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.
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.
Download options:
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.
Download options:
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.
Download options:
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.
Download options:
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.
Download options:
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.
Download options:
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.
Download options:
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.
Download options:
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).
Download options:
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.
Download options:
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.
Download options:
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.
Download options:
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.
Download options:
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.
Download options:
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.
Download options:
original poster (pdf): 864.5 kB (last change 28 May 2009)
Shude Mao: “Three decades of gravitational lenses”
summary
Download options:
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/.
Download options:
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.
Download options:
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.
Download options:
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.
Download options:
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.
Download options:
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.
Download options:
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.
Download options:
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.
Download options:
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.
Download options:
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.
Download options:
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.
Download options:
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.
Download options:
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.
Download options:
original talk slides (pdf): 2.7 MB (last change 21 Apr 2009)