Three decades of gravitational lenses

The programme can be found here. The list of abstracts and programme are also available as combined PDF file.

Below you find the abstracts and links to downloadable files.
Alternatively you may also go directly to the directory with downloadable files or use wget to fetch many at once from there.


Abstracts

Timo Anguita: “COSMOS 5921+0638: a new strong gravitational lensing system
contributed talk
Recently, about 70 new strong lens candidates have been discovered in the COSMOS field. We present follow-up observations and an in-depth study of one of these systems: COSMOS 5921+0638, which shows quadruply lensed images and a perfect Einstein ring (with a 0.71" radius). Using the available (COSMOS survey + follow-up) ground and space-based observations, we analyze the nature of the system, including its photometric, spectroscopic and physical properties. We have also performed an environmental study and both analytical and grid-based mass modeling. Our analysis shows that the source is a high redshift galaxy hosting a low luminosity AGN and the lens is an elliptical galaxy at a redshift zl=0.55. Through the lens modeling, we have additionally estimated the mass and mass-to-light ratio of the lensing galaxy. Finally, we discuss the cause of observed flux anomalies between the lensed AGN images.
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original talk slides (pdf): 1.7 MB (last change 22 Apr 2009)

Nick Bate: “Constraining accretion discs in anomalous lensed quasars
poster
Observations of gravitational microlensing offer a unique probe of quasar emission region structure on sub-arcsecond scales. In this talk I will present the results of a new technique to constrain quasar accretion disc size as a function of wavelength, using single-epoch multi-band imaging of lensed quasars displaying a flux ratio anomaly. We have analysed new and archival optical and near-IR data of MG 0414+0534 and SDSS 0924+0219, obtained with the 6.5-metre Magellan telescopes and the Hubble Space Telescope. In MG 0414+0534, the continuum emission region is found to be statistically consistent with alpha-prescription thin accretion disc models (including the standard Shakura-Sunyaev disc). In SDSS 0924+0219, however, these models are ruled out with a high degree of confidence.
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original poster (pdf): 596.2 kB (last change 11 May 2009)

Jean-Philippe Beaulieu: “Microlensing planet hunt with EUCLID
contributed talk
Microlensing planet hunt is a unique method to probe efficiently for frozen Super Earth orbiting the most common stars of our galaxy. It is nicely complementing the parameter space probed by very high accuracy radial velocity measurements and future space based detections of low mass transiting planets. In the near-term (over the next 5 years) we advocate a strategy of automated follow-up with existing and upgraded telescopes which will significantly increase the current planet detection efficiency. In the medium term, the next step is an international network of wide-field 2m class telescopes to discover Earth-mass and free-floating exo-planets such as the KMT developped in Korea (PI Han). In the longer term, we strongly advocate a space microlensing telescope which, when combined with Kepler, will provide a complete census of planets down to Earth mass at almost all separations. Such a survey could be undertaken as a science programme on Euclid, a dark energy probe with a wide-field imager which has been proposed to ESA's Cosmic Vision Programme. I will put a special emphasis on the synergy between Cosmic shear and microlensing technical requirements.

Sarah Bridle: “A halo model for intrinsic alignments
contributed talk
Correlations between intrinsic ellipticities of galaxies and between galaxy ellipticities and the surrounding dark matter are potentially dominant systematic errors when constraining dark energy properties from weak gravitational lensing surveys. In the absence of perfectly known galaxy redshifts some modeling of the galaxy intrinsic alignments is required to extract the lensing signal to sufficient accuracy. We present a new model based on the placement of galaxies into dark matter halos. We construct a constrained parameterization of the intrinsic alignment correlations that can be used when marginalizing over this systematic error to obtain dark energy constraints.

Sarah Bridle: “GREAT08
poster (not presented)
We present the GREAT08 Challenge to computer scientists. (The GREAT08 Challenge deadline is 30th April.)

Sarah Bryan: “Luminous Satellite Galaxies in Gravitational Lenses
contributed talk
Substructures, expected in cold dark matter haloes, have been proposed to explain the anomalous fux ratios in gravitational lenses. About 50 per cent of lenses in the Cosmic Lens All-Sky Survey (CLASS) appear to have luminous satellites within about 5 h-1 kpc of the main lensing galaxies, which are usually at redshift z ˜ 0.2-1. We have used the Millennium Simulation combined with galaxy catalogues from semi-analytical techniques to study the predicted frequency of such satellites in simulated haloes. The fraction of haloes that host bright satellites within the (projected) central regions is similar for red and blue hosts and is found to increase as a function of host halo mass and redshift. Specifically, at z = 1, about 11 per cent of galaxy-sized haloes (with masses between 1012 and 1013 h-1 solar masses) host bright satellite galaxies within a projected radius of 5 h-1 kpc. This fraction increases to about 17 per cent (25 per cent) if we consider bright (all) satellites of only group-sized haloes (with masses between 1013 and 1014 h-1 solar masses). These results are lower than the fraction (˜ 50 per cent) of CLASS lensing galaxies observed to host luminous satellites. At z=0, only ˜3 per cent of galaxy-sized haloes host bright satellite galaxies. The fraction rises to ˜6 per cent (10 per cent) if we consider bright (all) satellites of only group-sized haloes at z=0. However, most of the satellites found in the inner regions are 'orphan' galaxies where the dark matter haloes have been completely stripped. Thus, the results crucially depend on the true survival rate of these 'orphan' galaxies. We have also considered the effects of numerical resolution and different cosmologies on our results.

Bob Carswell: “Gravitational lensing - the first discoveries
invited review talk
The theoretical developments and events leading up to the accidental discovery and announcement of the first known lensed quasar, 0957+561, are described. There followed an explosion in research in the area, both observationally and theoretically. More lensed quasars were found quite quickly, and lensed galaxies found as apparent giant arcs. Lensing in its various forms - strong, weak and micro - has since become a significant tool in astronomy.
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original talk slides (ppt): 4.0 MB (last change 30 Apr 2009)
original talk slides (pdf): 3.2 MB (last change 14 May 2009)

Rajan Chhetri: “Searching for Gravitational Lenses in the Southern Hemisphere - an update
poster
The Australia Telescope 20 GHz (AT20G) Survey provided us with the opportunity to search for gravitational lenses in the southern hemisphere at the high frequency of 20 GHz. The AT20G is a blind survey of all declinations of the southern hemisphere with sensitivity level of 50 mJy. Being a complete survey, any identification of gravitational lenses using this survey will strengthen the constraining of cosmological parameters through lensing statistics. I will provide an overview and an update on the high resolution follow up of candidates using the Australia Telescope Compact Array.
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original poster (pdf): 367.0 kB (last change 27 May 2009)

Oliver Czoske: “Integral-Field Spectroscopy of SLACS Lenses
contributed talk
Gravitational lensing has become an important method for deriving detailed information on the mass distribution in galaxies, in particular in combination with other types of observation, like galaxy kinematics. In an ESO Large Program, we have obtained integral-field spectroscopy for early-type lens galaxies from the SLACS sample of gravitational lens systems. Here, we present the kinematic fields of the full sample of 17 systems. A fully self-consistent analysis of galaxy structure, simultaneously modelling both the gravitational lens configuration as well as the kinematic maps, is in progress. We present our results on the six systems that have been fully analysed so far.
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original talk slides (pdf): 1.8 MB (last change 22 Apr 2009)

Matt Darnley: “The Angstrom Project: Status Update
poster
The Angstrom Project in undertaking an optical survey of stellar micro lensing events across the bulge region of the Andromeda Galaxy (M31) using a distributed network of 2m class telescopes. The Angstrom Project Alert System (APAS) has been developed to identify candidate micro lensing and transient events in real-time, using data from the fully robotic Liverpool and Faulkes North telescopes. Here we briefly describe the Angstrom data reduction pipeline and the APAS. We present a few example light curves obtained during the APAS commissioning phase that clearly demonstrate its real-time capability to identify micro lensing candidates as well as other transient sources.
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original poster (pdf): 620.8 kB (last change 4 May 2009)

Jörg Dietrich: “Weak lensing observation of potentially X-ray underluminous galaxy
contributed talk
Optically selected clusters of galaxies display a relation between their optical mass estimates and their X-ray luminosities Lx with a large scatter. A substantial fraction of optically selected clusters have Lx estimates or upper limits significantly below the values expected from the Lx-mass relation established for X-ray selected clusters, i.e., these clusters are X-ray underluminous for their mass. Here we aim to confirm or falsify the X-ray underluminous nature of two clusters, Abell 315 and Abell 1456, with weak gravitational lensing as a third and independent measure of the clusters' masses. After accounting for projections of large-scale structure and halo triaxiality we find that A 315 is significantly X-ray underluminous for its mass. We re-evaluate earlier kinematic and X-ray analyses of these two clusters and discuss the nature of the X-ray underluminous cluster A315 and why A1456 was probably erroneously identified as X-ray underluminous. Our results on A315 give further support to the observation that the Lx-mass relation of optically selected clusters has a large asymmetric scatter extending to low X-ray luminosities.
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original talk slides (pdf): 2.9 MB (last change 22 Apr 2009)

Andrew Gould: “Microlensing: Planets, Dark Stars, Stellar Magnifying Glasses
invited review talk
Microlensing began as a probe of dark-matter “lenses”, but has now expanded to become a generalized technique to study both lenses and sources. Microlensing has so far detected 14 planets, and will become the most powerful planet-discovery method, with the broadest sensitivity of any method as functions of planet mass, star mass, planet-star separation, and Galactic environment. It is the best method to study “dark stars” like black holes, neutron stars, and old brown dwarfs. It is also being used as a powerful “magnifying glass” to obtain spectra of otherwise unobservable sources and to study stellar surfaces on nano-arcsecond scales. I review microlensing's 2 decades of successes and show how 100-fold improvements are possible in the near future.
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original talk slides (pdf): 3.8 MB (last change 16 Apr 2009)

Emma Grocutt: “Optimising Tomographic Weak Lensing Analysis for the CFHTLS
poster
Weak gravitational lensing allows us to measure the dark matter and dark energy components of the Universe, but observations are currently contaminated by other effects which mimic the appearance of lensing. Most notably the observed lensing signal contains contributions from “intrinsic galaxy alignments” due to galaxy formation mechanisms and “shear-shape correlations” between galaxies at different redshifts. Tomographic information of the weak lensing signal in different redshift bins enables us to extract these systematic effects and improve cosmological parameter estimates. In this poster we present the results of our current work that uses 3D ray-tracing simulations to optimise our joint lensing and systematics analysis. This work is in preparation for the tomographic lensing analysis of the now-complete 172 square degree CFHT Legacy Survey.
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original poster (pdf): 2.2 MB (last change 29 Apr 2009)

Victoria Hamilton-Morris: “LoCuSS: Weak Lensing Analysis of 21 Galaxy Clusters at z=0.15-0.3
contributed talk
The Local Cluster Substructure Survey (LoCuSS) is a multi-wavelength survey of 100 X-ray luminous galaxy clusters at 0.15<z<0.3, spanning X-ray to radio wavelengths. One of the main science goals is to measure the substructure of the Dark Matter distribution within clusters and to correlate cluster substructure with residuals on cluster mass-observable scaling relations. I will present a detailed structural analysis of 21 clusters using our HST/ACS SNAPSHOT data. Substructures found in the “non-parametric” lensing mass maps are compared with K-band luminosity maps, and Chandra X-ray flux maps. These three independent probes are in close agreement, including both structures detected within the ACS fields of view, and (in a sub-set of clusters) structures located outside the observed ACS fields. In contrast to all previous structural analyses of cluster samples that we are aware of, we then use Bayesian methods to obtain statistically robust conclusions on the complexity of the cluster mass distributions. Specifically, the new MCMC capability in Lenstool (Jullo et al., 2007) is used to calculate the bayesian evidence as a function of model complexity. These calculations form the basis for a new determination of the distribution of cluster substructure fractions that is compared with theoretical predictions, following Smith & Taylor (2008).
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original talk slides (pdf): 2.2 MB (last change 23 Apr 2009)

Henk Hoekstra: “Weak lensing studies of galaxy clusters
contributed talk
Weak gravitational lensing provides a unique way to study the mass distribution in clusters of galaxies without having to make assumptions about their dynamical state. Comparison of the results with other proxies for the mass can provide important insights into the physical properties of these important systems. Not only provides this a key piece of information for the use of clusters as probes of cosmology, it also provides ways to learn more about the physical processes that determine their observable properties. I will present results from the Canadian Cluster Comparison Project, which is one of the largest surveys of clusters at intermediate redshifts.
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original talk slides (pdf): 8.3 MB (last change 22 May 2009)

Neal Jackson: “Gravitational lensing: surveys and studies with new instruments
contributed talk
New instruments and surveys with greatly increased sensitivity at many wavelength ranges will shortly allow the detection and detailed study of many gravitational lenses. I describe programmes including a large e-MERLIN legacy survey to probe galaxy potentials at high redshift, and discovery of new lenses using existing surveys such as UKIDSS, and new instruments.
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original talk slides (ppt): 1.2 MB (last change 7 Apr 2009)
original talk slides (pdf): 1.2 MB (last change 29 Apr 2009)

Jean-Paul Kneib: “Cluster Lensing
invited review talk
I will review the recent advances in clusters lensing, covering: strong and weak lensing mass modeling, comparison of cluster lensing mass to X-ray properties, cosmological constraints and the use of cluster as cosmic telescope.
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original talk slides (ppt): 9.3 MB (last change 4 May 2009)
original talk slides (pdf): 4.8 MB (last change 15 May 2009)

Leon Koopmans: “Strong gravitational lensing by galaxies
invited review talk
Strong gravitational lensing has become a standard tool during the last three decades to study the structure, formation and evolution of galaxies. I will review the current status field of strong gravitational lensing by galaxies and its most important applications.
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original talk slides (pdf): 3.6 MB (last change 15 May 2009)

Ekaterina Koptelova, Victor Oknyanskij: “Optical monitoring and time delay determination in the gravitationally lensed quasar UM673
poster
We present the results of a monitoring campaign of the lensed quasar UM673 with the 1.5-m telescope of the Maidanak Observatory and with the 1.3-m SMARTS telescope during the 2003-2008 observational period. The detected brightness variations in the A and B quasar components allow us to estimate the time delay between brightness variations of quasar components. From cross-correlation analysis we find that the brightness variations in component B follow the brightness variations in component A by about 145 days. We also explore the possibility of measuring the wavelength-dependent time delay between the brightness variations in the V and R bands. We find that the brightness variation in the R band may follow the brightness variation in the V band by about 13 days. We show that combination of the multiband data corrected for the wavelength-dependent time delay can help to improve the time delay analysis of the quasar A and B light curves.
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original poster (ppt): 396.5 kB (last change 17 Apr 2009)
original poster (pdf): 108.9 kB (last change 17 Apr 2009)

Dominik Leier: “Stellar Population Synthesis for Gravitational Lenses
poster
Comparing baryonic mass estimates from Stellar Population Synthesis and total mass measurements via surface mass density reconstruction for lens galaxies opens a window to probe the dark matter content of early-type galaxies. With the photometric data for as many band passes as possible one can assemble pixel by pixel a generic galaxy with the same properties as the observed one in consideration of the most likely distribution of colours among the stars, assuming an initial mass function, a metallicity distribution and special chemical abundances for the lens galaxy to be synthesized. The pixel map out of the synthesis in combination with the reconstructed pixellated density mass map reveals a detailed view on the mass-to-light distribution within early-type galaxies. For a future analysis a sample of 20 lens galaxies from the CfA Arizona Space Telescope LEnsing Survey (CASTLES) can be used to study the interdependency between dark and luminous matter, such as which radius the dark halo becomes dominant over the stellar mass and how sharp this transition is. In the following we present first results for the lens B2045+265.
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original poster (pdf): 864.5 kB (last change 28 May 2009)

Shude Mao: “Three decades of gravitational lenses
summary
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original talk slides (ppt): 91.5 kB (last change 15 May 2009)
original talk slides (pdf): 51.3 kB (last change 15 May 2009)

Richard Massey: “Nine decades of gravitational lenses
contributed talk
The first observation of gravitational lensing was made in May 1919, to prove Einstein's theory of general relativity. Sir Arthur Eddington and the Royal Astronomical Society launched an historic expedition to image a total solar eclipse from the equatorial African island of Principe. The observed deflection of light from stars in the Hyades cluster behind the sun, consistent with GR, was one of the most important scientific results of the 20th century. I will discuss the history behind the expedition, and some of the adventures Eddington had en route. I will then describe an International Year of Astronomy expedition back to Principe, to celebrate the 90th anniversary of the original solar eclipse. More information is available from http://www.1919eclipse.org/.
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original talk slides (pptx): 10.5 MB (last change 26 Apr 2009)
original talk slides (slightly crippled pdf version): 14.1 MB (last change 18 May 2009)

John McKean: “First detection of water in the distant Universe
contributed talk
Astrophysical water masers (the microwave equivalent of a laser; rest-frame 22.23508 GHz) are found in clouds of dense gas that surround the super-massive black hole at the centre of most galaxies. Being within a few parsecs of the central engine, water masers give valuable information about the mass of the black hole and jet-outflows, and can even be used to determine a very accurate distance to the AGN host galaxy. However, water masers are quite rare locally (z < 0.06), and searches to higher redshifts are difficult due to the limited sensitivity of current radio telescopes. I will present the results of a survey for powerful water masers from 6 gravitationally lensed quasars with the Effelesberg radio telescope and the EVLA. Using the magnification provided by the foreground gravitational lens, water emission has been found in one quasar at redshift 2.64, a time when the Universe was only 1/5 the age it is today. The quasar, MG 0414+0534, is by far the most distant object water has been found in and the detection implies that water masers may be much more abundant in the past than first thought. Furthermore, our detection demonstrates the detectability of distant (unlensed) water masers with the next generation of radio arrays, for example, the SKA.
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original talk slides (pdf): 1.5 MB (last change 22 Apr 2009)

Danka Paraficz: “Results of optical monitoring of 5 SDSS double QSOs with the Nordic
poster
We present optical R-band light curves of five SDSS double QSOs obtained from monitoring at the Nordic Optical Telescope (NOT) between September 2005 and September 2007. We also present analytical and pixelated modeling of the observed systems. For SDSS J1206+4332, we measured the time delay to be 116 days, which, for a Singular Isothermal Ellipsoid model, corresponds to a Hubble constant of 73 km/s/Mpc. Simultaneous pixeleted modeling of five other systems for which a time delay has now been previously measured at the NOT leads to 61.5 km/s/Mpc. Finally, by comparing lightcurves of the two images of each system, suitably shifted by the predicted or observed time-delays, we found no evidence for microlensing variability over the course of the monitoring period.
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original poster (pdf): 3.1 MB (last change 30 Apr 2009)

Matthew Penny: “Orbital motion in gravitational microlenses
poster
A standard planetary microlensing lightcurve allows just two parameters of the lensing system to be measured: the mass ratio of the planet to its host, and the projected separation of the components in units of the Einstein radius. However, other exotic effects can provide more information about the lensing system. Orbital motion in the lens is one such effect, which if detected, can allow the system mass and planetary orbit to be determined. We attempt to quantify the probability of detecting lens orbital motion in binary microlensing events using Monte Carlo simulations. We also define an easily calculable quantity, the orbital measure, to describe the probability and inform the computationally expensive modeling process.
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original poster (pdf): 2.2 MB (last change 29 Apr 2009)
original poster, higher resolution figures (pdf): 8.5 MB (last change 18 Apr 2009)

Anooshiravan Roozrokh: “Reducing Data with THELI Pipeline
poster (not presented)
In astronomy, raw images from CCD detectors are not immediately usable for scientific exploitation but are instead contaminated by several instrumental effects. Generally speaking, data reduction is the transformation of raw data into a more applicable form. Thus, this involves: (i) Removal of instrumental signatures, like dark current and field curvature. (ii) Masking of unwanted signals, like cosmic rays, stellar halos and satellite tracks. (iii) Photometric and Astrometric Calibration. (iv) Coaddition of individual frames. In this poster we describe one of the methods available to automatically reduce large amount of data. We also present our own work with Abell 226 Optical Images.

Prasenjit Saha: “More than three decades of lensing theory
invited review talk
Gravitational lenses lived in theorists' dreams long before they were actually discovered in the sky. While many have contributed to lensing theory as we have it today, the insights of Sjur Refsdal from 1964 onwards are especially prophetic. This talk will review the development of theory so far and speculate about where it might go in the future, with special attention to Refsdal's work.
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original talk slides (pdf): 2.9 MB (last change 14 May 2009)
animation JAVA file (jar): 37.5 kB (last change 14 May 2009)

Satoru Sakai: “The effect of Gravitational Distortion of Spacetime on Pulsar Timing
poster
The aim of this research is to determine the impact of gravitational lensing on pulsar timing, and its implications for the detection of gravitational waves. Gravitational lensing occurs when a massive body passes close to the line-of-sight between the Earth and a source. From General Relativity, this causes space-time distortions which result in an extra path length that the light must travel, and subsequently a delay in the time of arrival. This research will look at the rate of change of (gravitational) Shapiro time delay

Mauro Sereno: “Lensing by the supermassive black hole in the Galactic centre
poster (not presented)
The supermassive black hole in the Galactic center offers an unique laboratory for testing general relativity in new regimes. Here, we discuss observational prospects and technological requirements to observe gravitational lensing events toward it, either multiple images of background sources or microlensing light curves. Successful observations would provide invaluable information on the properties of the black hole and the matter distribution in the Galactic center. We put particular emphasis on the effects of lens spin and relative motion.

Mauro Sereno: “Multi-wavelength analyses of strong lensing clusters: AC 114
poster (not presented)
Strong lensing analyses can provide detailed mass maps of the inner regions even in dynamically active galaxy clusters. We discuss a parametric method for strong lensing investigations in which the mass model accounts for: i) cluster-sized dark matter halos; ii) galaxies (whose stellar mass can be obtained from optical analyses) and iii) the main baryonic component, the intracluster medium, modelled according to X-ray observations. This gives an unbiased look at each matter component and allows a study of the dynamical status of the cluster. The method has been applied to AC 114, an irregular X-ray cluster whose dark matter distribution turns out to be in remarkable agreement with predictions form numerical simulations.

Dominique Sluse: “Microlensing as a tool to probe the quasar structure
contributed talk
Quasar micro-lensing is a promising tool to study the size and geometry of the inner regions of quasars. Indeed, the Einstein radii of stars and/or substructures in lensing galaxies of multiply imaged quasars have projected angular sizes of typically 10-2 pc. Consequently, both the continuum emission and the broad line emitting region of lensed quasars can be micro-lensed. Observationally, the most efficient micro-lensing studies of lensed quasars need spectroscopic data obtained on a regular basis. We will present the spectro-photometric monitoring of the Einstein Cross = Q2237+0305 carried out at the VLT and show the micro-lensed induced deformation of the quasar spectrum. We will explain how the comparison of numerical simulations with chromatic variations observed in the UV/optical continuum allow to constrain the energy profile of the quasar's accretion disk. We will finally briefly discuss the effect of micro-lensing on the broad emission lines and the implication these data have on the size of the regions emitting these lines.
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original talk slides (pdf): 20.4 MB (last change 30 Apr 2009)

Graham P. Smith: “LoCuSS: New Cluster Weak-lensing Results from Subaru
contributed talk
The Local Cluster Substructure Survey (LoCuSS) is a multi-wavelength survey of ˜100 massive galaxy clusters at z˜0.2 with science goals spanning the calibration of cosmological mass-observable scaling relations through to the evolution of galaxies in clusters. In this talk I will present new results, concentrating on the weak lensing analysis of Subaru/Suprime-Cam observations of the first batch of 30 clusters. For example, we fit NFW universal density profiles to the weak shear signals, and construct a concentration-mass relation. This empirical relation has a normalization ˜2x higher than is predicted from numerical simulations; the best-fit slope of the relation is alpha=-0.4±0.2, i.e. we detect the predicted anti-correlation of mass and concentration at 2 sigma significance. When the clusters are stacked we obtain a clear detection of curvature in the mean shear profile and thus reject singular isothermal sphere mass models at 6 and 14 sigma in low and high mass bins respectively. This sample of 30 clusters currently forms the basis for both our scaling relation and galaxy evolution studies. I will therefore also present (i) preliminary mass-Ysz scaling relation results obtained in partnership with the SZA collaboration, and (ii) early results from our panoramic Spitzer and GALEX observations of the cluster galaxy populations. Time permitting I'll close with a summary of future plans, including expansion of our Subaru sample towards the goal of 100 clusters.

Andy Taylor: “Weak Gravitational Lensing: Recent & Future Progress
invited review talk
Weak Gravitational Lensing is in a state of rapid development. In this talk I will discuss the basics of WL, review the status of current surveys for 2-D and 3-D Lensing and discuss the implications for Dark Matter and Cosmology. I will look ahead to the next-generation of surveys and beyond, and the possibility of probing Dark Energy and non-Einstein gravity and the potential problems which must be faced to get there.

Ismael Tereno: “Constraints on neutrino masses from CFHTLS cosmic shear
poster
We use weak lensing measurements from the latest release of the Canada-France-Hawaii Telescope Legacy Survey to probe suppression of cosmic shear correlations and consequently constrain neutrino masses. We obtain broad constraints which are greatly improved when we combine them with WMAP-5 cosmic microwave background anisotropy data, baryonic acoustic oscillations from SDSS and 2dFGRS and supernovae data from SNLS and Gold-set. The combined constraints on the sum of neutrino masses at 95\% confidence level are an upper bound of 0.54 eV and a lower bound of 0.03 eV. The preference for massive neutrinos vanishes when we include shear-measurement systematics in the analysis.
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original poster (pdf): 388.5 kB (last change 11 May 2009)

Aurora Ullán: “The first in the third decade: jet-accretion disc connection
poster
We present a current perspective on the first gravitational lens system, which was discovered in 1979. The use of modern instrumentation and sophisticated photometric techniques is allowing us to obtain accurate and reliable optical brightness records of the quasar components, and thus, to significantly improve our knowledge of the nature of the observed fluctuations. In January 2005 we started a long-term programme in the g and r Sloan bands with the 2.0m Liverpool robotic telescope (LRT). The first monitoring period (from January 2005 to July 2007) led to two important results: (i) there is no evidence of extrinsic variability caused by microlensing or another physical mechanism, and (ii) most observed variations (timescales of months) are very probably due to reverberation within a gas disc around a supermassive black hole. To obtain a global perspective of the quasar variability at red wavelengths over the third decade, we also used 515 R-band frames taken at IAC80 telescope between 1999 and 2005, as well as all available LRT images in the r-band (310 frames between 2005 and March 2009). A preliminary comparison between the light curves of the components confirms the intrinsic variability scenario, and rules out the presence of significant extrinsic fluctuations and the need for exotic ingredients.
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original poster (ppt): 944.0 kB (last change 4 May 2009)
original poster (pdf): 1.4 MB (last change 15 May 2009)

Lisa Voigt: “Fundamental limits to galaxy shear estimation
poster (not presented)
Gravitational lensing promises to provide the most powerful tool in astronomy for constraining the nature of dark energy. The images of distant galaxies are distorted by intervening mass; measuring these distortions enables us to map out the distribution of large-scale structure in the universe and thus constrain cosmological parameters. Accurate measurement of galaxy shear is crucial. In particular biases must be reduced below the small statistical uncertainties that will be obtained in future galaxy surveys. I will show there is a fundamental limit to the accuracy achievable by model-fitting techniques adopting elliptical isophotes and discuss the impact of these results on shape measurement methods.

Filomena Volino: “VLA observations of the brightest Lyman Break Galaxy
poster
The z=2.73 lensed source J002240.91+143110.4 is the brightest Lyman Break Galaxy doscovered so far. Thanks to the magnification provided by gravitational lensing we were able to carry out a detailed study of the radio properties of this source. In my poster I will present results from VLA observations.
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original poster (pdf): 238.5 kB (last change 29 Apr 2009)

Joachim Wambsganss: “Extragalactic Microlensing: Quasars, Caustics \& Dark Matter
invited review talk
Extragalactic microlensing was predicted right after the discovery of the first gravitationally lensed double quasar Q0957+561 by Sjur Refsdal and Kyongae Chang, exactly three decades ago. First detected in 1989, microlensing of quasars has developed into a versatile tool in extragalactic research. Its resolution power down to the microarcsecond scale makes microlensing very useful for studying the size and luminosity profile of accretion disks in quasars. The photometric signature of microlensing allows to determine properties of compact objects and smoothly distributed dark matter along the line-of-sight. This talk reviews the current achievements of extragalactic microlensing as well as it future potential.
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original talk slides (pdf): 6.7 MB (last change 30 Apr 2009)

Olaf Wucknitz: “The easy route to moving lenses
poster
Even though they are currently not of overwhelming astrophysical relevance, the effects of motion of a gravitational lens have been discussed in a number of publications. In spite of this, there still seems to be some confusion even about the first-order effects of radial motion of a lens. This contribution tries to clarify the situation by explaining that the scenarios discussed by different authors are in fact not equivalent, so that conflicting results have to be expected. The effects of purely radial motion can be described most easily via their influence on the angular size distances.
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original poster (pdf): 255.8 kB (last change 16 Apr 2009)

Olaf Wucknitz: “The magnification theorem
contributed talk
In this presentation I discuss the magnification theorem according to which any realistic mass distribution will always produce at least one image with a magnification above unity. To avoid the paradox that total flux would not be conserved, this theorem can only be valid if the un-lensed situation used for comparison is defined in such a way that the area over which the flux is distributed is different from the lensed situation. In an alternative scenario with unchanged total area, the magnification theorem does not hold anymore. This picture has the advantage that the magnification can be derived directly from the deflection angle, which is not strictly true in the standard scenario. As an interesting implication, the Poisson equation has to be modified to account for the fact that field lines cannot escape the compact celestial sphere.
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original talk slides (pdf): 1.8 MB (last change 9 Apr 2009)
printable version, 8 slides per page (pdf): 1.0 MB (last change 19 Apr 2009)

Dandan Xu: “Effects of Substructure on Gravitational Lensing: Results from Aquarius Simulations
contributed talk
In the hierarchical structure formation model with cold dark matter(CDM), large structures form via merger and accretion of smaller structures; the dense cores of smaller structures often survive as subhaloes (substructure) within the main halo. High resolution numerical simulations predict orders of magnitude more subhaloes in a Milky-Way type halo than the observed luminous satellite population. Gravitational lensing is a way to probe the abundance of these subhaloes. We use six galaxy-sized haloes from the collisionless Aquarius simulations performed in the concordance LCDM universe to study the effects of substructure on lensing. Subhaloes with masses larger than 105 h-1M(sun) are well resolved, at least two orders of magnitudes lower than those used in previous lensing studies. We incorporate a baryonic component modelled as a Hernquist profile and account for the response of the dark matter via adiabatic contraction. We focus on the “anomalous” flux ratio problem, in particular the violation of the cusp-caustic relation due to substructures. Detailed result will be reported.
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original talk slides (pdf): 2.7 MB (last change 21 Apr 2009)



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This document last modified Fri May 29 11:18:42 CEST 2009