliers by monitoring the width of the posterior likelihood function of redshift estimation for each galaxy. This clipping method may allow us to obtain clean tomographic redshift bins (here three bins are considered) that have almost no overlap, by discarding more than ~70% of galaxies with ill-defined photo-zs corresponding to the number densities of remaining galaxies less than ~20 arcmin-2 for a Subaru-type deep survey. Restricting the ranges of magnitudes and redshifts and/or adding near-IR data help us obtain a cleaner redshift binning. Using the Fisher information matrix formalism, we propagate photo-z errors into biases in the dark energy equation of state parameter w. We find that, by discarding most of the ill-defined photo-z galaxies, the bias in w can be reduced to a level comparable to the marginalized statistical error; however, the residual small systematic bias remains due to asymmetric scatters around the relation between photometric and true redshifts. We also use the mock catalog to estimate the cumulative signal-to-noise ratios (S/Ns) for measuring the angular cross-correlations of galaxies between finer photo-z bins, finding higher S/N values for the bins that include photo-z outliers.
Cosmology Constraints from the Weak Lensing Peak Counts and the Power Spectrum in CFHTLenS
Liu, Jia; May, Morgan; Petri, Andrea; Haiman, Zoltan; Hui, Lam; Kratochvil, Jan M.
2015-03-04
Lensing peaks have been proposed as a useful statistic, containing cosmological information from non-Gaussianities that is inaccessible from traditional two-point statistics such as the power spectrum or two-point correlation functions. Here we examine constraints on cosmological parameters from weak lensing peak counts, using the publicly available data from the 154 deg2 CFHTLenS survey. We utilize a new suite of ray-tracing N-body simulations on a grid of 91 cosmological models, covering broad ranges of the three parameters Ωm, σ8, and w, and replicating the galaxy sky positions, redshifts, and shape noise in the CFHTLenS observations. We then build an emulator thatmore » interpolates the power spectrum and the peak counts to an accuracy of ≤ 5%, and compute the likelihood in the three-dimensional parameter space (Ωm, σ8, w) from both observables. We find that constraints from peak counts are comparable to those from the power spectrum, and somewhat tighter when different smoothing scales are combined. Neither observable can constrain w without external data. When the power spectrum and peak counts are combined, the area of the error “banana” in the (Ωm, σ8) plane reduces by a factor of ≈ two, compared to using the power spectrum alone. For a flat Λ cold dark matter model, combining both statistics, we obtain the constraint σ8(Ωm/0.27)0.63 = 0.85+0.03-0.03.« less
Nishizawa, Atsushi J.; Takada, Masahiro; Hamana, Takashi; Furusawa, Hisanori
2010-08-01
We use a mock catalog of galaxies based on the COSMOS galaxy catalog, including information on photometric redshift (photo-z) and spectral energy distribution types of galaxies, in order to study how to define a galaxy subsample suitable for weak lensing tomography feasible with optical (and near-IR) multi-band data. Since most useful cosmological information arises from the sample variance limited regime for upcoming lensing surveys, a suitable subsample can be obtained by discarding a large fraction of galaxies that have less reliable photo-z estimations. We develop a method to efficiently identify photo-z outliers by monitoring the width of the posterior likelihood function of redshift estimation for each galaxy. This clipping method may allow us to obtain clean tomographic redshift bins (here three bins are considered) that have almost no overlap, by discarding more than {approx}70% of galaxies with ill-defined photo-zs corresponding to the number densities of remaining galaxies less than {approx}20 arcmin{sup -2} for a Subaru-type deep survey. Restricting the ranges of magnitudes and redshifts and/or adding near-IR data help us obtain a cleaner redshift binning. Using the Fisher information matrix formalism, we propagate photo-z errors into biases in the dark energy equation of state parameter w. We find that, by discarding most of the ill-defined photo-z galaxies, the bias in w can be reduced to a level comparable to the marginalized statistical error; however, the residual small systematic bias remains due to asymmetric scatters around the relation between photometric and true redshifts. We also use the mock catalog to estimate the cumulative signal-to-noise ratios (S/Ns) for measuring the angular cross-correlations of galaxies between finer photo-z bins, finding higher S/N values for the bins that include photo-z outliers.
Cosmology Constraints from the Weak Lensing Peak Counts and the Power Spectrum in CFHTLenS
Liu, Jia; May, Morgan; Petri, Andrea; Haiman, Zoltan; Hui, Lam; Kratochvil, Jan M.
2015-03-04
Lensing peaks have been proposed as a useful statistic, containing cosmological information from non-Gaussianities that is inaccessible from traditional two-point statistics such as the power spectrum or two-point correlation functions. Here we examine constraints on cosmological parameters from weak lensing peak counts, using the publicly available data from the 154 deg2 CFHTLenS survey. We utilize a new suite of ray-tracing N-body simulations on a grid of 91 cosmological models, covering broad ranges of the three parameters ?_{m}, ?_{8}, and w, and replicating the galaxy sky positions, redshifts, and shape noise in the CFHTLenS observations. We then build an emulator that interpolates the power spectrum and the peak counts to an accuracy of ? 5%, and compute the likelihood in the three-dimensional parameter space (?_{m}, ?_{8}, w) from both observables. We find that constraints from peak counts are comparable to those from the power spectrum, and somewhat tighter when different smoothing scales are combined. Neither observable can constrain w without external data. When the power spectrum and peak counts are combined, the area of the error banana in the (?_{m}, ?_{8}) plane reduces by a factor of ? two, compared to using the power spectrum alone. For a flat ? cold dark matter model, combining both statistics, we obtain the constraint ?_{8}(?_{m}/0.27)0.63 = 0.85^{+0.03}_{-0.03}.
NASA Technical Reports Server (NTRS)
Wagoner, Robert V.; Linder, Eric V.
1987-01-01
A review is presented concerning the gravitational lensing of supernovae by intervening condensed objects, including dark matter candidates such as dim stars and black holes. the expansion of the supernova beam within the lens produces characteristic time-dependent amplification and polarization which depend upon the mass of the lens. The effects of the shearing of the beam due to surrounding masses are considered, although the study of these effects is confined to isolated masses whose size is much less than that of the supernova (about 10 to the 15th cm). Equations for the effects of lensing and graphs comparing these effects in different classes of supernovae are compared. It is found that candidates for lensing would be those supernovae at least as bright as their parent galaxy, or above the range of luminosities expected for their spectral class.
Random walks in cosmology: Weak lensing, the halo model, and reionization
NASA Astrophysics Data System (ADS)
Zhang, Jun
This thesis discusses theoretical problems in three areas of cosmology: weak lensing, the halo model, and reionization. In weak lensing, we investigate the impact of the intrinsic alignment on the density-ellipticity correlations using the tidal torquing theory. Under the assumption of the Gaussianity of the tidal field, we find that the intrinsic alignment does not contaminate the density-ellipticity correlation even if the source clustering correlations are taken into account. The non-Gaussian contributions to both the intrinsic density-ellipticity and ellipticity- ellipticity correlations are often non-negligible. In a separate work, we discuss a useful scaling relation in weak lensing measurements. Given a foreground galaxy-density field or shear field, its cross-correlation with the shear field from a background population of source galaxies scales with the source redshift in a way that allows us to effectively measure geometrical distances as a function of redshift and thereby constrain dark energy properties without assuming anything about the galaxy-mass/mass power spectrum. Such a geometrical method can yield a ~ 0.03--0.07 [Special characters omitted.] measurement on the dark energy abundance and equation of state, for a photometric redshift accuracy of [Delta] z ~ 0.01--0.05 and a survey with median redshift of ~1. The geometrical method also provides a consistency check of the standard cosmological model because it is completely independent of structure formation. In the excursion set theory of the halo model, we derive the first-crossing distribution of random walks with a moving barrier of a general shape. Such a distribution is shown to satisfy an integral equation that can be solved by a simple matrix inversion, without the need for Monte Carlo simulations, making it useful for exploring a large parameter space. We discuss examples in which common analytic approximations fail, a failure that can be remedied using our method. In reionization, we calculate the large scale properties of the HII/HI and radiation distributions using the linear perturbation theory. Given the distribution and the spectrum of the ionizing sources, our formalism can be used to calculate the large scale bias of the HII regions from first principles by solving the equations of ionization balance and radiative transfer in Fourier space. We also discuss an approximate but easy way of solving these equations for UV dominated source spectra. Using the extended Press-Schechter model, we find: (1) reionization always proceeds inside-out, at least on large scales; (2) on sufficiently large scales, HII, HI and radiation exhibit a scale independent bias relative to dark matter; (3) the bias is suppressed on scales comparable to or smaller than the mean free path of the ionizing photons; (4) if the ionizing source spectrum is sufficiently soft, the HII bias closely tracks the source bias for most of the reionization process but drops precipitously after percolation; (5) if the ionizing source spectrum is hard, the HII bias drops in a more steady fashion throughout the reionization process. The tools developed here will be useful for interpreting future 21cm, CMB and Lyman-alpha forest observations, both to learn about the reionization astrophysics and to possibly extract interesting cosmological information.
NASA Astrophysics Data System (ADS)
Almosallami, Azzam
2011-03-01
In this paper we derived the relativistic Quantized force, where the force given as a function of frequency [1]. Where, in this paper we defined the relativistic momentum as a function of frequency equivalent to the energy held by a body, and time, and then the quantized force is given as the first derivative of the momentum with respect to time. Subsequently we introduce in section one Newton's second law as it is relativistic quantized, and in section two we introduce the relativistic quantized inertial force, and then the relativistic quantized gravitational force, and the quantized gravitational time dilation. At the end we shall generalize the Schwartzschild metric to describe the weak and strong gravitational field.
Resolving the High-energy Universe with Strong Gravitational Lensing: The Case of PKS 1830-211
NASA Astrophysics Data System (ADS)
Barnacka, Anna; Geller, Margaret J.; Dell'Antonio, Ian P.; Benbow, Wystan
2015-08-01
Gravitational lensing is a potentially powerful tool for elucidating the origin of gamma-ray emission from distant sources. Cosmic lenses magnify the emission from distant sources and produce time delays between mirage images. Gravitationally induced time delays depend on the position of the emitting regions in the source plane. The Fermi/LAT telescope continuously monitors the entire sky and detects gamma-ray flares, including those from gravitationally lensed blazars. Therefore, temporal resolution at gamma-ray energies can be used to measure these time delays, which, in turn, can be used to resolve the origin of the gamma-ray flares spatially. We provide a guide to the application and Monte Carlo simulation of three techniques for analyzing these unresolved light curves: the autocorrelation function, the double power spectrum, and the maximum peak method. We apply these methods to derive time delays from the gamma-ray light curve of the gravitationally lensed blazar PKS 1830-211. The result of temporal analysis combined with the properties of the lens from radio observations yield an improvement in spatial resolution at gamma-ray energies by a factor of 10,000. We analyze four active periods. For two of these periods the emission is consistent with origination from the core, and for the other two the data suggest that the emission region is displaced from the core by more than ˜1.5 kpc. For the core emission, the gamma-ray time delays, 23+/- 0.5 {days} and 19.7+/- 1.2 days, are consistent with the radio time delay of {26}-5+4 days.
Rapoport, Sharon; Onken, Christopher A.; Schmidt, Brian P.; Tucker, Brad E.; Wyithe, J. Stuart B.; Levan, Andrew J.
2012-08-01
Sixty percent of gamma-ray bursts (GRBs) reveal strong Mg II absorbing systems, which is a factor of {approx}2 times the rate seen along lines of sight to quasars. Previous studies argue that the discrepancy in the strong Mg II covering factor is most likely to be the result of either quasars being obscured due to dust or the consequence of many GRBs being strongly gravitationally lensed. We analyze observations of quasars that show strong foreground Mg II absorption. We find that GRB lines of sight pass closer to bright galaxies than would be expected for random lines of sight within the impact parameter expected for strong Mg II absorption. While this cannot be explained by obscuration in the GRB sample, it is a natural consequence of gravitational lensing. Upon examining the particular configurations of galaxies near a sample of GRBs with strong Mg II absorption, we find several intriguing lensing candidates. Our results suggest that lensing provides a viable contribution to the observed enhancement of strong Mg II absorption along lines of sight to GRBs, and we outline the future observations required to test this hypothesis conclusively.
NASA Astrophysics Data System (ADS)
Osato, Ken; Shirasaki, Masato; Yoshida, Naoki
2015-06-01
We study the impact of baryonic physics on cosmological parameter estimation with weak-lensing surveys. We run a set of cosmological hydrodynamics simulations with different galaxy formation models. We then perform ray-tracing simulations through the total matter density field to generate 100 independent convergence maps with a field of view of 25 {{deg }2}, and we use them to examine the ability of the following three lensing statistics as cosmological probes: power spectrum (PS), peak counts, and Minkowski functionals (MFs). For the upcoming wide-field observations, such as the Subaru Hyper Suprime-Cam (HSC) survey with a sky coverage of 1400 {{deg }2}, these three statistics provide tight constraints on the matter density, density fluctuation amplitude, and dark energy equation of state, but parameter bias is induced by baryonic processes such as gas cooling and stellar feedback. When we use PS, peak counts, and MFs, the magnitude of relative bias in the dark energy equation of state parameter w is at a level of, respectively, ? w? 0.017, 0.061, and 0.0011. For the HSC survey, these values are smaller than the statistical errors estimated from Fisher analysis. The bias could be significant when the statistical errors become small in future observations with a much larger survey area. We find that the bias is induced in different directions in the parameter space depending on the statistics employed. While the two-point statistic, i.e., PS, yields robust results against baryonic effects, the overall constraining power is weak compared with peak counts and MFs. On the other hand, using one of peak counts or MFs, or combined analysis with multiple statistics, results in a biased parameter estimate. The bias can be as large as 1? for the HSC survey and will be more significant for upcoming wider-area surveys. We suggest to use an optimized combination so that the baryonic effects on parameter estimation are mitigated. Such a calibrated combination can place stringent and robust constraints on cosmological parameters.
Gravitational lensing and ghost images in the regular Bardeen no-horizon spacetimes
NASA Astrophysics Data System (ADS)
Schee, Jan; Stuchlk, Zden?k
2015-06-01
We study deflection of light rays and gravitational lensing in the regular Bardeen no-horizon spacetimes. Flatness of these spacetimes in the central region implies existence of interesting optical effects related to photons crossing the gravitational field of the no-horizon spacetimes with low impact parameters. These effects occur due to existence of a critical impact parameter giving maximal deflection of light rays in the Bardeen no-horizon spacetimes. We give the critical impact parameter in dependence on the specific charge of the spacetimes, and discuss "ghost" direct and indirect images of Keplerian discs, generated by photons with low impact parameters. The ghost direct images can occur only for large inclination angles of distant observers, while ghost indirect images can occur also for small inclination angles. We determine the range of the frequency shift of photons generating the ghost images and determine distribution of the frequency shift across these images. We compare them to those of the standard direct images of the Keplerian discs. The difference of the ranges of the frequency shift on the ghost and direct images could serve as a quantitative measure of the Bardeen no-horizon spacetimes. The regions of the Keplerian discs giving the ghost images are determined in dependence on the specific charge of the no-horizon spacetimes. For comparison we construct direct and indirect (ordinary and ghost) images of Keplerian discs around Reissner-Nrdstrm naked singularities demonstrating a clear qualitative difference to the ghost direct images in the regular Bardeen no-horizon spacetimes. The optical effects related to the low impact parameter photons thus give clear signature of the regular Bardeen no-horizon spacetimes, as no similar phenomena could occur in the black hole or naked singularity spacetimes. Similar direct ghost images have to occur in any regular no-horizon spacetimes having nearly flat central region.
Misawa, Toru; Inada, Naohisa; Oguri, Masamune; Gandhi, Poshak; Horiuchi, Takashi; Koyamada, Suzuka; Okamoto, Rina
2014-10-20
We study the geometry and the internal structure of the outflowing wind from the accretion disk of a quasar by observing multiple sightlines with the aid of strong gravitational lensing. Using Subaru/High Dispersion Spectrograph, we performed high-resolution (R ∼ 36,000) spectroscopic observations of images A and B of the gravitationally lensed quasar SDSS J1029+2623 (at z {sub em} ∼ 2.197) whose image separation angle, θ ∼ 22.''5, is the largest among those discovered so far. We confirm that the difference in absorption profiles in images A and B discovered by Misawa et al. has remained unchanged since 2010, implying the difference is not due to time variability of the absorption profiles over the delay between the images, Δt ∼ 744 days, but rather due to differences along the sightlines. We also discovered a time variation of C IV absorption strength in both images A and B due to a change in the ionization condition. If a typical absorber's size is smaller than its distance from the flux source by more than five orders of magnitude, it should be possible to detect sightline variations among images of other smaller separation, galaxy-scale gravitationally lensed quasars.
A new model to predict weak-lensing peak counts. I. Comparison with N-body simulations
NASA Astrophysics Data System (ADS)
Lin, Chieh-An; Kilbinger, Martin
2015-04-01
Context. Weak-lensing peak counts have been shown to be a powerful tool for cosmology. They provide non-Gaussian information of large scale structures and are complementary to second-order statistics. Aims: We propose a new flexible method for predicting weak-lensing peak counts, which can be adapted to realistic scenarios, such as a real source distribution, intrinsic galaxy alignment, mask effects, and photo-z errors from surveys. The new model is also suitable for applying the tomography technique and nonlinear filters. Methods: A probabilistic approach to modeling peak counts is presented. First, we sample halos from a mass function. Second, we assign them density profiles. Third, we place those halos randomly on the field of view. The creation of these "fast simulations" requires much less computing time than do N-body runs. Then, we perform ray-tracing through these fast simulation boxes and select peaks from weak-lensing maps to predict peak number counts. The computation is achieved by our Camelus algorithm. Results: We compare our results to N-body simulations to validate our model. We find that our approach is in good agreement with full N-body runs. We show that the lensing signal dominates shape noise and Poisson noise for peaks with S/N between 4 and 6. Also, counts from the same S/N range are sensitive to ?m and ?8. We show how our model can distinguish between various combinations of those two parameters. Conclusions: In this paper, we offer a powerful tool for studying weak-lensing peaks. The potential of our forward model is its high flexibility, which makes the using peak counts under realistic survey conditions feasible. The Camelus source code is released via the website http://www.cosmostat.org/software/camelus/
Black hole solution and strong gravitational lensing in Eddington-inspired Born-Infeld gravity
NASA Astrophysics Data System (ADS)
Wei, Shao-Wen; Yang, Ke; Liu, Yu-Xiao
2015-06-01
A new theory of gravity called Eddington-inspired Born-Infeld (EiBI) gravity was recently proposed by Bañados and Ferreira. This theory leads to some exciting new features, such as free of cosmological singularities. In this paper, we first obtain a charged EiBI black hole solution with a nonvanishing cosmological constant when the electromagnetic field is included in. Then based on it, we study the strong gravitational lensing by the asymptotic flat charged EiBI black hole. The strong deflection limit coefficients and observables are shown to closely depend on the additional coupling parameter in the EiBI gravity. It is found that, compared with the corresponding charged black hole in general relativity, the positive coupling parameter