NASA Astrophysics Data System (ADS)
Pires, Sandrine; Starck, Jean-Luc; Leonard, Adrienne; Réfrégier, Alexandre
2012-03-01
This chapter reviews the data mining methods recently developed to solve standard data problems in weak gravitational lensing. We detail the different steps of the weak lensing data analysis along with the different techniques dedicated to these applications. An overview of the different techniques currently used will be given along with future prospects. Until about 30 years ago, astronomers thought that the Universe was composed almost entirely of ordinary matter: protons, neutrons, electrons, and atoms. The field of weak lensing has been motivated by the observations made in the last decades showing that visible matter represents only about 4-5% of the Universe (see Figure 14.1). Currently, the majority of the Universe is thought to be dark, that is, does not emit electromagnetic radiation. The Universe is thought to be mostly composed of an invisible, pressure less matter - potentially relic from higher energy theories - called "dark matter" (20-21%) and by an even more mysterious term, described in Einstein equations as a vacuum energy density, called "dark energy" (70%). This "dark" Universe is not well described or even understood; its presence is inferred indirectly from its gravitational effects, both on the motions of astronomical objects and on light propagation. So this point could be the next breakthrough in cosmology. Today's cosmology is based on a cosmological model that contains various parameters that need to be determined precisely, such as the matter density parameter Omega_m or the dark energy density parameter Omega_lambda. Weak gravitational lensing is believed to be the most promising tool to understand the nature of dark matter and to constrain the cosmological parameters used to describe the Universe because it provides a method to directly map the distribution of dark matter (see [1,6,60,63,70]). From this dark matter distribution, the nature of dark matter can be better understood and better constraints can be placed on dark energy
Weak gravitational lensing by galaxies
Brainerd, T.G. |; Blandford, R.D.; Smail, I. |
1996-08-01
We report a detection of weak, tangential distortion of the images of cosmologically distant, faint galaxies due to gravitational lensing by foreground galaxies. A mean image polarization of ({ital p})=0.011{plus_minus}0.006 (95{percent} confidence bounds) is obtained for 3202 pairs of source (23{lt}{ital r}{sub {ital s}}{le}24) and lens (20{le}{ital r}{sub {ital d}}{le}23) galaxies with projected separations of 5{double_prime}{le}{theta}{le}34{double_prime}. Averaged over annuli of inner radius 5{double_prime} and outer radius {theta}{sub max}, the signal is string for lens-source separations of {theta}{sub max}{approx_lt}90{double_prime} consistent with quasi-isothermal galaxy halos extending to large radii ({approx_gt}100{ital h}{sup {minus}1} kpc). The observed polarization is also consistent with the signal expected on the basis of simulations incorporating measured properties of local galaxies and modest extrapolations of the observed redshift distribution of faint galaxies (to which the results are somewhat sensitive). From the simulations we obtain formal best-fit model parameters for the dark halos of the lens galaxies that consist of a characteristic circular velocity of {ital V}{asterisk}{approximately}220{plus_minus}80 kms{sup {minus}1} and characteristic radial extent of {ital s}{asterisk}{approx_gt}100{ital h}{sup {minus}1} kpc. The predicted polarization based on the model is relatively insensitive to the characteristic radial extent of the halos, {ital s}{asterisk}, and very small halos ({ital s}{asterisk}{approximately}10{ital h}{sup {minus}1} kpc) are excluded only at the 2 {sigma} level. The formal best-fit halo parameters imply typical masses for the lens galaxies within a radius of 100{ital h}{sup -1} kpc on the order of 1.0{sup +1.2}{sub {minus}0.5}{times}10{sup 12} {ital h}{sup {minus}1}{ital M}{sub {circle_dot}} (90% confidence bounds), in agreement with recent dynamical estimates of the masses of local spiral galaxies.
Weak gravitational lensing theory and data analysis
NASA Astrophysics Data System (ADS)
Hirata, Christopher Michael
2005-12-01
This thesis describes methodology for analysis of weak gravitational lensing data. Weak lensing, i.e. the perturbative distortion of the images of distant objects by the gravitational deflection of light, is an important tool for understanding the distribution of matter in the universe. This is interesting because a number of extentions to the standard cosmological model, including dynamical dark energy and neutrino masses, affect the growth of structure and hence may be detectable using weak lensing. Studies of weak lensing are also motivated by lensing's ability to affect the modes in the cosmic microwave background (CMB) polarization that are sensitive to primordial gravitational waves. Both lensing of galaxies and lensing of the CMB are considered here. The section devoted to galaxies is principally concerned with measuring the lensing-induced shape distortions from galaxy images in the Sloan Digital Sky Survey (SDSS), although the methodology will be applicable to future projects. We investigate in detail the problem of separating lensing from other shape distortions such as those induced by the atmosphere, the telescope, and photon Poisson noise. Since the intrinsic shapes of observed galaxies are not known, weak lensing observations always attempt some sort of statistical averaging over galaxies that presumably have independent orientations. We investigate the extent to which this process "averages down" the intrinsic shapes and identify a new type of bias that can affect the weak lensing power spectrum. Selection biases are considered and their importance in SDSS estimated. We present some recent cosmological results using the SDSS analysis, including new upper limits on the neutrino mass. Lensing of the CMB has not yet been detected, nevertheless several experiments are being built that should have the sensitivity to see it. The statistical problem of extracting lensing information from the distortion of the CMB anisotropy is considered, and in the case of
Precision cosmology with weak gravitational lensing
NASA Astrophysics Data System (ADS)
Hearin, Andrew P.
In recent years, cosmological science has developed a highly predictive model for the universe on large scales that is in quantitative agreement with a wide range of astronomical observations. While the number and diversity of successes of this model provide great confidence that our general picture of cosmology is correct, numerous puzzles remain. In this dissertation, I analyze the potential of planned and near future galaxy surveys to provide new understanding of several unanswered questions in cosmology, and address some of the leading challenges to this observational program. In particular, I study an emerging technique called cosmic shear, the weak gravitational lensing produced by large scale structure. I focus on developing strategies to optimally use the cosmic shear signal observed in galaxy imaging surveys to uncover the physics of dark energy and the early universe. In chapter 1 I give an overview of a few unsolved mysteries in cosmology and I motivate weak lensing as a cosmological probe. I discuss the use of weak lensing as a test of general relativity in chapter 2 and assess the threat to such tests presented by our uncertainty in the physics of galaxy formation. Interpreting the cosmic shear signal requires knowledge of the redshift distribution of the lensed galaxies. This redshift distribution will be significantly uncertain since it must be determined photometrically. In chapter 3 I investigate the influence of photometric redshift errors on our ability to constrain dark energy models with weak lensing. The ability to study dark energy with cosmic shear is also limited by the imprecision in our understanding of the physics of gravitational collapse. In chapter 4 I present the stringent calibration requirements on this source of uncertainty. I study the potential of weak lensing to resolve a debate over a long-standing anomaly in CMB measurements in chapter 5. Finally, in chapter 6 I summarize my findings and conclude with a brief discussion of my
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⊙.
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.
Weak gravitational lensing in fourth order gravity
NASA Astrophysics Data System (ADS)
Stabile, A.; Stabile, An.
2012-02-01
For a general class of analytic functions f(R,RαβRαβ,RαβγδRαβγδ) we discuss the gravitational lensing in the Newtonian limit of theory. From the properties of the Gauss-Bonnet invariant it is enough to consider only one curvature invariant between the Ricci tensor and the Riemann tensor. Then, we analyze the dynamics of a photon embedded in a gravitational field of a generic f(R,RαβRαβ) gravity. The metric is time independent and spherically symmetric. The metric potentials are Schwarzschild-like, but there are two additional Yukawa terms linked to derivatives of f with respect to two curvature invariants. Considering first the case of a pointlike lens, and after the one of a generic matter distribution of the lens, we study the deflection angle and the angular position of images. Though the additional Yukawa terms in the gravitational potential modifies dynamics with respect to general relativity, the geodesic trajectory of the photon is unaffected by the modification if we consider only f(R) gravity. We find different results (deflection angle smaller than the angle of general relativity) only due to the introduction of a generic function of the Ricci tensor square. Finally, we can affirm that the lensing phenomena for all f(R) gravities are equal to the ones known for general relativity. We conclude the paper by showing and comparing the deflection angle and position of images for f(R,RαβRαβ) gravity with respect to the gravitational lensing of general relativity.
Compact Groups analysis using weak gravitational lensing
NASA Astrophysics Data System (ADS)
Chalela, Martín; Johana Gonzalez, Elizabeth; Garcia Lambas, Diego; Foëx, Gael
2017-01-01
We present a weak lensing analysis of a sample of SDSS Compact Groups (CGs). Using the measured radial density contrast profile, we derive the average masses under the assumption of spherical symmetry, obtaining a velocity dispersion for the Singular Isothermal Spherical model, σV = 270 ± 40 km s-1, and for the NFW model, R_{200}=0.53± 0.10 h_{70}^{-1}Mpc. We test three different definitions of CGs centres to identify which best traces the true dark matter halo centre, concluding that a luminosity weighted centre is the most suitable choice. We also study the lensing signal dependence on CGs physical radius, group surface brightness, and morphological mixing. We find that groups with more concentrated galaxy members show steeper mass profiles and larger velocity dispersions. We argue that both, a possible lower fraction of interloper and a true steeper profile, could be playing a role in this effect. Straightforward velocity dispersion estimates from member spectroscopy yields σV ≈ 230 km s-1 in agreement with our lensing results.
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.
Weak gravitational lensing with the Hyper Suprime-Cam survey
NASA Astrophysics Data System (ADS)
Mandelbaum, Rachel; Hyper Suprime-Cam (HSC) Collaboration
2017-01-01
Data from the Hyper Suprime-Cam (HSC) survey on the Subaru telescope show great promise for weak gravitational lensing science. The unprecedented combination of area, depth, and imaging quality of this survey (with median i-band seeing of 0.6 arcsec) will enable a wide array of weak lensing measurements, with significant contributions from lenses up to redshift z~1. Applications include cosmological weak lensing measurements from shear-shear and galaxy-shear correlations, which will be especially powerful when combined with the overlapping SDSS-III spectroscopic datasets; and studies of the dark matter halos of galaxies and galaxy clusters. In this talk, I will demonstrate the imaging quality and the tests used to validate the weak lensing measurements. These include null tests internal to the data, comparisons with external datasets, and image simulation-based tests. I will also show the lensing mass profiles of spectroscopic galaxies from the SDSS-III, illustrating the current signal-to-noise ratio on small and large scales and demonstrating the potential for innovative galaxy and cosmological science with the complete survey area.
Constraining dark energy from the abundance of weak gravitational lenses
NASA Astrophysics Data System (ADS)
Weinberg, Nevin N.; Kamionkowski, Marc
2003-05-01
We examine the prospect of using the observed abundance of weak gravitational lenses to constrain the equation-of-state parameter w=p/ρ of dark energy. Dark energy modifies the distance-redshift relation, the amplitude of the matter power spectrum, and the rate of structure growth. As a result, it affects the efficiency with which dark-matter concentrations produce detectable weak-lensing signals. Here we solve the spherical-collapse model with dark energy, clarifying some ambiguities found in the literature. We also provide fitting formulae for the non-linear overdensity at virialization and the linear-theory overdensity at collapse. We then compute the variation in the predicted weak-lens abundance with w. We find that the predicted redshift distribution and number count of weak lenses are highly degenerate in w and the present matter density Ω0. If we fix Ω0 the number count of weak lenses for w=-2/3 is a factor of ~2 smaller than for the Λ cold dark matter (CDM) model w=-1. However, if we allow Ω0 to vary with w such that the amplitude of the matter power spectrum as measured by the Cosmic Background Explorer (COBE) matches that obtained from the X-ray cluster abundance, the decrease in the predicted lens abundance is less than 25 per cent for -1 <=w< -0.4. We show that a more promising method for constraining dark energy - one that is largely unaffected by the Ω0-w degeneracy as well as uncertainties in observational noise - is to compare the relative abundance of virialized X-ray lensing clusters with the abundance of non-virialized, X-ray underluminous, lensing haloes. For aperture sizes of ~15 arcmin, the predicted ratio of the non-virialized to virialized lenses is greater than 40 per cent and varies by ~20 per cent between w=-1 and -0.6. Overall, we find that, if all other weak-lensing parameters are fixed, a survey must cover at least ~40 deg2 in order for the weak-lens number count to differentiate a ΛCDM cosmology from a dark-energy model with w
The general theory of secondary weak gravitational lensing
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 shear study of galaxy clusters by simulated gravitational lensing
NASA Astrophysics Data System (ADS)
Coss, David
Gravitational lensing has been simulated for numerical galaxy clusters in order to characterize the effects of substructure and shape variations of dark matter halos on the weak lensing properties of clusters. In order to analyze realistic galaxy clusters, 6 high-resolution Adaptive Refinement Tree N-body simulations of clusters with hydrodynamics are used, in addition to a simulation of one group undergoing a merger. For each cluster, the three-dimensional particle distribution is projected perpendicular to three orthogonal lines of sight, providing 21 projected mass density maps. The clusters have representative concentration and mass values for clusters in the concordance cosmology. Two gravitational lensing simulation methods are presented. In the first method, direct integration is used to calculate deflection angles. To overcome computational constraints inherent in this method, a distributed computing project was created for parallel computation. In addition to its use in gravitational lensing simulation, a description of the setup and function of this distributed computing project is presented as an alternative to in-house computing clusters, which has the added benefit of public enrollment in science and low cost. In the second method, shear maps are created using a fast Fourier transform method. From these shear maps, the effects of substructure and shape variation are related to observational gravitational lensing studies. Average shear in regions less than and greater than half of the virial radius demonstrates distinct dispersion, varying by 24% from the mean among the 21 maps. We estimate the numerical error in shear calculations to be of the order of 5%. Therefore, this shear dispersion is a reliable consequence of shape dispersion, correlating most strongly with the ratio of smallest-to-largest principal axis lengths of a cluster isodensity shell. On the other hand, image ellipticities, which are of great importance in mass reconstruction, are shown
Weak gravitational lensing analysis of Sloan Digital Sky Survey data
NASA Astrophysics Data System (ADS)
Mandelbaum, Rachel
Weak gravitational lensing, the distortion of images of distant galaxies due to gravitational deflection of light by more nearby masses, is a powerful tool that can address a wide variety of problems in astrophysics and cosmology. Observation of weak lensing requires large amounts of data since it can only be measured as an average over millions of galaxy shapes. This thesis focuses on lensing-related science that can be addressed using data from the Sloan Digital Sky Survey (SDSS), an excellent source of high-quality data. First, we discuss technical issues related to observing lensing in the data, with a description of our Reglens pipeline and constraints on systematic errors in current data. This is followed by a comparison of an analytical model known as the halo model (which can be used to relate the observed lensing signal to properties of the lens galaxies) against the lensing signal in N-body simulations. After these preliminaries, we address several very different science questions using our reductions of the SDSS data. The first is the question of intrinsic alignments of galaxies (alignments of galaxies on the sky due to local structure), which may be a contaminant for future lensing surveys that seek to determine the cosmological model to high precision. Second, we use a halo model analysis of the lensing signal to determine the relationship between galaxy luminosity, stellar mass, and halo mass, and to measure satellite fractions, all of which can help distinguish between models of galaxy formation. The third application we consider is methodology for the detection of dark matter halo ellipticity, including a first attempt at detecting it with SDSS lensing data, these results may be used to distinguish between cosmological models and learn more about galaxy intrinsic alignments. Finally, we measure the matter distributions around Luminous Red Galaxies (LRGs), which not only teaches us about the properties of these galaxies, but also gives us information
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.
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.
Lincoln, Don
2016-07-12
In a long line of intellectual triumphs, Einsteinâs 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, Fermilabâs 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.
Constraining Horava-Lifshitz gravity by weak and strong gravitational lensing
Horvath, Zsolt; Gergely, Laszlo A.; Keresztes, Zoltan; Harko, Tiberiu; Lobo, Francisco S. N.
2011-10-15
We discuss gravitational lensing in the Kehagias-Sfetsos space-time emerging in the framework of Horava-Lifshitz gravity. In weak lensing, we show that there are three regimes, depending on the value of {lambda}=1/{omega}d{sup 2}, where {omega} is the Horava-Lifshitz parameter and d characterizes the lensing geometry. When {lambda} is close to zero, light deflection typically produces two images, as in Schwarzschild lensing. For very large {lambda}, the space-time approaches flatness, therefore there is only one undeflected image. In the intermediate range of {lambda}, only the upper focused image is produced due to the existence of a maximal deflection angle {delta}{sub max}, a feature inexistent in the Schwarzschild weak lensing. We also discuss the location of Einstein rings, and determine the range of the Horava-Lifshitz parameter compatible with present-day lensing observations. Finally, we analyze in the strong lensing regime the first two relativistic Einstein rings and determine the constraints on the parameter range to be imposed by forthcoming experiments.
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.
First test of Verlinde's theory of emergent gravity using weak gravitational lensing measurements
NASA Astrophysics Data System (ADS)
Brouwer, Margot M.; Visser, Manus R.; Dvornik, Andrej; Hoekstra, Henk; Kuijken, Konrad; Valentijn, Edwin A.; Bilicki, Maciej; Blake, Chris; Brough, Sarah; Buddelmeijer, Hugo; Erben, Thomas; Heymans, Catherine; Hildebrandt, Hendrik; Holwerda, Benne W.; Hopkins, Andrew M.; Klaes, Dominik; Liske, Jochen; Loveday, Jon; McFarland, John; Nakajima, Reiko; Sifón, Cristóbal; Taylor, Edward N.
2017-04-01
Verlinde proposed that the observed excess gravity in galaxies and clusters is the consequence of emergent gravity (EG). In this theory, the standard gravitational laws are modified on galactic and larger scales due to the displacement of dark energy by baryonic matter. EG gives an estimate of the excess gravity (described as an apparent dark matter density) in terms of the baryonic mass distribution and the Hubble parameter. In this work, we present the first test of EG using weak gravitational lensing, within the regime of validity of the current model. Although there is no direct description of lensing and cosmology in EG yet, we can make a reasonable estimate of the expected lensing signal of low-redshift galaxies by assuming a background Lambda cold dark matter cosmology. We measure the (apparent) average surface mass density profiles of 33 613 isolated central galaxies and compare them to those predicted by EG based on the galaxies' baryonic masses. To this end, we employ the ∼180 deg2 overlap of the Kilo-Degree Survey with the spectroscopic Galaxy And Mass Assembly survey. We find that the prediction from EG, despite requiring no free parameters, is in good agreement with the observed galaxy-galaxy lensing profiles in four different stellar mass bins. Although this performance is remarkable, this study is only a first step. Further advancements on both the theoretical framework and observational tests of EG are needed before it can be considered a fully developed and solidly tested theory.
An accurate and practical method for inference of weak gravitational lensing from galaxy images
NASA Astrophysics Data System (ADS)
Bernstein, Gary M.; Armstrong, Robert; Krawiec, Christina; March, Marisa C.
2016-07-01
We demonstrate highly accurate recovery of weak gravitational lensing shear using an implementation of the Bayesian Fourier Domain (BFD) method proposed by Bernstein & Armstrong, extended to correct for selection biases. The BFD formalism is rigorously correct for Nyquist-sampled, background-limited, uncrowded images of background galaxies. BFD does not assign shapes to galaxies, instead compressing the pixel data D into a vector of moments M, such that we have an analytic expression for the probability P(M|g) of obtaining the observations with gravitational lensing distortion g along the line of sight. We implement an algorithm for conducting BFD's integrations over the population of unlensed source galaxies which measures ≈10 galaxies s-1 core-1 with good scaling properties. Initial tests of this code on ≈109 simulated lensed galaxy images recover the simulated shear to a fractional accuracy of m = (2.1 ± 0.4) × 10-3, substantially more accurate than has been demonstrated previously for any generally applicable method. Deep sky exposures generate a sufficiently accurate approximation to the noiseless, unlensed galaxy population distribution assumed as input to BFD. Potential extensions of the method include simultaneous measurement of magnification and shear; multiple-exposure, multiband observations; and joint inference of photometric redshifts and lensing tomography.
Gravitational lensing of gravitational wave
NASA Astrophysics Data System (ADS)
Kei Wong, Wang; Ng, Kwan Yeung
2017-01-01
Gravitational lensing phenomena are widespread in electromagnetic astrophysics, and in principle may also be uncovered with gravitational waves. We examine gravitational wave events lensed by elliptical galaxies in the limit of geometric optics, where we expect to see multiple signals from the same event with different arrival times and amplitudes. By using mass functions for compact binaries from population-synthesis simulations and a lensing probability calculated from Planck data, we estimate the rate of lensed signals for future gravitational wave missions.
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 20,000 deg{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 ☉}.
NASA Astrophysics Data System (ADS)
Harnois-Déraps, 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 ξ+(θ) and its error. We find that the most important quantities for FS modelling are the ratio between the measured angle θ and the angular size of the simulation box at the source redshift, θbox(zs), or the multipole equivalent ℓ/ℓbox(zs). When this ratio reaches 0.1, independently of the source redshift, the shear correlation function ξ+ 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 ξ-(θ), 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 ξ- covariance matrix, also 20 per cent accurate for most elements.
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.
Wittman; Tyson; Kirkman; Dell'Antonio; Bernstein
2000-05-11
Most of the matter in the Universe is not luminous, and can be observed only through its gravitational influence on the appearance of luminous matter. Weak gravitational lensing is a technique that uses the distortions of the images of distant galaxies as a tracer of dark matter: such distortions are induced as the light passes through large-scale distributions of dark matter in the foreground. The patterns of the induced distortions reflect the density of mass along the line of sight and its distribution, and the resulting 'cosmic shear' can be used to distinguish between alternative cosmologies. But previous attempts to measure this effect have been inconclusive. Here we report the detection of cosmic shear on angular scales of up to half a degree using 145,000 galaxies and along three separate lines of sight. We find that the dark matter is distributed in a manner consistent with either an open universe, or a flat universe that is dominated by a cosmological constant. Our results are inconsistent with the standard cold-dark-matter model.
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.
KiDS-450: cosmological parameter constraints from tomographic weak gravitational lensing
NASA Astrophysics Data System (ADS)
Hildebrandt, H.; Viola, M.; Heymans, C.; Joudaki, S.; Kuijken, K.; Blake, C.; Erben, T.; Joachimi, B.; Klaes, D.; Miller, L.; Morrison, C. B.; Nakajima, R.; Verdoes Kleijn, G.; Amon, A.; Choi, A.; Covone, G.; de Jong, J. T. A.; Dvornik, A.; Fenech Conti, I.; Grado, A.; Harnois-Déraps, J.; Herbonnet, R.; Hoekstra, H.; Köhlinger, F.; McFarland, J.; Mead, A.; Merten, J.; Napolitano, N.; Peacock, J. A.; Radovich, M.; Schneider, P.; Simon, P.; Valentijn, E. A.; van den Busch, J. L.; van Uitert, E.; Van Waerbeke, L.
2017-02-01
We present cosmological parameter constraints from a tomographic weak gravitational lensing analysis of ∼450 deg2 of imaging data from the Kilo Degree Survey (KiDS). For a flat Λ cold dark matter (ΛCDM) cosmology with a prior on H0 that encompasses the most recent direct measurements, we find S_8≡ σ _8√{Ω _m/0.3}=0.745± 0.039. This result is in good agreement with other low-redshift probes of large-scale structure, including recent cosmic shear results, along with pre-Planck cosmic microwave background constraints. A 2.3σ tension in S8 and 'substantial discordance' in the full parameter space is found with respect to the Planck 2015 results. We use shear measurements for nearly 15 million galaxies, determined with a new improved 'self-calibrating' version of lensFIT validated using an extensive suite of image simulations. Four-band ugri photometric redshifts are calibrated directly with deep spectroscopic surveys. The redshift calibration is confirmed using two independent techniques based on angular cross-correlations and the properties of the photometric redshift probability distributions. Our covariance matrix is determined using an analytical approach, verified numerically with large mock galaxy catalogues. We account for uncertainties in the modelling of intrinsic galaxy alignments and the impact of baryon feedback on the shape of the non-linear matter power spectrum, in addition to the small residual uncertainties in the shear and redshift calibration. The cosmology analysis was performed blind. Our high-level data products, including shear correlation functions, covariance matrices, redshift distributions, and Monte Carlo Markov chains are available at http://kids.strw.leidenuniv.nl.
NASA Astrophysics Data System (ADS)
Plazas, A. A.; Shapiro, C.; Kannawadi, A.; Mandelbaum, R.; Rhodes, J.; Smith, R.
2016-10-01
Weak gravitational lensing (WL) is one of the most powerful techniques to learn about the dark sector of the universe. To extract the WL signal from astronomical observations, galaxy shapes must be measured and corrected for the point-spread function (PSF) of the imaging system with extreme accuracy. Future WL missions—such as NASA’s Wide-Field Infrared Survey Telescope (WFIRST)—will use a family of hybrid near-infrared complementary metal-oxide-semiconductor detectors (HAWAII-4RG) that are untested for accurate WL measurements. Like all image sensors, these devices are subject to conversion gain nonlinearities (voltage response to collected photo-charge) that bias the shape and size of bright objects such as reference stars that are used in PSF determination. We study this type of detector nonlinearity (NL) and show how to derive requirements on it from WFIRST PSF size and ellipticity requirements. We simulate the PSF optical profiles expected for WFIRST and measure the fractional error in the PSF size (ΔR/R) and the absolute error in the PSF ellipticity (Δe) as a function of star magnitude and the NL model. For our nominal NL model (a quadratic correction), we find that, uncalibrated, NL can induce an error of ΔR/R = 1 × 10-2 and Δe 2 = 1.75 × 10-3 in the H158 bandpass for the brightest unsaturated stars in WFIRST. In addition, our simulations show that to limit the bias of ΔR/R and Δe in the H158 band to ˜10% of the estimated WFIRST error budget, the quadratic NL model parameter β must be calibrated to ˜1% and ˜2.4%, respectively. We present a fitting formula that can be used to estimate WFIRST detector NL requirements once a true PSF error budget is established.
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.
Means of confusion: how pixel noise affects shear estimates for weak gravitational lensing
NASA Astrophysics Data System (ADS)
Melchior, P.; Viola, M.
2012-08-01
Weak-lensing shear estimates show a troublesome dependence on the apparent brightness of the galaxies used to measure the ellipticity: in several studies, the amplitude of the inferred shear falls sharply with decreasing source significance. This dependence limits the overall ability of upcoming large weak-lensing surveys to constrain cosmological parameters. We seek to provide a concise overview of the impact of pixel noise on weak-lensing measurements, covering the entire path from noisy images to shear estimates. We show that there are at least three distinct layers, where pixel noise not only obscures but also biases the outcome of the measurements: (1) the propagation of pixel noise to the non-linear observable ellipticity; (2) the response of the shape-measurement methods to limited amount of information extractable from noisy images and (3) the reaction of shear estimation statistics to the presence of noise and outliers in the measured ellipticities. We identify and discuss several fundamental problems and show that each of them is able to introduce biases in the range of a few tens to a few per cent for galaxies with typical significance levels. Furthermore, all of these biases do not only depend on the brightness of galaxies but also depend on their ellipticity, with more elliptical galaxies often being harder to measure correctly. We also discuss existing possibilities to mitigate and novel ideas to avoid the biases induced by pixel noise. We present a new shear estimator that shows a more robust performance for noisy ellipticity samples. Finally, we release the open-source PYTHON code to predict and efficiently sample from the noisy ellipticity distribution and the shear estimators used in this work at https://github.com/pmelchior/epsnoise.
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)
Jönsson, J.; Goobar, A.; Mörtsell, 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)
Lombardi, Marco; Bertin, Giuseppe
1999-02-01
Recently, it has been shown that it is possible to reconstruct the projected mass distribution of a cluster from weak lensing provided that both the geometry of the universe and the probability distribution of galaxy redshifts are known; actually, when additional photometric data are taken to be available, the galaxy redshift distribution could be determined jointly with the cluster mass from the weak lensing analysis. In this paper we develop, in the spirit of a ``thought experiment,'' a method to constrain the geometry of the universe from weak lensing, provided that the redshifts of the source galaxies are measured. The quantitative limits and merits of the method are discussed analytically and with a set of simulations, in relation to point estimation, interval estimation, and test of hypotheses for homogeneous Friedmann-Lema\\^\\i tre models. The constraints turn out to be significant when a few thousand source galaxies are used.
Gravitational lensing in plasmic medium
Bisnovatyi-Kogan, G. S. Tsupko, O. Yu.
2015-07-15
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.
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.
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)
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.
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.
Investigations of galaxy clusters using gravitational lensing
NASA Astrophysics Data System (ADS)
Wiesner, Matthew P.
In this dissertation, we discuss the properties of galaxy clusters that have been determined using strong and weak gravitational lensing. A galaxy cluster is a collection of galaxies that are bound together by the force of gravity, while gravitational lensing is the bending of light by gravity. Strong lensing is the formation of arcs or rings of light surrounding clusters and weak lensing is a change in the apparent shapes of many galaxies. In this work we examine the properties of several samples of galaxy clusters using gravitational lensing. In Chapter 1 we introduce astrophysical theory of galaxy clusters and gravitational lensing. In Chapter 2 we examine evidence from our data that galaxy clusters are more concentrated than cosmology would predict. In Chapter 3 we investigate whether our assumptions about the number of galaxies in our clusters was valid by examining new data. In Chapter 4 we describe a determination of a relationship between mass and number of galaxies in a cluster at higher redshift than has been found before. In Chapter 5 we describe a model of the mass distribution in one of the ten lensing systems discovered by our group at Fermilab. Finally in Chapter 6 we summarize our conclusions.
Investigations of Galaxy Clusters Using Gravitational Lensing
Wiesner, Matthew P.
2014-08-01
In this dissertation, we discuss the properties of galaxy clusters that have been determined using strong and weak gravitational lensing. A galaxy cluster is a collection of galaxies that are bound together by the force of gravity, while gravitational lensing is the bending of light by gravity. Strong lensing is the formation of arcs or rings of light surrounding clusters and weak lensing is a change in the apparent shapes of many galaxies. In this work we examine the properties of several samples of galaxy clusters using gravitational lensing. In Chapter 1 we introduce astrophysical theory of galaxy clusters and gravitational lensing. In Chapter 2 we examine evidence from our data that galaxy clusters are more concentrated than cosmology would predict. In Chapter 3 we investigate whether our assumptions about the number of galaxies in our clusters was valid by examining new data. In Chapter 4 we describe a determination of a relationship between mass and number of galaxies in a cluster at higher redshift than has been found before. In Chapter 5 we describe a model of the mass distribution in one of the ten lensing systems discovered by our group at Fermilab. Finally in Chapter 6 we summarize our conclusions.
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
Roulettes: a weak lensing formalism for strong lensing: I. Overview
NASA Astrophysics Data System (ADS)
Clarkson, Chris
2016-08-01
We present a new perspective on gravitational lensing. We describe a new extension of the weak lensing formalism capable of describing strongly lensed images. By integrating the nonlinear geodesic deviation equation, the amplification matrix of weak lensing is generalised to a sum over independent amplification tensors of increasing rank. We show how an image distorted by a generic lens may be constructed as a sum over ‘roulettes’, which are the natural curves associated with the independent spin modes of the amplification tensors. Highly distorted images can be constructed even for large sources observed near or within the Einstein radius of a lens where the shear and convergence are large. The amplitude of each roulette is formed from a sum over appropriate derivatives of the lensing potential. Consequently, measuring these individual roulettes for images around a lens gives a new way to reconstruct a strong lens mass distribution without requiring a lens model. This formalism generalises the convergence, shear and flexion of weak lensing to arbitrary order, and provides a unified bridge between the strong and weak lensing regimes. This overview paper is accompanied by a much more detailed paper II, arXiv:1603.04652.
Probing Galaxy Clusters and Substructures using Gravitational Lensing
NASA Astrophysics Data System (ADS)
Choi, Miyoung; Nguyen, Hoang; King, Lindsay; Lee, Brandyn E.; McCarthy, Ian
2017-01-01
Gravitational lensing is one of the most promising methods of analyzing massive astronomical objects such as galaxy clusters. The weak gravitational lensing signal, which is called shear, is a measurement of the weak distortion of background galaxies in the linear regime of the lensing field. Shear analysis effectively estimates the main properties of galaxy clusters such as the mass and scale of the lensing system. The second order gravitational lensing signal, flexion, is dominant in the non-linear regime of the lensing field that bridges the strong and weak lensing regimes. It has also recently arisen as a robust method to detect substructures in galaxy clusters due to its sensitivity to the gradient of convergence and shear field. In this poster we propose that combining the shear and flexion analysis can give more information about the detailed structure of the lensing system.
CONSTRAINING SOURCE REDSHIFT DISTRIBUTIONS WITH GRAVITATIONAL LENSING
Wittman, D.; Dawson, W. A.
2012-09-10
We introduce a new method for constraining the redshift distribution of a set of galaxies, using weak gravitational lensing shear. Instead of using observed shears and redshifts to constrain cosmological parameters, we ask how well the shears around clusters can constrain the redshifts, assuming fixed cosmological parameters. This provides a check on photometric redshifts, independent of source spectral energy distribution properties and therefore free of confounding factors such as misidentification of spectral breaks. We find that {approx}40 massive ({sigma}{sub v} = 1200 km s{sup -1}) cluster lenses are sufficient to determine the fraction of sources in each of six coarse redshift bins to {approx}11%, given weak (20%) priors on the masses of the highest-redshift lenses, tight (5%) priors on the masses of the lowest-redshift lenses, and only modest (20%-50%) priors on calibration and evolution effects. Additional massive lenses drive down uncertainties as N{sub lens}{sup -1/2}, but the improvement slows as one is forced to use lenses further down the mass function. Future large surveys contain enough clusters to reach 1% precision in the bin fractions if the tight lens-mass priors can be maintained for large samples of lenses. In practice this will be difficult to achieve, but the method may be valuable as a complement to other more precise methods because it is based on different physics and therefore has different systematic errors.
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…
The Optical Gravitational Lensing Experiment
NASA Technical Reports Server (NTRS)
Udalski, A.; Szymanski, M.; Kaluzny, J.; Kubiak, M.; Mateo, Mario
1992-01-01
The technical features are described of the Optical Gravitational Lensing Experiment, which aims to detect a statistically significant number of microlensing events toward the Galactic bulge. Clusters of galaxies observed during the 1992 season are listed and discussed and the reduction methods are described. Future plans are addressed.
Gravitational Lensing Illustration
Simulation of a gravitational lens moving against a background field of galaxy. The gravity of the mass of the foreground object warps space. This bends the light of background galaxies making them...
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
Cosmological model discrimination with weak lensing
NASA Astrophysics Data System (ADS)
Pires, S.; Starck, J.-L.; Amara, A.; Réfrégier, A.; Teyssier, R.
2009-10-01
Weak gravitational lensing provides a unique way of mapping directly the dark matter in the Universe. The majority of lensing analyses use the two-point statistics of the cosmic shear field to constrain the cosmological model, a method that is affected by degeneracies, such as that between σ8 and Ωm which are respectively the rms of the mass fluctuations on a scale of 8 Mpc/h and the matter density parameter, both at z = 0. However, the two-point statistics only measure the Gaussian properties of the field, and the weak lensing field is non-Gaussian. It has been shown that the estimation of non-Gaussian statistics for weak lensing data can improve the constraints on cosmological parameters. In this paper, we systematically compare a wide range of non-Gaussian estimators to determine which one provides tighter constraints on the cosmological parameters. These statistical methods include skewness, kurtosis, and the higher criticism test, in several sparse representations such as wavelet and curvelet; as well as the bispectrum, peak counting, and a newly introduced statistic called wavelet peak counting (WPC). Comparisons based on sparse representations indicate that the wavelet transform is the most sensitive to non-Gaussian cosmological structures. It also appears that the most helpful statistic for non-Gaussian characterization in weak lensing mass maps is the WPC. Finally, we show that the σ8 - Ωm degeneracy could be even better broken if the WPC estimation is performed on weak lensing mass maps filtered by the wavelet method, MRLens.
Cosmological model discrimination from weak lensing data
NASA Astrophysics Data System (ADS)
Pires, S.; Starck, J.-L.; Amara, A.; Réfrégier, A.; Teyssier, R.
2010-06-01
Weak gravitational lensing provides a unique way of mapping directly the dark matter in the Universe. The majority of lensing analyses use the two-point statistics of the cosmic shear field to constrain the cosmological model, a method that is affected by degeneracies, such as that between σ8 and Ωm which are respectively the rms of the mass fluctuations on a scale of 8 Mpc/h and the matter density parameter, both at z = 0. However, the two-point statistics only measure the Gaussian properties of the field, and the weak lensing field is non-Gaussian. It has been shown that the estimation of non-Gaussian statistics for weak lensing data can improve the constraints on cosmological parameters. In this paper, we systematically compare a wide range of non-Gaussian estimators to determine which one provides tighter constraints on the cosmological parameters. These statistical methods include skewness, kurtosis, and the higher criticism test, in several sparse representations such as wavelet and curvelet; as well as the bispectrum, peak counting, and a newly introduced statistic called wavelet peak counting (WPC). Comparisons based on sparse representations indicate that the wavelet transform is the most sensitive to non-Gaussian cosmological structures. It also appears that the most helpful statistic for non-Gaussian characterization in weak lensing mass maps is the WPC. Finally, we show that the σ8-Ωm degeneracy could be even better broken if the WPC estimation is performed on weak lensing mass maps filtered by the wavelet method, MRLens.
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.
Numerical simulation of gravitational lenses
NASA Astrophysics Data System (ADS)
Cherniak, Yakov
Gravitational lens is a massive body or system of bodies with gravitational field that bends directions of light rays propagating nearby. This may cause an observer to see multiple images of a light source, e.g. a star, if there is a gravitational lens between the star and the observer. Light rays that form each individual image may have different distances to travel, which creates time delays between them. In complex gravitational fields generated by the system of stars, analytical calculation of trajectories and light intensities is virtually impossible. Gravitational lens of two massive bodies, one behind another, are able to create four images of a light source. Furthermore, the interaction between the four light beams can form a complicated interference pattern. This article provides a brief theory of light behavior in a gravitational field and describes the algorithm for constructing the trajectories of light rays in a gravitational field, calculating wave fronts and interference pattern of light. If you set gravitational field by any number of transparent and non- transparent objects (stars) and set emitters of radio wave beams, it is possible to calculate the interference pattern in any region of space. The proposed method of calculation can be applied even in the case of the lack of continuity between the position of the emitting stars and position of the resulting image. In this paper we propose methods of optimization, as well as solutions for some problems arising in modeling of gravitational lenses. The simulation of light rays in the sun's gravitational field is taken as an example. Also caustic is constructed for objects with uniform mass distribution.
Pixelation Effects in Weak Lensing
NASA Technical Reports Server (NTRS)
High, F. William; Rhodes, Jason; Massey, Richard; Ellis, Richard
2007-01-01
Weak gravitational lensing can be used to investigate both dark matter and dark energy but requires accurate measurements of the shapes of faint, distant galaxies. Such measurements are hindered by the finite resolution and pixel scale of digital cameras. We investigate the optimum choice of pixel scale for a space-based mission, using the engineering model and survey strategy of the proposed Supernova Acceleration Probe as a baseline. We do this by simulating realistic astronomical images containing a known input shear signal and then attempting to recover the signal using the Rhodes, Refregier, and Groth algorithm. We find that the quality of shear measurement is always improved by smaller pixels. However, in practice, telescopes are usually limited to a finite number of pixels and operational life span, so the total area of a survey increases with pixel size. We therefore fix the survey lifetime and the number of pixels in the focal plane while varying the pixel scale, thereby effectively varying the survey size. In a pure trade-off for image resolution versus survey area, we find that measurements of the matter power spectrum would have minimum statistical error with a pixel scale of 0.09' for a 0.14' FWHM point-spread function (PSF). The pixel scale could be increased to 0.16' if images dithered by exactly half-pixel offsets were always available. Some of our results do depend on our adopted shape measurement method and should be regarded as an upper limit: future pipelines may require smaller pixels to overcome systematic floors not yet accessible, and, in certain circumstances, measuring the shape of the PSF might be more difficult than those of galaxies. However, the relative trends in our analysis are robust, especially those of the surface density of resolved galaxies. Our approach thus provides a snapshot of potential in available technology, and a practical counterpart to analytic studies of pixelation, which necessarily assume an idealized shape
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.
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.
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.
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.
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.
Masses of Galaxy Clusters from Gravitational Lensing
NASA Astrophysics Data System (ADS)
Hoekstra, Henk; Bartelmann, Matthias; Dahle, Håkon; Israel, Holger; Limousin, Marceau; Meneghetti, Massimo
2013-08-01
Despite consistent progress in numerical simulations, the observable properties of galaxy clusters are difficult to predict ab initio. It is therefore important to compare both theoretical and observational results to a direct measure of the cluster mass. This can be done by measuring the gravitational lensing effects caused by the bending of light by the cluster mass distribution. In this review we discuss how this phenomenon can be used to determine cluster masses and study the mass distribution itself. As sample sizes increase, the accuracy of the weak lensing mass estimates needs to improve accordingly. We discuss the main practical aspects of these measurements. We review a number of applications and highlight some recent results.
Weak Gravitatational Lensing by Illustris-1 Galaxies
NASA Astrophysics Data System (ADS)
Brainerd, Tereasa G.; Koh, Patrick H.
2016-06-01
We compute the weak gravitational lensing signal of isolated, central galaxies obtained from the z=0.5 timestep of the ΛCDM Illustris-1 simulation. The galaxies have stellar masses ranging from 9.5 ≤ log10(M*/Msun) ≤ 11.0 and are located outside cluster and rich group environments. Although there is local substructure present in the form of small, luminous satellite galaxies, the central galaxies are the dominant objects within the virial radii (r200), and each central galaxy is at least 5 times brighter than any other luminous galaxy within the friends-of-friends halo. We compute the weak lensing signal within projected radii 0.05 < rp/r200 < 1.5 and investigate the degree to which the weak lensing signal is anisotropic. Since CDM halos are non-spherical, the weak lensing signal is expected to be anisotropic; however, the degree of anisotropy that is observed depends upon the symmetry axes that are used to define the geometry. The anisotropy is expected to be maximized when the major axis of the projected dark matter mass distribution is used to define the geomety. In practice in the observed universe, one must necessarily use the projected distribution of the luminous mass to define the geometry. If mass and light are not well-aligned, this results in a suppression of the weak lensing anistropy. Our initial analysis shows that the ellipticity of the projected dark matter halo is uncorrelated with the ellipticity of the projected stellar mass. That is ɛhalo ≠ f × ɛlight, where f is a constant multiplicative factor. In addition, in projection on the sky, the major axis of the dark matter mass is offset from that of the stellar mass by ˜40o on average. On scales rp ≤ 0.15 r200, the weak lensing anisotropy obtained when using the stellar mass to define the geometry is of order 7% and agrees well with the anisotropy obtained when using the dark matter mass to define the geometry. On scales rp ˜ r200, the anisotropy obtained when using the stellar mass to
Multi-wavelength applications of gravitational lensing
NASA Astrophysics Data System (ADS)
Fadely, Ross
2010-12-01
Using an array of multi-wavelength data, we examine a variety of astrophysical problems with gravitational lensing. First, we seek to understand the mass distribution of an early-type galaxy with an analysis of the lens Q0957+561. We dissect the lens galaxy into luminous and dark components, and model the environment using results from weak lensing. Combining constraints from newly-discovered lensed images and stellar population models, we find the lens has a density profile which is shallower than isothermal, unlike those of typical early-type galaxies. Finally, using the measured time delay between the quasar images we find the Hubble constant to be H 0 = 79.3+6.7-8.5 km s-1 Mpc-1 . One intriguing application of lensing is to exploit the lens magnification boost to study high-redshift objects in greater detail than otherwise possible. Here, we analyze the mid-infrared properties of two lensed z ˜ 2 star-forming galaxies, SDSS J120602.09+514229.5 and SDSS J090122.37+181432.3, using Spitzer /IRS spectra to study their rest-frame ˜ 5-12 μm emission. Both systems exhibit strong polycyclic aromatic hydrocarbon (PAH) features in the spectra, indicating strong star formation and the absence of significant AGN activity. For SDSS J090122.37+181432.3, this detection belies that inferred from optical measurements, indicating mid-IR spectroscopy provides key information needed to understand the properties of high-redshift star-forming galaxies. While lensing provides measurements of the macroscopic properties of lens systems, it can also shed light on small-scale structure of galaxies. To identify and understand lens substructure, we examine the multi-wavelength properties of flux ratios for six lenses. Variations of the flux ratios with wavelength can be used to study the lensed quasars and the small-scale mass distribution of lens galaxies. We detect strong multi-wavelength variations in the lenses HE 0435-1223 and SDSS 0806+2006. For HE 0435-1223, we study its
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.
Weak lensing corrections to tSZ-lensing cross correlation
Tröster, Tilman; Waerbeke, Ludovic Van E-mail: waerbeke@phas.ubc.ca
2014-11-01
The cross correlation between the thermal Sunyaev-Zeldovich (tSZ) effect and gravitational lensing in wide field has recently been measured. It can be used to probe the distribution of the diffuse gas in large scale structure, as well as inform us about the missing baryons. As for any lensing-based quantity, higher order lensing effects can potentially affect the signal. Here, we extend previous higher order lensing calculations to the case of tSZ-lensing cross correlations. We derive terms analogous to corrections due to the Born approximation, lens-lens coupling, and reduced shear up to order ℓ ∼> 3000.
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.
NASA Astrophysics Data System (ADS)
Shirasaki, Masato; Nishimichi, Takahiro; Li, Baojiu; Higuchi, Yuichi
2017-04-01
We investigate the information content of various cosmic shear statistics on the theory of gravity. Focusing on the Hu-Sawicki-type f(R) model, we perform a set of ray-tracing simulations and measure the convergence bispectrum, peak counts and Minkowski functionals. We first show that while the convergence power spectrum does have sensitivity to the current value of extra scalar degree of freedom |fR0|, it is largely compensated by a change in the present density amplitude parameter σ8 and the matter density parameter Ωm0. With accurate covariance matrices obtained from 1000 lensing simulations, we then examine the constraining power of the three additional statistics. We find that these probes are indeed helpful to break the parameter degeneracy, which cannot be resolved from the power spectrum alone. We show that especially the peak counts and Minkowski functionals have the potential to rigorously (marginally) detect the signature of modified gravity with the parameter |fR0| as small as 10-5 (10-6) if we can properly model them on small (∼1 arcmin) scale in a future survey with a sky coverage of 1500 deg2. We also show that the signal level is similar among the additional three statistics and all of them provide complementary information to the power spectrum. These findings indicate the importance of combining multiple probes beyond the standard power spectrum analysis to detect possible modifications to general relativity.
Lossy compression of weak lensing data
Vanderveld, R. Ali; Bernstein, Gary M.; Stoughton, Chris; ...
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
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.
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.
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.
Trapping light by mimicking gravitational lensing
NASA Astrophysics Data System (ADS)
Sheng, C.; Liu, H.; Wang, Y.; Zhu, S. N.; Genov, D. A.
2013-11-01
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 radiation. However, the development of experimental `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.
Gravitational Lensing from a Spacetime Perspective.
Perlick, Volker
2004-01-01
The theory of gravitational lensing is reviewed from a spacetime perspective, without quasi-Newtonian approximations. More precisely, the review covers all aspects of gravitational lensing where light propagation is described in terms of lightlike geodesics of a metric of Lorentzian signature. It includes the basic equations and the relevant techniques for calculating the position, the shape, and the brightness of images in an arbitrary general-relativistic spacetime. It also includes general theorems on the classification of caustics, on criteria for multiple imaging, and on the possible number of images. The general results are illustrated with examples of spacetimes where the lensing features can be explicitly calculated, including the Schwarzschild spacetime, the Kerr spacetime, the spacetime of a straight string, plane gravitational waves, and others.
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.
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
Magnified Weak Lensing Cross Correlation Tomography
Ulmer, Melville P., Clowe, Douglas I.
2010-11-30
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
Astrophysical Applications of Gravitational Lensing
NASA Astrophysics Data System (ADS)
Mediavilla, Evencio; Muñoz, Jose A.; Garzón, Francisco; Mahoney, Terence J.
2016-10-01
Contributors; Participants; Preface; Acknowledgements; 1. Lensing basics Sherry H. Suyu; 2. Exoplanet microlensing Andrew Gould; 3. Case studies of microlensing Veronica Motta and Emilio Falco; 4. Microlensing of quasars and AGN Joachim Wambsganss; 5. DM in clusters and large-scale structure Peter Schneider; 6. The future of strong lensing Chris Fassnacht; 7. Methods for strong lens modelling Charles Keeton; 8. Tutorial on inverse ray shooting Jorge Jimenez-Vicente.
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.
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.
BAYESIAN INFERENCE OF CMB GRAVITATIONAL LENSING
Anderes, Ethan; Wandelt, Benjamin D.; Lavaux, Guilhem
2015-08-01
The Planck satellite, along with several ground-based telescopes, has mapped the cosmic microwave background (CMB) at sufficient resolution and signal-to-noise so as to allow a detection of the subtle distortions due to the gravitational influence of the intervening matter distribution. A natural modeling approach is to write a Bayesian hierarchical model for the lensed CMB in terms of the unlensed CMB and the lensing potential. So far there has been no feasible algorithm for inferring the posterior distribution of the lensing potential from the lensed CMB map. We propose a solution that allows efficient Markov Chain Monte Carlo sampling from the joint posterior of the lensing potential and the unlensed CMB map using the Hamiltonian Monte Carlo technique. The main conceptual step in the solution is a re-parameterization of CMB lensing in terms of the lensed CMB and the “inverse lensing” potential. We demonstrate a fast implementation on simulated data, including noise and a sky cut, that uses a further acceleration based on a very mild approximation of the inverse lensing potential. We find that the resulting Markov Chain has short correlation lengths and excellent convergence properties, making it promising for applications to high-resolution CMB data sets in the future.
Gravitational Lensing of STU Black Holes
NASA Astrophysics Data System (ADS)
Saadat, H.
2013-12-01
In this paper we study gravitational lensing by STU black holes. We considered extremal limit of two special cases of zero-charged and one-charged black holes, and obtain the deflection angle. We find that the black hole charge increases the deflection angle.
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.
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.
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.
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.
Measuring the dark side (with weak lensing)
Amendola, Luca
2008-04-15
We introduce a convenient parameterization of dark energy models that is general enough to include several modified gravity models and generalized forms of dark energy. In particular we take into account the linear perturbation growth factor, the anisotropic stress and the modified Poisson equation. We discuss the sensitivity of large-scale weak lensing surveys like the proposed DUNE satellite to these parameters (assuming systematic errors can be controlled). We find that a large-scale weak lensing tomographic survey is able to easily distinguish the Dvali-Gabadadze-Porrati model from {Lambda}CDM and to determine the perturbation growth index to an absolute error of 0.02-0.04.
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.
Gravitational lensing statistics of amplified supernovae
NASA Technical Reports Server (NTRS)
Linder, Eric V.; Wagoner, Robert V.; Schneider, P.
1988-01-01
Amplification statistics of gravitationally lensed supernovae can provide a valuable probe of the lensing matter in the universe. A general probability distribution for amplification by compact objects is derived which allows calculation of the lensed fraction of supernovae at or greater than an amplification A and at or less than an apparent magnitude. Comparison of the computed fractions with future results from ongoing supernova searches can lead to determination of the mass density of compact dark matter components with masses greater than about 0.001 solar mass, while the time-dependent amplification (and polarization) of the expanding supernovae constrain the individual masses. Type II supernovae are found to give the largest fraction for deep surveys, and the optimum flux-limited search is found to be at approximately 23d magnitude, if evolution of the supernova rate is neglected.
Probing Cosmology with Minkowski Functionals of Weak Lensing Maps
NASA Astrophysics Data System (ADS)
Kratochvil, Jan Michael; Lim, E. A.; Wang, S.; Haiman, Z.; May, M.; Huffenberger, K.
2011-01-01
Minkowski functionals (MFs) are alternative probes of non-Gaussianity of random fields and probe the morphology and topology. We apply them to constrain cosmological parameters from weak gravitational lensing maps. We use MFs with Monte Carlo-optimized threshold bins to distinguish between different cosmological models from simulated convergence maps. We find that MFs discern better than the power spectrum from the same maps, thus providing evidence that they probe nonlinear structure formation and measure information beyond the power spectrum. The lensing maps were created with our new huge Inspector Gadget lensing simulation pipeline on the IBM Blue Gene at Brookhaven National Laboratory, allowing us to create an extensive simulation suite of ninety 5123-particle N-body simulations and sample many cosmological models and initial conditions.
Invariants of simple gravitational lenses
NASA Astrophysics Data System (ADS)
Kassiola, Aggeliki; Kovner, Israel
1995-01-01
We present approximate tests which can be applied to a newly observed quadruple QSO, or to a quadruplet of extended objects distorted by a foreground cluster of galaxies. These tests indicate whether the responsible gravitational lens may have a simple mass distribution. If the lens galaxy is detected, the tests give an approximate orientation for it, which can be compared with the observed orientation of the galaxy. The tests do not require construction of an explicit lens model, and therefore can save time and effort. In the case of many objects distorted by a cluster, these diagnostics can help to select possible quadruplet candidates.
The Theory of Multiscale Gravitational Lensing
NASA Astrophysics Data System (ADS)
Keeton, Charles
2005-07-01
Strong gravitational lensing probes the mass distributions of distant galaxies on scales from tens of kiloparsecs {dark matter halos and "macrolensing"} through parsecs {dark matter substructure and "millilensing"} all the way down to individual stars {"microlensing"}. Wonderful data are now available, thanks in large part to HST. However, the theoretical understanding of lensing on different scales is much less mature, which has complicated efforts to interpret the data. We have begun a comprehensive theoretical study of multiscale lensing, to develop a formalism that will enable us both to interpret existing data and to inspire and guide new observations. In this proposal, we specifically seek to develop the first code that simultaneously includes macro-, milli-, and microlensing. We will then use it to: {1} Find clear observational signatures that reveal the scale{s} being probed in data, and then resolve the debate about whether millilensing truly reveals Cold Dark Matter substructure. {2} Show how observations at different scales can constrain the mass function of stars in lens galaxies, and apply the method to existing HST data for seven distant galaxies. {3} Examine non-linearities that link micro-, milli-, and macrolensing, and use the combined analysis to open a new window on dark matter studies with strong lensing. We will also make the code available to the community as part of PI Keeton's public lensing software.
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
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.
Gravitational lensing and the Lyman-alpha forest
NASA Technical Reports Server (NTRS)
Ikeuchi, Satoru; Turner, Edwin L.
1991-01-01
Possible connections between the inhomogeneities responsible for the Lyman-alpha forest in quasar spectra and gravitational lensing effects are investigated. For most models of the Lyman-alpha forest, no significant lensing is expected. For some versions of the CDM model-based minihalo hypothesis, gravitational lensings on scales less than abour 0.1 arcsec would occur with a frequency approaching that with which ordinary galaxies cause arcsecond scale lensing.
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.
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.
Weak gravitational shear and flexion with polar shapelets
NASA Astrophysics Data System (ADS)
Massey, Richard; Rowe, Barnaby; Refregier, Alexandre; Bacon, David J.; Bergé, Joel
2007-09-01
We derive expressions, in terms of `polar shapelets', for the image distortion operations associated with weak gravitational lensing. Shear causes galaxy shapes to become elongated, and is sensitive to the second derivative of the projected gravitational potential along their line of sight; flexion bends galaxy shapes into arcs, and is sensitive to the third derivative. Polar shapelets provide a natural representation, in which both shear and flexion transformations are compact. Through this tool, we understand progress in several weak lensing methods. We then exploit various symmetries of shapelets to construct a range of shear estimators with useful properties. Through an analogous investigation, we also explore several flexion estimators. In particular, some of the estimators can be measured simultaneously and independently for every galaxy, and will provide unique checks for systematics in future weak lensing analyses. Using simulated images from the Shear TEsting Programme, we show that we can recover input shears with no significant bias. A complete software package to parametrize astronomical images in terms of polar shapelets, and to perform a full weak lensing analysis, is available on the Internet.
Multimessenger time delays from lensed gravitational waves
NASA Astrophysics Data System (ADS)
Baker, Tessa; Trodden, Mark
2017-03-01
We investigate the potential of high-energy astrophysical events, from which both massless and massive signals are detected, to probe fundamental physics. In particular, we consider how strong gravitational lensing can induce time delays in multimessenger signals from the same source. Obvious messenger examples are massless photons and gravitational waves, and massive neutrinos, although more exotic applications can also be imagined, such as to massive gravitons or axions. The different propagation times of the massive and massless particles can, in principle, place bounds on the total neutrino mass and probe cosmological parameters. Whilst measuring such an effect may pose a significant experimental challenge, we believe that the "massive time delay" represents an unexplored fundamental physics phenomenon.
Weak lensing of large scale structure in the presence of screening
Tessore, Nicolas; Metcalf, R. Benton; Giocoli, Carlo E-mail: hans.winther@astro.ox.ac.uk E-mail: pedro.ferreira@physics.ox.ac.uk
2015-10-01
A number of alternatives to general relativity exhibit gravitational screening in the non-linear regime of structure formation. We describe a set of algorithms that can produce weak lensing maps of large scale structure in such theories and can be used to generate mock surveys for cosmological analysis. By analysing a few basic statistics we indicate how these alternatives can be distinguished from general relativity with future weak lensing surveys.
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.
The CASTLES Imaging Survey of Gravitational Lenses
NASA Astrophysics Data System (ADS)
Peng, C. Y.; Falco, E. E.; Lehar, J.; Impey, C. D.; Kochanek, C. S.; McLeod, B. A.; Rix, H.-W.
1997-12-01
The CASTLES survey (Cfa-Arizona-(H)ST-Lens-Survey) is imaging most known small-separation gravitational lenses (or lens candidates), using the NICMOS camera (mostly H-band) and the WFPC2 (V and I band) on HST. To date nearly half of the IR imaging survey has been completed. The main goals are: (1) to search for lens galaxies where none have been directly detected so far; (2) obtain photometric redshift estimates (VIH) for the lenses where no spectroscopic redshifts exist; (3) study and model the lens galaxies in detail, in part to study the mass distribution within them, in part to identify ``simple" systems that may permit accurate time delay estimates for H_0; (3) measure the M/L evolution of the sample of lens galaxies with look-back time (to z ~ 1); (4) determine directly which fraction of sources are lensed by ellipticals vs. spirals. We will present the survey specifications and the images obtained so far.
Gravitational lensing of Type Ia supernovae
NASA Astrophysics Data System (ADS)
Goliath, M.; Mörtsell, 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.
Not only Gravitational Lensing, but in general Medium Lensing
NASA Astrophysics Data System (ADS)
Smarandache, Florentin
2013-05-01
According to the General Theory of Relativity the gravity curves the spacetime and everything over there follows a curved path. The space being curved near massive cosmic bodies is just a metaphor, not a fact. We dough that gravity is only geometry. The deflection of light (Gravitational Lensing) near massive cosmic bodies is not due because of a ``curved space'', but because of the medium composition (medium that could be formed by waves, particles, plasma, dust, gaseous, fluids, solids, etc.), to the medium density, medium heterogeneity, and to the electromagnetic and gravitational fields contained in that medium that light passes through. This medium deviates the light direction, because of the interactions of photons with other particles. The space is not empty; it has various nebulae and fields and corpuscles, etc. Light bends not only because of the gravity but also because of the medium gradient and refraction index, similarly as light bends when it leaves or enters a liquid, a plastic, a glass, or a quartz. The inhomogeneous medium may act as an optical lens such that its refractive index varies in a fashion, alike the Gradient-Index Lens. We talk about a Medium Lensing, which means that photons interact with other particles in the medium. For example, the interaction between a photon of electromagnetic radiation with a charged particle (let's say with a free electron), which is known as Compton Effect, produces an increase in the photon's wavelength. In the Inverse Compton Effect the low-energy photons gain energy because they were scattered by much-higher energy free electrons.
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.
Fitting gravitational lenses: truth or delusion
NASA Astrophysics Data System (ADS)
Evans, N. Wyn; Witt, Hans J.
2003-11-01
The observables in a strong gravitational lens are usually just the image positions and sometimes the flux ratios. We develop a new and simple algorithm which allows a set of models to be fitted exactly to the observations. Taking our cue from the strong body of evidence that early-type galaxies are close to isothermal, we assume that the lens is scale-free with a flat rotation curve. External shear can be easily included. Our algorithm allows full flexibility regarding the angular structure of the lensing potential. Importantly, all the free parameters enter linearly into the model and so the lens and flux ratio equations can always be solved by straightforward matrix inversion. The models are only restricted by the fact that the surface mass density must be positive. We use this new algorithm to examine some of the claims made for anomalous flux ratios. It has been argued that such anomalies betray the presence of substantial amounts of substructure in the lensing galaxy. We demonstrate by explicit construction that some of the lens systems for which substructure has been claimed can be well fitted by smooth lens models. This is especially the case when the systematic errors in the flux ratios (caused by microlensing or differential extinction) are taken into account. However, there is certainly one system (B1422+231) for which the existing smooth models are definitely inadequate and for which substructure may be implicated. Within a few tens of kpc of the lensing galaxy centre, dynamical friction and tidal disruption are known to be very efficient at dissolving any substructure. Very little substructure is projected within the Einstein radius. The numbers of strong lenses for which substructure is currently being claimed may be so large that this contradicts rather than supports cold dark matter theories.
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.
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.
Origin of weak lensing convergence peaks
NASA Astrophysics Data System (ADS)
Liu, Jia; Haiman, Zoltán
2016-08-01
Weak lensing convergence peaks are a promising tool to probe nonlinear structure evolution at late times, providing additional cosmological information beyond second-order statistics. Previous theoretical and observational studies have shown that the cosmological constraints on Ωm and σ8 are improved by a factor of up to ≈2 when peak counts and second-order statistics are combined, compared to using the latter alone. We study the origin of lensing peaks using observational data from the 154 deg2 Canada-France-Hawaii Telescope Lensing Survey. We found that while high peaks (with height κ >3.5 σκ , where σκ is the rms of the convergence κ ) are typically due to one single massive halo of ≈1 015M⊙ , low peaks (κ ≲σκ ) are associated with constellations of 2-8 smaller halos (≲1 013M⊙ ). In addition, halos responsible for forming low peaks are found to be significantly offset from the line of sight towards the peak center (impact parameter ≳ their virial radii), compared with ≈0.25 virial radii for halos linked with high peaks, hinting that low peaks are more immune to baryonic processes whose impact is confined to the inner regions of the dark matter halos. Our findings are in good agreement with results from the simulation work by Yang et al. [Phys. Rev. D 84, 043529 (2011)].
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.
Gravitational lensing by ring-like structures
NASA Astrophysics Data System (ADS)
Lake, Ethan; Zheng, Zheng
2017-02-01
We study a class of gravitational lensing systems consisting of an inclined ring/belt, with and without an added point mass at the centre. We show that a common feature of such systems are so-called pseudo-caustics, across which the magnification of a point source changes discontinuously and yet remains finite. Such a magnification change can be associated with either a change in image multiplicity or a sudden change in the size of a lensed image. The existence of pseudo-caustics and the complex interplay between them and the formal caustics (which correspond to points of infinite magnification) can lead to interesting consequences, such as truncated or open caustics and a non-conservation of total image parity. The origin of the pseudo-caustics is found to be the non-differentiability of the solutions to the lens equation across the ring/belt boundaries, with the pseudo-caustics corresponding to ring/belt boundaries mapped into the source plane. We provide a few illustrative examples to understand the pseudo-caustic features, and in a separate paper consider a specific astronomical application of our results to study microlensing by extrasolar asteroid belts.
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.
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.
2016-06-01
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-fitting cosmology, the amplitude of the DES×SPT cross-power is found to be ASPT = 0.88 ± 0.30 and that from DES×Planck to be APlanck = 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 intrinsic alignment 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 ratio of the combination of the five-year DES survey and SPT-3G.
Strong field gravitational lensing by a charged Galileon black hole
NASA Astrophysics Data System (ADS)
Zhao, Shan-Shan; Xie, Yi
2016-07-01
Strong field gravitational lensings are dramatically disparate from those in the weak field by representing relativistic images due to light winds one to infinity loops around a lens before escaping. We study such a lensing caused by a charged Galileon black hole, which is expected to have possibility to evade no-hair theorem. We calculate the angular separations and time delays between different relativistic images of the charged Galileon black hole. All these observables can potentially be used to discriminate a charged Galileon black hole from others. We estimate the magnitudes of these observables for the closest supermassive black hole Sgr A*. The strong field lensing observables of the charged Galileon black hole can be close to those of a tidal Reissner-Nordström black hole or those of a Reissner-Nordström black hole. It will be helpful to distinguish these black holes if we can separate the outermost relativistic images and determine their angular separation, brightness difference and time delay, although it requires techniques beyond the current limit.
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.
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.
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)
Alexie, Leauthaud; Reiko, Nakajima [Berkeley Center for Cosmological Physics, Berkely, California, United States
2016-07-12
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 [Berkeley Center for Cosmological Physics
2016-07-12
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.
Weak lensing by voids in modified lensing potentials
Barreira, Alexandre; Cautun, Marius; Li, Baojiu; Baugh, Carlton M.; Pascoli, Silvia E-mail: m.c.cautun@durham.ac.uk E-mail: c.m.baugh@durham.ac.uk
2015-08-01
We study lensing by voids in Cubic Galileon and Nonlocal gravity cosmologies, which are examples of theories of gravity that modify the lensing potential. We find voids in the dark matter and halo density fields of N-body simulations and compute their lensing signal analytically from the void density profiles, which we show are well fit by a simple analytical formula. In the Cubic Galileon model, the modifications to gravity inside voids are not screened and they approximately double the size of the lensing effects compared to GR. The difference is largely determined by the direct effects of the fifth force on lensing and less so by the modified density profiles. For this model, we also discuss the subtle impact on the force and lensing calculations caused by the screening effects of haloes that exist in and around voids. In the Nonlocal model, the impact of the modified density profiles and the direct modifications to lensing are comparable, but they boost the lensing signal by only ≈ 10%, compared with that of GR. Overall, our results suggest that lensing by voids is a promising tool to test models of gravity that modify lensing.
Exciting discoveries of strong gravitational lenses from the HSC Survey
NASA Astrophysics Data System (ADS)
More, Anupreeta; Team 1: Masayuki Tanaka, Kenneth Wong, et al.; Team 2: Chien-Hsiu Lee, Masamune Oguri, et al.
2017-01-01
Strong gravitational lenses have numerous applications in astrophysics and cosmology. We expect to discover thousands of strong gravitational lenses from the Hyper Suprime-Cam (HSC) Survey, thanks to its unique combination of deep and wide imaging. I will give highlights on a few interesting gravitational lenses that were discovered recently from early HSC data, for example, the first spectroscopically confirmed double source plane (DSP) lens system dubbed ''Eye of Horus'' and the highest-redshift quadruply-lensed low-luminosity Active Galactic Nucleus (LLAGN).DSP lenses such as ''Eye of Horus'' are even more rare than ordinary lenses but provide tighter constraints on the lens mass distribution and can also be useful to measure cosmological parameters such as Dark Energy and Matter density parameter. The lensed LLAGN discovered recently from HSC is only the second such lens system in our knowledge. LLAGNs are thought to have differentmechanisms driving their nuclear activity compared to their brighter counterparts i.e. quasars. Our knowledge about this abundant but faint population of AGNs is limited to the local universe so far. But lensing magnification will allow studies of distant LLAGNs which should be discovered in large numbers from a deep survey like HSC for the first time. Also, owing to the variable nature of LLAGNs, they could potentially be used as a cosmological probe similar to the lensed quasars.
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).
Setting limits on q0 from gravitational lensing
NASA Technical Reports Server (NTRS)
Gott, J. Richard, III; Park, Myeong-Gu; Lee, Hyung Mok
1989-01-01
Gravitational lensing by galaxies in a wide variety of cosmological models is considered. For closed models, the lensing depends on the parameter beta(crit). If beta(crit) is greater than zero, a normal lensing case can be obtained with two bright images separated by an angle twice beta(crit) and a third, arbitrarily dim image between them coincident with the position of the lensing galaxy nucleus. As the QSO approaches the antipodal redshift, which can occur in models with large values of the cosmological constant, the cross sections for lensing blow up. An overfocused case where beta(crit) is less than zero can be obtained for a QSO beyond the antipodal redshift. In this case, when a lensing event occurs, only one arbitrarily dim image coincident with the position of the lensing galaxy nucleus is seen. If galaxy rotation curves are always flat or slowly rising, the overfocused case always produces one image.
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.
Our warped universe: the power of gravitational lensing for probing the cosmos
NASA Astrophysics Data System (ADS)
Nord, Brian
2017-01-01
Gravitational lensing epitomizes a maxim of Einstein's General Relativity: space tells energy how to move and energy tells space how to curve. Through lensing, massive objects magnify and distort the shapes of distant objects, likes galaxies and quasars. The connection between the lens's mass distribution and the degree of distortion in the images allows us to observe faint, distant objects, and to infer the matter distribution and cosmic expansion in the nearby universe. Current and future surveys, both ground- and space-based, will provide data sets unprecedented in size and precision with which to probe dark energy, dark matter and the early universe through gravitational lensing. I will discuss recent advances in observations and analysis techniques in both weak and strong lensing, and the burgeoning potential of these techniques to derive important and competitive cosmological constraints from surveys of large-scale structure.
Scaling the universe: gravitational lenses and the Hubble constant.
Myers, S T
1999-04-13
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 Omegao and Lambdao that control the evolution of the volume of the Universe with cosmic time.
Weak lensing galaxy cluster field reconstruction
NASA Astrophysics Data System (ADS)
Jullo, E.; Pires, S.; Jauzac, M.; Kneib, J.-P.
2014-02-01
In this paper, we compare three methods to reconstruct galaxy cluster density fields with weak lensing data. The first method called FLens integrates an inpainting concept to invert the shear field with possible gaps, and a multi-scale entropy denoising procedure to remove the noise contained in the final reconstruction, that arises mostly from the random intrinsic shape of the galaxies. The second and third methods are based on a model of the density field made of a multi-scale grid of radial basis functions. In one case, the model parameters are computed with a linear inversion involving a singular value decomposition (SVD). In the other case, the model parameters are estimated using a Bayesian Monte Carlo Markov Chain optimization implemented in the lensing software LENSTOOL. Methods are compared on simulated data with varying galaxy density fields. We pay particular attention to the errors estimated with resampling. We find the multi-scale grid model optimized with Monte Carlo Markov Chain to provide the best results, but at high computational cost, especially when considering resampling. The SVD method is much faster but yields noisy maps, although this can be mitigated with resampling. The FLens method is a good compromise with fast computation, high signal-to-noise ratio reconstruction, but lower resolution maps. All three methods are applied to the MACS J0717+3745 galaxy cluster field, and reveal the filamentary structure discovered in Jauzac et al. We conclude that sensitive priors can help to get high signal-to-noise ratio, and unbiased reconstructions.
Probing the dark matter issue in f( R)-gravity via gravitational lensing
NASA Astrophysics Data System (ADS)
Lubini, M.; Tortora, C.; Näf, J.; Jetzer, Ph.; Capozziello, S.
2011-12-01
For a general class of analytic f( R)-gravity theories, we discuss the weak field limit in view of gravitational lensing. Though an additional Yukawa term in the gravitational potential modifies dynamics with respect to the standard Newtonian limit of General Relativity, the motion of massless particles results unaffected thanks to suitable cancellations in the post-Newtonian limit. Thus, all the lensing observables are equal to the ones known from General Relativity. Since f( R)-gravity is claimed, among other things, to be a possible solution to overcome for the need of dark matter in virialized systems, we discuss the impact of our results on the dynamical and gravitational lensing analyses. In this framework, dynamics could, in principle, be able to reproduce the astrophysical observations without recurring to dark matter, but in the case of gravitational lensing we find that dark matter is an unavoidable ingredient. Another important implication is that gravitational lensing, in the post-Newtonian limit, is not able to constrain these extended theories, since their predictions do not differ from General Relativity.
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.
Gravitational lensing, time delay, and gamma-ray bursts
NASA Technical Reports Server (NTRS)
Mao, Shude
1992-01-01
The probability distributions of time delay in gravitational lensing by point masses and isolated galaxies (modeled as singular isothermal spheres) are studied. For point lenses (all with the same mass) the probability distribution is broad, and with a peak at delta(t) of about 50 S; for singular isothermal spheres, the probability distribution is a rapidly decreasing function with increasing time delay, with a median delta(t) equals about 1/h month, and its behavior depends sensitively on the luminosity function of galaxies. The present simplified calculation is particularly relevant to the gamma-ray bursts if they are of cosmological origin. The frequency of 'recurrent' bursts due to gravitational lensing by galaxies is probably between 0.05 and 0.4 percent. Gravitational lensing can be used as a test of the cosmological origin of gamma-ray bursts.
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.
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.
Model-free analysis of quadruply imaged gravitationally lensed systems
NASA Astrophysics Data System (ADS)
Woldesenbet, Addishiwot Girma
Gravitational lensing has proven to be a very valuable tool as a probe to better understand our universe. Parametric modeling of one multiple image gravitational lens system at a time is a common practice in the field of lensing. Instead of individual lens modeling, an alternative approach is to use symmetries in different spaces to make conclusions about families of lenses. The latter method is the focus of this thesis. Three types of lenses are defined based on whether they do or do not obey two-fold and double mirror symmetries. The analysis concentrates on quadruply imaged systems, or quads, and uses only the relative polar angles of quads around the center of the lens. The analysis is statistical in nature, and model-free because its conclusions relate to whole classes of models, instead of specific models. The work done here is twofold. Firstly, exploratory analysis is done to check for possible existence of degeneracies. Type I lenses which obey both symmetries mentioned above are found to form a nearly invariant surface in the 3D space of relative image angles. In the same space, lenses that break the double mirror symmetry, grouped as Type II, form two distinct surfaces. In addition, degeneracy in this class of lenses is discovered. A preliminary study of the last group of lenses, Type III, that break both symmetries, is done. Secondly, quad distributions in the 3D space from each of the three families were compared to observed galaxy-lens quads. Three quarters of observed quads were inconsistent with the distribution of quads of Type I lenses. Type II lenses reproduce most individual lens systems but fail to reproduce the population properties of observed quads. Preliminary exploration of Type III lenses shows a very promising agreement with observations. Examples of Type IIIs are lenses with substructure (with clump masses larger than those responsible for flux ratio anomalies in quads), and lenses with luminous or dark nearby perturber galaxies, or line
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.
High resolution weak lensing mass mapping combining shear and flexion
NASA Astrophysics Data System (ADS)
Lanusse, F.; Starck, J.-L.; Leonard, A.; Pires, S.
2016-06-01
Aims: We propose a new mass mapping algorithm, specifically designed to recover small-scale information from a combination of gravitational shear and flexion. Including flexion allows us to supplement the shear on small scales in order to increase the sensitivity to substructures and the overall resolution of the convergence map without relying on strong lensing constraints. Methods: To preserve all available small scale information, we avoid any binning of the irregularly sampled input shear and flexion fields and treat the mass mapping problem as a general ill-posed inverse problem, which is regularised using a robust multi-scale wavelet sparsity prior. The resulting algorithm incorporates redshift, reduced shear, and reduced flexion measurements for individual galaxies and is made highly efficient by the use of fast Fourier estimators. Results: We tested our reconstruction method on a set of realistic weak lensing simulations corresponding to typical HST/ACS cluster observations and demonstrate our ability to recover substructures with the inclusion of flexion, which are otherwise lost if only shear information is used. In particular, we can detect substructures on the 15'' scale well outside of the critical region of the clusters. In addition, flexion also helps to constrain the shape of the central regions of the main dark matter halos. Our mass mapping software, called Glimpse2D, is made freely available at http://www.cosmostat.org/software/glimpse
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.
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
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
PICS: Simulations of Strong Gravitational Lensing in Galaxy Clusters
NASA Astrophysics Data System (ADS)
Li, Nan; Gladders, Michael D.; Rangel, Esteban M.; Florian, Michael K.; Bleem, Lindsey E.; Heitmann, Katrin; Habib, Salman; Fasel, Patricia
2016-09-01
Gravitational lensing has become one of the most powerful tools available for investigating the “dark side” of the universe. Cosmological strong gravitational lensing, in particular, probes the properties of the dense cores of dark matter halos over decades in mass and offers the opportunity to study the distant universe at flux levels and spatial resolutions otherwise unavailable. Studies of strongly lensed variable sources offer even further scientific opportunities. One of the challenges in realizing the potential of strong lensing is to understand the statistical context of both the individual systems that receive extensive follow-up study, as well as that of the larger samples of strong lenses that are now emerging from survey efforts. Motivated by these challenges, we have developed an image simulation pipeline, Pipeline for Images of Cosmological Strong lensing (PICS), to generate realistic strong gravitational lensing signals from group- and cluster-scale lenses. PICS uses a low-noise and unbiased density estimator based on (resampled) Delaunay Tessellations to calculate the density field; lensed images are produced by ray-tracing images of actual galaxies from deep Hubble Space Telescope observations. Other galaxies, similarly sampled, are added to fill in the light cone. The pipeline further adds cluster member galaxies and foreground stars into the lensed images. The entire image ensemble is then observed using a realistic point-spread function that includes appropriate detector artifacts for bright stars. Noise is further added, including such non-Gaussian elements as noise window-paning from mosaiced observations, residual bad pixels, and cosmic rays. The aim is to produce simulated images that appear identical—to the eye (expert or otherwise)—to real observations in various imaging surveys.
Gravitational lensing of massive particles in Schwarzschild gravity
NASA Astrophysics Data System (ADS)
Liu, Xionghui; Yang, Nan; Jia, Junji
2016-09-01
Both massless light ray and objects with nonzero mass experience trajectory bending in a gravitational field. In this work the bending of trajectories of massive objects in a Schwarzschild spacetime and the corresponding gravitational lensing (GL) effects are studied. A particle sphere for Schwarzschild black hole (BH) is found with its radius a simple function of the particle velocity and proportional to the BH mass. A single master formula for both the massless and massive particle bending angle is found, in the form of an elliptic function depending only on the velocity and impact parameter. This bending angle is expanded in both large and small velocity limits and large and small impact parameter limits. The corresponding deflection angle for weak and strong GL of massive particles are analyzed, and their corrections to the light ray deflection angles are obtained. The dependence of the deflection angles on the source angle and the particle speed is investigated. Finally we discuss the potential applications of the results in hypervelocity star observations and in determining mass/mass hierarchy of slow particles/objects.
Planck 2015 results. XV. Gravitational lensing
NASA Astrophysics Data System (ADS)
Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Bartolo, N.; Basak, S.; Battaner, E.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bock, J. J.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bucher, M.; Burigana, C.; Butler, R. C.; Calabrese, E.; Cardoso, J.-F.; Catalano, A.; Challinor, A.; Chamballu, A.; Chiang, H. C.; Christensen, P. R.; Church, S.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Combet, C.; 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.; Delabrouille, J.; Désert, F.-X.; Diego, J. M.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Ducout, A.; Dunkley, J.; Dupac, X.; Efstathiou, G.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Fergusson, J.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Frejsel, A.; Galeotta, S.; Galli, S.; Ganga, K.; Giard, M.; Giraud-Héraud, Y.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Hansen, F. K.; Hanson, D.; Harrison, D. L.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hovest, W.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lähteenmäki, A.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Lawrence, C. R.; Leonardi, R.; Lesgourgues, J.; Levrier, F.; Lewis, A.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maggio, G.; Maino, D.; Mandolesi, N.; Mangilli, A.; Maris, M.; Martin, P. G.; Martínez-González, E.; Masi, S.; Matarrese, S.; McGehee, P.; Meinhold, P. R.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mitra, S.; Miville-Deschênes, 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.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Paoletti, D.; Pasian, F.; Patanchon, G.; Perdereau, O.; Perotto, L.; Perrotta, F.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Popa, L.; Pratt, G. W.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reach, W. T.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rossetti, M.; Roudier, G.; Rowan-Robinson, M.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savelainen, M.; Savini, G.; Scott, D.; Seiffert, M. D.; Shellard, E. P. S.; Spencer, L. D.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sunyaev, R.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Tuovinen, J.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Wade, L. A.; Wandelt, B. D.; Wehus, I. K.; White, M.; Yvon, D.; Zacchei, A.; Zonca, A.
2016-09-01
We present the most significant measurement of the cosmic microwave background (CMB) lensing potential to date (at a level of 40σ), using temperature and polarization data from the Planck 2015 full-mission release. Using a polarization-only estimator, we detect lensing at a significance of 5σ. We cross-check the accuracy of our measurement using the wide frequency coverage and complementarity of the temperature and polarization measurements. Public products based on this measurement include an estimate of the lensing potential over approximately 70% of the sky, an estimate of the lensing potential power spectrum in bandpowers for the multipole range 40 ≤ L ≤ 400, and an associated likelihood for cosmological parameter constraints. We find good agreement between our measurement of the lensing potential power spectrum and that found in the ΛCDM model that best fits the Planck temperature and polarization power spectra. Using the lensing likelihood alone we obtain a percent-level measurement of the parameter combination σ8Ω0.25m = 0.591 ± 0.021. We combine our determination of the lensing potential with the E-mode polarization, also measured by Planck, to generate an estimate of the lensing B-mode. We show that this lensing B-mode estimate is correlated with the B-modes observed directly by Planck at the expected level and with a statistical significance of 10σ, confirming Planck's sensitivity to this known sky signal. We also correlate our lensing potential estimate with the large-scale temperature anisotropies, detecting a cross-correlation at the 3σ level, as expected because of dark energy in the concordance ΛCDM model.
An analytical approach to gravitational lensing by an ensemble of axisymmetric lenses
NASA Technical Reports Server (NTRS)
Lee, Man Hoi; Spergel, David N.
1990-01-01
The problem of gravitational lensing by an ensemble of identical axisymmetric lenses randomly distributed on a single lens plane is considered and a formal expression is derived for the joint probability density of finding shear and convergence at a random point on the plane. The amplification probability for a source can be accurately estimated from the distribution in shear and convergence. This method is applied to two cases: lensing by an ensemble of point masses and by an ensemble of objects with Gaussian surface mass density. There is no convergence for point masses whereas shear is negligible for wide Gaussian lenses.
Gravitational lensing by a smoothly variable surface mass density
NASA Technical Reports Server (NTRS)
Paczynski, Bohdan; Wambsganss, Joachim
1989-01-01
The statistical properties of gravitational lensing due to smooth but nonuniform distributions of matter are considered. It is found that a majority of triple images had a parity characteristic for 'shear-induced' lensing. Almost all cases of triple or multiple imaging were associated with large surface density enhancements, and lensing objects were present between the images. Thus, the observed gravitational lens candidates for which no lensing object has been detected between the images are unlikely to be a result of asymmetric distribution of mass external to the image circle. In a model with smoothly variable surface mass density, moderately and highly amplified images tended to be single rather than multiple. An opposite trend was found in models which had singularities in the surface mass distribution.
HSC Weak Lensing Measurement of ACTPol SZ-selected Galaxy Clusters
NASA Astrophysics Data System (ADS)
Miyatake, Hironao; HSC Collaboration; ACTPol Collaboration
2017-01-01
Although the abundance of galaxy clusters is one of the most powerful cosmological probes, the precision of abundance measurement is currently limited by systematic uncertainties in cluster mass calibration. Weak gravitational lensing is a valuable tool to calibrate cluster mass, since it directly probes the dark matter distribution without physical assumptions such as hydrostatic equilibrium. In this talk, combining the cutting-edge optical and microwave data from Subaru Hyper Suprime-Cam (HSC) and ACTPol, we report the weak lensing mass measurement of galaxy clusters selected based on thermal Sunyaev-Zel'dovich (SZ) effect. Thanks to the high number density of source galaxies, we obtain a stacked weak lensing signal with a signal to noise ratio of ~20. We present detailed systematic tests such as background galaxy selection as well as a comparison of our mass calibration to previous results in the literature.
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.
Magnified Views of Relativistic Outflows in Gravitationally Lensed Quasars
NASA Astrophysics Data System (ADS)
Chartas, G.; Cappi, M.; Hamann, F.; Eracleous, M.; Strickland, S.; Vignali, C.; Dadina, M.; Giustini, M.; Saez, C.; Misawa, T.
2016-06-01
We presents results from X-ray observations of relativistic outflows in lensed quasars. The lensing magnification of the observed objects provides high signal-to-noise X-ray spectra of quasars showing the absorption signatures of relativistic outflows at redshifts near a crucial phase of black hole growth and the peak of cosmic AGN activity. We summarise the properties of the wide-angle relativistic outflow of the z = 1.51 NAL quasar HS 0810 detected in recent deep XMM-Newton and Chandra observations of this object. We also present preliminary results from a mini-survey of gravitationally lensed mini-BAL quasars performed with XMM-Newton.
Black hole tidal charge constrained by strong gravitational lensing
NASA Astrophysics Data System (ADS)
Horváth, Zs.; Gergely, L. Á.
2013-11-01
Spherically symmetric brane black holes have tidal charge which modifies both weak and strong lensing characteristics. Even if lensing measurements are in agreement with a Schwarzschild lens, the margin of error of the detecting instrument allows for a certain tidal charge only. In this paper we derive the respective constraint on the tidal charge of the supermassive black hole (SMBH) in the center of our galaxy, based on the radius of the first relativistic Einstein ring due to strong lensing. We find that even if general relativistic predictions are confirmed by high precision strong lensing measurements, SMBHs could have a much larger tidal charge than the Sun or neutron stars.
THE MISSING WEAK LENSING MASS IN A781
Cook, Richard I.; Dell'Antonio, I. P.
2012-05-10
Measuring cluster masses accurately is important for testing the cosmological paradigm. Weak lensing is one of the most promising methods for detecting, measuring, and calibrating cluster mass estimates made using other mass proxies (e.g., X-ray, Sunyaev-Zel'dovich effect, spectroscopy). However, it is still essential to characterize and understand the causes of systematic error and bias in weak lensing measurements. A781D is a cluster of galaxies with a mass and redshift that places it well within the theoretical detection limits of weak lensing analyses from the ground yet has evaded detection in previous weak lensing studies. Previous weak lensing measurements in the region surrounding this cluster from the Deep Lens Survey were unable to detect it and placed a 1{sigma} limit on the mass of <5 Multiplication-Sign 10{sup 13} M{sub Sun }. Given independent estimates of the cluster mass by X-ray and spectroscopic measurements and its spectroscopically confirmed redshift of 0.43, it is difficult to explain its absence from the weak lensing mass reconstructions. We re-analyzed this cluster using imaging from the Orthogonal Parallel Transfer Imaging Camera and archival Suprime-Cam data. We successfully detect A781A in both analyses, but A781D remains undetected. We use these two new independent analyses to rule out systematic effects from the telescope, instrument, and point-spread function correction as the cause of the null detection. We also demonstrate the first use of an orthogonal transfer camera for weak lensing analysis and demonstrate its suitability for weak lensing studies.
To the horizon and beyond: Weak lensing of the CMB and binary inspirals into horizonless objects
NASA Astrophysics Data System (ADS)
Kesden, Michael
This thesis examines two predictions of general relativity: weak lensing and gravitational waves. The cosmic microwave background (CMB) is gravitationally lensed by the large-scale structure between the observer and the last- scattering surface. This weak lensing induces non-Gaussian correlations that can be used to construct estimators for the deflection field. The error and bias of these estimators are derived and used to analyze the viability of lensing reconstruction for future CMB experiments. Weak lensing also affects the one-point probability distribution function of the CMB. The skewness and kurtosis induced by lensing and the Sunayev- Zel'dovich (SZ) effect are calculated as functions of the angular smoothing scale of the map. While these functions offer the advantage of easy computability, only the skewness from lensing-SZ correlations can potentially be detected, even in the limit of the largest amplitude fluctuations allowed by observation. Lensing estimators are also essential to constrain inflation, the favored explanation for large-scale isotropy and the origin of primordial perturbations. B-mode polarization is considered to be a "smoking-gun" signature of inflation, and lensing estimators can be used to recover primordial B-modes from lensing-induced contamination. The ability of future CMB experiments to constrain inflation is assessed as functions of survey size and instrumental sensitivity. A final application of lensing estimators is to constrain a possible cutoff in primordial density perturbations on near-horizon scales. The paucity of independent modes on such scales limits the statistical certainty of such a constraint. Measurements of the deflection field can be used to constrain at the 3s level the existence of a cutoff large enough to account for current CMB observations. A final chapter of this thesis considers an independent topic: the gravitational-wave (GW) signature of a binary inspiral into a horizonless object. If the supermassive
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
A maximum-likelihood multi-resolution weak lensing mass reconstruction method
NASA Astrophysics Data System (ADS)
Khiabanian, Hossein
Gravitational lensing is formed when the light from a distant source is "bent" around a massive object. Lensing analysis has increasingly become the method of choice for studying dark matter, so much that it is one of the main tools that will be employed in the future surveys to study the dark energy and its equation of state as well as the evolution of galaxy clustering. Unlike other popular techniques for selecting galaxy clusters (such as studying the X-ray emission or observing the over-densities of galaxies), weak gravitational lensing does not have the disadvantage of relying on the luminous matter and provides a parameter-free reconstruction of the projected mass distribution in clusters without dependence on baryon content. Gravitational lensing also provides a unique test for the presence of truly dark clusters, though it is otherwise an expensive detection method. Therefore it is essential to make use of all the information provided by the data to improve the quality of the lensing analysis. This thesis project has been motivated by the limitations encountered with the commonly used direct reconstruction methods of producing mass maps. We have developed a multi-resolution maximum-likelihood reconstruction method for producing two dimensional mass maps using weak gravitational lensing data. To utilize all the shear information, we employ an iterative inverse method with a properly selected regularization coefficient which fits the deflection potential at the position of each galaxy. By producing mass maps with multiple resolutions in the different parts of the observed field, we can achieve a uniform signal to noise level by increasing the resolution in regions of higher distortions or regions with an over-density of background galaxies. In addition, we are able to better study the sub- structure of the massive clusters at a resolution which is not attainable in the rest of the observed field.
Probing cosmology with weak lensing peak counts
Kratochvil, Jan M.; Haiman, Zoltan; May, Morgan
2010-02-15
We propose counting peaks in weak lensing (WL) maps, as a function of their height, to probe models of dark energy and to constrain cosmological parameters. Because peaks can be identified in two-dimensional WL maps directly, they can provide constraints that are free from potential selection effects and biases involved in identifying and determining the masses of galaxy clusters. As a pilot study, we have run cosmological N-body simulations to produce WL convergence maps in three models with different constant values of the dark energy equation-of-state parameter, w=-0.8, -1, and -1.2, with a fixed normalization of the primordial power spectrum (corresponding to present-day normalizations of {sigma}{sub 8}=0.742, 0.798, and 0.839, respectively). By comparing the number of WL peaks in eight convergence bins in the range of -0.1<{kappa}<0.4, in multiple realizations of a single simulated 3x3 degree field, we show that the first (last) pair of models differ at the 95% (85%) confidence level. A survey with depth and area comparable to those expected from the Large Synoptic Survey Telescope should have a factor of {approx_equal}50 better parameter sensitivity. These results warrant further investigation, in order to assess the constraints available when marginalization over other uncertain parameters is included, and with the specifications of a realistic survey folded into the analysis. Here we find that relatively low-amplitude peaks ({kappa}{approx}0.03), which typically do not correspond to a single collapsed halo along the line of sight, account for most of the parameter sensitivity. We study a range of smoothing scales and source galaxy redshifts (z{sub s}). With a fixed source galaxy density of 15 arcmin{sup -2}, the best results are provided by the smallest scale we can reliably simulate, 1 arcmin, and z{sub s}=2 provides substantially better sensitivity than z{sub s{<=}}1.5.
A Method for Weak-Lensing Flexion Analysis by the HOLICs Moment Approach
NASA Astrophysics Data System (ADS)
Okura, Yuki; Umetsu, Keiichi; Futamase, Toshifumi
2008-06-01
We have developed a method for measuring higher order weak-lensing distortions of faint background galaxies, namely, the weak gravitational flexion, by fully extending the Kaiser, Squires, and Broadhurst method to include higher order lensing image characteristics (HOLICs) introduced by Okura, Umetsu, and Futamase. We take into account explicitly the weight function in calculations of noisy shape moments and the effect of higher order point-spread function (PSF) anisotropy, as well as isotropic PSF smearing. Our HOLICs formalism allows accurate measurements of flexion from practical observational data in the presence of a noncircular, anisotropic PSF. We test our method using mock observations of simulated galaxy images and actual, ground-based Subaru observations of the massive galaxy cluster A1689 (z = 0.183). From the high-precision measurements of the spin-1 first flexion, we obtain a high-resolution mass map in the central region of A1689. The reconstructed mass map shows a bimodal feature in the central 4' × 4' region of the cluster. The major, pronounced peak is associated with the brightest cluster galaxy and central cluster members, while the secondary mass peak is associated with a local concentration of bright galaxies. The refined, high-resolution mass map of A1689 demonstrates the power of the generalized weak-lensing analysis techniques for quantitative and accurate measurements of the weak gravitational lensing signal. Based in part on data collected at the Subaru Telescope, which is operated by the National Astronomical Society of Japan.
Comparison of CMB lensing efficiency of gravitational waves and large scale structure
NASA Astrophysics Data System (ADS)
Padmanabhan, Hamsa; Rotti, Aditya; Souradeep, Tarun
2013-09-01
We provide a detailed treatment and comparison of the weak lensing effects due to large scale structure (LSS), or scalar density perturbations and those due to gravitational waves (GWs) or tensor perturbations, on the temperature and polarization power spectra of the cosmic microwave background (CMB). We carry out the analysis both in real space by using the correlation function method, as well as in the spherical harmonic space. We find an intriguing similarity between the lensing kernels associated with LSS lensing and GW lensing. It is found that the lensing kernels only differ in relative negative signs and their form is very reminiscent of even and odd parity bipolar spherical harmonic coefficients. Through a numerical study of these lensing kernels, we establish that lensing due to GW is more efficient at distorting the CMB spectra as compared to LSS lensing, particularly for the polarization power spectra. Finally we argue that the CMB B-mode power spectra measurements can be used to place interesting constraints on GW energy densities.
Gravitational lensing of the cosmic microwave background by non-linear structures
NASA Astrophysics Data System (ADS)
Merkel, Philipp M.; Schäfer, Björn Malte
2011-02-01
Weak gravitational lensing changes the angular power spectra of the cosmic microwave background (CMB) temperature and polarization in a characteristic way containing valuable information for cosmological parameter estimation. So far, analytical expressions for the lensed CMB power spectra assume the probability density function (PDF) of the lensing excursion angle to be Gaussian. However, coherent light deflection by non-linear structures at low redshifts causes deviations from a pure Gaussian PDF. Working in the flat-sky limit, we develop a method for computing the lensed CMB power spectra which takes these non-Gaussian features into account. Our method does not assume any specific PDF but uses instead an expansion of the characteristic function of the lensing excursion angle into its moments. Measuring these in the CMB lensing deflection field obtained from the Millennium Simulation we show that the change in the lensed power spectra is only at the 0.1-0.4 per cent level on very small scales (Δθ≲ 4 arcmin, l≳ 2500) and demonstrate that the assumption of a Gaussian lensing excursion angle PDF is well applicable.
The impact of camera optical alignments on weak lensing measures for the Dark Energy Survey
Antonik, M. L.; Bacon, D. J.; Bridle, S.; Doel, P.; Brooks, D.; Worswick, S.; Bernstein, G.; Bernstein, R.; DePoy, D.; Flaugher, B.; Frieman, J. A.; Gladders, M.; Gutierrez, G.; Jain, B.; Jarvis, M.; Kent, S. M.; Lahav, O.; Parker, S. -. J.; Roodman, A.; Walker, A. R.
2013-04-10
Telescope point spread function (PSF) quality is critical for realizing the potential of cosmic weak lensing observations to constrain dark energy and test general relativity. In this paper, we use quantitative weak gravitational lensing measures to inform the precision of lens optical alignment, with specific reference to the Dark Energy Survey (DES). We compute optics spot diagrams and calculate the shear and flexion of the PSF as a function of position on the focal plane. For perfect optical alignment, we verify the high quality of the DES optical design, finding a maximum PSF contribution to the weak lensing shear of 0.04 near the edge of the focal plane. However, this can be increased by a factor of approximately 3 if the lenses are only just aligned within their maximum specified tolerances. We calculate the E- and B-mode shear and flexion variance as a function of the decentre or tilt of each lens in turn. We find tilt accuracy to be a few times more important than decentre, depending on the lens considered. Finally, we consider the compound effect of decentre and tilt of multiple lenses simultaneously, by sampling from a plausible range of values of each parameter. We find that the compound effect can be around twice as detrimental as when considering any one lens alone. Furthermore, this combined effect changes the conclusions about which lens is most important to align accurately. For DES, the tilt of the first two lenses is the most important.
Possible Approaches to Measuring the Distance-Redshift Relation via Gravitational Lensing
NASA Astrophysics Data System (ADS)
Stankus, Paul
2005-04-01
The primary evidence for an accelerating Universe, currently, is found in the departure from the Hubble relation for distance vs redshift as measured in distant supernovae. These methods rely on knowing the intrinsic luminosities of ancient supernovae, and while there is no reason to doubt them it is clearly desirable to have alternate measurements of the distance-redshift relation which do not involve luminosities. Gravitational lensing of distant galaxies may afford such a measurement. Outlines for two possible approaches are described: (1) Strong lensing of CMB anisotropies in coincidence with strong lensing of a distant galaxy; (2) Statistical correlation of weak lensing signatures with redshift. Feasibility using current and future instruments are briefly discussed.
MEASURING GRAVITATIONAL LENSING FLEXION IN A1689 USING AN ANALYTIC IMAGE MODEL
Cain, Benjamin
2011-07-20
Measuring dark matter substructure within galaxy cluster halos is a fundamental probe of the {Lambda}CDM model of structure formation. Gravitational lensing is a technique for measuring the total mass distribution which is independent of the nature of the gravitating matter, making it a vital tool for studying these dark-matter-dominated objects. We present a new method for measuring weak gravitational lensing flexion fields, the gradients of the lensing shear field, to measure mass distributions on small angular scales. While previously published methods for measuring flexion focus on measuring derived properties of the lensed images, such as shapelet coefficients or surface brightness moments, our method instead fits a mass-sheet transformation invariant Analytic Image Model (AIM) to each galaxy image. This simple parametric model traces the distortion of lensed image isophotes and constrains the flexion fields. We test the AIM method using simulated data images with realistic noise and a variety of unlensed image properties, and show that it successfully reproduces the input flexion fields. We also apply the AIM method for flexion measurement to Hubble Space Telescope observations of A1689 and detect mass structure in the cluster using flexion measured with this method. We also estimate the scatter in the measured flexion fields due to the unlensed shape of the background galaxies and find values consistent with previous estimates.
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.
Sample variance in weak lensing: How many simulations are required?
NASA Astrophysics Data System (ADS)
Petri, Andrea; Haiman, Zoltán; May, Morgan
2016-03-01
Constraining cosmology using weak gravitational lensing consists of comparing a measured feature vector of dimension Nb with its simulated counterpart. An accurate estimate of the Nb×Nb feature covariance matrix C is essential to obtain accurate parameter confidence intervals. When C is measured from a set of simulations, an important question is how large this set should be. To answer this question, we construct different ensembles of Nr realizations of the shear field, using a common randomization procedure that recycles the outputs from a smaller number Ns≤Nr of independent ray-tracing N -body simulations. We study parameter confidence intervals as a function of (Ns , Nr ) in the range 1 ≤Ns≤200 and 1 ≤Nr≲105. Previous work [S. Dodelson and M. D. Schneider, Phys. Rev. D 88, 063537 (2013)] has shown that Gaussian noise in the feature vectors (from which the covariance is estimated) lead, at quadratic order, to an O (1 /Nr) degradation of the parameter confidence intervals. Using a variety of lensing features measured in our simulations, including shear-shear power spectra and peak counts, we show that cubic and quartic covariance fluctuations lead to additional O (1 /Nr2) error degradation that is not negligible when Nr is only a factor of few larger than Nb. We study the large Nr limit, and find that a single, 240 Mpc /h sized 5123-particle N -body simulation (Ns=1 ) can be repeatedly recycled to produce as many as Nr=few×104 shear maps whose power spectra and high-significance peak counts can be treated as statistically independent. As a result, a small number of simulations (Ns=1 or 2) is sufficient to forecast parameter confidence intervals at percent accuracy.
Sample variance in weak lensing: How many simulations are required?
Petri, Andrea; May, Morgan; Haiman, Zoltan
2016-03-24
Constraining cosmology using weak gravitational lensing consists of comparing a measured feature vector of dimension Nb with its simulated counterpart. An accurate estimate of the Nb × Nb feature covariance matrix C is essential to obtain accurate parameter confidence intervals. When C is measured from a set of simulations, an important question is how large this set should be. To answer this question, we construct different ensembles of Nr realizations of the shear field, using a common randomization procedure that recycles the outputs from a smaller number Ns ≤ Nr of independent ray-tracing N-body simulations. We study parameter confidence intervalsmore » as a function of (Ns, Nr) in the range 1 ≤ Ns ≤ 200 and 1 ≤ Nr ≲ 105. Previous work [S. Dodelson and M. D. Schneider, Phys. Rev. D 88, 063537 (2013)] has shown that Gaussian noise in the feature vectors (from which the covariance is estimated) lead, at quadratic order, to an O(1/Nr) degradation of the parameter confidence intervals. Using a variety of lensing features measured in our simulations, including shear-shear power spectra and peak counts, we show that cubic and quartic covariance fluctuations lead to additional O(1/N2r) error degradation that is not negligible when Nr is only a factor of few larger than Nb. We study the large Nr limit, and find that a single, 240 Mpc/h sized 5123-particle N-body simulation (Ns = 1) can be repeatedly recycled to produce as many as Nr = few × 104 shear maps whose power spectra and high-significance peak counts can be treated as statistically independent. Lastly, a small number of simulations (Ns = 1 or 2) is sufficient to forecast parameter confidence intervals at percent accuracy.« less
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).
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.
Weak lensing generated by vector perturbations and detectability of cosmic strings
Yamauchi, Daisuke; Namikawa, Toshiya; Taruya, Atsushi E-mail: namikawa@utap.phys.s.u-tokyo.ac.jp
2012-10-01
We study the observational signature of vector metric perturbations through the effect of weak gravitational lensing. In the presence of vector perturbations, the non-vanishing signals for B-mode cosmic shear and curl-mode deflection angle, which have never appeared in the case of scalar metric perturbations, naturally arise. Solving the geodesic and geodesic deviation equations, we drive the full-sky formulas for angular power spectra of weak lensing signals, and give the explicit expressions for E-/B-mode cosmic shear and gradient-/curl-mode deflection angle. As a possible source for seeding vector perturbations, we then consider a cosmic string network, and discuss its detectability from upcoming weak lensing and CMB measurements. Based on the formulas and a simple model for cosmic string network, we calculate the angular power spectra and expected signal-to-noise ratios for the B-mode cosmic shear and curl-mode deflection angle. We find that the weak lensing signals are enhanced for a smaller intercommuting probability of the string network, P, and they are potentially detectable from the upcoming cosmic shear and CMB lensing observations. For P ∼ 10{sup −1}, the minimum detectable tension of the cosmic string will be down to Gμ ∼ 5 × 10{sup −8}. With a theoretically inferred smallest value P ∼ 10{sup −3}, we could even detect the string with Gμ ∼ 5 × 10{sup −10}.
Weak Lensing by Galaxy Clusters: from Pixels to Cosmology
Gruen, Daniel
2015-03-11
The story of the origin and evolution of our Universe is told, equivalently, by space-time itself and by the structures that grow inside of it. Clusters of galaxies are the frontier of bottom-up structure formation. They are the most massive objects to have collapsed at the present epoch. By that virtue, their abundance and structural parameters are highly sensitive to the composition and evolution of the Universe. The most common probe of cluster cosmology, abundance, uses samples of clusters selected by some observable. Applying a mass-observable relation (MOR), cosmological parameters can be constrained by comparing the sample to predicted cluster abundances as a function of observable and redshift. Arguably, however, cluster probes have not yet entered the era of per cent level precision cosmology. The primary reason for this is our imperfect understanding of the MORs. The overall normalization, the slope of mass vs. observable, the redshift evolution, and the degree and correlation of intrinsic scatters of observables at fixed mass have to be constrained for interpreting abundances correctly. Mass measurement of clusters by means of the differential deflection of light from background sources in their gravitational field, i.e. weak lensing, is a powerful approach for achieving this. This thesis presents new methods for and scientific results of weak lensing measurements of clusters of galaxies. The former include, on the data reduction side, (i) the correction of CCD images for non-linear effects due to the electric fields of accumulated charges and (ii) a method for masking artifact features in sets of overlapping images of the sky by comparison to the median image. Also, (iii) I develop a method for the selection of background galaxy samples based on their color and apparent magnitude that includes a new correction for contamination with cluster member galaxies. The main scientific results are the following. (i) For the Hubble Frontier Field cluster RXC J
Quasar structure from microlensing in gravitationally lensed quasars
NASA Astrophysics Data System (ADS)
Morgan, Christopher Warren
2008-02-01
I analyze microlensing in gravitationally lensed quasars to yield measurements of the structure of their continuum emission regions. I first describe our lensed quasar monitoring program and RETROCAM, the auxiliary port camera I built for the 2.4m Hiltner telescope to monitor lensed quasars. I describe the application of our Monte Carlo microlensing analysis technique to SDSS 0924+0219, a system with a highly anomalous optical flux ratio. For an inclination angle i, I find an optical scale radius log[( r s /cm)[Special characters omitted.] ] = [Special characters omitted.] . I extrapolate the best-fitting light curves into the future to find a roughly 45% probability that the anomalous image (D) will brighten by at least an order of magnitude during the next decade. I expand our method to make simultaneous estimates of the time delays and structure of HE1104-1805 and QJ0158-4325, two doubly-imaged quasars with microlensing and intrinsic variability on comparable time scales. For HE1104- 1805 I find a time delay of D t AB = t A - t B = [Special characters omitted.] days and estimate a scale radius of log[( r s /cm)[Special characters omitted.] ] = [Special characters omitted.] at 0.2mm in the rest frame. I am unable to measure a time delay for QJ0158-4325, but the scale radius is log[( r s /cm) [Special characters omitted.] ] = 14.9 ±1 0.3 at 0.3mm in the rest frame. I then apply our Monte Carlo microlensing analysis technique to the optical light curves of 11 lensed quasar systems to show that quasar accretion disk sizes at 2500Å are related to black hole mass ( M BH ) by log( R 2500 /cm) = (15.7 ± 0.16) + (0.64± 0.18) log( M BH /10 9 [Special characters omitted.] ). This scaling is consistent with the expectation from thin disk theory (R 0( [Special characters omitted.] ), but it implies that black holes radiate with relatively low efficiency, log(e) = -1.54 ± 0.36 + log( L/L E ) where e=3D L / ( M c 2 ). These sizes are also larger, by a factor of ~ 3, than
Gravitational lensing of the CMB: A Feynman diagram approach
NASA Astrophysics Data System (ADS)
Jenkins, Elizabeth E.; Manohar, Aneesh V.; Waalewijn, Wouter J.; Yadav, Amit P. S.
2014-09-01
We develop a Feynman diagram approach to calculating correlations of the Cosmic Microwave Background (CMB) in the presence of distortions. As one application, we focus on CMB distortions due to gravitational lensing by Large Scale Structure (LSS). We study the Hu-Okamoto quadratic estimator for extracting lensing from the CMB and derive the noise of the estimator up to O(ϕ4) in the lensing potential ϕ. By identifying the diagrams responsible for the previously noted large O(ϕ4) term, we conclude that the lensing expansion does not break down. The convergence can be significantly improved by a reorganization of the ϕ expansion. Our approach makes it simple to obtain expressions for quadratic estimators based on any CMB channel, including many previously unexplored cases. We briefly discuss other applications to cosmology of this diagrammatic approach, such as distortions of the CMB due to patchy reionization, or due to Faraday rotation from primordial axion fields.
Strong gravitational lensing in a noncommutative black-hole spacetime
Ding Chikun; Kang Shuai; Chen Changyong; Chen Songbai; Jing Jiliang
2011-04-15
Noncommutative geometry may be a starting point to a quantum gravity. We study the influence of the spacetime noncommutative parameter on the strong field gravitational lensing in the noncommutative Schwarzschild black-hole spacetime and obtain the angular position and magnification of the relativistic images. Supposing that the gravitational field of the supermassive central object of the galaxy can be described by this metric, we estimate the numerical values of the coefficients and observables for strong gravitational lensing. In comparison to the Reissner-Norstroem black hole, we find that the influences of the spacetime noncommutative parameter is similar to those of the charge, but these influences are much smaller. This may offer a way to distinguish a noncommutative black hole from a Reissner-Norstroem black hole, and may permit us to probe the spacetime noncommutative constant {theta} by the astronomical instruments in the future.
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 galaxy’s polarized emission is both unaffected by lensing and is related to the galaxy’s 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.
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.
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.
Gravitational Lensing in the metric theory proposed by Sobouti
NASA Astrophysics Data System (ADS)
Bernal, Tula; Mendoza, Sergio
2008-12-01
Recently, Y. Sobouti (2007) has provided a metric theory f(R) that can account for certain dynamical anomalies observed in spiral galaxies. Mendoza & Rosas-Guevara (2007) have shown that in this theory there is an extra-bending as compared to standard general relativity. In the present work we have developed in more specific detail this additional lensing effect and we have made evaluations of the α parameter used in the model adjusting the theory to observations in X-rays of 13 clusters of galaxies with gravitational lensing ([6]).
NASA Astrophysics Data System (ADS)
Collett, Thomas E.; Bacon, David
2017-03-01
Probing the relative speeds of gravitational waves and light acts as an important test of general relativity and alternative theories of gravity. Measuring the arrival time of gravitational waves (GWs) and electromagnetic (EM) counterparts can be used to measure the relative speeds, but only if the intrinsic time lag between emission of the photons and gravitational waves is well understood. Here we suggest a method that does not make such an assumption, using future strongly lensed GW events and EM counterparts; Biesiada et al. [J. Cosmol. Astropart. Phys.10 (2014) 080, 10.1088/1475-7516/2014/10/080] forecast that 50-100 strongly lensed GW events will be observed each year with the Einstein Telescope. A single strongly lensed GW event would produce robust constraints on cGW/cγ at the 10-7 level, if a high-energy EM counterpart is observed within the field of view of an observing γ -ray burst monitor.
Observable properties of strong gravitational lenses
NASA Astrophysics Data System (ADS)
Tessore, Nicolas
2017-01-01
It is shown which properties of a strong gravitational lens can in principle be recovered from observations of multiple extended images when no assumptions are made about the deflector or sources. The mapping between individual multiple images is identified as the carrier of information about the gravitational lens and it is shown how this information can be extracted from a hypothetical observation. The derivatives of the image map contain information about convergence ratios and reduced shears over the regions of the multiple images. For two observed images, it is not possible to reconstruct the convergence ratio and shear at the same time. For three observed images, it is possible to recover the convergence ratios and reduced shears identically. For four or more observed images, the system of constraints is overdetermined, but the same quantities can theoretically be recovered.
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.
Speed of Gravitational Waves from Strongly Lensed Gravitational Waves and Electromagnetic Signals.
Fan, Xi-Long; Liao, Kai; Biesiada, Marek; Piórkowska-Kurpas, Aleksandra; Zhu, Zong-Hong
2017-03-03
We propose a new model-independent measurement strategy for the propagation speed of gravitational waves (GWs) based on strongly lensed GWs and their electromagnetic (EM) counterparts. This can be done in two ways: by comparing arrival times of GWs and their EM counterparts and by comparing the time delays between images seen in GWs and their EM counterparts. The lensed GW-EM event is perhaps the best way to identify an EM counterpart. Conceptually, this method does not rely on any specific theory of massive gravitons or modified gravity. Its differential setting (i.e., measuring the difference between time delays in GW and EM domains) makes it robust against lens modeling details (photons and GWs travel in the same lensing potential) and against internal time delays between GW and EM emission acts. It requires, however, that the theory of gravity is metric and predicts gravitational lensing similar to general relativity. We expect that such a test will become possible in the era of third-generation gravitational-wave detectors, when about 10 lensed GW events would be observed each year. The power of this method is mainly limited by the timing accuracy of the EM counterpart, which for kilonovae is around 10^{4} s. This uncertainty can be suppressed by a factor of ∼10^{10}, if strongly lensed transients of much shorter duration associated with the GW event can be identified. Candidates for such short transients include short γ-ray bursts and fast radio bursts.
Speed of Gravitational Waves from Strongly Lensed Gravitational Waves and Electromagnetic Signals
NASA Astrophysics Data System (ADS)
Fan, Xi-Long; Liao, Kai; Biesiada, Marek; Piórkowska-Kurpas, Aleksandra; Zhu, Zong-Hong
2017-03-01
We propose a new model-independent measurement strategy for the propagation speed of gravitational waves (GWs) based on strongly lensed GWs and their electromagnetic (EM) counterparts. This can be done in two ways: by comparing arrival times of GWs and their EM counterparts and by comparing the time delays between images seen in GWs and their EM counterparts. The lensed GW-EM event is perhaps the best way to identify an EM counterpart. Conceptually, this method does not rely on any specific theory of massive gravitons or modified gravity. Its differential setting (i.e., measuring the difference between time delays in GW and EM domains) makes it robust against lens modeling details (photons and GWs travel in the same lensing potential) and against internal time delays between GW and EM emission acts. It requires, however, that the theory of gravity is metric and predicts gravitational lensing similar to general relativity. We expect that such a test will become possible in the era of third-generation gravitational-wave detectors, when about 10 lensed GW events would be observed each year. The power of this method is mainly limited by the timing accuracy of the EM counterpart, which for kilonovae is around 1 04 s . This uncertainty can be suppressed by a factor of ˜1 010, if strongly lensed transients of much shorter duration associated with the GW event can be identified. Candidates for such short transients include short γ -ray bursts and fast radio bursts.
SKA weak lensing - I. Cosmological forecasts and the power of radio-optical cross-correlations
NASA Astrophysics Data System (ADS)
Harrison, Ian; Camera, Stefano; Zuntz, Joe; Brown, Michael L.
2016-12-01
We construct forecasts for cosmological parameter constraints from weak gravitational lensing surveys involving the Square Kilometre Array (SKA). Considering matter content, dark energy and modified gravity parameters, we show that the first phase of the SKA (SKA1) can be competitive with other Stage III experiments such as the Dark Energy Survey and that the full SKA (SKA2) can potentially form tighter constraints than Stage IV optical weak lensing experiments, such as those that will be conducted with LSST, WFIRST-AFTA or Euclid-like facilities. Using weak lensing alone, going from SKA1 to SKA2 represents improvements by factors of ˜10 in matter, ˜10 in dark energy and ˜5 in modified gravity parameters. We also show, for the first time, the powerful result that comparably tight constraints (within ˜5 per cent) for both Stage III and Stage IV experiments, can be gained from cross-correlating shear maps between the optical and radio wavebands, a process which can also eliminate a number of potential sources of systematic errors which can otherwise limit the utility of weak lensing cosmology.
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.
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.
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.
Gravitational lensing in a cold dark matter universe
NASA Technical Reports Server (NTRS)
Narayan, Ramesh; White, Simon D. M.
1988-01-01
Gravitational lensing due to mass condensations in a biased cold dark matter (CDM) universe is investigated using the Press-Schechter (1974) theory with density fluctuation amplitudes taken from previous N-body work. Under the critical assumption that CDM haloes have small core radii, a distribution of image angular separations for high-z lensed quasars with a peak at about 1 arcsec and a half-width of a factor of about 10. Allowing for selection effects at small angular separations, this is in good agreement with the observed separations. The estimated frequency of lensing is somewhat lower than that observed, but the discrepancy can be removed by invoking amplification bias and by making a small upward adjustment to the density fluctuation amplitudes assumed in the CDM model.
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.
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.
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}.
Gravitational lensing by an ensemble of isothermal galaxies
NASA Astrophysics Data System (ADS)
Katz, Neal; Paczynski, Bohdan
1987-06-01
Calculation of 28,000 models of gravitational lensing of a distant quasar by an ensemble of randomly placed galaxies, each having a singular isothermal mass distribuiton, is reported. The average surface mass density was 0.2 of the critical value in all models. It is found that the surface mass density averaged over the area of the smallest circle that encompasses the multiple images is 0.82, only slightly smaller than expected from a simple analytical model of Turner et al. (1984). The probability of getting multiple images is also as large as expected analytically. Gravitational lensing is dominated by the matter in the beam; i.e., by the beam convergence. The cases where the multiple imaging is due to asymmetry in mass distribution (i.e., due to shear) are very rare. Therefore, the observed gravitational-lens candidates for which no lensing object has been detected between the images cannot be a result of asymmetric mass distribution outside the images, at least in a model with randomly distributed galaxies. A surprisingly large number of large separations between the multiple images is found: up to 25 percent of multiple images have their angular separation 2 to 4 times larger than expected in a simple analytical model.
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.
Mass to light ratio of galaxies and gravitational lensing
NASA Astrophysics Data System (ADS)
Li, Nan; Li, Ran; Er, Xin-Zhong
2013-09-01
We investigate the potential of constraining the mass to light ratio of field galaxies using weak lensing shear and flexions. A suite of Monte Carlo simulations are used to generate weak lensing observations with different noise models. Using mock data, we find that the inclusion of flexions can improve the estimate of foreground halo parameters, but the details are strongly dependent on noise in the model. In the intrinsic noise limit, both shear and flexions are promising tools to study the mass to light ratio of galaxies. However, if the noise model of flexions follows the form described by Rowe et al., there is only ~5% improvement in the constraints even with next generation lensing observations.
Sample variance in weak lensing: How many simulations are required?
Petri, Andrea; May, Morgan; Haiman, Zoltan
2016-03-24
Constraining cosmology using weak gravitational lensing consists of comparing a measured feature vector of dimension N_{b} with its simulated counterpart. An accurate estimate of the N_{b} × N_{b} feature covariance matrix C is essential to obtain accurate parameter confidence intervals. When C is measured from a set of simulations, an important question is how large this set should be. To answer this question, we construct different ensembles of N_{r} realizations of the shear field, using a common randomization procedure that recycles the outputs from a smaller number N_{s} ≤ N_{r} of independent ray-tracing N-body simulations. We study parameter confidence intervals as a function of (N_{s}, N_{r}) in the range 1 ≤ N_{s} ≤ 200 and 1 ≤ N_{r} ≲ 105. Previous work [S. Dodelson and M. D. Schneider, Phys. Rev. D 88, 063537 (2013)] has shown that Gaussian noise in the feature vectors (from which the covariance is estimated) lead, at quadratic order, to an O(1/N_{r}) degradation of the parameter confidence intervals. Using a variety of lensing features measured in our simulations, including shear-shear power spectra and peak counts, we show that cubic and quartic covariance fluctuations lead to additional O(1/N^{2}_{r}) error degradation that is not negligible when N_{r} is only a factor of few larger than N_{b}. We study the large N_{r} limit, and find that a single, 240 Mpc/h sized 512^{3}-particle N-body simulation (N_{s} = 1) can be repeatedly recycled to produce as many as N_{r} = few × 10^{4} shear maps whose power spectra and high-significance peak counts can be treated as statistically independent. Lastly, a small number of simulations (N_{s} = 1 or 2) is sufficient to forecast parameter confidence intervals at percent accuracy.
Faint radio sources and gravitational lensing
Langston, G.I.; Conner, S.R.; Heflin, M.B.; Lehar, J.; Burke, B.F. MIT, Cambridge, MA )
1990-04-01
Measurements of the surface density of radio sources resulting from a deep VLA integration at 5 GHz and the MIT-Green Bank (MG) II 5 GHz survey are summarized. The faint source counts are combined with previous observations and fitted to a power-law function of surface density vs. limiting flux density. The surface density of radio sources brighter than 1 mJy is k = 0.019 + or - 0.004/arcmin. The power-law exponent is best fit by -0.93 + or - 0.14. Between 15 and 100 mJy, the surface density of radio sources varies nearly as predicted by Euclidian models of the universe. Estimates are given for the number of chance alignments of radio sources in the VLA snapshot observations of the MIT-Princeton-Caltech gravitational lens search. The probability of lens candidate configurations occurring by chance alignment is calculated. 28 refs.
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.
Cosmic variance of the galaxy cluster weak lensing signal
Gruen, D.; Seitz, S.; Becker, M. R.; ...
2015-04-13
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 M200m ≈ 1014…1015h–1M⊙, z = 0.25…0.5 in a cosmological simulation. We show that weak lensing measurements of clusters significantly underestimate mass uncertainties if intrinsic profile variationsmore » 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 M200m ≈ 1015h–1M⊙ 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). Furthermore, 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.« less
QUANTIFYING THE BIASES OF SPECTROSCOPICALLY SELECTED GRAVITATIONAL LENSES
Arneson, Ryan A.; Brownstein, Joel R.; Bolton, Adam S. E-mail: joelbrownstein@astro.utah.edu
2012-07-01
Spectroscopic selection has been the most productive technique for the selection of galaxy-scale strong gravitational lens systems with known redshifts. Statistically significant samples of strong lenses provide a powerful method for measuring the mass-density parameters of the lensing population, but results can only be generalized to the parent population if the lensing selection biases are sufficiently understood. We perform controlled Monte Carlo simulations of spectroscopic lens surveys in order to quantify the bias of lenses relative to parent galaxies in velocity dispersion, mass axis ratio, and mass-density profile. For parameters typical of the SLACS and BELLS surveys, we find (1) no significant mass axis ratio detection bias of lenses relative to parent galaxies; (2) a very small detection bias toward shallow mass-density profiles, which is likely negligible compared to other sources of uncertainty in this parameter; (3) a detection bias toward smaller Einstein radius for systems drawn from parent populations with group- and cluster-scale lensing masses; and (4) a lens-modeling bias toward larger velocity dispersions for systems drawn from parent samples with sub-arcsecond mean Einstein radii. This last finding indicates that the incorporation of velocity-dispersion upper limits of non-lenses is an important ingredient for unbiased analyses of spectroscopically selected lens samples. In general, we find that the completeness of spectroscopic lens surveys in the plane of Einstein radius and mass-density profile power-law index is quite uniform, up to a sharp drop in the region of large Einstein radius and steep mass-density profile, and hence that such surveys are ideally suited to the study of massive field galaxies.
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.
Strong gravitational lensing statistics as a test of cosmogonic scenarios
NASA Technical Reports Server (NTRS)
Cen, Renyue; Gott, J. Richard, III; Ostriker, Jeremiah P.; Turner, Edwin L.
1994-01-01
Gravitational lensing statistics can provide a direct and powerful test of cosmic structure formation theories. Since lensing tests, directly, the magnitude of the nonlinear mass density fluctuations on lines of sight to distant objects, no issues of 'bias' (of mass fluctuations with respect to galaxy density fluctuations) exist here, although lensing observations provide their own ambiguities of interpretation. We develop numerical techniques for generating model density distributions with the very large spatial dynamic range required by lensing considerations and for identifying regions of the simulations capable of multiple image lensing in a conservative and computationally efficient way that should be accurate for splittings significantly larger than 3 seconds. Applying these techniques to existing standard Cold dark matter (CDM) (Omega = 1) and Primeval Baryon Isocurvature (PBI) (Omega = 0.2) simulations (normalized to the Cosmic Background Explorer Satellite (COBE) amplitude), we find that the CDM model predicts large splitting (greater than 8 seconds) lensing events roughly an order-of-magnitude more frequently than the PBI model. Under the reasonable but idealized assumption that lensing structrues can be modeled as singular isothermal spheres (SIS), the predictions can be directly compared to observations of lensing events in quasar samples. Several large splitting (Delta Theta is greater than 8 seconds) cases are predicted in the standard CDM model (the exact number being dependent on the treatment of amplification bias), whereas none is observed. In a formal sense, the comparison excludes the CDM model at high confidence (essentially for the same reason that CDM predicts excessive small-scale cosmic velocity dispersions.) A very rough assessment of low-density but flat CDM model (Omega = 0.3, Lambda/3H(sup 2 sub 0) = 0.7) indicates a far lower and probably acceptable level of lensing. The PBI model is consistent with, but not strongly tested by, the
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 κ-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.
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
Strong gravitational lensing by a Konoplya-Zhidenko rotating non-Kerr compact object
NASA Astrophysics Data System (ADS)
Wang, Shangyun; Chen, Songbai; Jing, Jiliang
2016-11-01
Konoplya and Zhidenko have proposed recently a rotating non-Kerr black hole metric beyond General Relativity and make an estimate for the possible deviations from the Kerr solution with the data of GW 150914. We here study the strong gravitational lensing in such a rotating non-Kerr spacetime with an extra deformation parameter. We find that the condition of existence of horizons is not inconsistent with that of the marginally circular photon orbit. Moreover, the deflection angle of the light ray near the weakly naked singularity covered by the marginally circular orbit diverges logarithmically in the strong-field limit. In the case of the completely naked singularity, the deflection angle near the singularity tends to a certain finite value, whose sign depends on the rotation parameter and the deformation parameter. These properties of strong gravitational lensing are different from those in the Johannsen-Psaltis rotating non-Kerr spacetime and in the Janis-Newman-Winicour spacetime. Modeling the supermassive central object of the Milk Way Galaxy as a Konoplya-Zhidenko rotating non-Kerr compact object, we estimated the numerical values of observables for the strong gravitational lensing including the time delay between two relativistic images.
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.
Creating images by adding masses to gravitational point lenses
NASA Astrophysics Data System (ADS)
Sète, Olivier; Luce, Robert; Liesen, Jörg
2015-04-01
A well-studied maximal gravitational point lens construction of S. H. Rhie produces images of a light source using deflector masses. The construction arises from a circular, symmetric deflector configuration on masses (producing only images) by adding a tiny mass in the center of the other mass positions (and reducing all the other masses a little bit). In a recent paper we studied this "image creating effect" from a purely mathematical point of view (Sète, Luce & Liesen, Comput. Methods Funct. Theory 15(1), 2014). Here we discuss a few consequences of our findings for gravitational microlensing models. We present a complete characterization of the effect of adding small masses to these point lens models, with respect to the number of images. In particular, we give several examples of maximal lensing models that are different from Rhie's construction and that do not share its highly symmetric appearance. We give generally applicable conditions that allow the construction of maximal point lenses on masses from maximal lenses on masses.
Testing the DGP model with gravitational lensing statistics
NASA Astrophysics Data System (ADS)
Zhu, Zong-Hong; Sereno, M.
2008-09-01
Aims: The self-accelerating braneworld model (DGP) appears to provide a simple alternative to the standard ΛCDM cosmology to explain the current cosmic acceleration, which is strongly indicated by measurements of type Ia supernovae, as well as other concordant observations. Methods: We investigate observational constraints on this scenario provided by gravitational-lensing statistics using the Cosmic Lens All-Sky Survey (CLASS) lensing sample. Results: We show that a substantial part of the parameter space of the DGP model agrees well with that of radio source gravitational lensing sample. Conclusions: In the flat case, Ω_K=0, the likelihood is maximized, L=L_max, for ΩM = 0.30-0.11+0.19. If we relax the prior on Ω_K, the likelihood peaks at Ω_M,Ωr_c ≃ 0.29, 0.12, slightly in the region of open models. The confidence contours are, however, elongated such that we are unable to discard any of the close, flat or open models.
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.
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 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
NASA Astrophysics Data System (ADS)
Hopwood, R.; Wardlow, J.; Cooray, A.; Khostovan, A. A.; Kim, S.; Negrello, M.; da Cunha, E.; Burgarella, D.; Aretxaga, I.; Auld, R.; Baes, M.; Barton, E.; Bertoldi, F.; Bonfield, D. G.; Blundell, R.; Buttiglione, S.; Cava, A.; Clements, D. L.; Cooke, J.; Dannerbauer, H.; Dariush, A.; de Zotti, G.; Dunlop, J.; Dunne, L.; Dye, S.; Eales, S.; Fritz, J.; Frayer, D.; Gurwell, M. A.; Hughes, D. H.; Ibar, E.; Ivison, R. J.; Jarvis, M. J.; Lagache, G.; Leeuw, L.; Maddox, S.; Michałowski, M. J.; Omont, A.; Pascale, E.; Pohlen, M.; Rigby, E.; Rodighiero, G.; Scott, D.; Serjeant, S.; Smail, I.; Smith, D. J. B.; Temi, P.; Thompson, M. A.; Valtchanov, I.; van der Werf, P.; Verma, A.; Vieira, J. D.
2011-02-01
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 μm, 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 μm 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 V ~ 4-5 and star formation rates of ~100 M sun yr-1. They have low gas fractions and low dynamical masses compared with 850 μm selected galaxies.
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.
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.
Effects of supermassive binary black holes on gravitational lenses
NASA Astrophysics Data System (ADS)
Li, Nan; Mao, Shude; Gao, Liang; Loeb, Abraham; di Stefano, R.
2012-01-01
Recent observations indicate that many, if not all, galaxies host massive central black holes (BHs). In this paper, we explore the influence of supermassive binary black holes (SMBBHs) on their actions as gravitational lenses. When lenses are modelled as singular isothermal ellipsoids, binary BHs change the critical curves and caustics differently as a function of distance. Each BH can in principle create at least one additional image, which, if observed, provides evidence of BHs. By studying how SMBBHs affect the cumulative distribution of magnification for images created by BHs, we find that the cross-section for at least one such additional image to have a magnification larger than 10-5 is comparable to the cross-section for producing multiple images in singular isothermal lenses. Such additional images may be detectable with high-resolution and large dynamic range maps of multiply imaged systems from future facilities, such as the Square Kilometre Array. The probability of detecting at least one image (two images) with magnification above 10-3 is ˜0.2fBH (˜0.05fBH) in a multiply imaged lens system, where fBH is the fraction of galaxies housing binary BHs. We also study the effects of SMBBHs on the core images when galaxies have shallower central density profiles (modelled as non-singular isothermal ellipsoids). We find that the cross-section of the usually faint core images is further suppressed by SMBBHs. Thus, their presence should also be taken into account when one constrains the core radius from the lack of central images in gravitational lenses.
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 2500Å is related to the black hole mass by log(R2500/cm) = (15.70±0.16) + (0.64±0.18)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(η) = -1.54±0.36 + log(L/LE) where η=L/(Mdotc2). With one exception, these sizes are larger by a factor of 4 than the size needed to produce the observed 0.8µm 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.
The impact of AGN feedback and baryonic cooling on galaxy clusters as gravitational lenses
NASA Astrophysics Data System (ADS)
Mead, James M. G.; King, Lindsay J.; Sijacki, Debora; Leonard, Adrienne; Puchwein, Ewald; McCarthy, Ian G.
2010-07-01
We investigate the impact of active galactic nucleus (AGN) feedback on the gravitational lensing properties of a sample of galaxy clusters with masses in the range 1014-1015 Msolar, using state-of-the-art simulations. Adopting a ray-tracing algorithm, we compute the cross-section of giant arcs from clusters simulated with dark matter (DM) only physics, DM plus gas with cooling and star formation (CSF) and DM plus gas with cooling, star formation and AGN feedback (CSFBH). Once AGN feedback is included, baryonic physics boosts the strong-lensing cross-section by much less than previously estimated using clusters simulated with only CSF. For a cluster with a virial mass of 7.4 × 1014 Msolar, inclusion of baryonic physics without feedback can boost the cross-section by as much as a factor of 3, in agreement with previous studies, whereas once AGN feedback is included this maximal figure falls to a factor of 2 at most. Typically, clusters simulated with DM and CSFBH physics have similar cross-sections for the production of giant arcs. We also investigate how baryonic physics affects the weak-lensing properties of the simulated clusters by fitting NFW profiles to synthetic weak-lensing data sets using a Markov Chain Monte Carlo approach, and by performing non-parametric mass reconstructions. Without the inclusion of AGN feedback, measured concentration parameters can be much larger than those obtained with AGN feedback, which are similar to the DM-only case.
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, ΛCDM, 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 ΛCDM, 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 ΛCDM 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 ΛCDM. We point out that, should the R{sub h}=ct universe eventually
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, ΛCDM, 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 ΛCDM, 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 ΛCDM 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 ΛCDM. We point out that, should the {{R}h}=ct universe eventually emerge as
NASA Astrophysics Data System (ADS)
Larsen, Patricia; Challinor, Anthony
2016-10-01
Correlations of galaxy ellipticities with large-scale structure, due to galactic tidal interactions, provide a potentially significant contaminant to measurements of cosmic shear. However, these intrinsic alignments are still poorly understood for galaxies at the redshifts typically used in cosmic shear analyses. For spiral galaxies, it is thought that tidal torquing is significant in determining alignments resulting in zero correlation between the intrinsic ellipticity and the gravitational potential in linear theory. Here, we calculate the leading-order correction to this result in the tidal-torque model from non-linear evolution, using second-order perturbation theory, and relate this to the contamination from intrinsic alignments to the recently measured cross-correlation between galaxy ellipticities and the cosmic microwave background (CMB) lensing potential. On the scales relevant for CMB lensing observations, the squeezed limit of the gravitational bispectrum dominates the correlation. Physically, the large-scale mode that sources CMB lensing modulates the small-scale power and hence the intrinsic ellipticity, due to non-linear evolution. We find that the angular cross-correlation from tidal torquing has a very similar scale dependence as in the linear alignment model, believed to be appropriate for elliptical galaxies. The amplitude of the cross-correlation is predicted to depend strongly on the formation redshift, being smaller for galaxies that formed at higher redshift when the bispectrum of the gravitational potential was smaller. Finally, we make simple forecasts for constraints on intrinsic alignments from the correlation of forthcoming cosmic shear measurements with current CMB lensing measurements. We note that cosmic variance can be significantly reduced in measurements of the difference in the intrinsic alignments for elliptical and spiral galaxies if these types can be separated (e.g. using colour).
A note on a linearized approach to gravitational lensing
NASA Astrophysics Data System (ADS)
Walters, S. J.; Forbes, L. K.
2011-10-01
A recent paper by Walters, Forbes and Jarvis presented new kinematic formulae for ray tracing in gravitational lensing models. The approach can generate caustic maps, but is computationally expensive. Here, a linearized approximation to that formulation is presented. Although still complicated, the linearized equations admit a remarkable closed-form solution. As a result, linearized approximations to the caustic patterns may be generated extremely rapidly, and are found to be in good agreement with the results of full non-linear computation. The usual Einstein-angle approximation is derived as a small angle approximation to the solution presented here.
The DES Science Verification Weak Lensing Shear Catalogs
Jarvis, M.
2016-05-01
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 DES Science Verification weak lensing shear catalogues
NASA Astrophysics Data System (ADS)
Jarvis, M.; Sheldon, E.; Zuntz, J.; Kacprzak, T.; Bridle, S. L.; Amara, A.; Armstrong, R.; Becker, M. R.; Bernstein, G. M.; Bonnett, C.; Chang, C.; Das, R.; Dietrich, J. P.; Drlica-Wagner, A.; Eifler, T. F.; Gangkofner, C.; Gruen, D.; Hirsch, M.; Huff, E. M.; Jain, B.; Kent, S.; Kirk, D.; MacCrann, N.; Melchior, P.; Plazas, A. A.; Refregier, A.; Rowe, B.; Rykoff, E. S.; Samuroff, S.; Sánchez, C.; Suchyta, E.; Troxel, M. A.; Vikram, V.; Abbott, T.; Abdalla, F. B.; Allam, S.; Annis, J.; Benoit-Lévy, A.; Bertin, E.; Brooks, D.; Buckley-Geer, E.; Burke, D. L.; Capozzi, D.; Carnero Rosell, A.; Carrasco Kind, M.; Carretero, J.; Castander, F. J.; Clampitt, J.; Crocce, M.; Cunha, C. E.; D'Andrea, C. B.; da Costa, L. N.; DePoy, D. L.; Desai, S.; Diehl, H. T.; Doel, P.; Fausti Neto, A.; Flaugher, B.; Fosalba, P.; Frieman, J.; Gaztanaga, E.; Gerdes, D. W.; Gruendl, R. A.; Gutierrez, G.; Honscheid, K.; James, D. J.; Kuehn, K.; Kuropatkin, N.; Lahav, O.; Li, T. S.; Lima, M.; March, M.; Martini, P.; Miquel, R.; Mohr, J. J.; Neilsen, E.; Nord, B.; Ogando, R.; 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.; Swanson, M. E. C.; Tarle, G.; Thaler, J.; Thomas, D.; Walker, A. R.; Wechsler, R. H.
2016-08-01
We present weak lensing shear catalogues 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 catalogues of 2.12 million and 3.44 million galaxies, respectively. We 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. We also discuss some of the planned algorithmic improvements that will be necessary to produce sufficiently accurate shear catalogues for the full 5-yr DES, which is expected to cover 5000 square degrees.
The DES Science Verification Weak Lensing Shear Catalogs
Jarvis, M.
2016-05-01
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 SVmore » 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.« less
Weak lensing mass of nearby clusters of galaxies
Joffre, Michael; et al.
1999-09-01
We describe first results of a project to create weak lensing mass maps for a complete, X-ray luminosity-limited sample of 19 nearby (z < 0.1) southern galaxy clusters scheduled for Sunyaev-Zel'dovich observations by the Viper Telescope at the South Pole. We have collected data on 1/3 of the sample and present motivation for the project as well as projected mass maps of two clusters.
Cosmic variance of the galaxy cluster weak lensing signal
Gruen, D.; Seitz, S.; Becker, M. R.; Friedrich, O.; Mana, A.
2015-04-13
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}…10^{15}h^{–1}M_{⊙}, z = 0.25…0.5 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). Furthermore, 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.
SKA weak lensing- II. Simulated performance and survey design considerations
NASA Astrophysics Data System (ADS)
Bonaldi, Anna; Harrison, Ian; Camera, Stefano; Brown, Michael L.
2016-12-01
We construct a pipeline for simulating weak lensing cosmology surveys with the Square Kilometre Array (SKA), taking as inputs telescope sensitivity curves; correlated source flux, size and redshift distributions; a simple ionospheric model; source redshift and ellipticity measurement errors. We then use this simulation pipeline to optimize a 2-yr weak lensing survey performed with the first deployment of the SKA (SKA1). Our assessments are based on the total signal to noise of the recovered shear power spectra, a metric that we find to correlate very well with a standard dark energy figure of merit. We first consider the choice of frequency band, trading off increases in number counts at lower frequencies against poorer resolution; our analysis strongly prefers the higher frequency Band 2 (950-1760 MHz) channel of the SKA-MID telescope to the lower frequency Band 1 (350-1050 MHz). Best results would be obtained by allowing the centre of Band 2 to shift towards lower frequency, around 1.1 GHz. We then move on to consider survey size, finding that an area of 5000 deg2 is optimal for most SKA1 instrumental configurations. Finally, we forecast the performance of a weak lensing survey with the second deployment of the SKA. The increased survey size (3π steradian) and sensitivity improves both the signal to noise and the dark energy metrics by two orders of magnitude.
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.; ...
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
Gravitational lensing in an exact locally inhomogeneous cosmology
NASA Astrophysics Data System (ADS)
Attard, Allen
2005-11-01
A Recursive Swiss-Cheese (RSC) cosmological model is an exact solution to Einstein's general relativistic field equations allowing for dramatic local density inhomogeneities while maintaining global homogeneity and isotropy. It is constructed by replacing spherical regions of an FRW background with higher density cores placed at the centre of a Schwarzschild vacuum, with each core itself potentially being given the same treatment and the process repeated to generate a range of multifractal structures. Code was developed to tightly pack spheres into spaces of constant curvature in an efficient manner, and was used to develop libraries of packings with positive, negative, and zero curvature. Various projections are used to illustrate their structure, and means of measuring its dimensionality are discussed. A method by which these packings can be used as building blocks of an RSC model, along with a way of selecting parameters to define the model, is described, and a coordinate system allowing a relativistically consistent means of synchronizing its various components is developed. Formulations of the optical scalar equations for the expansion and shear rates of a beam are considered, and a set suitable for numerical integration selected. The forms of the null geodesic beam trajectories in each region of the model are computed, and a parallel propagated shadow plane basis that can be consistently followed between the various model sections is established. This allowed the development of code using a fourth order, variable step size Runge-Kutta integration routine to compute the gravitational lensing effect within an RSC model by tracking the amplification and distortion of a series of beams that are propagated through it. The output generated allows the redshift evolution of these quantities to be plotted for each beam, and enables maps to be made of the "observed sky". The amplification signature produced by a single lens in the model is examined, and the form shown
The impact of baryonic matter on gravitational lensing by galaxy clusters
NASA Astrophysics Data System (ADS)
Lee, Brandyn E.; King, Lindsay; Applegate, Douglas; McCarthy, Ian
2017-01-01
Since the bulk of the matter comprising galaxy clusters exists in the form of dark matter, gravitational N-body simulations have historically been an effective way to investigate large scale structure formation and the astrophysics of galaxy clusters. However, upcoming telescopes such as the Large Synoptic Survey Telescope are expected to have lower systematic errors than older generations, reducing measurement uncertainties and requiring that astrophysicists better quantify the impact of baryonic matter on the cluster lensing signal. Here we outline the effects of baryonic processes on cluster density profiles and on weak lensing mass and concentration estimates. Our analysis is done using clusters grown in the suite of cosmological hydrodynamical simulations known as cosmo-OWLS.
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.
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.
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.
NASA Astrophysics Data System (ADS)
Takahashi, Ryuichi
2017-01-01
In this study we demonstrate that general relativity predicts arrival time differences between gravitational wave (GW) and electromagnetic (EM) signals caused by the wave effects in gravitational lensing. The GW signals can arrive earlier than the EM signals in some cases if the GW/EM signals have passed through a lens, even if both signals were emitted simultaneously by a source. GW wavelengths are much larger than EM wavelengths; therefore, the propagation of the GWs does not follow the laws of geometrical optics, including the Shapiro time delay, if the lens mass is less than approximately 105 M⊙(f/Hz)‑1, where f is the GW frequency. The arrival time difference can reach ∼0.1 s (f/Hz)‑1 if the signals have passed by a lens of mass ∼8000 M⊙(f/Hz)‑1 with the impact parameter smaller than the Einstein radius; therefore, it is more prominent for lower GW frequencies. For example, when a distant supermassive black hole binary (SMBHB) in a galactic center is lensed by an intervening galaxy, the time lag becomes of the order of 10 days. Future pulsar timing arrays including the Square Kilometre Array and X-ray detectors may detect several time lags by measuring the orbital phase differences between the GW/EM signals in the SMBHBs. Gravitational lensing imprints a characteristic modulation on a chirp waveform; therefore, we can deduce whether a measured arrival time lag arises from intrinsic source properties or gravitational lensing. Determination of arrival time differences would be extremely useful in multimessenger observations and tests of general relativity.
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.
The central image of a gravitationally lensed quasar.
Winn, Joshua N; Rusin, David; Kochanek, Christopher S
2004-02-12
A galaxy can act as a gravitational lens, producing multiple images of a background object. Theory predicts that there should be an odd number of images produced by the lens, but hitherto almost all lensed objects have two or four images. The missing 'central' images, which should be faint and appear near the centre of the lensing galaxy, have long been sought as probes of galactic cores too distant to resolve with ordinary observations. There are five candidates for central images, but in one case the third image is not necessarily the central one, and in the others the putative central images might be foreground sources. Here we report a secure identification of a central image, based on radio observations of one of the candidates. Lens models using the central image reveal that the massive black hole at the centre of the lensing galaxy has a mass of <2 x 10(8) solar masses (M(o)), and the galaxy's surface density at the location of the central image is > 20,000M(o) pc(-2), which is in agreement with expections based on observations of galaxies that are much closer to the Earth.
Weak lensing by galaxy troughs in DES Science Verification data
Gruen, D.; Friedrich, O.; Amara, A.; ...
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.
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 (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. 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.; 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.
Collett, Thomas E; Bacon, David
2017-03-03
Probing the relative speeds of gravitational waves and light acts as an important test of general relativity and alternative theories of gravity. Measuring the arrival time of gravitational waves (GWs) and electromagnetic (EM) counterparts can be used to measure the relative speeds, but only if the intrinsic time lag between emission of the photons and gravitational waves is well understood. Here we suggest a method that does not make such an assumption, using future strongly lensed GW events and EM counterparts; Biesiada et al. [J. Cosmol. Astropart. Phys.10 (2014) 080JCAPBP1475-751610.1088/1475-7516/2014/10/080] forecast that 50-100 strongly lensed GW events will be observed each year with the Einstein Telescope. A single strongly lensed GW event would produce robust constraints on c_{GW}/c_{γ} at the 10^{-7} level, if a high-energy EM counterpart is observed within the field of view of an observing γ-ray burst monitor.
How to Find Gravitationally Lensed Type Ia Supernovae
NASA Astrophysics Data System (ADS)
Goldstein, Daniel A.; Nugent, Peter E.
2017-01-01
Type Ia supernovae (SNe Ia) that are multiply imaged by gravitational lensing can extend the SN Ia Hubble diagram to very high redshifts (z ≳ 2), probe potential SN Ia evolution, and deliver high-precision constraints on H0, w, and Ωm via time delays. However, only one, iPTF16geu, has been found to date, and many more are needed to achieve these goals. To increase the multiply imaged SN Ia discovery rate, we present a simple algorithm for identifying gravitationally lensed SN Ia candidates in cadenced, wide-field optical imaging surveys. The technique is to look for supernovae that appear to be hosted by elliptical galaxies, but that have absolute magnitudes implied by the apparent hosts’ photometric redshifts that are far brighter than the absolute magnitudes of normal SNe Ia (the brightest type of supernovae found in elliptical galaxies). Importantly, this purely photometric method does not require the ability to resolve the lensed images for discovery. Active galactic nuclei, the primary sources of contamination that affect the method, can be controlled using catalog cross-matches and color cuts. Highly magnified core-collapse SNe will also be discovered as a byproduct of the method. Using a Monte Carlo simulation, we forecast that the Large Synoptic Survey Telescope can discover up to 500 multiply imaged SNe Ia using this technique in a 10 year z-band search, more than an order of magnitude improvement over previous estimates. We also predict that the Zwicky Transient Facility should find up to 10 multiply imaged SNe Ia using this technique in a 3 year R-band search—despite the fact that this survey will not resolve a single system.
Problems using ratios of galaxy shape moments in requirements for weak lensing surveys
NASA Astrophysics Data System (ADS)
Israel, H.; Kitching, T. D.; Massey, R.; Cropper, M.
2017-01-01
Context. The shapes of galaxies are typically quantified by ratios of their quadrupole moments. Knowledge of these ratios (i.e. their measured standard deviation) is commonly used to assess the efficiency of weak gravitational lensing surveys. For faint galaxies, observational noise can make the denominator close to zero, so the ratios become ill-defined. Aims: Since the requirements cannot be formally tested for faint galaxies, we explore two complementary mitigation strategies. In many weak lensing contexts, the most problematic sources can be removed by a cut in measured size. This first technique is applied frequently. As our second strategy, we propose requirements directly on the quadrupole moments rather than their ratio. Methods: As an example of the first strategy, we have investigated how a size cut affects the required precision of the charge transfer inefficiency model for two shape measurement settings. For the second strategy, we analysed the joint likelihood distribution of the image quadrupole moments measured from simulated galaxies, and propagate their (correlated) uncertainties into ellipticities. Results: Using a size cut, we find slightly wider tolerance margins for the charge transfer inefficiency parameters compared to the full size distribution. However, subtle biases in the data analysis chain may be introduced. These can be avoided using the second strategy. To optimally exploit a Stage-IV dark energy survey, we find that the mean and standard deviation of a population of galaxies' quadrupole moments must to be known to better than 1.4 × 10-3 arcsec2, or the Stokes parameters to 1.9 × 10-3 arcsec2. Conclusions: Cuts in measured size remove sources that otherwise make ellipticity statistics of weak lensing galaxy samples diverge. However, size cuts bias the source population non-trivially. Assessing weak lensing data quality directly on the quadrupole moments instead mitigates the need for size cuts. Such testable requirements can form
CFHTLenS: The Environmental Dependence of Galaxy Halo Masses from Weak Lensing
NASA Astrophysics Data System (ADS)
Gillis, Bryan; Hudson, M. J.; Erben, T.; Heymans, C.; Hildebrandt, H.; Hoekstra, H.; Kitching, T. D.; Mellier, Y.; Miller, L.; van Waerbeke, L.; Bonnett, C.; Coupon, J.; Fu, L.; Hilbert, S.; Rowe, B.; Schrabback, T.; Semboloni, E.; van Uitert, E.; Velander, M.; Cfhtlens Team
2013-07-01
We use weak gravitational lensing to analyse the dark matter halos around satellite galaxies in galaxy groups in the CFHTLenS dataset. This dataset is derived from the CFHTLS-Wide survey, and encompasses 154 sq. deg of high-quality shape data. Using the photometric redshifts, we divide the sample of lens galaxies with stellar masses in the range 10^9 Msun to 10^10.5 Msun into those likely to lie in high-density environments (HDE) and those likely to lie in low-density environments (LDE). Through comparison with galaxy catalogues extracted from the Millennium Simulation, we show that the sample of HDE galaxies should primarily 61%) consist of satellite galaxies in groups, while the sample of LDE galaxies should consist of mostly 87%) non-satellite (field and central) galaxies. Comparing the lensing signals around samples of HDE and LDE galaxies matched in stellar mass, the lensing signal around HDE galaxies clearly shows a positive contribution from their host groups on their lensing signals at radii of ~500--1000 kpc, the typical separation between satellites and group centres. More importantly, the subhalos of HDE galaxies are less massive than those around LDE galaxies by a factor 0.65 +/- 0.12, significant at the 2.9 sigma level. A natural explanation is that the halos of satellite galaxies are stripped through tidal effects in the group environment. Our results are consistent with a typical tidal truncation radius of ~40 kpc.
NASA Astrophysics Data System (ADS)
Tagore, Amitpal Singh
Gravitational lens modeling of spatially resolved sources is a challenging inverse problem that can involve many observational constraints and model parameters. I present a new software package, pixsrc, that works in conjunction with the lensmodel software and builds on established pixel-based source reconstruction (PBSR) algorithms for de-lensing a source and constraining lens model parameters. Using test data, I explore statistical and systematic uncertainties associated with gridding, source regularization, interpolation errors, noise, and telescope pointing. I compare two gridding schemes in the source plane: a fully adaptive grid and an adaptive Cartesian grid. I also consider regularization schemes that minimize derivatives of the source and introduce a scheme that minimizes deviations from an analytic source profile. Careful choice of gridding and regularization can reduce "discreteness noise" in the chi2 surface that is inherent in the pixel-based methodology. With a gridded source, errors due to interpolation need to be taken into account (especially for high S/N data). Different realizations of noise and telescope pointing lead to slightly different values for lens model parameters, and the scatter between different "observations" can be comparable to or larger than the model uncertainties themselves. The same effects create scatter in the lensing magnification at the level of a few percent for a peak S/N of 10. I then apply pixsrc to observations of lensed, high-redshift galaxies. SDSS J0901+1814, is an ultraluminous infrared galaxy at z=2.26 that is also UV-bright, and it is lensed by a foreground group of galaxies at z=0.35. I constrain the lens model using maps of CO(3-2) rotational line emission and optical imaging and apply the lens model to observations of CO(1-0), H-alpha, and [NII] line emission as well. Using the de-lensed images, I calculate properties of the source, such as the gas mass fraction and dynamical mass. Finally, I examine a
IMPROVED CONSTRAINTS ON THE GRAVITATIONAL LENS Q0957+561. II. STRONG LENSING
Fadely, R.; Keeton, C. R.; Nakajima, R.; Bernstein, G. M. E-mail: keeton@physics.rutgers.ed E-mail: rnakajima@berkeley.ed
2010-03-01
We present a detailed strong lensing analysis of a Hubble Space Telescope/Advanced Camera for Surveys legacy data set for the first gravitational lens, Q0957+561. With deep imaging we identify 24 new strongly lensed features, which we use to constrain mass models. We model the stellar component of the lens galaxy using the observed luminosity distribution and the dark matter halo using several different density profiles. We draw on the weak lensing analysis by Nakajima et al. to constrain the mass sheet and environmental terms in the lens potential. Adopting the well-measured time delay, we find H{sub 0} = 85{sup +14}{sub -13} km s{sup -1} Mpc{sup -1} (68% CL) using lensing constraints alone. The principal uncertainties in H{sub 0} are tied to the stellar mass-to-light ratio (a variant of the radial profile degeneracy in lens models). Adding constraints from stellar population synthesis models, we obtain H{sub 0} = 79.3{sup +6.7}{sub -8.5} km s{sup -1} Mpc{sup -1} (68% CL). We infer that the lens galaxy has a rising rotation curve and a dark matter distribution with an inner core. Intriguingly, we find the quasar flux ratios predicted by our models to be inconsistent with existing radio measurements, suggesting the presence of substructure in the lens.
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.
2016-03-10
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.
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.
Applegate, D. E; Mantz, A.; Allen, S. W.; von der Linden, A.; Morris, R. G.; Hilbert, S.; Kelly, P. L.; Burke, D. L.; Ebeling, H.; Rapetti, D. A.; Schmidt, R. W.
2016-02-04
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 (r_{2500}) determined from the X-ray data, we measure a lensing to X-ray mass ratio of 0.96 ± 9% (stat) ± 9% (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^{+4.4}_{–1.8}. In conclusion, 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%, leading to similar improvements in cosmological constraints that employ X-ray hydrostatic mass estimates, such as on Ω_{m} from the cluster gas mass fraction.
Applegate, D. E; Mantz, A.; Allen, S. W.; ...
2016-02-04
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 amore » characteristic radius (r2500) determined from the X-ray data, we measure a lensing to X-ray mass ratio of 0.96 ± 9% (stat) ± 9% (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 c200 = 3.0+4.4–1.8. In conclusion, 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%, leading to similar improvements in cosmological constraints that employ X-ray hydrostatic mass estimates, such as on Ωm from the cluster gas mass fraction.« less
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.
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.
NASA Astrophysics Data System (ADS)
Herbonnet, Ricardo; Buddendiek, Axel; Kuijken, Konrad
2017-03-01
Context. Current optical imaging surveys for cosmology cover large areas of sky. Exploiting the statistical power of these surveys for weak lensing measurements requires shape measurement methods with subpercent systematic errors. Aims: We introduce a new weak lensing shear measurement algorithm, shear nulling after PSF Gaussianisation (SNAPG), designed to avoid the noise biases that affect most other methods. Methods: SNAPG operates on images that have been convolved with a kernel that renders the point spread function (PSF) a circular Gaussian, and uses weighted second moments of the sources. The response of such second moments to a shear of the pre-seeing galaxy image can be predicted analytically, allowing us to construct a shear nulling scheme that finds the shear parameters for which the observed galaxies are consistent with an unsheared, isotropically oriented population of sources. The inverse of this nulling shear is then an estimate of the gravitational lensing shear. Results: We identify the uncertainty of the estimated centre of each galaxy as the source of noise bias, and incorporate an approximate estimate of the centroid covariance into the scheme. We test the method on extensive suites of simulated galaxies of increasing complexity, and find that it is capable of shear measurements with multiplicative bias below 0.5 percent.
Relativistic weak lensing from a fully non-linear cosmological density field
Thomas, D.B.; Bruni, M.; Wands, D. E-mail: marco.bruni@port.ac.uk
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.
Gravitational light-bending prevents γγ absorption in gravitational lenses
NASA Astrophysics Data System (ADS)
Böttcher, Markus; Thiersen, Hannes
2016-10-01
The magnification effect that is due to gravitational lensing enhances the chances of detecting moderate-redshift (z ~ 1) sources in very high-energy (VHE; E > 100 GeV) γ-rays by ground-based atmospheric Cherenkov telescope facilities. It has been shown in previous work that this prospect is not hampered by potential γ-γ absorption effects by the intervening (lensing) galaxy, nor by any individual star within the intervening galaxy. In this paper, we expand this study to simulate the light-bending effect of a realistic ensemble of stars. We first demonstrate that for realistic parameters of the galaxy's star field, it is extremely unlikely (probability ≲10-6) that the direct line of sight between the γ-ray source and the observer passes by any star in the field close enough to be subject to significant γγ absorption. Our simulations then focus on the rare cases where γγ absorption by (at least) one individual star might be non-negligible. We show that gravitational light-bending will have the effect of avoiding the γ-γ absorption spheres around massive stars in the intervening galaxy. This confirms previous results and re-inforces arguments in favour of VHE γ-ray observations of lensed moderate-redshift blazars to extend the redshift range of objects detected in VHE γ-rays, and to probe the location of the γ-ray emission region in these blazars.
Roulettes: a weak lensing formalism for strong lensing: II. Derivation and analysis
NASA Astrophysics Data System (ADS)
Clarkson, Chris
2016-12-01
We present a new extension of the weak lensing formalism capable of describing strongly lensed images. This paper accompanies Paper I (Clarkson C 2016 Class. Quantum Grav. 33 16LT01), where we provide a condensed overview of the approach and illustrated how it works. Here we give all the necessary details, together with some more explicit examples. We solve the nonlinear geodesic deviation equation order-by-order, keeping the leading derivatives of the optical tidal matrix, giving rise to a series of maps from which a complete strongly lensed image is formed. The family of maps are decomposed by separating the trace and trace-free parts of each map. Each trace-free tensor represents an independent spin mode, which distorts circles into a variety of roulettes in the screen-space. It is shown how summing this series expansion allows us to create large strongly lensed images in regions where convergence, shear and flexion are not sufficient. This paper is a detailed exposition of Paper I [1], which presents the key elements of the subject matter in a wider context.
Kaluza-Klein magnetized cylindrical wormhole and its gravitational lensing
NASA Astrophysics Data System (ADS)
Hashemi, S. Sedigheh; Riazi, Nematollah
2016-10-01
A new exact vacuum solution in five dimensions, which describes a magnetized cylindrical wormhole in 3+1 dimensions is presented. The magnetic field lines are stretched along the wormhole throat and are concentrated near to it. We study the motion of neutral and charged test particles under the influence of the magnetized wormhole. The effective potential for a neutral test particle around and across the magnetized wormhole has a repulsive character. The gravitational lensing for the magnetized wormhole for various lens parameters are calculated and compared. The total magnetic flux on either side of the wormhole is obtained. We present analytic expressions which show regions in which the null energy condition is violated.
The correlation function of galaxy ellipticities produced by gravitational lensing
NASA Technical Reports Server (NTRS)
Miralda-Escude, Jordi
1991-01-01
The correlation of galaxy ellipticities produced by gravitational lensing is calculated as a function of the power spectrum of density fluctuations in the universe by generalizing an analytical method developed by Gunn (1967). The method is applied to a model where identical objects with spherically symmetric density profiles are randomly laid down in space, and to the cold dark matter model. The possibility of detecting this correlation is discussed. Although an ellipticity correlation can also be caused by an intrinsic alignment of the axes of galaxies belonging to a cluster or a supercluster, a method is suggested by which one type of correlation can be distinguished from another. The advantage of this ellipticity correlation is that it is one of the few astronomical observations that can directly probe large-scale mass fluctuations in the universe.
Three quasi-stellar objects acting as strong gravitational lenses
NASA Astrophysics Data System (ADS)
Courbin, F.; Faure, C.; Djorgovski, S. G.; Rérat, F.; Tewes, M.; Meylan, G.; Stern, D.; Mahabal, A.; Boroson, T.; Dheeraj, R.; Sluse, D.
2012-04-01
We report the discovery of three new cases of quasi-stellar objects (QSOs) acting as strong gravitational lenses on background emission line galaxies: SDSS J0827+5224 (zQSO = 0.293, zs = 0.412), SDSS J0919+2720 (zQSO = 0.209, zs = 0.558), SDSS J1005+4016 (zQSO = 0.230, zs = 0.441). The selection was carried out using a sample of 22,298 SDSS spectra displaying at least four emission lines at a redshift beyond that of the foreground QSO. The lensing nature is confirmed from Keck imaging and spectroscopy, as well as from HST/WFC3 imaging in the F475W and F814W filters. Two of the QSOs have face-on spiral host galaxies and the third is a QSO+galaxy pair. The velocity dispersion of the host galaxies, inferred from simple lens modeling, is between σ = 210 and 285 km s-1, making these host galaxies comparable in mass with the SLACS sample of early-type strong lenses. Based on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Also based on observations made 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 NAS 5-26555. These observations are associated with program #GO12233.
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, σ2, 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 σ2 at the so-called sweet-spot radius. Achieving 7% is possible if we can determine σ2 with 5% precision.
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
Jee, I.; Komatsu, E.; Suyu, S.H. E-mail: komatsu@mpa-garching.mpg.de
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 (z{sub L}=0.6304) and RXJ1131−1231 (z{sub L}=0.295), to show that the uncertainty in the inferred angular diameter distances is dominated by that in the velocity dispersion, σ{sup 2}, and its anisotropy. We find that the current data on these systems should yield about 16% uncertainty in D{sub A} per object. This improves to 13% when we measure σ{sup 2} at the so-called sweet-spot radius. Achieving 7% is possible if we can determine σ{sup 2} with 5% precision.
The Distance Duality Relation from Strong Gravitational Lensing
NASA Astrophysics Data System (ADS)
Liao, Kai; Li, Zhengxiang; Cao, Shuo; Biesiada, Marek; Zheng, Xiaogang; Zhu, Zong-Hong
2016-05-01
Under very general assumptions of the metric theory of spacetime, photons traveling along null geodesics and photon number conservation, two observable concepts of cosmic distance, i.e., the angular diameter and the luminosity distances are related to each other by the so-called distance duality relation (DDR) {D}L={D}A{(1+z)}2. Observational validation of this relation is quite important because any evidence of its violation could be a signal of new physics. In this paper we introduce a new method to test the DDR based on strong gravitational lensing systems and type Ia supernovae (SNe Ia) under a flat universe. The method itself is worth attention because unlike previously proposed techniques, it does not depend on all other prior assumptions concerning the details of cosmological model. We tested it using a new compilation of strong lensing (SL) systems and JLA compilation of SNe Ia and found no evidence of DDR violation. For completeness, we also combined it with previous cluster data and showed its power on constraining the DDR. It could become a promising new probe in the future in light of forthcoming massive SL surveys and because of expected advances in galaxy cluster modeling.
Red nuggets grow inside-out: evidence from gravitational lensing
NASA Astrophysics Data System (ADS)
Oldham, Lindsay; Auger, Matthew W.; Fassnacht, Christopher D.; Treu, Tommaso; Brewer, Brendon J.; Koopmans, L. V. E.; Lagattuta, David; Marshall, Philip; McKean, John; Vegetti, Simona
2017-03-01
We present a new sample of strong gravitational lens systems where both the foreground lenses and background sources are early-type galaxies. Using imaging from Hubble Space Telescope (HST)/Advanced Camera for Studies (ACS) and Keck/NIRC2, we model the surface brightness distributions and show that the sources form a distinct population of massive, compact galaxies at redshifts 0.4 ≲ z ≲ 0.7, lying systematically below the size-mass relation of the global elliptical galaxy population at those redshifts. These may therefore represent relics of high-redshift red nuggets or their partly evolved descendants. We exploit the magnifying effect of lensing to investigate the structural properties, stellar masses and stellar populations of these objects with a view to understanding their evolution. We model these objects parametrically and find that they generally require two Sérsic components to properly describe their light profiles, with one more spheroidal component alongside a more envelope-like component, which is slightly more extended though still compact. This is consistent with the hypothesis of the inside-out growth of these objects via minor mergers. We also find that the sources can be characterized by red-to-blue colour gradients as a function of radius which are stronger at low redshift - indicative of ongoing accretion - but that their environments generally appear consistent with that of the general elliptical galaxy population, contrary to recent suggestions that these objects are pre-dominantly associated with clusters.
Observing Gravitational Lensing Effects by Sgr A* with GRAVITY
NASA Astrophysics Data System (ADS)
Bozza, V.; Mancini, L.
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 LS, γ, K], where D LS is the distance between the lens and the source, γ 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.
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.
On the use of measured time delays in gravitational lenses to determine the Hubble constant
NASA Technical Reports Server (NTRS)
Alcock, C.; Anderson, N.
1985-01-01
Gravitational lenses are rare in the known samples of quasars, indicating that the conditions involved in their formation are unusual. In particular, the distribution of matter along the light rays from the observer through the deflector to the quasar may be very different from mean conditions. It is shown that reasonable deviations in the density of matter along the beams can significantly alter the relationship between time delays and the Hubble constant, and it is concluded that gravitational lenses are not promising estimators of this constant. However, should an independent, precise determination of the Hubble constant become available, gravitational lenses could be used to probe long-range density fluctuations.
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.
CFHTLenS: the environmental dependence of galaxy halo masses from weak lensing
NASA Astrophysics Data System (ADS)
Gillis, Bryan R.; Hudson, Michael J.; Erben, Thomas; Heymans, Catherine; Hildebrandt, Hendrik; Hoekstra, Henk; Kitching, Thomas D.; Mellier, Yannick; Miller, Lance; van Waerbeke, Ludovic; Bonnett, Christopher; Coupon, Jean; Fu, Liping; Hilbert, Stefan; Rowe, Barnaby T. P.; Schrabback, Tim; Semboloni, Elisabetta; van Uitert, Edo; Velander, Malin
2013-05-01
We use weak gravitational lensing to analyse the dark matter haloes around satellite galaxies in galaxy groups in the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) data set. This data set is derived from the Canada-France-Hawaii Telescope Legacy Survey Wide survey, and encompasses 154 deg2 of high-quality shape data. Using the photometric redshifts, we divide the sample of lens galaxies with stellar masses in the range 109-1010.5 M⊙ into those likely to lie in high-density environments (HDE) and those likely to lie in low-density environments (LDE). Through comparison with galaxy catalogues extracted from the Millennium Simulation, we show that the sample of HDE galaxies should primarily (˜61 per cent) consist of satellite galaxies in groups, while the sample of LDE galaxies should consist of mostly (˜87 per cent) non-satellite (field and central) galaxies. Comparing the lensing signals around samples of HDE and LDE galaxies matched in stellar mass, the lensing signal around HDE galaxies clearly shows a positive contribution from their host groups on their lensing signals at radii of ˜500-1000 kpc, the typical separation between satellites and group centres. More importantly, the subhaloes of HDE galaxies are less massive than those around LDE galaxies by a factor of 0.65 ± 0.12, significant at the 2.9σ level. A natural explanation is that the haloes of satellite galaxies are stripped through tidal effects in the group environment. Our results are consistent with a typical tidal truncation radius of ˜40 kpc.
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.
Weak Lensing Measurement of Galaxy Clusters in the CFHTLS-Wide Survey
NASA Astrophysics Data System (ADS)
Shan, HuanYuan; Kneib, Jean-Paul; Tao, Charling; Fan, Zuhui; Jauzac, Mathilde; Limousin, Marceau; Massey, Richard; Rhodes, Jason; Thanjavur, Karun; McCracken, Henry J.
2012-03-01
We present the first weak gravitational lensing analysis of the completed Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). We study the 64 deg2 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 ν > 3.5, consistent with predictions of a ΛCDM model. Of these peaks, 126 lie within 3farcm0 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 deg2 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 χ2 reduced < 3.0, at a mean redshift langzc rang = 0.36 and velocity dispersion langσ c rang = 658.8 km s-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.
Weak lensing calibration of mass bias in the REFLEX+BCS X-ray galaxy cluster catalogue
NASA Astrophysics Data System (ADS)
Simet, Melanie; Battaglia, Nicholas; Mandelbaum, Rachel; Seljak, Uroš
2017-04-01
The use of large, X-ray-selected Galaxy cluster catalogues for cosmological analyses requires a thorough understanding of the X-ray mass estimates. Weak gravitational lensing is an ideal method to shed light on such issues, due to its insensitivity to the cluster dynamical state. We perform a weak lensing calibration of 166 galaxy clusters from the REFLEX and BCS cluster catalogue and compare our results to the X-ray masses based on scaled luminosities from that catalogue. To interpret the weak lensing signal in terms of cluster masses, we compare the lensing signal to simple theoretical Navarro-Frenk-White models and to simulated cluster lensing profiles, including complications such as cluster substructure, projected large-scale structure and Eddington bias. We find evidence of underestimation in the X-ray masses, as expected, with
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 Δw {sub 0} ∼ 0.25 by the lensing MFs alone, but biases induced by the systematics can be comparable to the 1σ 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 Ω{sub m0}=0.256±{sub 0.046}{sup 0.054}.
Gravitational microlensing - The effect of random motion of individual stars in the lensing galaxy
NASA Technical Reports Server (NTRS)
Kundic, Tomislav; Wambsganss, Joachim
1993-01-01
We investigate the influence of random motion of individual stars in the lensing galaxy on the light curve of a gravitationally lensed background quasar. We compare this with the effects of the transverse motion of the galaxy. We find that three-dimensional random motion of stars with a velocity dispersion sigma in each dimension is more effective in producing 'peaks' in a microlensed light curve by a factor a about 1.3 than motion of the galaxy with a transverse velocity v(t) = sigma. This effectiveness parameter a seems to depend only weakly on the surface mass density. With an assumed transverse velocity of v(t) = 600 km/s of the galaxy lensing the QSO 2237+0305 and a measured velocity dispersion of sigma = 215 km/s, the expected rate of maxima in the light curves calculated for bulk motion alone has to be increased by about 10 percent due to the random motion of stars. As a consequence, the average time interval Delta t between two high-magnification events is smaller than the time interval Delta(t) bulk, calculated for bulk motion alone, Delta t about 0.9 Delta(t) bulk.
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
Gravitational lensing in the supernova legacy survey (SNLS)
NASA Astrophysics Data System (ADS)
Kronborg, T.; Hardin, D.; Guy, J.; Astier, P.; Balland, C.; Basa, S.; Carlberg, R. G.; Conley, A.; Fouchez, D.; Hook, I. M.; Howell, D. A.; Jönsson, J.; Pain, R.; Pedersen, K.; Perrett, K.; Pritchet, C. J.; Regnault, N.; Rich, J.; Sullivan, M.; Palanque-Delabrouille, N.; Ruhlmann-Kleider, V.
2010-05-01
Aims: The observed brightness of type Ia supernovae is affected by gravitational lensing caused by the mass distribution along the line of sight, which introduces an additional dispersion into the Hubble diagram. We look for evidence of lensing in the SuperNova Legacy Survey 3-year data set. Methods: We investigate the correlation between the residuals from the Hubble diagram and the gravitational magnification based on a modeling of the mass distribution of foreground galaxies. A deep photometric catalog, photometric redshifts, and well established mass luminosity relations are used. Results: We find evidence of a lensing signal with a 2.3σ significance. The current result is limited by the number of SNe, their redshift distribution, and the other sources of scatter in the Hubble diagram. Separating the galaxy population into a red and a blue sample has a positive impact on the significance of the signal detection. On the other hand, increasing the depth of the galaxy catalog, the precision of photometric redshifts or reducing the scatter in the mass luminosity relations have little effect. We show that for the full SuperNova Legacy Survey sample (~400 spectroscopically confirmed type Ia SNe and ~200 photometrically identified type Ia SNe), there is an 80% probability of detecting the lensing signal with a 3σ significance. 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 the Canadian Astronomy Data Centre as part of the Canada-France-Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNRS. Based on observations obtained at the European Southern Observatory using the Very Large Telescope on
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)
Nord, Brian
2017-01-01
Strong gravitational lenses have potential as very powerful probes of dark energy and cosmic structure. However, efficiently finding lenses poses a significant challenge—especially in the era of large-scale cosmological surveys. I will present a new application of deep machine learning algorithms to find strong lenses, as well as the strong lens discovery program of the Dark Energy Survey (DES).Strong lenses provide unique information about the evolution of distant galaxies, the nature of dark energy, and the shapes of dark matter haloes. Current and future surveys, like DES and the Large Synoptic Survey Telescope, present an opportunity to find many thousands of strong lenses, far more than have ever been discovered. By and large, searches have heretofore relied on the time-consuming effort of human scanners. Deep machine learning frameworks, like convolutional neural nets, have revolutionized the task of image recognition, and have a natural place in the processing of astronomical images, including the search for strong lenses.Over five observing seasons, which started in August 2013, DES will carry out a wide-field survey of 5000 square degrees of the Southern Galactic Cap. DES has identified nearly 200 strong lensing candidates in the first two seasons of data. We have performed spectroscopic follow-up on a subsample of these candidates at Gemini South, confirming over a dozen new strong lenses. I will present this DES discovery program, including searches and spectroscopic follow-up of galaxy-scale, cluster-scale and time-delay lensing systems.I will focus, however, on a discussion of the successful search for strong lenses using deep learning methods. In particular, we show that convolutional neural nets present a new set of tools for efficiently finding lenses, and accelerating advancements in strong lensing science.
NASA Astrophysics Data System (ADS)
Umetsu, Keiichi; Zitrin, Adi; Gruen, Daniel; Merten, Julian; Donahue, Megan; Postman, Marc
2016-04-01
We present a comprehensive analysis of strong-lensing, weak-lensing shear and magnification data for a sample of 16 X-ray-regular and 4 high-magnification galaxy clusters at 0.19≲ z≲ 0.69 selected from Cluster Lensing And Supernova survey with Hubble (CLASH). Our analysis combines constraints from 16-band Hubble Space Telescope observations and wide-field multi-color imaging taken primarily with Suprime-Cam on the Subaru Telescope, spanning a wide range of cluster radii (10″-16‧). We reconstruct surface mass density profiles of individual clusters from a joint analysis of the full lensing constraints, and determine masses and concentrations for all of the clusters. We find the internal consistency of the ensemble mass calibration to be ≤5% ± 6% in the one-halo regime (200-2000 kpc h-1) compared to the CLASH weak-lensing-only measurements of Umetsu et al. For the X-ray-selected subsample of 16 clusters, we examine the concentration-mass (c-M) relation and its intrinsic scatter using a Bayesian regression approach. Our model yields a mean concentration of c{| }z=0.34=3.95+/- 0.35 at M200c ≃ 14 × 1014 M⊙ and an intrinsic scatter of σ ({ln}{c}200{{c}})=0.13+/- 0.06, which is in excellent agreement with Λ cold dark matter predictions when the CLASH selection function based on X-ray morphological regularity and the projection effects are taken into account. We also derive an ensemble-averaged surface mass density profile for the X-ray-selected subsample by stacking their individual profiles. The stacked lensing signal is detected at 33σ significance over the entire radial range ≤4000 kpc h-1, accounting for the effects of intrinsic profile variations and uncorrelated large-scale structure along the line of sight. The stacked mass profile is well described by a family of density profiles predicted for cuspy dark-matter-dominated halos in gravitational equilibrium, namely, the Navarro-Frenk-White (NFW), Einasto, and DARKexp models, whereas the single
Umetsu, Keiichi; Zitrin, Adi; Gruen, Daniel; Merten, Julian; Donahue, Megan; Postman, Marc
2016-04-20
Here, we present a comprehensive analysis of strong-lensing, weak-lensing shear and magnification data for a sample of 16 X-ray-regular and 4 high-magnification galaxy clusters at $0.19\\lesssim z\\lesssim 0.69$ selected from Cluster Lensing And Supernova survey with Hubble (CLASH). Our analysis combines constraints from 16-band Hubble Space Telescope observations and wide-field multi-color imaging taken primarily with Suprime-Cam on the Subaru Telescope, spanning a wide range of cluster radii (10''–16'). We reconstruct surface mass density profiles of individual clusters from a joint analysis of the full lensing constraints, and determine masses and concentrations for all of the clusters. We find the internal consistency of the ensemble mass calibration to be ≤5% ± 6% in the one-halo regime (200–2000 kpc h^{–1}) compared to the CLASH weak-lensing-only measurements of Umetsu et al. For the X-ray-selected subsample of 16 clusters, we examine the concentration–mass (c–M) relation and its intrinsic scatter using a Bayesian regression approach. Our model yields a mean concentration of $c{| }_{z=0.34}=3.95\\pm 0.35$ at M200c sime 14 × 1014 M⊙ and an intrinsic scatter of $\\sigma (\\mathrm{ln}{c}_{200{\\rm{c}}})=0.13\\pm 0.06$, which is in excellent agreement with Λ cold dark matter predictions when the CLASH selection function based on X-ray morphological regularity and the projection effects are taken into account. We also derive an ensemble-averaged surface mass density profile for the X-ray-selected subsample by stacking their individual profiles. The stacked lensing signal is detected at 33σ significance over the entire radial range ≤4000 kpc h^{–1}, accounting for the effects of intrinsic profile variations and uncorrelated large-scale structure along the line of sight. The stacked mass profile is well described by a family of density profiles predicted for cuspy dark-matter-dominated halos in gravitational equilibrium, namely
Umetsu, Keiichi; Zitrin, Adi; Gruen, Daniel; ...
2016-04-20
Here, we present a comprehensive analysis of strong-lensing, weak-lensing shear and magnification data for a sample of 16 X-ray-regular and 4 high-magnification galaxy clusters atmore » $$0.19\\lesssim z\\lesssim 0.69$$ selected from Cluster Lensing And Supernova survey with Hubble (CLASH). Our analysis combines constraints from 16-band Hubble Space Telescope observations and wide-field multi-color imaging taken primarily with Suprime-Cam on the Subaru Telescope, spanning a wide range of cluster radii (10''–16'). We reconstruct surface mass density profiles of individual clusters from a joint analysis of the full lensing constraints, and determine masses and concentrations for all of the clusters. We find the internal consistency of the ensemble mass calibration to be ≤5% ± 6% in the one-halo regime (200–2000 kpc h–1) compared to the CLASH weak-lensing-only measurements of Umetsu et al. For the X-ray-selected subsample of 16 clusters, we examine the concentration–mass (c–M) relation and its intrinsic scatter using a Bayesian regression approach. Our model yields a mean concentration of $$c{| }_{z=0.34}=3.95\\pm 0.35$$ at M200c sime 14 × 1014 M⊙ and an intrinsic scatter of $$\\sigma (\\mathrm{ln}{c}_{200{\\rm{c}}})=0.13\\pm 0.06$$, which is in excellent agreement with Λ cold dark matter predictions when the CLASH selection function based on X-ray morphological regularity and the projection effects are taken into account. We also derive an ensemble-averaged surface mass density profile for the X-ray-selected subsample by stacking their individual profiles. The stacked lensing signal is detected at 33σ significance over the entire radial range ≤4000 kpc h–1, accounting for the effects of intrinsic profile variations and uncorrelated large-scale structure along the line of sight. The stacked mass profile is well described by a family of density profiles predicted for cuspy dark-matter-dominated halos in gravitational equilibrium, namely, the
HST Observations of the Luminous IRAS Source FSC10214+4724: A Gravitationally Lensed Infrared Quasar
NASA Technical Reports Server (NTRS)
Eisenhardt, P. R.; Armus, L.; Hogg, D. W.; Soifer, B. T.; Neugebauer, G.; Werner, M. W.
1995-01-01
Hubble Space Telescope (HST) data taken of the IRAS source FSC 10214+4724 suggest that the object has been gravitationally lensed by a galaxy in the foreground and that this lensing may be magnifying the apparent brightness by roughly 100 times.
Magnification of light from many distant quasars by gravitational lenses.
Wyithe, J Stuart B; Loeb, Abraham
2002-06-27
Exceptionally bright quasars with redshifts up to z = 6.28 have recently been discovered. Quasars are thought to be powered by the accretion of gas onto supermassive black holes at the centres of galaxies. Their maximum (Eddington) luminosity depends on the mass of the black hole, and the brighter quasars are inferred to have black holes with masses of more than a few billion solar masses. The existence of such massive black holes poses a challenge to models for the formation of structures in the early Universe, as it requires their formation within one billion years of the Big Bang. Here we show that up to one-third of known quasars with z approximately equal to 6 will have had their observed flux magnified by a factor of ten or more, as a consequence of gravitational lensing by galaxies along the line of sight. The inferred abundance of quasar host galaxies, as well as the luminosity density provided by the quasars, has therefore been substantially overestimated.
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.
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.
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.
Hojjati, Alireza; Harnois-Deraps, Joachim; Waerbeke, Ludovic Van; Hinshaw, Gary; McCarthy, Ian G.; Brun, Amandine M.C. Le; Ma, Yin-Zhe E-mail: i.g.mccarthy@ljmu.ac.uk E-mail: mayinzhe@manchester.ac.uk E-mail: hinshaw@phas.ubc.ca
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, ξ{sub yκ}(θ), well. The uncertainty arising from different possible feedback models appears to be important on small scales only (0θ ∼< 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 σ{sub 8}, Ω{sub m} and Ω{sub b}). 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 (M{sub halo} ∼< 10{sup 14} M{sub ⊙}) 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 (∼> 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.
Optimized detection of shear peaks in weak lensing maps
NASA Astrophysics Data System (ADS)
Marian, Laura; Smith, Robert E.; Hilbert, Stefan; Schneider, Peter
2012-06-01
We present a new method to extract cosmological constraints from weak lensing (WL) peak counts, which we denote as ‘the hierarchical algorithm’. The idea of this method is to combine information from WL maps sequentially smoothed with a series of filters of different size, from the largest down to the smallest, thus increasing the cosmological sensitivity of the resulting peak function. We compare the cosmological constraints resulting from the peak abundance measured in this way and the abundance obtained by using a filter of fixed size, which is the standard practice in WL peak studies. For this purpose, we employ a large set of WL maps generated by ray tracing through N-body simulations, and the Fisher matrix formalism. We find that if low signal-to-noise ratio (?) peaks are included in the analysis (?), the hierarchical method yields constraints significantly better than the single-sized filtering. For a large future survey such as Euclid or Large Synoptic Survey Telescope, combined with information from a cosmic microwave background experiment like Planck, the results for the hierarchical (single-sized) method are Δns= 0.0039 (0.004), ΔΩm= 0.002 (0.0045), Δσ8= 0.003 (0.006) and Δw= 0.019 (0.0525). This forecast is conservative, as we assume no knowledge of the redshifts of the lenses, and consider a single broad bin for the redshifts of the sources. If only peaks with ? are considered, then there is little difference between the results of the two methods. We also examine the statistical properties of the hierarchical peak function: Its covariance matrix has off-diagonal terms for bins with ? and aperture mass of M < 3 × 1014 h-1 M⊙, the higher bins being largely uncorrelated and therefore well described by a Poisson distribution.
Chen, Songbai; Jing, Jiliang E-mail: jljing@hunnu.edu.cn
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.
A gravitationally lensed quasar with quadruple images separated by 14.62 arcseconds.
Inada, Naohisa; Oguri, Masamune; Pindor, Bartosz; Hennawi, Joseph F; Chiu, Kuenley; Zheng, Wei; Ichikawa, Shin-Ichi; Gregg, Michael D; Becker, Robert H; Suto, Yasushi; Strauss, Michael A; Turner, Edwin L; Keeton, Charles R; Annis, James; Castander, Francisco J; Eisenstein, Daniel J; Frieman, Joshua A; Fukugita, Masataka; Gunn, James E; Johnston, David E; Kent, Stephen M; Nichol, Robert C; Richards, Gordon T; Rix, Hans-Walter; Sheldon, Erin Scott; Bahcall, Neta A; Brinkmann, J; Ivezić, Zeljko; Lamb, Don Q; McKay, Timothy A; Schneider, Donald P; York, Donald G
2003-12-18
Gravitational lensing is a powerful tool for the study of the distribution of dark matter in the Universe. The cold-dark-matter model of the formation of large-scale structures (that is, clusters of galaxies and even larger assemblies) predicts the existence of quasars gravitationally lensed by concentrations of dark matter so massive that the quasar images would be split by over 7 arcsec. Numerous searches for large-separation lensed quasars have, however, been unsuccessful. All of the roughly 70 lensed quasars known, including the first lensed quasar discovered, have smaller separations that can be explained in terms of galaxy-scale concentrations of baryonic matter. Although gravitationally lensed galaxies with large separations are known, quasars are more useful cosmological probes because of the simplicity of the resulting lens systems. Here we report the discovery of a lensed quasar, SDSS J1004 + 4112, which has a maximum separation between the components of 14.62 arcsec. Such a large separation means that the lensing object must be dominated by dark matter. Our results are fully consistent with theoretical expectations based on the cold-dark-matter model.
Strong deflection limit analysis and gravitational lensing of an Ellis wormhole
NASA Astrophysics Data System (ADS)
Tsukamoto, Naoki
2016-12-01
Observations of gravitational lenses in strong gravitational fields give us a clue to understanding dark compact objects. In this paper, we extend a method to obtain a deflection angle in a strong deflection limit provided by Bozza [Phys. Rev. D 66, 103001 (2002)] to apply to ultrastatic spacetimes. We also discuss on the order of an error term in the deflection angle. Using the improved method, we consider gravitational lensing by an Ellis wormhole, which is an ultrastatic wormhole of the Morris-Thorne class.
THE EFFECT OF ENVIRONMENT ON SHEAR IN STRONG GRAVITATIONAL LENSES
Wong, Kenneth C.; Zabludoff, Ann I.; Keeton, Charles R.; Williams, Kurtis A.; Momcheva, Ivelina G. E-mail: azabludoff@as.arizona.edu
2011-01-10
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 {gamma} = 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 {gamma} = 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.
Detections of Planets in Binaries Through the Channel of Chang–Refsdal Gravitational Lensing Events
NASA Astrophysics Data System (ADS)
Han, Cheongho; Shin, In-Gu; Jung, Youn Kil
2017-02-01
Chang–Refsdal (C–R) lensing, which refers to the gravitational lensing of a point mass perturbed by a constant external shear, provides a good approximation in describing lensing behaviors of either a very wide or a very close binary lens. C–R lensing events, which are identified by short-term anomalies near the peak of high-magnification lensing light curves, are routinely detected from lensing surveys, but not much attention is paid to them. In this paper, we point out that C–R lensing events provide an important channel to detect planets in binaries, both in close and wide binary systems. Detecting planets through the C–R lensing event channel is possible because the planet-induced perturbation occurs in the same region of the C–R lensing-induced anomaly and thus the existence of the planet can be identified by the additional deviation in the central perturbation. By presenting the analysis of the actually observed C–R lensing event OGLE-2015-BLG-1319, we demonstrate that dense and high-precision coverage of a C–R lensing-induced perturbation can provide a strong constraint on the existence of a planet in a wide range of planet parameters. The sample of an increased number of microlensing planets in binary systems will provide important observational constraints in giving shape to the details of planet formation, which have been restricted to the case of single stars to date.
Subaru weak lensing observations of ACT SZ-selected galaxy clusters
NASA Astrophysics Data System (ADS)
Takada, Masahiro
2010-07-01
The abundance of massive clusters as a function of redshift is a very powerful probe of cosmology, including the equation of state of dark energy, when combined with precise constraints on the initial conditions of structure formation from WMAP. The Sunyaev-Zel'dovich (SZ) effect, which is independent of redshift, offers a unique means of finding clusters up to high redshifts. However, systematic SZ surveys of cosmological volumes are currently in their infancy, and require crosscalibration with weak gravitational lensing to determine the relationship between SZ observables and mass. We request one night for a multi-band observation with Suprime-Cam of the two most SZ luminous clusters (previously unknown) in ~ 200 sq. deg. of early data from the equatorial region of the Atacama Cosmology Telescope (ACT) survey, with estimated masses of 10^15h^-1M_sun at redshifts z = 0.46 and 0.81. To obtain unbiased lensing signals, multi-band imaging is needed so that a pure catalog of background galaxies can be identified via photometric redshifts. This observation will allow for a determination of the masses to within 10-20%, and is the first step in enabling precision cosmology with SZ-selected cluster samples, eventually done in combination with the Hyper Suprime-Cam Survey.
Planck SZ Cluster Mass Calibration using HSC Weak Lensing
NASA Astrophysics Data System (ADS)
Medezinski, Elinor; Battaglia, Nicholas; Strauss, Michael A.; Spergel, David N.; Miyatake, Hironao; Mandelbaum, Rachel; Oguri, Masamune; Umetsu, Keiichi; HSC
2017-01-01
The Planck satellite has delivered an SZ cluster catalog from which precise cosmological constraints, in particular on σ8, have been derived. However, SZ does not provide a direct mass observable, and needs to be calibrated via independent methods. In the calibration of the Planck SZ masses, X-ray mass measurements from XMM-Newton assuming hydrostatic equilibrium have been used, and the subsequent constraint on σ8 is in mild tension with CMB-temperature derived values (Planck collaboration 2015). Weak lensing (WL) provides a direct measure of the total halo mass, regardless of the underlying physics or dynamics of the system. Here, we make use of the first ~240 deg2 Subaru Hyper Suprime-Cam (HSC) survey data and stack the shear around ~10 Planck clusters, yielding ~20σ detection of the mean Planck cluster mass profile and calibrate the SZ-WL mass scaling relation. Once the HSC survey has finished to observe ~1400 deg2, we expect to have a ~60σ detection, which will enable constraints on σ8 to a level of 1%. We will test whether the Planck tension stems from systematics in the cluster mass calibration, or whether this tension is due to some cosmological origin, e.g. massive neutrinos.
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.
Testing PSF Interpolation in Weak Lensing with Real Data
NASA Astrophysics Data System (ADS)
Lu, Tianhuan; Zhang, Jun; Dong, Fuyu; Li, Yingke; Liu, Dezi; Fu, Liping; Li, Guoliang; Fan, Zuhui
2017-04-01
Reconstruction of the point-spread function (PSF) is a critical process in weak lensing measurement. We develop a real-data based and galaxy-oriented pipeline to compare the performances of various PSF reconstruction schemes. Making use of a large amount of the CFHTLenS data, the performances of three classes of interpolating schemes—polynomial, Kriging, and Shepard—are evaluated. We find that polynomial interpolations with optimal orders and domains perform the best. We quantify the effect of the residual PSF reconstruction error on shear recovery in terms of the multiplicative and additive biases, and their spatial correlations using the shear measurement method of Zhang et al. We find that the impact of PSF reconstruction uncertainty on the shear–shear correlation can be significantly reduced by cross correlating the shear estimators from different exposures. It takes only 0.2 stars (S/N ≳ 100) per square arcmin on each exposure to reach the best performance of PSF interpolation, a requirement that is satisfied in most of the CFHTlenS data.
An Instrumentation Systematic for Weak Lensing from WFIRST
NASA Astrophysics Data System (ADS)
Jayaraman, Arun; Shapiro, Charles; Mandelbaum, Rachel; Hirata, Christopher M.; Kruk, Jeffrey W.; Rhodes, Jason
2016-06-01
The Wide Field Infra-Red Space Telescope (WFIRST), which is planned to be launched in 2025, will image the Universe in the near-Infrared bands and help measure shapes of ~400M galaxies according to the current survey design. Given such a big dataset, in order to be able to make precise weak lensing measurements and thereby understand the dark sectors of the Universe, it is necessary to not be biased by systematic effects. An understanding of systematic effects that arise from both astrophysical situations and from the instrumentation becomes crucial. The detectors used in WFIRST are made of HgCdTe and have CMOS based readout electronics, thus suffering from systematic effects that are different from that of CCDs. In this talk, I will focus on one such effect called the 'Interpixel Capacitance' (IPC) effect, which is a form of electrical crosstalk between neighboring pixels. I will show some results on how the shape of observed PSF, which will include the effect of IPC, varies as a function of the IPC parameters. I will also show how the shear measurement bias is affected if the IPC in the individual exposures is not perfectly corrected for, due to the misestimation of the IPC parameters. The requirements on PSF shapes and measurement biases can be translated into requirements on the IPC parameters and thus be used to specify the desired level of detector performance.
Measuring weak lensing correlations of Type Ia supernovae
NASA Astrophysics Data System (ADS)
Scovacricchi, D.; Nichol, R. C.; Macaulay, E.; Bacon, D.
2017-03-01
We study the feasibility of detecting weak lensing spatial correlations between supernova (SN) Type Ia magnitudes with present (Dark Energy Survey, DES) and future (Large Synoptic Survey Telescope, LSST) surveys. We investigate the angular auto-correlation function of SN magnitudes (once the background cosmology has been subtracted) and cross-correlation with galaxy catalogues. We examine both analytical and numerical predictions, the latter using simulated galaxy catalogues from the MICE Grand Challenge Simulation. We predict that we will be unable to detect the SN auto-correlation in DES, while it should be detectable with the LSST SN deep fields (15 000 SNe on 70 deg2) at ≃6σ level of confidence (assuming 0.15 mag of intrinsic dispersion). The SN-galaxy cross-correlation function will deliver much higher signal to noise, being detectable in both surveys with an integrated signal to noise of ∼100 (up to 30 arcmin separations). We predict joint constraints on the matter density parameter (Ωm) and the clustering amplitude (σ8) by fitting the auto-correlation function of our mock LSST deep fields. When assuming a Gaussian prior for Ωm, we can achieve a 25 per cent measurement of σ8 from just these LSST supernovae (assuming 0.15 mag of intrinsic dispersion). These constraints will improve significantly if the intrinsic dispersion of SNe Ia can be reduced.
NASA Astrophysics Data System (ADS)
Joachimi, B.; Semboloni, E.; Hilbert, S.; Bett, P. E.; Hartlap, J.; Hoekstra, H.; Schneider, P.
2013-11-01
Intrinsic galaxy alignments constitute the major astrophysical systematic of forthcoming weak gravitational lensing surveys but also yield unique insights into galaxy formation and evolution. We build analytic models for the distribution of galaxy shapes based on halo properties extracted from the Millennium Simulation, differentiating between early- and late-type galaxies as well as central galaxies and satellites. The resulting ellipticity correlations are investigated for their physical properties and compared to a suite of current observations. The best-faring model is then used to predict the intrinsic alignment contamination of planned weak lensing surveys. We find that late-type galaxy models generally have weak intrinsic ellipticity correlations, marginally increasing towards smaller galaxy separation and higher redshift. The signal for early-type models at fixed halo mass strongly increases by three orders of magnitude over two decades in galaxy separation, and by one order of magnitude from z = 0 to z = 2. The intrinsic alignment strength also depends strongly on halo mass, but not on galaxy luminosity at fixed mass, or galaxy number density in the environment. We identify models that are in good agreement with all observational data, except that all models overpredict alignments of faint early-type galaxies. The best model yields an intrinsic alignment contamination of a Euclid-like survey between 0.5 and 10 per cent at z > 0.6 and on angular scales larger than a few arcminutes. Cutting 20 per cent of red foreground galaxies using observer-frame colours can suppress this contamination by up to a factor of 2.
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}.
IM3SHAPE: a maximum likelihood galaxy shear measurement code for cosmic gravitational lensing
NASA Astrophysics Data System (ADS)
Zuntz, Joe; Kacprzak, Tomasz; Voigt, Lisa; Hirsch, Michael; Rowe, Barnaby; Bridle, Sarah
2013-09-01
We present and describe IM3SHAPE, a new publicly available galaxy shape measurement code for weak gravitational lensing shear. IM3SHAPE performs a maximum likelihood fit of a bulge-plus-disc galaxy model to noisy images, incorporating an applied point spread function. We detail challenges faced and choices made in its design and implementation, and then discuss various limitations that affect this and other maximum likelihood methods. We assess the bias arising from fitting an incorrect galaxy model using simple noise-free images and find that it should not be a concern for current cosmic shear surveys. We test IM3SHAPE on the Gravitational Lensing Accuracy Testing 2008 (GREAT08) challenge image simulations, and meet the requirements for upcoming cosmic shear surveys in the case that the simulations are encompassed by the fitted model, using a simple correction for image noise bias. For the fiducial branch of GREAT08 we obtain a negligible additive shear bias and sub-two per cent level multiplicative bias, which is suitable for analysis of current surveys. We fall short of the sub-per cent level requirement for upcoming surveys, which we attribute to a combination of noise bias and the mismatch between our galaxy model and the model used in the GREAT08 simulations. We meet the requirements for current surveys across all branches of GREAT08, except those with small or high noise galaxies, which we would cut from our analysis. Using the GREAT08 metric we we obtain a score of Q = 717 for the usable branches, relative to the goal of Q = 1000 for future experiments. The code is freely available from https://bitbucket.org/joezuntz/im3shape
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.
Statistical connection of peak counts to power spectrum and moments in weak-lensing field
NASA Astrophysics Data System (ADS)
Shirasaki, Masato
2017-02-01
The number density of local maxima of weak-lensing field, referred to as weak-lensing peak counts, can be used as a cosmological probe. However, its relevant cosmological information is still unclear. We study the relationship between the peak counts and other statistics in weak-lensing field by using 1000 ray-tracing simulations. We construct a local transformation of lensing field K to a new Gaussian field y, named local-Gaussianized transformation. We calibrate the transformation with numerical simulations so that the one-point distribution and the power spectrum of K can be reproduced from a single Gaussian field y and monotonic relation between y and K. Therefore, the correct information of two-point clustering and any order of moments in weak-lensing field should be preserved under local-Gaussianized transformation. We then examine if local-Gaussianized transformation can predict weak-lensing peak counts in simulations. The local-Gaussianized transformation is insufficient to explain weak-lensing peak counts in the absence of shape noise. The prediction by local-Gaussianized transformation underestimates the simulated peak counts with a level of ∼20-30 per cent over a wide range of peak heights. Local-Gaussianized transformation can predict the weak-lensing peak counts with an ∼10 per cent accuracy in the presence of shape noise. Our analyses suggest that the cosmological information beyond power spectrum and its moments would be necessary to predict the weak-lensing peak counts with a percent-level accuracy, which is an expected statistical uncertainty in upcoming wide-field galaxy surveys.
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.
IMPACT OF ATMOSPHERIC CHROMATIC EFFECTS ON WEAK LENSING MEASUREMENTS
Meyers, Joshua E.; Burchat, Patricia R.
2015-07-10
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.
3D weak lensing: Modified theories of gravity
NASA Astrophysics Data System (ADS)
Pratten, Geraint; Munshi, Dipak; Valageas, Patrick; Brax, Philippe
2016-05-01
Weak lensing (WL) promises to be a particularly sensitive probe of both the growth of large-scale structure as well as the fundamental relation between matter density perturbations and metric perturbations, thus providing a powerful tool with which we may constrain modified theories of gravity (MG) on cosmological scales. Future deep, wide-field WL surveys will provide an unprecedented opportunity to constrain deviations from General Relativity. Employing a 3D analysis based on the spherical Fourier-Bessel expansion, we investigate the extent to which MG theories will be constrained by a typical 3D WL survey configuration including noise from the intrinsic ellipticity distribution σɛ of source galaxies. Here, we focus on two classes of screened theories of gravity: (i) f (R ) chameleon models and (ii) environmentally dependent dilaton models. We use one-loop perturbation theory combined with halo models in order to accurately model the evolution of the matter power spectrum with redshift in these theories. Using a χ2 analysis, we show that for an all-sky spectroscopic survey, the parameter fR0 can be constrained in the range fR0<5 ×10-6(9 ×10-6) for n =1 (2 ) with a 3 σ confidence level. This can be achieved by using relatively low-order angular harmonics ℓ<100 . Higher-order harmonics ℓ>100 could provide tighter constraints but are subject to nonlinear effects, such as baryonic feedback, that must be accounted for. We also employ a Principal Component Analysis in order to study the parameter degeneracies in the MG parameters. The confusion from intrinsic ellipticity correlation and modification of the matter power spectrum at a small scale due to feedback mechanisms is briefly discussed.
Probing cluster potentials through gravitational lensing of background X-ray sources
NASA Technical Reports Server (NTRS)
Refregier, A.; Loeb, A.
1996-01-01
The gravitational lensing effect of a foreground galaxy cluster, on the number count statistics of background X-ray sources, was examined. The lensing produces a deficit in the number of resolved sources in a ring close to the critical radius of the cluster. The cluster lens can be used as a natural telescope to study the faint end of the (log N)-(log S) relation for the sources which account for the X-ray background.
Sub-pixel calibration for Weak Lensing and Astrometry
NASA Astrophysics Data System (ADS)
Shao, Michael
We have recently developed and demonstrated a new method of sub-pixel detector calibration that offers orders of magnitude improvement in astrometry with CCD focal planes. Using this technique we have demonstrated centroiding of images to 1e 5 lambda/D in laboratory conditions. Our method allows reconstructing the true optical point spread function (PSF) of a telescope from pixelated stellar images. Although this technique was originally developed for centroiding of images across a large focal plane, it can also be applied to weak lensing program on WFIRST. We use a laser metrology technique to measure geometric imperfections in the focal plane array from pixel placement errors to non-uniform quantum efficiency (QE) within every pixel. With precise sub-pixel calibration one can use dithered images (e.g., a 2×2 dither) to derive Nyquist-sampled image of stars. The WFIRST telescope has a large 0.28 sq.deg field of view (FOV) with theoretical PSF varying considerably over that FOV. However, even at high galactic latitude there will be over 1,000 stars brighter than 16 mag and, with Nyquist-sampled images, it should be possible to calculate the spatially varying PSF at 1,000 locations in the focal plane. With knowledge of the optical PSF and sub-pixel calibration of the detector, one can remove biases in the shapes of galaxies introduced by the spatially varying PSF. The technique of sub-pixel calibration has so far only been demonstrated in with visible CCD detectors and applied to achieve ultra-precise image centroiding. The purpose of this proposal is to extend the technique of removing biases in the shape of galaxies due to pixilation and spatially varying PSF and to extend the calibration of visible detectors to NIR detectors. The new technique could be used to enable 4 10 microarcsecond (μas) astrometry within the 0.28 sq.deg FOV of the WFIRST telescope. Using the upcoming Gaia catalogue accurate to ~10 μas, we will be able to stitch the HgCdTe arrays on
SDSS J0246-0825: A New Gravitationally Lensed Quasar from the Sloan Digital Sky Survey
Inada, N; Burles, S; Gregg, M D; Becker, R H; Schechter, P L; Eisenstein, D J; Oguri, M; Castander, F J; Hall, P B; Johnston, D E; Pindor, B; Richards, G T; Schneider, D P; White, R L; Brinkmann, J; Szalay, A; York, D G
2005-11-10
We report the discovery of a new two-image gravitationally lensed quasar, SDSS J024634.11-082536.2 (SDSS J0246-0825). This object was selected as a lensed quasar candidate from the Sloan Digital Sky Survey (SDSS) by the same algorithm that was used to discover other SDSS lensed quasars (e.g., SDSS J0924+0219). Multicolor imaging with the Magellan Consortium's Walter Baade 6.5-m telescope and the spectroscopic observations using the W. M. Keck Observatory's Keck II telescope confirm that SDSS J0246-0825 consists of two lensed images ({Delta}{theta} = 1''.04) of a source quasar at z = 1.68. Imaging observations with the Keck telescope and the Hubble Space Telescope reveal an extended object between the two quasar components, which is likely to be a lensing galaxy of this system. From the absorption lines in the spectra of quasar components and the apparent magnitude of the galaxy, combined with the expected absolute magnitude from the Faber-Jackson relation, we estimate the redshift of the lensing galaxy to be z = 0.724. A highly distorted ring is visible in the Hubble Space Telescope images, which is likely to be the lensed host galaxy of the source quasar. Simple mass modeling predicts the possibility that there is a small (faint) lensing object near the primary lensing galaxy.
NASA Astrophysics Data System (ADS)
Liu, Xiangkun; Li, Baojiu; Zhao, Gong-Bo; Chiu, Mu-Chen; Fang, Wei; Pan, Chuzhong; Wang, Qiao; Du, Wei; Yuan, Shuo; Fu, Liping; Fan, Zuhui
2016-07-01
In this Letter, we report the observational constraints on the Hu-Sawicki f (R ) theory derived from weak lensing peak abundances, which are closely related to the mass function of massive halos. In comparison with studies using optical or x-ray clusters of galaxies, weak lensing peak analyses have the advantages of not relying on mass-baryonic observable calibrations. With observations from the Canada-France-Hawaii-Telescope Lensing Survey, our peak analyses give rise to a tight constraint on the model parameter |fR 0| for n =1 . The 95% C.L. is log10|fR 0|<-4.82 given WMAP9 priors on (Ωm , As ). With Planck15 priors, the corresponding result is log10|fR 0|<-5.16 .
Liu, Xiangkun; Li, Baojiu; Zhao, Gong-Bo; Chiu, Mu-Chen; Fang, Wei; Pan, Chuzhong; Wang, Qiao; Du, Wei; Yuan, Shuo; Fu, Liping; Fan, Zuhui
2016-07-29
In this Letter, we report the observational constraints on the Hu-Sawicki f(R) theory derived from weak lensing peak abundances, which are closely related to the mass function of massive halos. In comparison with studies using optical or x-ray clusters of galaxies, weak lensing peak analyses have the advantages of not relying on mass-baryonic observable calibrations. With observations from the Canada-France-Hawaii-Telescope Lensing Survey, our peak analyses give rise to a tight constraint on the model parameter |f_{R0}| for n=1. The 95% C.L. is log_{10}|f_{R0}|<-4.82 given WMAP9 priors on (Ω_{m}, A_{s}). With Planck15 priors, the corresponding result is log_{10}|f_{R0}|<-5.16.
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
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.
Probabilities for gravitational lensing by point masses in a locally inhomogeneous universe
NASA Technical Reports Server (NTRS)
Isaacson, Jeffrey A.; Canizares, Claude R.
1989-01-01
Probability functions for gravitational lensing by point masses that incorporate Poisson statistics and flux conservation are formulated in the Dyer-Roeder construction. Optical depths to lensing for distant sources are calculated using both the method of Press and Gunn (1973) which counts lenses in an otherwise empty cone, and the method of Ehlers and Schneider (1986) which projects lensing cross sections onto the source sphere. These are then used as parameters of the probability density for lensing in the case of a critical (q0 = 1/2) Friedmann universe. A comparison of the probability functions indicates that the effects of angle-averaging can be well approximated by adjusting the average magnification along a random line of sight so as to conserve flux.
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.
A weak lensing analysis of the PLCK G100.2-30.4 cluster
NASA Astrophysics Data System (ADS)
Radovich, M.; Formicola, I.; Meneghetti, M.; Bartalucci, I.; Bourdin, H.; Mazzotta, P.; Moscardini, L.; Ettori, S.; Arnaud, M.; Pratt, G. W.; Aghanim, N.; Dahle, H.; Douspis, M.; Pointecouteau, E.; Grado, A.
2015-07-01
We present a mass estimate of the Planck-discovered cluster PLCK G100.2-30.4, derived from a weak lensing analysis of deep Subaru griz images. We perform a careful selection of the background galaxies using the multi-band imaging data, and undertake the weak lensing analysis on the deep (1 h) r -band image. The shape measurement is based on the Kaiser-Squires-Broadhurst algorithm; we adopt the PSFex software to model the point spread function (PSF) across the field and correct for this in the shape measurement. The weak lensing analysis is validated through extensive image simulations. We compare the resulting weak lensing mass profile and total mass estimate to those obtained from our re-analysis of XMM-Newton observations, derived under the hypothesis of hydrostatic equilibrium. The total integrated mass profiles agree remarkably well, within 1σ across their common radial range. A mass M500 ~ 7 × 1014M⊙ is derived for the cluster from our weak lensing analysis. Comparing this value to that obtained from our reanalysis of XMM-Newton data, we obtain a bias factor of (1-b) = 0.8 ± 0.1. This is compatible within 1σ with the value of (1-b) obtained in Planck 2015 from the calibration of the bias factor using newly available weak lensing reconstructed masses. Based on data collected at Subaru Telescope (University of Tokyo).
Rotation of galaxies as a signature of cosmic strings in weak lensing surveys.
Thomas, Daniel B; Contaldi, Carlo R; Magueijo, João
2009-10-30
Vector perturbations sourced by topological defects can generate rotations in the lensing of background galaxies. This is a potential smoking gun for the existence of defects since rotation generates a curl-like component in the weak lensing signal which is not generated by standard density perturbations at linear order. This rotation signal is calculated as generated by cosmic strings. Future large scale weak lensing surveys should be able to detect this signal even for string tensions an order of magnitude lower than current constraints.
Measuring primordial non-Gaussianity with weak lensing surveys
NASA Astrophysics Data System (ADS)
Hilbert, Stefan; Marian, Laura; Smith, Robert E.; Desjacques, Vincent
2012-11-01
Measuring the non-Gaussianity of the initial matter density fluctuations may provide powerful insights into cosmic inflation and the origin of structures. Although current information on primordial non-Gaussianity comes mostly from the cosmic microwave background, obtaining constraints from lower redshift observables will be an important task for future surveys. We study the ability of future weak lensing (WL) surveys to constrain primordial non-Gaussianity of the local type. We use a large ensemble of simulated WL maps with survey specifications relevant to Euclid and Large Synoptic Survey Telescope. The simulations assume cold dark matter cosmologies that vary certain parameters around fiducial values: the non-Gaussianity parameter fNL; the matter density parameter Ωm; the amplitude of the matter power spectrum σ8; the spectral index of the primordial power spectrum ns and the dark-energy equation-of-state parameter w0. We assess the sensitivity of the cosmic shear correlation functions, the third-order aperture mass statistics and the abundance of shear peaks to these parameters. We find that each of the considered probes provides unmarginalized constraints of Δ fNL ˜ 20 on fNL. Marginalized constraints from any individual WL probe are much weaker due to strong correlations between parameters. However, the parameter errors can be substantially reduced by combining information from different WL probes. Combining all WL probes yields the following marginal (68 per cent confidence level) uncertainties: Δ fNL ˜ 50; Δ Ωm ˜ 0.002; Δσ8 ˜ 0.004; Δ ns ˜ 0.007 and Δw0 ˜ 0.03. We examine the bias induced by neglecting fNL on the constraints on the other parameters. We find σ8 and w0 to be the most affected. Moreover, neglecting non-Gaussianity leads to a severe underestimation of the uncertainties in the other cosmological parameters. We conclude that a full exploitation of future WL surveys requires a joint analysis of different WL probes. Furthermore, if
A weak-lensing analysis of the Abell 383 cluster
NASA Astrophysics Data System (ADS)
Huang, Z.; Radovich, M.; Grado, A.; Puddu, E.; Romano, A.; Limatola, L.; Fu, L.
2011-05-01
Aims: We use deep CFHT and SUBARU uBVRIz archival images of the Abell 383 cluster (z = 0.187) to estimate its mass by weak-lensing. Methods: To this end, we first use simulated images to check the accuracy provided by our Kaiser-Squires-Broadhurst (KSB) pipeline. These simulations include shear testing programme (STEP) 1 and 2 simulations, as well as more realistic simulations of the distortion of galaxy shapes by a cluster with a Navarro-Frenk-White (NFW) profile. From these simulations we estimate the effect of noise on shear measurement and derive the correction terms. The R-band image is used to derive the mass by fitting the observed tangential shear profile with an NFW mass profile. Photometric redshifts are computed from the uBVRIz catalogs. Different methods for the foreground/background galaxy selection are implemented, namely selection by magnitude, color, and photometric redshifts, and the results are compared. In particular, we developed a semi-automatic algorithm to select the foreground galaxies in the color-color diagram, based on the observed colors. Results: Using color selection or photometric redshifts improves the correction of dilution from foreground galaxies: this leads to higher signals in the inner parts of the cluster. We obtain a cluster mass Mvir = 7.5+2.7_{-1.9 × 1014} M⊙: this value is 20% higher than previous estimates and is more consistent the mass expected from X-ray data. The R-band luminosity function of the cluster is computed and gives a total luminosity Ltot = (2.14 ± 0.5) × 1012 L⊙ and a mass-to-luminosity ratio M/L 300 M⊙/L⊙. Based on: data collected with the Subaru Telescope (University of Tokyo) and obtained from the SMOKA, which is operated by the Astronomy Data Center, National Astronomical Observatory of Japan; 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
Fast generation of weak lensing maps by the inverse-Gaussianization method
NASA Astrophysics Data System (ADS)
Yu, Yu; Zhang, Pengjie; Jing, Yipeng
2016-10-01
To take full advantage of the unprecedented power of upcoming weak lensing surveys, understanding the noise, such as cosmic variance and geometry/mask effects, is as important as understanding the signal itself. Accurately quantifying the noise requires a large number of statistically independent mocks for a variety of cosmologies. This is impractical for weak lensing simulations, which are costly for simultaneous requirements of large box size (to cover a significant fraction of the past light cone) and high resolution (to robustly probe the small scale where most lensing signal resides). Therefore, fast mock generation methods are desired and are under intensive investigation. We propose a new fast weak lensing map generation method, named the inverse-Gaussianization method, based on the finding that a lensing convergence field can be Gaussianized to excellent accuracy by a local transformation [43 Y. Yu, P. Zhang, W. Lin, W. Cui, and J. N. Fry, Phys. Rev. D 84, 023523 (2011).]. Given a simulation, it enables us to produce as many as infinite statistically independent lensing maps as fast as producing the simulation initial conditions. The proposed method is tested against simulations for each tomography bin centered at lens redshift z ˜0.5 , 1, and 2, with various statistics. We find that the lensing maps generated by our method have reasonably accurate power spectra, bispectra, and power spectrum covariance matrix. Therefore, it will be useful for weak lensing surveys to generate realistic mocks. As an example of application, we measure the probability distribution function of the lensing power spectrum, from 16384 lensing maps produced by the inverse-Gaussianization method.
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.
Sneaky Gamma-Rays: Using Gravitational Lensing to Avoid Gamma-Gamma-Absorption
NASA Astrophysics Data System (ADS)
Boettcher, Markus; Barnacka, Anna
2014-08-01
It has recently been suggested that gravitational lensing studies of gamma-ray blazars might be a promising avenue to probe the location of the gamma-ray emitting region in blazars. Motivated by these prospects, we have investigated potential gamma-gamma absorption signatures of intervening lenses in the very-high-energy gamma-ray emission from lensedblazars. We considered intervening galaxies and individual stars within these galaxies. We find that the collective radiation field of galaxies acting as sources of macrolensing are not expected to lead to significant gamma-gamma absorption. Individual stars within intervening galaxies could, in principle, cause a significant opacity to gamma-gamma absorption for VHE gamma-rays if the impact parameter (the distance of closest approach of the gamma-ray to the center of the star) is small enough. However, we find that the curvature of the photon path due to gravitational lensing will cause gamma-ray photons to maintain a sufficiently large distance from such stars to avoid significant gamma-gamma absorption. This re-inforces the prospect of gravitational-lensing studies of gamma-ray blazars without interference due to gamma-gamma absorption due to the lensing objects.
On the numbers of images of two stochastic gravitational lensing models
NASA Astrophysics Data System (ADS)
Wei, Ang
2017-02-01
We study two gravitational lensing models with Gaussian randomness: the continuous mass fluctuation model and the floating black hole model. The lens equations of these models are related to certain random harmonic functions. Using Rice's formula and Gaussian techniques, we obtain the expected numbers of zeros of these functions, which indicate the amounts of images in the corresponding lens systems.
Role of deficit solid angle and quintessence-like matter in strong field gravitational lensing
NASA Astrophysics Data System (ADS)
Geng, Jin-Ling; Zhang, Yu; Li, En-Kun; Duan, Peng-Fei
2016-12-01
Using the strong field limit approach, the strong field gravitational lensing in a black hole with deficit solid angle (DSA) and surrounded by quintessence-like matter (QM) has been investigated. The results show that the DSA ɛ2, the energy density of QM ρ0 and the equation of state (EOS) parameter w have some distinct effects on the strong field gravitational lensing. As ɛ2 or ρ0 increases, the deflection angle and the strong field limit coefficients all increase faster and faster. Moreover, the evolution of the main observables also has been studied, which shows that the curves at w = -2/3 are more steepy than those of w = -1/3. Compared with the Schwarzschild black hole, the black hole surrounded by QM has smaller relative magnitudes, and at w = -1/3 both the angular position and angular separation are slightly bigger than those of Schwarzschild black hole, but when w = -2/3, the angular position and the relative magnitudes all diminish significantly. Therefore, by studying the strong gravitational lensing, we can distinguish the black hole with a DSA and surrounded by QM from the Schwarzschild black hole and the effects of the DSA and QM on the strong gravitational lensing by black holes can be known better.
Nonsingular Density Profiles of Dark Matter Halos and Strong Gravitational Lensing
NASA Astrophysics Data System (ADS)
Chen, Da-Ming
2005-08-01
We use the statistics of strong gravitational lenses to investigate whether mass profiles with a flat density core are supported. The probability for lensing by halos modeled by a nonsingular truncated isothermal sphere (NTIS) with image separations greater than a certain value (ranging from 0" to 10") is calculated. NTIS is an analytical model for the postcollapse equilibrium structure of virialized objects derived by Shapiro, Iliev, & Raga. This profile has a soft core and matches quite well with the mass profiles of dark matter-dominated dwarf galaxies deduced from their observed rotation curves. It also agrees well with the NFW (Navarro-Frenk-White) profile at all radii outside of a few NTIS core radii. Unfortunately, comparing the results with those for singular lensing halos (NFW and SIS + NFW) and strong lensing observations, the probabilities for lensing by NTIS halos are far too low. As this result is valid for any other nonsingular density profile (with a large core radius), we conclude that nonsingular density profiles (with a large core radius) for CDM halos are ruled out by statistics of strong gravitational lenses.
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 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.
Ding, Xuheng; Biesiada, Marek; Zhu, Zong-Hong E-mail: marek.biesiada@us.edu.pl
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.
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.
Mocking the weak lensing universe: The LensTools Python computing package
NASA Astrophysics Data System (ADS)
Petri, A.
2016-10-01
We present a newly developed software package which implements a wide range of routines frequently used in Weak Gravitational Lensing (WL). With the continuously increasing size of the WL scientific community we feel that easy to use Application Program Interfaces (APIs) for common calculations are a necessity to ensure efficiency and coordination across different working groups. Coupled with existing open source codes, such as CAMB (Lewis et al., 2000) and Gadget2 (Springel, 2005), LensTools brings together a cosmic shear simulation pipeline which, complemented with a variety of WL feature measurement tools and parameter sampling routines, provides easy access to the numerics for theoretical studies of WL as well as for experiment forecasts. Being implemented in PYTHON (Rossum, 1995), LensTools takes full advantage of a range of state-of-the art techniques developed by the large and growing open-source software community (Jones et al., 2001; McKinney, 2010; Astrophy Collaboration, 2013; Pedregosa et al., 2011; Foreman-Mackey et al., 2013). We made the LensTools code available on the Python Package Index and published its documentation on http://lenstools.readthedocs.io.
NASA Astrophysics Data System (ADS)
Petri, Andrea; May, Morgan; Haiman, Zoltán
2016-09-01
Weak gravitational lensing is becoming a mature technique for constraining cosmological parameters, and future surveys will be able to constrain the dark energy equation of state w . When analyzing galaxy surveys, redshift information has proven to be a valuable addition to angular shear correlations. We forecast parameter constraints on the triplet (Ωm,w ,σ8) for a LSST-like photometric galaxy survey, using tomography of the shear-shear power spectrum, convergence peak counts and higher convergence moments. We find that redshift tomography with the power spectrum reduces the area of the 1 σ confidence interval in (Ωm,w ) space by a factor of 8 with respect to the case of the single highest redshift bin. We also find that adding non-Gaussian information from the peak counts and higher-order moments of the convergence field and its spatial derivatives further reduces the constrained area in (Ωm,w ) by factors of 3 and 4, respectively. When we add cosmic microwave background parameter priors from Planck to our analysis, tomography improves power spectrum constraints by a factor of 3. Adding moments yields an improvement by an additional factor of 2, and adding both moments and peaks improves by almost a factor of 3 over power spectrum tomography alone. We evaluate the effect of uncorrected systematic photometric redshift errors on the parameter constraints. We find that different statistics lead to different bias directions in parameter space, suggesting the possibility of eliminating this bias via self-calibration.
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
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
Weak lensing by galaxy troughs with modified gravity
NASA Astrophysics Data System (ADS)
Barreira, Alexandre; Bose, Sownak; Li, Baojiu; Llinares, Claudio
2017-02-01
We study the imprints that theories of gravity beyond GR can leave on the lensing signal around line of sight directions that are predominantly halo-underdense (called troughs) and halo-overdense. To carry out our investigations, we consider the normal branch of DGP gravity, as well as a phenomenological variant thereof that directly modifies the lensing potential. The predictions of these models are obtained with N-body simulation and ray-tracing methods using the ECOSMOG and Ray-Ramses codes. We analyse the stacked lensing convergence profiles around the underdense and overdense lines of sight, which exhibit, respectively, a suppression and a boost w.r.t. the mean in the field of view. The modifications to gravity in these models strengthen the signal w.r.t. ΛCDM in a scale-independent way. We find that the size of this effect is the same for both underdense and overdense lines of sight, which implies that the density field along the overdense directions on the sky is not sufficiently evolved to trigger the suppression effects of the screening mechanism. These results are robust to variations in the minimum halo mass and redshift ranges used to identify the lines of sight, as well as to different line of sight aperture sizes and criteria for their underdensity and overdensity thresholds.
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.
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.
The origin of peak-offsets in weak-lensing maps
NASA Astrophysics Data System (ADS)
Dietrich, J. P.; Böhnert, A.; Lombardi, M.; Hilbert, S.; Hartlap, J.
2012-02-01
Centroid positions of peaks identified in weak-lensing mass maps often show offsets with respect to other means of identifying halo centres, such as position of the brightest cluster galaxy or X-ray emission centroid. Here we study the effect of projected large-scale structure (LSS), smoothing of mass maps, and shape noise on the weak-lensing peak positions. In addition, we compare the offsets in mass maps to those found in parametric model fits. Using ray-tracing simulations through the Millennium Run N-body simulation, we find that projected LSS does not alter the weak-lensing peak position within the limits of our simulations' spatial resolution, which exceeds the typical resolution of weak-lensing maps. We conclude that projected LSS, although a major contaminant for weak-lensing mass estimates, is not a source of confusion for identifying halo centres. The typically reported offsets in the literature are caused by a combination of shape noise and smoothing alone. This is true for centroid positions derived both from mass maps and model fits.
NASA Astrophysics Data System (ADS)
Rozo, Eduardo; Wu, Hao-Yi; Schmidt, Fabian
2011-07-01
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 ≈2% precision (statistical only), which can improve the figure of merit of the DES cluster abundance experiment by a factor of ~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.
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.
Discovery and Characterization of Gravitationally Lensed X-ray Sources in the CLASH Sample
NASA Astrophysics Data System (ADS)
Pasha, Imad; Van Weeren, Reinout J.; Santos, Felipe A.
2017-01-01
We present the discovery of ~20 gravitationally lensed X-ray sources in the Cluster Lensing And Supernova survey with Hubble (CLASH) survey, a sample of massive clusters of galaxies between z ~ 0.2-0.9 observed with the Hubble Space Telescope (HST). By combining CLASH imaging with Chandra X-ray Observatory observations of the same clusters, we select those sources in the HST images which are gravitationally lensed X-ray sources behind the clusters. Of those discovered sources, we determine various properties including source redshifts and magnifications, as well as performing X-ray spectral fits to determine source fluxes and luminosities. Prior to this study, only four lensed X-ray sources behind clusters have been found, thus to the best of our knowledge, our program is the first to systematically categorize lensed X-ray sources behind galaxy clusters.This work was supported by the SAO REU program, which is funded in part by the National Science Foundation REU and Department of Defense ASSURE programs under NSF Grant no. 1262851, and by the Smithsonian Institution.
Galaxy–Galaxy Weak-lensing Measurements from SDSS. I. Image Processing and Lensing Signals
NASA Astrophysics Data System (ADS)
Luo, Wentao; Yang, Xiaohu; Zhang, Jun; Tweed, Dylan; Fu, Liping; Mo, H. J.; van den Bosch, Frank C.; Shu, Chenggang; Li, Ran; Li, Nan; Liu, Xiangkun; Pan, Chuzhong; Wang, Yiran; Radovich, Mario
2017-02-01
We present our image processing pipeline that corrects the systematics introduced by the point-spread function (PSF). Using this pipeline, we processed Sloan Digital Sky Survey (SDSS) DR7 imaging data in r band and generated a galaxy catalog containing the shape information. Based on our shape measurements of the galaxy images from SDSS DR7, we extract the galaxy–galaxy (GG) lensing signals around foreground spectroscopic galaxies binned in different luminosities and stellar masses. We estimated the systematics, e.g., selection bias, PSF reconstruction bias, PSF dilution bias, shear responsivity bias, and noise rectification bias, which in total is between ‑9.1% and 20.8% at 2σ levels. The overall GG lensing signals we measured are in good agreement with Mandelbaum et al. The reduced χ 2 between the two measurements in different luminosity bins are from 0.43 to 0.83. Larger reduced χ 2 from 0.60 to 1.87 are seen for different stellar mass bins, which is mainly caused by the different stellar mass estimator. The results in this paper with higher signal-to-noise ratio are due to the larger survey area than SDSS DR4, confirming that more luminous/massive galaxies bear stronger GG lensing signals. We divide the foreground galaxies into red/blue and star-forming/quenched subsamples and measure their GG lensing signals. We find that, at a specific stellar mass/luminosity, the red/quenched galaxies have stronger GG lensing signals than their counterparts, especially at large radii. These GG lensing signals can be used to probe the galaxy–halo mass relations and their environmental dependences in the halo occupation or conditional luminosity function framework.
Nemesis, Tyche, Planet Nine Hypotheses. I. Can We Detect the Bodies Using Gravitational Lensing?
NASA Astrophysics Data System (ADS)
Philippov, J. P.; Chobanu, M. I.
2016-08-01
In this paper, the hypothesis of the existence of a massive dark body (Nemesis, Tyche, Planet Nine, or any other trans-Plutonian planet) at the Solar system periphery is analysed. Basic physical properties and orbital characteristics of such massive bodies are considered. The problem of the definition of a scattering angle of a photon in the gravitational field of a spherical lens is studied. It is shown that, the required value of the scattering angle can be measured for the cases of Nemesis and Tyche. The formation of gravitational lensing images is studied here for a point mass event. It is demonstrated that in most cases of the close rapprochement of a source and the lens (for Nemesis and Tyche), it is possible to resolve two images. The possibility of resolving these images is one of the main arguments favouring the gravitational lensing method as its efficiency in searching for dark massive objects at the edge of the Solar System is higher than the one corresponding to other methods such as stellar occultation. For the cases of Planet Nine and any other trans-Plutonian planet, the strong gravitational lensing is impossible because at least one of the images is always eclipsed.
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.
SDSSJ102111.02+491330.4: A Newly Discovered Gravitationally Lensed Quasar
Pindor, B; Eisenstein, D J; Gregg, M D; Becker, R H; Inada, N; Oguri, M; Hall, P B; Johnston, D E; Richards, G T; Schneider, D P; Turner, E L; Brasi, G; Hinz, P M; Kenworthy, M A; Miller, D; Barentine, J C; Brewington, H J; Brinkmann, J; Harvanek, M; Kleinman, S J; Krzesinski, J; Long, D; Neilsen Jr., E H; Newman, P R; Nitta, A; Snedden, S A; York, D G
2005-11-10
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.
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.
NASA Astrophysics Data System (ADS)
Hunt, L. R.; Pisano, D. J.; Edel, S.
2016-08-01
Neutral hydrogen (Hi) provides a very important fuel for star formation, but is difficult to detect at high redshift due to weak emission, limited sensitivity of modern instruments, and terrestrial radio frequency interference (RFI) at low frequencies. We report the first attempt to use gravitational lensing to detect Hi line emission from three gravitationally lensed galaxies behind the cluster Abell 773, two at redshifts of 0.398 and one at z = 0.487, using the Green Bank Telescope. We find that a 3σ upper limit for a galaxy with a rotation velocity of 200 km s-1 is M H i = 6.58 × 109 and 1.5 × 1010 M ⊙ at z = 0.398 and z = 0.487. The estimated Hi masses of the sources at z = 0.398 and z = 0.487 are factors of 3.7 and ˜30 times lower than our detection limits at the respective redshifts. To facilitate these observations we have used sigma-clipping to remove both narrow- and wideband RFI but retain the signal from the source. We are able to reduce the noise of the spectrum by ˜25% using our routine instead of discarding observations with too much RFI. The routine is most effective when ˜10% of the integrations or fewer contain RFI. These techniques can be used to study Hi in highly magnified distant galaxies that are otherwise too faint to detect.
NASA Astrophysics Data System (ADS)
Okura, Yuki; Petri, Andrea; May, Morgan; Plazas, Andrés A.; Tamagawa, Toru
2016-07-01
Weak gravitational lensing causes subtle changes in the apparent shapes of galaxies due to the bending of light by the gravity of foreground masses. By measuring the shapes of large numbers of galaxies (millions in recent surveys, up to tens of billions in future surveys) we can infer the parameters that determine cosmology. Imperfections in the detectors used to record images of the sky can introduce changes in the apparent shapes of galaxies, which in turn can bias the inferred cosmological parameters. In this paper we consider the effect of two widely discussed sensor imperfections: tree rings, due to impurity gradients that cause transverse electric fields in the charge-coupled devices (CCDs), and pixel size variation, due to periodic CCD fabrication errors. These imperfections can be observed when the detectors are subject to uniform illumination (flat-field images). We develop methods to determine the spurious shear and convergence (due to the imperfections) from the flat-field images. We calculate how the spurious shear when added to the lensing shear will bias the determination of cosmological parameters. We apply our methods to candidate sensors of the Large Synoptic Survey Telescope (LSST) as a timely and important example, analyzing flat-field images recorded with LSST prototype CCDs in the laboratory. We find that tree rings and periodic pixel size variation present in the LSST CCDs will introduce negligible bias to cosmological parameters determined from the lensing power spectrum, specifically w, {{{Ω }}}m, and {σ }8.
Detecting Gravitational Lensing of the Cosmic Microwave Background by Galaxy Clusters
Baxter, Eric Jones
2014-08-01
Clusters of galaxies gravitationally lens the Cosmic Microwave Background (CMB) leading to a distinct signal in the CMB on arcminute scales. Measurement of the cluster lensing effect offers the exciting possibility of constraining the masses of galaxy clusters using CMB data alone. Improved constraints on cluster masses are in turn essential to the use of clusters as cosmological probes: uncertainties in cluster masses are currently the dominant systematic affecting cluster abundance constraints on cosmology. To date, however, the CMB cluster lensing signal remains undetected because of its small magnitude and angular size. In this thesis, we develop a maximum likelihood approach to extracting the signal from CMB temperature data. We validate the technique by applying it to mock data designed to replicate as closely as possible real data from the South Pole Telescope’s (SPT) Sunyaev-Zel’dovich (SZ) survey: the effects of the SPT beam, transfer function, instrumental noise and cluster selection are incorporated. We consider the effects of foreground emission on the analysis and show that uncertainty in amount of foreground lensing results in a small systematic error on the lensing constraints. Additionally, we show that if unaccounted for, the SZ effect leads to unacceptably large biases on the lensing constraints and develop an approach for removing SZ contamination. The results of the mock analysis presented here suggest that a 4σ first detection of the cluster lensing effect can be achieved with current SPT-SZ data.
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.
VizieR Online Data Catalog: Globular clusters as gravitational lenses (Bukhmastova, 2003)
NASA Astrophysics Data System (ADS)
Bukhmastova, Yu. L.
2003-10-01
We argue that globular clusters (GCs) are good candidates for gravitational lenses in explaining quasar-galaxy associations. The catalog of associations (Bukhmastova, 2001, Cat.
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%.
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.
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 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.
Weak-lensing measurement of the mass-richness relation using the SDSS data base
NASA Astrophysics Data System (ADS)
Gonzalez, Elizabeth Johana; Rodriguez, Facundo; García Lambas, Diego; Merchán, Manuel; Foëx, Gael; Chalela, Martín
2017-02-01
We study the mass-richness relation using galaxy catalogues and images from the Sloan Digital Sky Survey. We use two independent methods: In the first one, we calibrate the scaling relation with weak-lensing mass estimates. In the second procedure, we apply a background subtraction technique to derive the probability distribution, P(M∣N), that groups with N-members have a virialized halo mass M. Lensing masses are derived in different richness bins for two galaxy systems sets: the maxBCG catalogue and a catalogue based on a group finder algorithm developed by Yang et al. Results of maxBCG are used to test the lensing methodology. The lensing mass-richness relation for the Yang et al. group sample shows a good agreement with P(M∣N) obtained independently with a straightforward procedure.
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.
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.
A NEW APPROACH TO IDENTIFYING THE MOST POWERFUL GRAVITATIONAL LENSING TELESCOPES
Wong, Kenneth C.; Zabludoff, Ann I.; Ammons, S. Mark; Keeton, Charles R.; Hogg, David W.; Gonzalez, Anthony H.
2013-05-20
The best gravitational lenses for detecting distant galaxies are those with the largest mass concentrations and the most advantageous configurations of that mass along the line of sight. Our new method for finding such gravitational telescopes uses optical data to identify projected concentrations of luminous red galaxies (LRGs). LRGs are biased tracers of the underlying mass distribution, so lines of sight with the highest total luminosity in LRGs are likely to contain the largest total mass. We apply this selection technique to the Sloan Digital Sky Survey and identify the 200 fields with the highest total LRG luminosities projected within a 3.'5 radius over the redshift range 0.1 {<=} z {<=} 0.7. The redshift and angular distributions of LRGs in these fields trace the concentrations of non-LRG galaxies. These fields are diverse; 22.5% contain one known galaxy cluster and 56.0% contain multiple known clusters previously identified in the literature. Thus, our results confirm that these LRGs trace massive structures and that our selection technique identifies fields with large total masses. These fields contain two to three times higher total LRG luminosities than most known strong-lensing clusters and will be among the best gravitational lensing fields for the purpose of detecting the highest redshift galaxies.
Caustics of 1/r{sup n} binary gravitational lenses: from galactic haloes to exotic matter
Bozza, V.; Melchiorre, C. E-mail: cmelchiorre@unisa.it
2016-03-01
We investigate the caustic topologies for binary gravitational lenses made up of two objects whose gravitational potential declines as 1/r{sup n}. 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.
Probing the mass distribution at the outskirts of galaxy clusters using weak lensing
NASA Astrophysics Data System (ADS)
Fong, Matthew; King, Lindsay J.
2017-01-01
Galaxy clusters are often described by NFW (Navarro, Frenk & White) profiles which are a good description of cluster scale halos formed in cosmological dark matter simulations. Here we discuss the lensing signals of high-resolution clusters extracted from cosmological dark matter and hydrodynamic simulations, and determine on what scales the clusters’ average weak lensing shear is best described by the shear of the Diemer-Kravtsov (DK) or NFW profile. In particular, we assess the number of clusters and the type of observations (e.g. number of galaxies available for the weak lensing analysis) that must be stacked in order to distinguish between these and other profiles, focusing on the larger scales where the best-fit shear profiles differ.
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.
ALGORITHMS AND PROGRAMS FOR STRONG GRAVITATIONAL LENSING IN KERR SPACE-TIME INCLUDING POLARIZATION
Chen, Bin; Maddumage, Prasad; Kantowski, Ronald; Dai, Xinyu; Baron, Eddie
2015-05-15
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.
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.
Candidate Gravitationally Lensed Dusty Star-forming Galaxies in the Herschel Wide Area Surveys
NASA Astrophysics Data System (ADS)
Nayyeri, H.; Keele, M.; Cooray, A.; Riechers, D. A.; Ivison, R. J.; Harris, A. I.; Frayer, D. T.; Baker, A. J.; Chapman, S. C.; Eales, S.; Farrah, D.; Fu, H.; Marchetti, L.; Marques-Chaves, R.; Martinez-Navajas, P. I.; Oliver, S. J.; Omont, A.; Perez-Fournon, I.; Scott, D.; Vaccari, M.; Vieira, J.; Viero, M.; Wang, L.; Wardlow, J.
2016-05-01
We present a list of candidate gravitationally lensed dusty star-forming galaxies (DSFGs) from the HerMES Large Mode Survey and the Herschel Stripe 82 Survey. Together, these partially overlapping surveys cover 372 deg2 on the sky. After removing local spiral galaxies and known radio-loud blazars, our candidate list of lensed DSFGs is composed of 77 sources with 500 μm flux densities (S 500) greater than 100 mJy. Such sources are dusty starburst galaxies similar to the first bright sub-millimeter galaxies (SMGs) discovered with SCUBA. We expect a large fraction of this list to be strongly lensed, with a small fraction made up of bright SMG-SMG mergers that appear as hyper-luminous infrared galaxies ({L}{IR}\\gt {10}13 {L}⊙ ). Thirteen of the 77 candidates have spectroscopic redshifts from CO spectroscopy with ground-based interferometers, putting them at z\\gt 1 and well above the redshift of the foreground lensing galaxies. The surface density of our sample is 0.21 ± 0.03 deg-2. We present follow-up imaging of a few of the candidates to confirm their lensing nature. The sample presented here is an ideal tool for higher-resolution imaging and spectroscopic observations to understand the detailed properties of starburst phenomena in distant galaxies. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Measuring the power spectrum of dark matter substructure using strong gravitational lensing
NASA Astrophysics Data System (ADS)
Hezaveh, Yashar; Dalal, Neal; Holder, Gilbert; Kisner, Theodore; Kuhlen, Michael; Perreault Levasseur, Laurence
2016-11-01
In recent years, it has become possible to detect individual dark matter subhalos near images of strongly lensed extended background galaxies. Typically, only the most massive subhalos in the strong lensing region may be detected this way. In this work, we show that strong lenses may also be used to constrain the much more numerous population of lower mass subhalos that are too small to be detected individually. In particular, we show that the power spectrum of projected density fluctuations in galaxy halos can be measured using strong gravitational lensing. We develop the mathematical framework of power spectrum estimation, and test our method on mock observations. We use our results to determine the types of observations required to measure the substructure power spectrum with high significance. We predict that deep observations (~10 hours on a single target) with current facilities can measure this power spectrum at the 3σ level, with no apparent degeneracy with unknown clumpiness in the background source structure or fluctuations from detector noise. Upcoming ALMA measurements of strong lenses are capable of placing strong constraints on the abundance of dark matter subhalos and the underlying particle nature of dark matter.
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.
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.
Petri, Andrea; May, Morgan; Haiman, Zoltán
2016-09-30
Weak gravitational lensing is becoming a mature technique for constraining cosmological parameters, and future surveys will be able to constrain the dark energy equation of state w. When analyzing galaxy surveys, redshift information has proven to be a valuable addition to angular shear correlations. We forecast parameter constraints on the triplet (Ω_{m},w,σ_{8}) for a LSST-like photometric galaxy survey, using tomography of the shear-shear power spectrum, convergence peak counts and higher convergence moments. Here we find that redshift tomography with the power spectrum reduces the area of the 1σ confidence interval in (Ω_{m},w) space by a factor of 8 with respect to the case of the single highest redshift bin. We also find that adding non-Gaussian information from the peak counts and higher-order moments of the convergence field and its spatial derivatives further reduces the constrained area in (Ω_{m},w) by factors of 3 and 4, respectively. When we add cosmic microwave background parameter priors from Planck to our analysis, tomography improves power spectrum constraints by a factor of 3. Adding moments yields an improvement by an additional factor of 2, and adding both moments and peaks improves by almost a factor of 3 over power spectrum tomography alone. We evaluate the effect of uncorrected systematic photometric redshift errors on the parameter constraints. In conclusion, we find that different statistics lead to different bias directions in parameter space, suggesting the possibility of eliminating this bias via self-calibration.
Petri, Andrea; May, Morgan; Haiman, Zoltán
2016-09-30
Weak gravitational lensing is becoming a mature technique for constraining cosmological parameters, and future surveys will be able to constrain the dark energy equation of state w. When analyzing galaxy surveys, redshift information has proven to be a valuable addition to angular shear correlations. We forecast parameter constraints on the triplet (Ωm,w,σ8) for a LSST-like photometric galaxy survey, using tomography of the shear-shear power spectrum, convergence peak counts and higher convergence moments. Here we find that redshift tomography with the power spectrum reduces the area of the 1σ confidence interval in (Ωm,w) space by a factor of 8 with respectmore » to the case of the single highest redshift bin. We also find that adding non-Gaussian information from the peak counts and higher-order moments of the convergence field and its spatial derivatives further reduces the constrained area in (Ωm,w) by factors of 3 and 4, respectively. When we add cosmic microwave background parameter priors from Planck to our analysis, tomography improves power spectrum constraints by a factor of 3. Adding moments yields an improvement by an additional factor of 2, and adding both moments and peaks improves by almost a factor of 3 over power spectrum tomography alone. We evaluate the effect of uncorrected systematic photometric redshift errors on the parameter constraints. In conclusion, we find that different statistics lead to different bias directions in parameter space, suggesting the possibility of eliminating this bias via self-calibration.« less
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 Sérsic 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 Sérsic 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.
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.
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.
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
2014-04-04
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 4.0σ and indication of the presence of a lensing B-mode signal at a significance of 2.3σ. 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.
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).
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.
Multi Dark Lens Simulations: weak lensing light-cones and data base presentation
NASA Astrophysics Data System (ADS)
Giocoli, Carlo; Jullo, Eric; Metcalf, R. Benton; de la Torre, Sylvain; Yepes, Gustavo; Prada, Francisco; Comparat, Johan; Göttlober, Stefan; Kyplin, Anatoly; Kneib, Jean-Paul; Petkova, Margarita; Shan, Huan Yuan; Tessore, Nicolas
2016-09-01
In this paper we present a large data base of weak lensing light cones constructed using different snapshots from the Big MultiDark simulation (BigMDPL). The ray-tracing through different multiple plane has been performed with the GLAMER code accounting both for single source redshifts and for sources distributed along the cosmic time. This first paper presents weak lensing forecasts and results according to the geometry of the VIPERS-W1 and VIPERS-W4 field of view. Additional fields will be available on our data base and new ones can be run upon request. Our data base also contains some tools for lensing analysis. In this paper we present results for convergence power spectra, one point and high order weak lensing statistics useful for forecasts and for cosmological studies. Covariance matrices have also been computed for the different realizations of the W1 and W4 fields. In addition we compute also galaxy-shear and projected density contrasts for different halo masses at two lens redshift according to the CFHTLS source redshift distribution both using stacking and cross-correlation techniques, finding very good agreement.
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
2003-06-06
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.
NASA Astrophysics Data System (ADS)
Lanusse, Francois; Ravanbakhsh, Siamak; Mandelbaum, Rachel; Schneider, Jeff; Poczos, Barnabas
2017-01-01
Weak gravitational lensing has long been identified as one of the most powerful probes to investigate the nature of dark energy. As such, weak lensing is at the heart of the next generation of cosmological surveys such as LSST, Euclid or WFIRST.One particularly crititcal source of systematic errors in these surveys comes from the shape measurement algorithms tasked with estimating galaxy shapes. GREAT3, the last community challenge to assess the quality of state-of-the-art shape measurement algorithms has in particular demonstrated that all current methods are biased to various degrees and, more importantly, that these biases depend on the details of the galaxy morphologies. These biases can be measured and calibrated by generating mock observations where a known lensing signal has been introduced and comparing the resulting measurements to the ground-truth. Producing these mock observations however requires input galaxy images of higher resolution and S/N than the simulated survey, which typically implies acquiring extremely expensive space-based observations.The goal of this work is to train a deep generative model on already available Hubble Space Telescope data which can then be used to sample new galaxy images conditioned on parameters such as magnitude, size or redshift and exhibiting complex morphologies. Such model can allow us to inexpensively produce large set of realistic realistic images for calibration purposes.We implement a conditional generative model based on state-of-the-art deep learning methods and fit it to deep galaxy images from the COSMOS survey. The quality of the model is assessed by computing an extensive set of galaxy morphology statistics on the generated images. Beyond simple second moment statistics such as size and ellipticity, we apply more complex statistics specifically designed to be sensitive to disturbed galaxy morphologies. We find excellent agreement between the morphologies of real and model generated galaxies.Our results
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 θ{sub E}/2 ≤ θ ≤ 2θ{sub E} (where θ{sub E} is the Einstein angle) by a factor of ∼ 3 and 1.5 in the HUDF (df/dν{sub 0} ∼ 9 nJy) and medium-deep JWST surveys (df/dν{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.
Effects of gravitational lensing and companion motion on the binary pulsar timing
Rafikov, Roman R.; Lai Dong
2006-03-15
The measurement of the Shapiro time delay in binary pulsar systems with highly-inclined orbit can be affected both by the motion of the pulsar's companion because of the finite time it takes a photon to cross the binary, and by the gravitational light bending if the orbit is sufficiently edge-on relative to the line of sight. Here we calculate the effect of retardation due to the companion's motion on various time delays in pulsar binaries, including the Shaipro delay, the geometric lensing delay, and the lens-induced delays associated with the pulsar rotation. Our results can be applied to systems so highly inclined that near conjunction gravitational lensing of the pulsar radiation by the companion becomes important (the recently discovered double pulsar system J0737-3039 may exemplify such a system). To the leading order, the effect of retardation is to shift all the delay curves backward in time around the orbit conjunction, without affecting the shape and amplitude of the curves. The time shift is of order the photon orbit crossing time, and ranges from a second to a few minutes for the observed binary pulsar systems. In the double pulsar system J0737-3039, the motion of the companion may also affect the interpretation of the recent correlated interstellar scintillation measurements. Finally, we show that lensing sets an upper limit on the magnitude of the frame-dragging time delay caused by the companion's spin, and makes this delay unobservable in stellar-mass binary pulsar systems.
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.
A MEASUREMENT OF GRAVITATIONAL LENSING OF THE MICROWAVE BACKGROUND USING SOUTH POLE TELESCOPE DATA
Van Engelen, A.; De Haan, T.; Dobbs, M. A.; Dudley, J.; Holder, G. P.; Keisler, R.; Benson, B. A.; Bleem, L. E.; Carlstrom, J. E.; Chang, C. L.; Crawford, T. M.; Crites, A. T.; Hoover, S.; Zahn, O.; Aird, K. A.; Cho, H. M.; George, E. M.; Holzapfel, W. L.; Halverson, N. W.; Hou, Z.; and others
2012-09-10
We use South Pole Telescope data from 2008 and 2009 to detect the non-Gaussian signature in the cosmic microwave background (CMB) produced by gravitational lensing and to measure the power spectrum of the projected gravitational potential. We constrain the ratio of the measured amplitude of the lensing signal to that expected in a fiducial {Lambda}CDM cosmological model to be 0.86 {+-} 0.16, with no lensing disfavored at 6.3{sigma}. Marginalizing over {Lambda}CDM cosmological models allowed by the Wilkinson Microwave Anisotropy Probe (WMAP7) results in a measurement of A{sub lens} 0.90 {+-} 0.19, indicating that the amplitude of matter fluctuations over the redshift range 0.5 {approx}< z {approx}< 5 probed by CMB lensing is in good agreement with predictions. We present the results of several consistency checks. These include a clear detection of the lensing signature in CMB maps filtered to have no overlap in Fourier space, as well as a 'curl' diagnostic that is consistent with the signal expected for {Lambda}CDM. We perform a detailed study of bias in the measurement due to noise, foregrounds, and other effects and determine that these contributions are relatively small compared to the statistical uncertainty in the measurement. We combine this lensing measurement with results from WMAP7 to improve constraints on cosmological parameters when compared to those from WMAP7 alone: we find a factor of 3.9 improvement in the measurement of the spatial curvature of the universe, {Omega}{sub k} = -0.0014 {+-} 0.0172; a 10% improvement in the amplitude of matter fluctuations within {Lambda}CDM, {sigma}{sub 8} = 0.810 {+-} 0.026; and a 5% improvement in the dark energy equation of state, w = -1.04 {+-} 0.40. When compared with the measurement of w provided by the combination of WMAP7 and external constraints on the Hubble parameter, the addition of the lensing data improves the measurement of w by 15% to give w -1.087 {+-} 0.096.
LoCuSS: exploring the selection of faint blue background galaxies for cluster weak-lensing
NASA Astrophysics Data System (ADS)
Ziparo, Felicia; Smith, Graham P.; Okabe, Nobuhiro; Haines, Chris P.; Pereira, Maria J.; Egami, Eiichi
2016-12-01
Cosmological constraints from galaxy clusters rely on accurate measurements of the mass and internal structure of clusters. An important source of systematic uncertainty in cluster mass and structure measurements is the secure selection of background galaxies that are gravitationally lensed by clusters. This issue has been shown to be particular severe for faint blue galaxies. We therefore explore the selection of faint blue background galaxies, by reference to photometric redshift catalogues derived from the Cosmological Evolution Survey (COSMOS) and our own observations of massive galaxy clusters at z ≃ 0.2. We show that methods relying on photometric redshifts of galaxies in/behind clusters based on observations through five filters, and on deep 30-band COSMOS photometric redshifts are both inadequate to identify safely faint blue background galaxies with the same 1 per cent contamination level that we have achieved with red galaxies. This is due to the small number of filters used by the former, and absence of massive galaxy clusters at redshifts of interest in the latter. Nevertheless, our least contaminated blue galaxy sample yields stacked weak-lensing results consistent with our previously published results based on red galaxies, and we show that the stacked clustercentric number density profile of these faint blue galaxies is consistent with expectations from consideration of the lens magnification signal of the clusters. Indeed, the observed number density of blue background galaxies changes by ˜10-30 per cent across the radial range over which other surveys assume it to be flat.
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.
New Methods for Identifying Nearby Gravitational Lenses in All-Sky Surveys
NASA Astrophysics Data System (ADS)
McCandlish, Samuel; Di Stefano, R.
2011-01-01
All-sky catalogs provide a wealth of information about gravitational lensing events that has not yet been utilized. We present a method for matching lensing events to catalogs and finding the probability that the association is genuine. Given a likely candidate for the lens object associated with an event, it is possible to break the inherent degeneracy in microlensing and estimate the mass of the lens, depending on its distance. Eight percent of microlensing events have matches in the 2MASS catalog, and there are many more matches in catalogs that cover other wave bands. In addition to detecting the associated lens or source, it is possible that the cataloged object is a companion or host to the actual lens. This opens up the possibility of finding dark nearby lenses, such as stellar remnants or planets that are associated with cataloged objects. We propose various methods for determining which events are most likely to be caused by nearby lenses, and apply them to our matches. We present some interesting matched objects and the results of observations of those objects. This work is supported in part by the NSF REU and DOD ASSURE programs under NSF grant no. 0754568 and by the Smithsonian Institution.
Matter in the Beam: Weak Lensing, Substructures, and the Temperature of Dark Matter
NASA Astrophysics Data System (ADS)
Mahdi, Hareth S.; Elahi, Pascal J.; Lewis, Geraint F.; Power, Chris
2016-08-01
Warm dark matter (WDM) models offer an attractive alternative to the current cold dark matter (CDM) cosmological model. We present a novel method to differentiate between WDM and CDM cosmologies, namely, using weak lensing; this provides a unique probe as it is sensitive to all of the “matter in the beam,” not just dark matter haloes and the galaxies that reside in them, but also the diffuse material between haloes. We compare the weak lensing maps of CDM clusters to those in a WDM model corresponding to a thermally produced 0.5 keV dark matter particle. Our analysis clearly shows that the weak lensing magnification, convergence, and shear distributions can be used to distinguish between CDM and WDM models. WDM models increase the probability of weak magnifications, with the differences being significant to ≳5σ, while leaving no significant imprint on the shear distribution. WDM clusters analyzed in this work are more homogeneous than CDM ones, and the fractional decrease in the amount of material in haloes is proportional to the average increase in the magnification. This difference arises from matter that would be bound in compact haloes in CDM being smoothly distributed over much larger volumes at lower densities in WDM. Moreover, the signature does not solely lie in the probability distribution function but in the full spatial distribution of the convergence field.
SHEAR-SELECTED CLUSTERS FROM THE DEEP LENS SURVEY. III. MASSES FROM WEAK LENSING
Abate, Alexandra; Wittman, D.; Margoniner, V. E.; Gee, Perry; Tyson, J. Anthony; Bridle, S. L.; Dell'Antonio, Ian P. E-mail: dwittman@physics.ucdavis.edu
2009-09-01
We present weak lensing mass estimates of seven shear-selected galaxy cluster candidates from the deep lens survey. The clusters were previously identified as mass peaks in convergence maps of 8.6 deg{sup 2} of R-band imaging, and followed up with X-ray and spectroscopic confirmation, spanning a redshift range 0.19-0.68. Most clusters contained multiple X-ray peaks, yielding 17 total mass concentrations. In this paper, we constrain the masses of these X-ray sources with weak lensing, using photometric redshifts from the full set of BVRz' imaging to properly weight background galaxies according to their lensing distance ratios. We fit both NFW and singular isothermal sphere profiles, and find that the results are insensitive to the assumed profile. We also show that the results do not depend significantly on the assumed prior on the position of the mass peak, but that this may become an issue in future larger samples. The inferred velocity dispersions for the extended X-ray sources range from 250 to 800 km s{sup -1}, with the exception of one source for which no lensing signal was found. This work further establishes shear selection as a viable technique for finding clusters, but also highlights some unresolved issues such as determination of the mass profile center without biasing the mass estimate, and fully accounting for line-of-sight projections. A follow-up paper will examine the mass-X-ray scaling relations of these clusters.
Weak lensing measurement of the mass–richness relation of SDSS redMaPPer clusters
Simet, Melanie; McClintock, Tom; Mandelbaum, Rachel; ...
2016-12-15
Here, we perform a measurement of the mass–richness relation of the redMaPPer galaxy cluster catalogue using weak lensing data from the Sloan Digital Sky Survey. We carefully characterized a broad range of systematic uncertainties, including shear calibration errors, photo-zz biases, dilution by member galaxies, source obscuration, magnification bias, incorrect assumptions about cluster mass profiles, cluster centering, halo triaxiality, and projection effects. We then compare measurements of the lensing signal from two independently-produced shear and photometric redshift catalogues to characterize systematic errors in the lensing signal itself. Using a sample of 5,570 clusters from 0.1 ≤ zz ≤ 0.33, the normalization of our power-law mass vs. λ relation is log10[M200m/h-1 M⊙] = 14.344 ± 0.021 (statistical) ±0.023 (systematic) at a richness λ = 40, a 7 per cent calibration uncertainty, with a power-law index of 1.33+0.09-0.101.33more » $$+0.09\\atop{-0.10}$$ (1σ). Finally, the detailed systematics characterization in this work renders it the definitive weak lensing mass calibration for SDSS redMaPPer clusters at this time.« less
Weak lensing measurement of the mass–richness relation of SDSS redMaPPer clusters
Simet, Melanie; McClintock, Tom; Mandelbaum, Rachel; Rozo, Eduardo; Rykoff, Eli; Sheldon, Erin; Wechsler, Risa H.
2016-12-15
Here, we perform a measurement of the mass–richness relation of the redMaPPer galaxy cluster catalogue using weak lensing data from the Sloan Digital Sky Survey. We carefully characterized a broad range of systematic uncertainties, including shear calibration errors, photo-zz biases, dilution by member galaxies, source obscuration, magnification bias, incorrect assumptions about cluster mass profiles, cluster centering, halo triaxiality, and projection effects. We then compare measurements of the lensing signal from two independently-produced shear and photometric redshift catalogues to characterize systematic errors in the lensing signal itself. Using a sample of 5,570 clusters from 0.1 ≤ zz ≤ 0.33, the normalization of our power-law mass vs. λ relation is log_{10}[M_{200m}/h^{-1} M_{⊙}] = 14.344 ± 0.021 (statistical) ±0.023 (systematic) at a richness λ = 40, a 7 per cent calibration uncertainty, with a power-law index of 1.33+0.09-0.101.33$+0.09\\atop{-0.10}$ (1σ). Finally, the detailed systematics characterization in this work renders it the definitive weak lensing mass calibration for SDSS redMaPPer clusters at this time.
Weak lensing measurement of the mass-richness relation of SDSS redMaPPer clusters
NASA Astrophysics Data System (ADS)
Simet, Melanie; McClintock, Tom; Mandelbaum, Rachel; Rozo, Eduardo; Rykoff, Eli; Sheldon, Erin; Wechsler, Risa H.
2017-04-01
We perform a measurement of the mass-richness relation of the redMaPPer galaxy cluster catalogue using weak lensing data from the Sloan Digital Sky Survey (SDSS). We have carefully characterized a broad range of systematic uncertainties, including shear calibration errors, photo-z biases, dilution by member galaxies, source obscuration, magnification bias, incorrect assumptions about cluster mass profiles, cluster centring, halo triaxiality and projection effects. We also compare measurements of the lensing signal from two independently produced shear and photometric redshift catalogues to characterize systematic errors in the lensing signal itself. Using a sample of 5570 clusters from 0.1 ≤ z ≤ 0.33, the normalization of our power-law mass versus λ relation is log10[M200m/h-1 M⊙] = 14.344 ± 0.021 (statistical) ±0.023 (systematic) at a richness λ = 40, a 7 per cent calibration uncertainty, with a power-law index of 1.33^{+0.09}_{-0.10} (1σ). The detailed systematics characterization in this work renders it the definitive weak lensing mass calibration for SDSS redMaPPer clusters at this time.
Using the Greenbank Telescope with Gravitational Lensing and the VLA to search for HI Beyond z=0.25
NASA Astrophysics Data System (ADS)
Hunt, Lucas; Pisano, Daniel J.; Crawford, Steve; CHILES
2017-01-01
HI provides an important fuel for star formation, a good indicator of galactic environment, and more accurate information on mass, size, and velocity. Studies of Neutral Hydrogen (HI) in individual galaxies beyond z=0.25 have been limited by current technology. Most available telescopes do not have the frequency coverage, or sensitivity to detect the weak HI signal in a reasonable integration time. My thesis concentrates on pushing the limits on currently available telescopes to detect HI in individual sources out to higher redshifts. The COSMOS HI Large Extragalactic Survey (CHILES) team has pointed the JVLA toward the COSMOS field in a blind search of HI out to z=0.45. I am planning to use the data to study the HI properties of Luminous Compact Blue Galaxies, a heterogenous class of galaxies with high star formation rates, and metallicity amongst an older stellar population. These objects are numerous have a star formation rate density roughly equal to grand-design spiral galaxies at z~1, but become rare at z=0. A number of local LCBGs have been studied to determine HI, H2, and dynamical mass, and gas depletion timescales, and with the information provided from CHILES I can compare the properties of local LCBGs to intermediate redshift LCBGs. In preparation for final data products, I have generated a Luminosity function for LCBGs in the COSMOS field to track the evolution of their number density, star formation rate density, and how much they contribute to the overall luminosity function. I have also attempted to detect HI in gravitationally lensed galaxies using the Green Bank Telescope. The magnification provided by strong gravitational lensing should allow us to determine the HI mass of a small number of galaxies out to z~0.8 and beyond.
Okura, Yuki; Petri, Andrea; May, Morgan; Plazas, Andrés A.; Tamagawa, Toru
2016-06-27
Weak gravitational lensing causes subtle changes in the apparent shapes of galaxies due to the bending of light by the gravity of foreground masses. By measuring the shapes of large numbers of galaxies (millions in recent surveys, up to tens of billions in future surveys) we can infer the parameters that determine cosmology. Imperfections in the detectors used to record images of the sky can introduce changes in the apparent shape of galaxies, which in turn can bias the inferred cosmological parameters. Here in this paper we consider the effect of two widely discussed sensor imperfections: tree-rings, due to impurity gradients which cause transverse electric fields in the Charge-Coupled Devices (CCD), and pixel-size variation, due to periodic CCD fabrication errors. These imperfections can be observed when the detectors are subject to uniform illumination (flat field images). We develop methods to determine the spurious shear and convergence (due to the imperfections) from the flat-field images. We calculate how the spurious shear when added to the lensing shear will bias the determination of cosmological parameters. We apply our methods to candidate sensors of the Large Synoptic Survey Telescope (LSST) as a timely and important example, analyzing flat field images recorded with LSST prototype CCDs in the laboratory. In conclusion, we find that tree-rings and periodic pixel-size variation present in the LSST CCDs will introduce negligible bias to cosmological parameters determined from the lensing power spectrum, specifically w,Ω_{m} and σ_{8}.
Okura, Yuki; Petri, Andrea; May, Morgan; ...
2016-06-27
Weak gravitational lensing causes subtle changes in the apparent shapes of galaxies due to the bending of light by the gravity of foreground masses. By measuring the shapes of large numbers of galaxies (millions in recent surveys, up to tens of billions in future surveys) we can infer the parameters that determine cosmology. Imperfections in the detectors used to record images of the sky can introduce changes in the apparent shape of galaxies, which in turn can bias the inferred cosmological parameters. Here in this paper we consider the effect of two widely discussed sensor imperfections: tree-rings, due to impuritymore » gradients which cause transverse electric fields in the Charge-Coupled Devices (CCD), and pixel-size variation, due to periodic CCD fabrication errors. These imperfections can be observed when the detectors are subject to uniform illumination (flat field images). We develop methods to determine the spurious shear and convergence (due to the imperfections) from the flat-field images. We calculate how the spurious shear when added to the lensing shear will bias the determination of cosmological parameters. We apply our methods to candidate sensors of the Large Synoptic Survey Telescope (LSST) as a timely and important example, analyzing flat field images recorded with LSST prototype CCDs in the laboratory. In conclusion, we find that tree-rings and periodic pixel-size variation present in the LSST CCDs will introduce negligible bias to cosmological parameters determined from the lensing power spectrum, specifically w,Ωm and σ8.« less
Probing small-scale structure in galaxies with strong gravitational lensing
NASA Astrophysics Data System (ADS)
Congdon, Arthur Benjamin
We use gravitational lensing to study the small-scale distribution of matter in galaxies. First, we examine galaxies and their dark matter halos. Roughly half of all observed four-image quasar lenses have image flux ratios that differ from the values predicted by simple lens potentials. We show that smooth departures from elliptical symmetry fail to explain anomalous radio fluxes, strengthening the case for dark matter substructure. Our results have important implications for the "missing satellites'' problem. We then consider how time delays between lensed images can be used to identify lens galaxies containing small-scale structure. We derive an analytic relation for the time delay between the close pair of images in a "fold'' lens, and perform Monte Carlo simulations to investigate the utility of time delays for probing small- scale structure in realistic lens populations. We compare our numerical predictions with systems that have measured time delays and discover two anomalous lenses. Next, we consider microlensing, where stars in the lens galaxy perturb image magnifications. This is relevant at optical wavelengths, where the size of the lensed source is comparable to the Einstein radius of a typical star. Our simulations of negative-parity images show that raising the fraction of dark matter relative to stars increases image flux variability for small sources, and decreases it for large sources. This suggests that quasar accretion disks and broad-emission-line regions may respond differently to microlensing. We also consider extended sources with a range of ellipticities, which has relevance to a population of inclined accretion disks. Depending on their orientation, more elongated sources lead to more rapid variability, which may complicate the interpretation of microlensing light curves. Finally, we consider prospects for observing strong lensing by the supermassive black hole at the center of the Milky Way, Sgr A*. Assuming a black hole on the million
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.
A sampling strategy for high-dimensional spaces applied to free-form gravitational lensing
NASA Astrophysics Data System (ADS)
Lubini, Mario; Coles, Jonathan
2012-10-01
We present a novel proposal strategy for the Metropolis-Hastings algorithm designed to efficiently sample general convex polytopes in 100 or more dimensions. This improves upon previous sampling strategies used for free-form reconstruction of gravitational lenses, but is general enough to be applied to other fields. We have written a parallel implementation within the lens modelling framework GLASS. Testing shows that we are able to produce uniform uncorrelated random samples which are necessary for exploring the degeneracies inherent in lens reconstruction.
Discovery of an Exceptionally Bright Gravitationally Lensed Submillimeter Galaxy at z=4.69
NASA Astrophysics Data System (ADS)
Egami, Eiichi; Herschel Lensing Survey (HLS) Team
2012-05-01
We report the discovery of an exceptionally bright gravitationally lensed submillimeter galaxy at z=4.69. Through our on-going Herschel survey of gravitationally lensed high-redshift galaxies in the fields of massive galaxy clusters ("The Herschel Lensing Survey (HLS)" - PI: Egami), we identified in the field of a z=0.3 cluster a bright Herschel/SPIRE source ( 100 mJy at 500 um) whose far-infrared/submillimeter spectral energy distribution is peaking toward 500 um, indicating that its redshift is likely above 4. The APEX/LABOCA 870 um image showed that this source is not only bright (60 mJy at 870 um) but also spatially extended even with the LABOCA resolution of 20'', although it is invisible in the HST/ACS F606W image. The spectroscopic redshift came from the IRAM30m/EMIR observations, which detected the CO(4-3) and CO(5-4) lines with the corresponding redshift of 4.69. The high-resolution (beam=0.8"x0.7") SMA 345 GHz map has subsequently resolved this source into four components, which are likely four lensed images of the same background galaxy. This lensing interpretation has been confirmed by the HST WFC3/IR observations, which not only revealed the same morphology for the multiple sources but also detected the 5th image at the predicted location. We therefore conclude that this lensed system exhibits a rare hyperbolic umbilic image configuration, which produces a large magnification factor of x100-200 when the four components are combined. What is even more remarkable is that the four HST sources are not spatially coincident with the four SMA sources. In other words, this z=4.69 galaxy appears to consist of two spatially distinct components, one of which (the one responsible for the bright IR/submm emission) is completely invisible in the HST near-infrared images. This suggests that there may exist a population of dust-obscured galaxies at z>4 that are hidden from our deep optical/near-infrared view.
Purely radiating and nonradiating scalar, electromagnetic and weak gravitational sources
NASA Astrophysics Data System (ADS)
Marengo, Edwin A.; Ziolkowski, Richard W.
2000-03-01
It has been known for some time that localized sources to the scalar wave equation and Maxwell's equations exist which do not radiate. Such sources, referred to as non-radiating (NR) sources, generate vanishing fields outside their spatial support which prevents them from interacting with nearby objects by means of their fields. Work on NR sources dates back to Sommerfeld, Herglotz, Hertz, Ehrenfest and Schott who studied these objects in connection with electron and atom models. NR sources have also appeared extensively in inverse source/scattering theories as members of the null space of the source-to-field mapping. In this presentation, we provide a new description of scalar, vector or tensor NR sources and of a complementary class of sources, namely, sources that lack a NR part, i.e., `purely radiating' sources. We show that the class of square-integrable localized purely radiating scalar, electromagnetic or weak gravitational sources is exactly the class of solutions - within the source's support - of the homogeneous form of the associated partial differential equation relating the sources to their fields, i.e., purely radiating sources are themselves fields. As a consequence of this result, NR sources are shown to be inseparable components of a broad class of physically relevant sources, thereby having a physical significance that transcends their use in wave-theoretic inversion models. Localized NR sources are characterized in connection with the concept of reciprocity as non-interactors. The role of NR sources in absorption of radiation and energy storage is addressed. The general theoretical results are illustrated with the aid of a one-dimensional (1D) electromagnetic example corresponding to a transmission line system (equivalently, a 1D plane wave system) with uniformly distributed sources/loads.
A technique for using radio jets as extended gravitational lensing probes
NASA Technical Reports Server (NTRS)
Kronberg, Philipp P.; Dyer, Charles C.; Burbidge, E. Margaret; Junkkarinen, Vesa T.
1991-01-01
A new and potentially powerful method of measuring the mass of a galaxy (or dark matter concentration) which lies close in position to a background polarized radio jet is proposed. Using the fact that the polarization angle is not changed by lensing, an 'alignment-breaking parameter' is defined which is a sensitive indicator of gravitational distortion. The method remains sensitive over a wide redshift range of the gravitational lens. This technique is applied to the analysis of polarimetric observations of the jet of 3C 9 at z = 2.012, combined with a newly discovered 20.3 mag foreground galaxy at z = 0.2538 to 'weigh' the galaxy and obtain an approximate upper limit to the mass-to-light ratio.
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.
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.
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.
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.
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)
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(φ) ∝ φ{sup −α} (α > 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.
A new hybrid framework to efficiently model lines of sight to gravitational lenses
NASA Astrophysics Data System (ADS)
McCully, Curtis; Keeton, Charles R.; Wong, Kenneth C.; Zabludoff, Ann I.
2014-10-01
In strong gravitational lens systems, the light bending is usually dominated by one main galaxy, but may be affected by other mass along the line of sight (LOS). Shear and convergence can be used to approximate the contributions from less significant perturbers (e.g. those that are projected far from the lens or have a small mass), but higher order effects need to be included for objects that are closer or more massive. We develop a framework for multiplane lensing that can handle an arbitrary combination of tidal planes treated with shear and convergence and planes treated exactly (i.e. including higher order terms). This framework addresses all of the traditional lensing observables including image positions, fluxes, and time delays to facilitate lens modelling that includes the non-linear effects due to mass along the LOS. It balances accuracy (accounting for higher order terms when necessary) with efficiency (compressing all other LOS effects into a set of matrices that can be calculated up front and cached for lens modelling). We identify a generalized multiplane mass sheet degeneracy, in which the effective shear and convergence are sums over the lensing planes with specific, redshift-dependent weighting factors.
A study of the gravitational lensing potential in MG 0414+0534
NASA Astrophysics Data System (ADS)
Falco, Emilio
1997-07-01
We proposed to use WFPC2 and NICMOS to observe the quadruple gravitational lens system MG 0414+0534, a QSO at z = 2.64 that is lensed by a single elliptical galaxy. However, we limit our plans to the 5 orbits that the TAC imposed for us to concentrate on NICMOS. We recently observed the system with HST and WFPC2/PC1 {Falco, Leh'ar & Shapiro 1997, AJ 112, 897; hereafter FLS96}. We measured a light profile for the lens galaxy G, and discovered a blue arc connecting the 3 brightest images of the QSO. Although our elliptical single-potential lens models account qualitatively for all the properties of the system, they fail quantitatively, with fits that achieve only chi^2/N_dof 5. Adding an independent shear axis allows a good fit to the data, but the physical source of such a shear remains to be determined. We intend to investigate whether the primary lens galaxy and its dark halo suffice to explain the observed lensing geometry or whether there are significant external tidal perturbations. We propose to use NICMOS to obtain a high-SNR determination of the brightness profile of the lens galaxy in the J, H and K bands. We would also obtain IR fluxes for the images that we would use to study extinction in this system, and to determine whether it originates in the lens galaxy or in the host galaxy of the lensed QSO. SAO proposal ID # P3878-9-96
NASA Astrophysics Data System (ADS)
Congdon, Arthur B.; Keeton, Charles R.; Nordgren, C. Erik
2008-09-01
Gravitational lensing provides a unique and powerful probe of the mass distributions of distant galaxies. Four-image lens systems with fold and cusp configurations have two or three bright images near a critical point. Within the framework of singularity theory, we derive analytic relations that are satisfied for a light source that lies a small but finite distance from the astroid caustic of a four-image lens. Using a perturbative expansion of the image positions, we show that the time delay between the close pair of images in a fold lens scales with the cube of the image separation, with a constant of proportionality that depends on a particular third derivative of the lens potential. We also apply our formalism to cusp lenses, where we develop perturbative expressions for the image positions, magnifications and time delays of the images in a cusp triplet. Some of these results were derived previously for a source asymptotically close to a cusp point, but using a simplified form of the lens equation whose validity may be in doubt for sources that lie at astrophysically relevant distances from the caustic. Along with the work of Keeton, Gaudi & Petters, this paper demonstrates that perturbation theory plays an important role in theoretical lensing studies.
Battaglia, N.; Hill, J. C.; Murray, N.
2015-10-20
Recent first detections of the cross-correlation of the thermal Sunyaev–Zel’dovich (tSZ) signal in Planck cosmic microwave background (CMB) temperature maps with gravitational lensing maps inferred from the Planck CMB data and the CFHTLenS galaxy survey provide new probes of the relationship between baryons and dark matter. Using cosmological hydrodynamics simulations, we show that these cross-correlation signals are dominated by contributions from hot gas in the intracluster medium (ICM), rather than diffuse, unbound gas located beyond the virial radius (the “missing baryons”). Thus, these cross-correlations offer a tool with which to study the ICM over a wide range of halo masses and redshifts. In particular, we show that the tSZ—CMB lensing cross-correlation is more sensitive to gas in lower-mass, higher-redshift halos and gas at larger cluster-centric radii than the tSZ—galaxy lensing cross-correlation. Combining these measurements with primary CMB data will constrain feedback models through their signatures in the ICM pressure profile. We forecast the ability of ongoing and future experiments to constrain the parameters of a phenomenological ICM model, including the mean amplitude of the pressure–mass relation, the redshift evolution of this amplitude, and the mean outer logarithmic slope of the pressure profile. The results are promising, with ≈5%–20% precision constraints achievable with upcoming experiments, even after marginalizing over cosmological parameters.
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.
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.
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.
MACS J1423.8+2404: gravitational lensing by a massive, relaxed cluster of galaxies at z = 0.54
NASA Astrophysics Data System (ADS)
Limousin, M.; Ebeling, H.; Ma, C.-J.; Swinbank, A. M.; Smith, G. P.; Richard, J.; Edge, A. C.; Jauzac, M.; Kneib, J.-P.; Marshall, P.; Schrabback, T.
2010-06-01
We present results of a gravitational lensing and optical study of MACS J1423.8+2404 (z = 0.545, MACS J1423), the most relaxed cluster in the high-redshift subsample of clusters discovered in the MAssive Cluster Survey (MACS). Our analysis uses high-resolution images taken with the Hubble Space Telescope in the F555W and F814W passbands, ground-based imaging in eight optical and near-infrared filters obtained with Subaru and Canada-France-Hawaii Telescope, as well as extensive spectroscopic data gathered with the Keck telescopes. At optical wavelengths, the cluster exhibits no sign of substructure and is dominated by a cD galaxy that is 2.1 mag (K band) brighter than the second brightest cluster member, suggesting that MACS J1423 is close to be fully virialized. Analysis of the redshift distribution of 140 cluster members reveals a Gaussian distribution, mildly disturbed by the presence of a loose galaxy group that may be falling into the cluster along the line of sight. Combining strong-lensing constraints from two spectroscopically confirmed multiple-image systems near the cluster core with a weak-lensing measurement of the gravitational shear on larger scales, we derive a parametric mass model for the mass distribution. All constraints can be satisfied by a unimodal mass distribution centred on the cD galaxy and exhibiting very little substructure. The derived projected mass of M[< 65 arcsec (415kpc)] = (4.3 +/- 0.6) × 1014 Msolar is about 30 per cent higher than the one derived from X-ray analyses assuming spherical symmetry, suggesting a slightly prolate mass distribution consistent with the optical indication of residual line-of-sight structure. The similarity in shape and excellent alignment of the centroids of the total mass, K-band light and intracluster gas distributions add to the picture of a highly evolved system. The existence of a massive cluster like MACS J1423, nearly fully virialized only ~7 Gyr after the big bang, may have important implications
NASA Astrophysics Data System (ADS)
Sotani, Hajime; Miyamoto, Umpei
2015-08-01
We systematically examine the properties of null geodesics around an electrically charged, asymptotically flat black hole in Eddington-inspired Born-Infeld gravity, varying the electric charge of the black hole and the coupling constant in the theory. We find that the radius of the unstable circular orbit for a massless particle decreases with the coupling constant, if the value of the electrical charge is fixed. Additionally, we consider the strong gravitational lensing around such a black hole. We show that the deflection angle, the position angle of the relativistic images, and the magnification due to the light bending in strong gravitational field are quite sensitive to the parameters determining the black hole solution. Thus, through the accurate observations associated with the strong gravitational lensing, it might be possible to reveal the gravitational theory in a strong field regime.
[The use of a detector of the extremely weak radiation as a variometer of gravitation field].
Gorshkov, E S; Bondarenko, E G; Shapovalov, S N; Sokolovskiĭ, V V; Troshichev, O A
2001-01-01
It was shown that the detector of extremely weak radiation with selectively increased sensitivity to the nonelectromagnetic, including the gravitational component of the spectrum of active physical fields can be used as the basis for constructing a variometer of gravitational field of a new type.
NASA Astrophysics Data System (ADS)
Choi, J.-Y.; Shin, I.-G.; Park, S.-Y.; Han, C.; Gould, A.; Sumi, T.; Udalski, A.; Beaulieu, J.-P.; Street, R.; Dominik, M.; Allen, W.; Almeida, L. A.; Bos, M.; Christie, G. W.; Depoy, D. L.; Dong, S.; Drummond, J.; Gal-Yam, A.; Gaudi, B. S.; Henderson, C. B.; Hung, L.-W.; Jablonski, F.; Janczak, J.; Lee, C.-U.; Mallia, F.; Maury, A.; McCormick, J.; McGregor, D.; Monard, L. A. G.; Moorhouse, D.; Muñoz, J. A.; Natusch, T.; Nelson, C.; Park, B.-G.; Pogge, R. W.; "TG" Tan, T.-G.; Thornley, G.; Yee, J. C.; μFUN Collaboration; Abe, F.; Barnard, E.; Baudry, J.; Bennett, D. P.; Bond, I. A.; Botzler, C. S.; Freeman, M.; Fukui, A.; Furusawa, K.; Hayashi, F.; Hearnshaw, J. B.; Hosaka, S.; Itow, Y.; Kamiya, K.; Kilmartin, P. M.; Kobara, S.; Korpela, A.; Lin, W.; Ling, C. H.; Makita, S.; Masuda, K.; Matsubara, Y.; Miyake, N.; Muraki, Y.; Nagaya, M.; Nishimoto, K.; Ohnishi, K.; Okumura, T.; Omori, K.; Perrott, Y. C.; Rattenbury, N.; Saito, To.; Skuljan, L.; Sullivan, D. J.; Suzuki, D.; Suzuki, K.; Sweatman, W. L.; Takino, S.; Tristram, P. J.; Wada, K.; Yock, P. C. M.; MOA Collaboration; Szymański, M. K.; Kubiak, M.; Pietrzyński, G.; Soszyński, I.; Poleski, R.; Ulaczyk, K.; Wyrzykowski, Ł.; Kozłowski, S.; Pietrukowicz, P.; OGLE Collaboration; Albrow, M. D.; Bachelet, E.; Batista, V.; Bennett, C. S.; Bowens-Rubin, R.; Brillant, S.; Cassan, A.; Cole, A.; Corrales, E.; Coutures, Ch.; Dieters, S.; Dominis Prester, D.; Donatowicz, J.; Fouqué, P.; Greenhill, J.; Kane, S. R.; Menzies, J.; Sahu, K. C.; Wambsganss, J.; Williams, A.; Zub, M.; PLANET Collaboration; Allan, A.; Bramich, D. M.; Browne, P.; Clay, N.; Fraser, S.; Horne, K.; Kains, N.; Mottram, C.; Snodgrass, C.; Steele, I.; Tsapras, Y.; RoboNet Collaboration; Alsubai, K. A.; Bozza, V.; Burgdorf, M. J.; Calchi Novati, S.; Dodds, P.; Dreizler, S.; Finet, F.; Gerner, T.; Glitrup, M.; Grundahl, F.; Hardis, S.; Harpsøe, K.; Hinse, T. C.; Hundertmark, M.; Jørgensen, U. G.; Kerins, E.; Liebig, C.; Maier, G.; Mancini, L.; Mathiasen, M.; Penny, M. T.; Proft, S.; Rahvar, S.; Ricci, D.; Scarpetta, G.; Schäfer, S.; Schönebeck, F.; Skottfelt, J.; Surdej, J.; Southworth, J.; Zimmer, F.; MiNDSTEp Consortium
2012-05-01
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 θE ~ 0.08 mas combined with the short timescale of t E ~ 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 ~0.84 M ⊙ 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.
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.
A search for gravitationally lensed water masers in dusty quasars and star-forming galaxies
NASA Astrophysics Data System (ADS)
McKean, J. P.; Impellizzeri, C. M. V.; Roy, A. L.; Castangia, P.; Samuel, F.; Brunthaler, A.; Henkel, C.; Wucknitz, O.
2011-02-01
Luminous extragalactic water masers are known to be associated with active galactic nuclei and have provided accurate estimates for the mass of the central supermassive black hole and the size and structure of the circumnuclear accretion disc in nearby galaxies. To find water maser systems at much higher redshifts, we have begun a survey of known gravitationally lensed quasars and star-forming galaxies. In this paper, we present a search for 22 GHz (rest-frame) water masers towards five dusty, gravitationally lensed quasars and star-forming galaxies at redshifts between 2.3 and 2.9 with the Effelsberg radio telescope and the Expanded Very Large Array (EVLA). Our observations do not find any new definite examples of high-redshift water maser galaxies, suggesting that large reservoirs of dust and gas are not a sufficient condition for powerful water maser emission. However, we do find the tentative detection of a water maser system in the active galaxy IRAS 10214+4724 at redshift 2.285. Our survey has now doubled the number of gravitationally lensed galaxies and quasars that have been searched for high-redshift water maser emission. We also present an updated analysis of the high-redshift water maser luminosity function that is based on the results presented here and from the only cosmologically distant (z > 1) water maser galaxy found thus far, MG J0414+0534 at redshift 2.64. By comparing with the water maser luminosity function locally and at moderate redshifts, we find that there must be some evolution in the luminosity function of water maser galaxies at high redshifts. By assuming a moderate evolution [(1 +z)4] in the water maser luminosity function, we find that blind surveys for water maser galaxies are only worthwhile with extremely high sensitivity like that of the planned Square Kilometre Array (Phase 2), which is scheduled to be completed by 2020. However, instruments like the EVLA and MeerKAT will be capable of detecting water maser systems similar to the
LoCuSS: weak-lensing mass calibration of galaxy clusters
NASA Astrophysics Data System (ADS)
Okabe, Nobuhiro; Smith, Graham P.
2016-10-01
We present weak-lensing mass measurements of 50 X-ray luminous galaxy clusters at 0.15 ≤ z ≤ 0.3, based on uniform high-quality observations with Suprime-Cam mounted on the 8.2-m Subaru telescope. We pay close attention to possible systematic biases, aiming to control them at the ≲4 per cent level. The dominant source of systematic bias in weak-lensing measurements of the mass of individual galaxy clusters is contamination of background galaxy catalogues by faint cluster and foreground galaxies. We extend our conservative method for selecting background galaxies with (V - i') colours redder than the red sequence of cluster members to use a colour-cut that depends on cluster-centric radius. This allows us to define background galaxy samples that suffer ≤1 per cent contamination, and comprise 13 galaxies per square arcminute. Thanks to the purity of our background galaxy catalogue, the largest systematic that we identify in our analysis is a shape measurement bias of 3 per cent, that we measure using simulations that probe weak shears up to g = 0.3. Our individual cluster mass and concentration measurements are in excellent agreement with predictions of the mass-concentration relation. Equally, our stacked shear profile is in excellent agreement with the Navarro Frenk and White profile. Our new Local Cluster Substructure Survey mass measurements are consistent with the Canadian Cluster Cosmology Project and Cluster Lensing And Supernova Survey with Hubble surveys, and in tension with the Weighing the Giants at ˜1σ-2σ significance. Overall, the consensus at z ≤ 0.3 that is emerging from these complementary surveys represents important progress for cluster mass calibration, and augurs well for cluster cosmology.
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 Ωm and the density fluctuation amplitude σ8. 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.
Radio weak lensing shear measurement in the visibility domain - I. Methodology
NASA Astrophysics Data System (ADS)
Rivi, M.; Miller, L.; Makhathini, S.; Abdalla, F. B.
2016-12-01
The high sensitivity of the new generation of radio telescopes such as the Square Kilometre Array (SKA) will allow cosmological weak lensing measurements at radio wavelengths that are competitive with optical surveys. We present an adaptation to radio data of lensfit, a method for galaxy shape measurement originally developed and used for optical weak lensing surveys. This likelihood method uses an analytical galaxy model and makes a Bayesian marginalization of the likelihood over uninteresting parameters. It has the feature of working directly in the visibility domain, which is the natural approach to adopt with radio interferometer data, avoiding systematics introduced by the imaging process. As a proof of concept, we provide results for visibility simulations of individual galaxies with flux density S ≥ 10 μJy at the phase centre of the proposed SKA1-MID baseline configuration, adopting 12 frequency channels in the band 950-1190 MHz. Weak lensing shear measurements from a population of galaxies with realistic flux and scalelength distributions are obtained after natural gridding of the raw visibilities. Shear measurements are expected to be affected by `noise bias': we estimate the bias in the method as a function of signal-to-noise ratio (SNR). We obtain additive and multiplicative bias values that are comparable to SKA1 requirements for SNR > 18 and SNR > 30, respectively. The multiplicative bias for SNR >10 is comparable to that found in ground-based optical surveys such as CFHTLenS, and we anticipate that similar shear measurement calibration strategies to those used for optical surveys may be used to good effect in the analysis of SKA radio interferometer data.
SKA weak lensing - III. Added value of multiwavelength synergies for the mitigation of systematics
NASA Astrophysics Data System (ADS)
Camera, Stefano; Harrison, Ian; Bonaldi, Anna; Brown, Michael L.
2017-02-01
In this third paper of a series on radio weak lensing for cosmology with the Square Kilometre Array, we scrutinize synergies between cosmic shear measurements in the radio and optical/near-infrared (IR) bands for mitigating systematic effects. We focus on three main classes of systematics: (i) experimental systematic errors in the observed shear; (ii) signal contamination by intrinsic alignments and (iii) systematic effects due to an incorrect modelling of non-linear scales. First, we show that a comprehensive, multiwavelength analysis provides a self-calibration method for experimental systematic effects, only implying <50 per cent increment on the errors on cosmological parameters. We also illustrate how the cross-correlation between radio and optical/near-IR surveys alone is able to remove residual systematics with variance as large as 10-5, i.e. the same order of magnitude of the cosmological signal. This also opens the possibility of using such a cross-correlation as a means to detect unknown experimental systematics. Secondly, we demonstrate that, thanks to polarization information, radio weak lensing surveys will be able to mitigate contamination by intrinsic alignments, in a way similar but fully complementary to available self-calibration methods based on position-shear correlations. Lastly, we illustrate how radio weak lensing experiments, reaching higher redshifts than those accessible to optical surveys, will probe dark energy and the growth of cosmic structures in regimes less contaminated by non-linearities in the matter perturbations. For instance, the higher redshift bins of radio catalogues peak at z ≃ 0.8-1, whereas their optical/near-IR counterparts are limited to z ≲ 0.5-0.7. This translates into having a cosmological signal 2-5 times less contaminated by non-linear perturbations.
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.
NASA Astrophysics Data System (ADS)
Samuroff, S.; Troxel, M. A.; Bridle, S. L.; Zuntz, J.; MacCrann, N.; Krause, E.; Eifler, T.; Kirk, D.
2017-02-01
We investigate the expected cosmological constraints from a combination of cosmic shear and large-scale galaxy clustering using realistic photometric redshift distributions. Introducing a systematic bias in the lensing distributions (of 0.05 in redshift) produces a >2σ bias in the recovered matter power spectrum amplitude and dark energy equation of state for preliminary Stage III surveys. We demonstrate that cosmological error can be largely removed by marginalizing over biases in the assumed weak-lensing redshift distributions. Furthermore, the cosmological constraining power is retained despite removing much of the information on the lensing redshift biases. This finding relies upon high-quality redshift estimates for the clustering sample, but does not require spectroscopy. All galaxies in this analysis can thus be assumed to come from a single photometric survey. We show that this internal constraint on redshift biases arises from complementary degeneracy directions between cosmic shear and the combination of galaxy clustering and shear-density cross-correlations. Finally we examine a case where the assumed redshift distributions differ from the truth by more than a simple uniform bias. We find that the effectiveness of this self-calibration method will depend on the survey details and the nature of the uncertainties on the estimated redshift distributions.
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.
Escape and trapping of low-frequency gravitationally lensed rays by compact objects within plasma
NASA Astrophysics Data System (ADS)
Rogers, Adam
2017-02-01
We consider the gravitational lensing of rays emitted by a compact object (CO) within a distribution of plasma with power-law density ∝r-h. For the simplest case of a cloud of spherically symmetric cold non-magnetized plasma, the diverging effect of the plasma and the converging effect of gravitational lensing compete with one another. When h < 2, the plasma effect dominates over the vacuum Schwarzschild curvature, potentially shifting the radius of the unstable circular photon orbit outside the surface of the CO. When this occurs, we define two relatively narrow radio frequency bands in which plasma effects are particularly significant. Rays in the escape window have ω0 < ω ≤ ω+ and are free to propagate to infinity from the CO surface. To a distant observer, the visible portion of the CO surface appears to shrink as the observed frequency is reduced, and vanishes entirely at ω0, in excess of the plasma frequency at the CO surface. We define the anomalous propagation window for frequencies ω- < ω ≤ ω0. Rays emitted from the CO surface within this frequency range are dominated by optical effects from the plasma and curve back to the surface of the CO, effectively cloaking the star from distant observers. We conclude with a study of neutron star (NS) compactness ratios for a variety of nuclear matter equations of state (EoS). For h = 1, NSs generated from stiff EoS should display significant frequency dependence in the EW, and lower values of h with softer EoS can also show these effects.
NASA Astrophysics Data System (ADS)
Mediavilla, E.; Mediavilla, T.; Muñoz, J. A.; Ariza, O.; 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 -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.
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.
Correlation of CMB with large-scale structure. II. Weak lensing
Hirata, Christopher M.; Padmanabhan, Nikhil; Seljak, Uros
2008-08-15
We investigate the correlation of gravitational lensing of the cosmic microwave background (CMB) with several tracers of large-scale structure, including luminous red galaxies (LRGs), quasars, and radio sources. The lensing field is reconstructed based on the CMB maps from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite; the LRGs and quasars are observed by the Sloan Digital Sky Survey (SDSS); and the radio sources are observed in the NRAO VLA Sky Survey (NVSS). Combining all three large-scale structure samples, we find evidence for a positive cross correlation at the 2.5{sigma} level (1.8{sigma} for the SDSS samples and 2.1{sigma} for NVSS); the cross correlation amplitude is 1.06{+-}0.42 times that expected for the WMAP cosmological parameters. Our analysis extends other recent analyses in that we carefully determine bias-weighted redshift distribution of the sources, which is needed for a meaningful cosmological interpretation of the detected signal. We investigate contamination of the signal by galactic emission, extragalactic radio and infrared sources, thermal and kinetic Sunyaev-Zel'dovich effects, and the Rees-Sciama effect, and find all of them to be negligible.
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.
Visualizing the gravitational lensing and vortex and tendex lines of colliding black holes
NASA Astrophysics Data System (ADS)
Khan, Haroon; Lovelace, Geoffery; SXS Collaboration
2016-03-01
Gravitational waves (GW's) are ripples of space and time that are created when the universe unleashes its violent nature in the presence of strong gravity. Merging black holes (BH) are one of the most promising sources of GW's. In order to detect and physically study the GW's emitted by merging BH with ground based detectors such as Advanced LIGO, we must accurately predict how the waveforms look and behave. This can only be done by numerically simulating BH mergers on supercomputers, because all analytical approximations fail near the time of merger. This poster focuses on using these simulations to answer the question of ``What do merging BH look like''? I will present visualizations made using the Spectral Einstein Code (SpEC) and in particular a raytracing lensing code, developed by the SXS Lensing team, that shows how merging BH bend the light around them. I will also present visualizations of the vortex and tendex lines for a binary BH system, using SpEC. Vortex lines describe how an observer will be twisted by the BH and the tendex lines describe how much an observer would be stretched and squeezed. I am exploring how these lines change with time.
Spitzer Observations of a Gravitationally Lensed Quasar, QSO 2237+0305
NASA Astrophysics Data System (ADS)
Agol, Eric; Gogarten, Stephanie M.; Gorjian, Varoujan; Kimball, Amy
2009-06-01
The four-image gravitationally lensed quasar QSO 2237+0305 is microlensed by stars in the lens galaxy. The amplitude of microlensing variability can be used to infer the relative size of the quasar as a function of wavelength; this provides a test of quasar models. Toward this end, we present Spitzer Space Telescope Infrared Spectrograph and Infrared Array Camera (IRAC) observations of QSO 2237+0305, finding the following. (1) The infrared (IR) spectral energy distribution (SED) is similar to that of other bright radio-quiet quasars, contrary to an earlier claim. (2) A dusty torus model with a small opening angle fits the overall shape of the IR SED well, but the quantitative agreement is poor due to an offset in wavelength of the silicate feature. (3) The flux ratios of the four lensed images can be derived from the IRAC data despite being unresolved. We find that the near-IR fluxes are increasingly affected by microlensing toward shorter wavelengths. (4) The wavelength dependence of the IRAC flux ratios is consistent with the standard quasar model in which an accretion disk and a dusty torus both contribute near 1 μm in the rest frame. This is also consistent with recent IR spectropolarimetry of nearby quasars.
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.
NASA Astrophysics Data System (ADS)
Rusu, Cristian E.; Oguri, Masamune; Minowa, Yosuke; Iye, Masanori; Inada, Naohisa; Oya, Shin; Kayo, Issha; Hayano, Yutaka; Hattori, Masayuki; Saito, Yoshihiko; Ito, Meguru; Pyo, Tae-Soo; Terada, Hiroshi; Takami, Hideki; Watanabe, Makoto
2016-05-01
We present the results of an imaging observation campaign conducted with the Subaru Telescope adaptive optics system (IRCS+AO188) on 28 gravitationally lensed quasars and candidates (23 doubles, 1 quad, 1 possible triple, and 3 candidates) from the SDSS Quasar Lens Search. We develop a novel modelling technique that fits analytical and hybrid point spread functions (PSFs), while simultaneously measuring the relative astrometry, photometry, as well as the lens galaxy morphology. We account for systematics by simulating the observed systems using separately observed PSF stars. The measured relative astrometry is comparable with that typically achieved with the Hubble Space Telescope, even after marginalizing over the PSF uncertainty. We model for the first time the quasar host galaxies in five systems, without a priori knowledge of the PSF, and show that their luminosities follow the known correlation with the mass of the supermassive black hole. For each system, we obtain mass models far more accurate than those previously published from low-resolution data, and we show that in our sample of lensing galaxies the observed light profile is more elliptical than the mass, for ellipticity ≳0.25. We also identify eight doubles for which the sources of external and internal shear are more reliably separated, and should therefore be prioritized in monitoring campaigns aimed at measuring time delays in order to infer the Hubble constant.
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 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.
Constraining cosmic curvature by using age of galaxies and gravitational lenses
NASA Astrophysics Data System (ADS)
Rana, Akshay; Jain, Deepak; Mahajan, Shobhit; Mukherjee, Amitabha
2017-03-01
We use two model-independent methods to constrain the curvature of the universe. In the first method, we study the evolution of the curvature parameter (Ωk0) with redshift by using the observations of the Hubble parameter and transverse comoving distances obtained from the age of galaxies. Secondly, we also use an indirect method based on the mean image separation statistics of gravitationally lensed quasars. The basis of this methodology is that the average image separation of lensed images will show a positive, negative or zero correlation with the source redshift in a closed, open or flat universe respectively. In order to smoothen the datasets used in both the methods, we use a non-parametric method namely, Gaussian Process (GP). Finally from first method we obtain Ωk0 = 0.025±0.57 for a presumed flat universe while the cosmic curvature remains constant throughout the redshift region 0 < z < 1.37 which indicates that the universe may be homogeneous. Moreover, the combined result from both the methods suggests that the universe is marginally closed. However, a flat universe can be incorporated at 3σ level.
Thermal corrections to the Casimir energy in a general weak gravitational field
NASA Astrophysics Data System (ADS)
Nazari, Borzoo
2016-12-01
We calculate finite temperature corrections to the energy of the Casimir effect of a two conducting parallel plates in a general weak gravitational field. After solving the Klein-Gordon equation inside the apparatus, mode frequencies inside the apparatus are obtained in terms of the parameters of the weak background. Using Matsubara’s approach to quantum statistical mechanics gravity-induced thermal corrections of the energy density are obtained. Well-known weak static and stationary gravitational fields are analyzed and it is found that in the low temperature limit the energy of the system increases compared to that in the zero temperature case.
The merger history of the complex cluster Abell 1758: a combined weak lensing and spectroscopic view
NASA Astrophysics Data System (ADS)
Monteiro-Oliveira, R.; Cypriano, E. S.; Machado, R. E. G.; Lima Neto, G. B.; Ribeiro, A. L. B.; Sodré, L.; Dupke, R.
2017-04-01
We present a weak-lensing and dynamical study of the complex cluster Abell 1758 (A1758, bar{z} = 0.278) supported by hydrodynamical simulations. This cluster is composed of two main structures called A1758N and A1758S. The northern structure is composed of A1758NW and A1758NE, with lensing determined masses of 7.90_{-1.55}^{+1.89} × 1014 M⊙ and 5.49_{-1.33}^{+1.67} × 1014 M⊙, respectively. They show a remarkable feature: while in A1758NW, there is a spatial agreement among weak-lensing mass distribution, intracluster medium and its brightest cluster galaxy (BCG), in A1758NE, the X-ray peak is located 96_{-15}^{+14} arcsec away from the mass peak and BCG positions. Given the detachment between gas and mass, we could use the local surface mass density to estimate an upper limit for the dark matter self-interaction cross-section: σ/m < 5.83 cm2 g-1. Combining our velocity data with hydrodynamical simulations, we have shown that A1758 NW and NE had their closest approach 0.27 Gyr ago and their merger axis is 21° ± 12° from the plane of the sky. In the A1758S system, we have measured a total mass of 4.96_{-1.19}^{+1.08} × 10^{14} M⊙ and, using radial velocity data, we found that the main merger axis is located at 70° ± 4° from the plane of the sky, therefore closest to the line of sight.
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.
Cosmic discordance: are Planck CMB and CFHTLenS weak lensing measurements out of tune?
MacCrann, Niall; Zuntz, Joe; Bridle, Sarah; Jain, Bhuvnesh; Becker, M. R.
2015-06-17
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 percent 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.
Cosmic discordance: are Planck CMB and CFHTLenS weak lensing measurements out of tune?
MacCrann, Niall; Zuntz, Joe; Bridle, Sarah; ...
2015-06-17
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 percent confidence contours of CFHTLenS and Planck+WMAP only just touch, butmore » 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.« less
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.
2016-05-01
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 colours of the galaxies: photometric data from the COSMic evOlution Survey are used to train the colour 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 × 1015 M⊙] ranges, mimicking medium-deep multicolour imaging observations [e.g. Subaru, Large Binocular Telescope]. 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 multiband (BVRi) data are publicly available.
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
NASA Astrophysics Data System (ADS)
Egami, E.
2011-09-01
On the extragalactic side, one of the most remarkable results coming out of Herschel is the discovery of extremely bright (>100 mJy in the SPIRE bands) gravitationally lensed galaxies. The great sensitivity and mapping speed of SPIRE have enabled us to find these rare extraordinary objects. What is truly exciting about these bright lensed galaxies is that they enable a variety of detailed multi-wavelength follow-up observations, shedding new light on the physical properties of these high-redshift sources. In this regard, our OT1 program, "SPIRE Snapshot Survey of Massive Galaxy Clusters" turned out to be a great success. After imaging ~50 galaxies out of 279 in the program, we have already found two spectacularly bright lensed galaxies, one of which is at a redshift of 4.69. This type of cluster-lensed sources are not only bright but also spatially stretched over a large scale, so ALMA (or NOEMA in the north) is likely to be able to study them at the level of individual GMCs. Such studies will open up a new frontier in the study of high-redshift galaxies. Here, we propose to extend this highly efficient and effective survey of gravitationally lensed galaxies to another 353 clusters carefully chosen from the SPT and CODEX cluster samples. These samples contain newly discovered high-redshift (z>0.3) massive (>3-4e14 Msun) clusters, which can be used as powerful gravitational lenses to magnify sources at high redshift. With the OT1 and OT2 surveys together, we expect to find ~20 highly magnified SPIRE sources with exceptional brightnesses (assuming a discovery rate of ~1/30). Such a unique sample of extraordinary objects will enable a variety of follow-up sciences, and will therefore remain as a great legacy of the Herschel mission for years to come.
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.
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.
Impact of spurious shear on cosmological parameter estimates from weak lensing observables
Petri, Andrea; May, Morgan; Haiman, Zoltán; ...
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
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 (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.
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.
Weak lensing study of 16 DAFT/FADA clusters: Substructures and filaments
NASA Astrophysics Data System (ADS)
Martinet, Nicolas; Clowe, Douglas; Durret, Florence; Adami, Christophe; Acebrón, Ana; Hernandez-García, Lorena; Márquez, Isabel; Guennou, Loic; Sarron, Florian; Ulmer, Mel
2016-05-01
While our current cosmological model places galaxy clusters at the nodes of a filament network (the cosmic web), we still struggle to detect these filaments at high redshifts. We perform a weak lensing study for a sample of 16 massive, medium-high redshift (0.4
A Weak Lensing View of the Downsizing of Star-forming Galaxies
NASA Astrophysics Data System (ADS)
Utsumi, Yousuke; Geller, Margaret J.; Dell'Antonio, Ian P.; Kamata, Yukiko; Kawanomoto, Satoshi; Koike, Michitaro; Komiyama, Yutaka; Koshida, Shintaro; Mineo, Sogo; Miyazaki, Satoshi; Sakurai, Junya; Tait, Philip J.; Terai, Tsuyoshi; Tomono, Daigo; Usuda, Tomonori; Yamada, Yoshihiko; Zahid, Harus J.
2016-12-01
We describe a weak lensing view of the downsizing of star-forming galaxies based on cross-correlating a weak lensing (κ) map with a predicted map constructed from a redshift survey. Moderately deep and high-resolution images with Subaru/Hyper Suprime-Cam covering the 4 {\\deg }2 DLS F2 field provide a κ map with 1 arcmin resolution. A dense complete redshift survey of the F2 field including 12,705 galaxies with R≤slant 20.6 is the basis for construction of the predicted map. The zero-lag cross-correlation between the κ and predicted maps is significant at the 30σ level. The width of the cross-correlation peak is comparable to the angular scale of rich clusters at z˜ 0.3, the median depth of the redshift survey. Slices of the predicted map in δ z=0.05 redshift bins enable exploration of the impact of structure as a function of redshift. The zero-lag normalized cross-correlation has significant local maxima at redshifts coinciding with known massive X-ray clusters. Even in slices where there are no known massive clusters, there is a significant signal in the cross-correlation originating from lower mass groups that trace the large-scale of the universe. Spectroscopic {D}n4000 measurements enable division of the sample into star-forming and quiescent populations. In regions surrounding massive clusters of galaxies, the significance of the cross-correlation with maps based on star-forming galaxies increases with redshift from 5σ at z = 0.3 to 7σ at z=0.5; the fractional contribution of the star-forming population to the total cross-correlation signal also increases with redshift. This weak lensing view is consistent with the downsizing picture of galaxy evolution established from other independent studies. Based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.
Schlaufman, K
2004-10-11
Atmospheric turbulence can mimic the effects of weak lensing in astronomical images, so it is necessary to understand to what degree turbulence affects weak lensing measurements. In particular, we studied the ellipticity induced upon the point-spread functions (PSFs) of a grid of simulated stars separated by distances (d {approx} 1{prime}) that will be characteristic of Large Synoptic Survey Telescope (LSST) images. We observe that atmospherically induced ellipticity changes on small scales (d < 0.5{prime}) and use linear interpolation between stars separated by d = 0.5{prime} to determine the induced ellipticity everywhere in the field-of-view.
FLITECAM H-alpha Spectroscopy of the 1 Jy Gravitationally Lensed Galaxy at z=3
NASA Astrophysics Data System (ADS)
Egami, Eiichi
An exceptionally bright z=3.005