Results for "L. V. E. Koopmans"

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Gravitational Lensing & Stellar Dynamics: Dark-Matter and Baryons in Early-type Galaxies to z=1Dec 22 2004Gravitational lensing and stellar dynamics provide two complementary, nearly orthogonal, constraints on the mass distribution of early-type lens galaxies. This allows the luminous and dark-matter distribution in higher-redshift (z>0.1) galaxies to be ... More
Gravitational Lensing & Stellar DynamicsNov 04 2005Strong gravitational lensing and stellar dynamics provide two complementary and orthogonal constraints on the density profiles of galaxies. Based on spherically symmetric, scale-free, mass models, it is shown that the combination of both techniques is ... More
Gravitational Imaging of CDM SubstructureJan 16 2005Aug 17 2005We propose the novel method of ``gravitational imaging'' to detect and quantify luminous and dark-matter substructure in gravitational-lens galaxies. The method utilizes highly-magnified Einstein rings and arcs as sensitive probes of small perturbations ... More
Ionospheric Power-Spectrum Tomography in Radio InterferometryMay 11 2010A tomographic method is described to quantify the three-dimensional power-spectrum of the ionospheric electron-density fluctuations based on radio-interferometric observations by a two-dimensional planar array. The method is valid to first-order Born ... More
Statistics of mass substructure from strong gravitational lensing: quantifying the mass fraction and mass functionMar 27 2009Sep 29 2009A Bayesian statistical formalism is developed to quantify the level at which the mass function slope (alpha) and the projected cumulative mass fraction (f) of (CDM) substructure in strong gravitational-lens galaxies, with arcs or Einstein rings, can be ... More
The Structure and Dynamics of Luminous and Dark Matter in the Early-Type Lens Galaxy of 0047-281 at z=0.485May 16 2002Oct 02 2002We have measured the kinematic profile of the early-type (E/S0) lens galaxy in the system 0047-281 (z=0.485) with the {\sl Echelle Spectrograph and Imager} (ESI) on the W.M. Keck--II Telescope, as part of the {\sl Lenses Structure and Dynamics (LSD) Survey}. ... More
The Hubble Constant from (CLASS) Gravitational LensesJan 19 2001One of the main objectives of the Cosmic Lens All-Sky Survey (CLASS) collaboration has been to find gravitational lens (GL) systems at radio wavelengths that are suitable for the determination of time delays between image pairs. The survey is now near ... More
The Kinematics of High Proper Motion Halo White DwarfsJul 18 2001We analyse the kinematics of the entire spectroscopic sample of 99 recently discovered high proper-motion white dwarfs by Oppenheimer et al. using a maximum-likelihood analysis, and discuss the claim that the high-velocity white dwarfs are members of ... More
The Lenses Structure & Dynamics Survey: The internal structure and evolution of E/S0 galaxies and the determination of H_0 from time-delay systemsAug 04 2003The Lenses Structure & Dynamics (LSD) Survey aims at studying the internal structure of luminous and dark matter - as well as their evolution - of field early-type (E/SO) galaxies to z~1. In particular, E/S0 lens galaxies are studied by combining gravitational ... More
Probing dark matter distribution with gravitational lensing and stellar dynamicsMay 20 2002The Lenses Structure and Dynamics (LSD) Survey aims at measuring the luminous and dark matter distribution of high redshift early-type galaxies by combining gravitational lens analysis with newly determined velocity dispersion profiles. Here we describe ... More
On Identifiability and Estimability of Direction Dependent Calibration of Radio Interferometric ArraysFeb 07 2019Calibration is a key step in the signal processing pipeline of any radio astronomical instrument. The required sky, ionospheric and instrumental models for this step can suffer from various kinds of incompleteness. In this paper we analyze several important ... More
White Dwarfs: Contributors and Tracers of the Galactic Dark-Matter HaloJun 21 2001Jul 19 2001We examine the claim by Oppenheimer et al. (2001) that the local halo density of white dwarfs is an order of magnitude higher than previously thought. As it stands, the observational data support the presence of a kinematically distinct population of ... More
On the Probability of Microlensing in GRB AfterglowsNov 01 2000Jan 20 2001The declining lightcurve of the optical afterglow of gamma-ray burst GRB000301C showed rapid variability with one particularly bright feature at about t-t0=3.8 days. This event was interpreted as gravitational microlensing by Garnavich, Loeb & Stanek ... More
The stellar velocity dispersion of the lens galaxy in MG2016+112 at z=1.004Jan 02 2002Mar 01 2002We present a direct measurement of the stellar velocity dispersion of the early-type lens galaxy D in the system MG2016+112 (z=1.004), determined from a spectrum obtained with the Echelle Spectrograph and Imager (ESI) on the W.M. Keck-II Telescope, as ... More
Quantifying Suppression of the Cosmological 21-cm Signal due to Direction Dependent Gain Calibration in Radio InterferometersSep 11 2018The 21-cm signal of neutral hydrogen - emitted during the Epoch of Reionization - promises to be an important source of information for the study of the infant universe. However, its detection is impossible without sufficient mitigation of other strong ... More
Scintillation noise power spectrum and its impact on high redshift 21-cm observationsDec 01 2015Visibility scintillation resulting from wave propagation through the turbulent ionosphere can be an important sources of noise at low radio frequencies ($\nu\lesssim 200$ MHz). Many low frequency experiments are underway to detect the power spectrum of ... More
A determination of H_0 with the CLASS gravitational lens B1608+656: II. Mass models and the Hubble constant from lensingJul 20 1999EDITED FROM PAPER: We present mass models of the four-image gravitational lens system B1608+656. A mass model for the lens galaxies has been determined that reproduces the image positions, two out of three flux-density ratios and the model time delays. ... More
Scintillation noise in widefield radio interferometryDec 03 2014Dec 01 2015In this paper, we consider random phase fluctuations imposed during wave propagation through a turbulent plasma (e.g. ionosphere) as a source of additional noise in interferometric visibilities. We derive expressions for visibility variance for the wide ... More
Bayesian Strong Gravitational-Lens Modeling on Adaptive Grids: Objective Detection of Mass Substructure in GalaxiesMay 02 2008Dec 16 2008We introduce a new adaptive and fully Bayesian grid-based method to model strong gravitational lenses with extended images. The primary goal of this method is to quantify the level of luminous and dark-mass substructure in massive galaxies, through their ... More
Microlensing of multiply-imaged compact radio sources: Evidence for compact halo objects in the disk galaxy of B1600+434Apr 07 2000Apr 18 2000We present the first unambiguous case of external variability of a radio gravitational lens, CLASS B1600+434. The VLA 8.5-GHz difference light curve of the lensed images, taking the proper time-delay into account, shows the presence of external variability ... More
Quantifying dwarf satellites through gravitational imaging: the case of SDSS J120602.09+514229.5Feb 25 2010Mar 03 2010SDSS J120602.09+514229.5 is a gravitational lens system formed by a group of galaxies at redshift z=0.422 lensing a bright background galaxy at redshift z=2.001. The main peculiarity of this system is the presence of a luminous satellite near the Einstein ... More
Microlensing & Scintillation of Gravitationally Lensed Compact Radio Sources: Evidence for MACHOs?Oct 11 1999We present the first unambiguous case of external variability of an extra-galactic radio source, the CLASS gravitational lens B1600+434, consisting of two images lensed by an edge-on disk galaxy. The VLA 8.5-GHz difference light curve of the lens images ... More
A hierarchical Bayesian approach for reconstructing the Initial Mass Function of Single Stellar PopulationsAug 18 2016Recent studies based on the integrated light of distant galaxies suggest that the initial mass function (IMF) might not be universal. Variations of the IMF with galaxy type and/or formation time may have important consequences for our understanding of ... More
Galaxy Number Counts and Implications for Strong LensingSep 23 2009Feb 28 2011We compare galaxy number counts in HST/ACS fields containing moderate-redshift (0.2<z<1.0) strong gravitational lenses with those in two control samples: (1) the first square degree of the COSMOS survey, comprising 259 ACS fields and (2) 20 "pure parallel" ... More
HI kinematics in a massive spiral galaxy at z=0.89Nov 25 2003We present a kinematic model of the neutral-hydrogen in the spiral galaxy of the lens system PKS1830-211, based on a Multi Element Radio-Linked Interferometer (MERLIN) 1.4-GHz radio map and the integrated and redshifted 21-cm hydrogen absorption-line ... More
The edge-on spiral gravitational lens B1600+434Jan 20 1998We present new observations of the gravitational lens (GL) system B1600+434, strongly suggesting that the lens is an edge-on spiral galaxy. These observations are used to constrain the mass model of the system, in particular the oblateness and velocity ... More
The impact of interference excision on 21-cm Epoch of Reionization power spectrum analysesJan 15 2019We investigate the implications of interference detection for experiments that are pursuing a detection of the redshifted 21-cm signals from the Epoch of Reionization. Interference detection causes samples to be sporadically flagged and rejected. As a ... More
Micro & strong lensing with the Square Kilometer Array: The mass--function of compact objects in high--redshift galaxiesJan 07 2000We present the results from recent VLA 8.5-GHz and WSRT 1.4 and 4.9-GHz monitoring campaigns of the CLASS gravitational lens B1600+434 and show how the observed variations argue strongly in favor of microlensing by MACHOs in the halo of a dark-matter ... More
Robust Foregrounds Removal for 21-cm ExperimentsJan 18 2018Direct detection of the Epoch of Reionization via the redshifted 21-cm line will have unprecedented implications on the study of structure formation in the early Universe. To fulfill this promise current and future 21-cm experiments will need to detect ... More
Data Multiplexing in Radio Interferometric CalibrationNov 28 2017Nov 29 2017New and upcoming radio interferometers will produce unprecedented amounts of data that demand extremely powerful computers for processing. This is a limiting factor due to the large computational power and energy costs involved. Such limitations restrict ... More
The Influence of Central Black Holes on Gravitational LensesJul 02 2000Recent observations indicate that many if not all galaxies host massive central black holes. In this paper we explore the influence of black holes on the lensing properties. We model the lens as an isothermal ellipsoid with a finite core radius plus a ... More
A Bayesian analysis of redshifted 21-cm HI signal and foregrounds: Simulations for LOFARJun 16 2015Observations of the EoR with the 21-cm hyperfine emission of neutral hydrogen (HI) promise to open an entirely new window onto the formation of the first stars, galaxies and accreting black holes. In order to characterize the weak 21-cm signal, we need ... More
The Sloan Lens ACS Survey. III - The Structure and Formation of Early-type Galaxies and their Evolution since z~1Jan 26 2006Mar 24 2006(Abridged) We present a joint gravitational lensing and stellar dynamical analysis of fifteen massive field early-type galaxies, selected from the Sloan Lens (SLACS) Survey. The following numerical results are found: (i) A joint-likelihood gives an average ... More
VLA 8.4-GHz monitoring observations of the CLASS gravitational lens B1933+503Apr 20 2000The complex ten-component gravitational lens system B1933+503 has been monitored with the VLA during the period February to June 1998 with a view to measuring the time delay between the four compact components and hence to determine the Hubble parameter. ... More
A Determination of H_0 with the CLASS Gravitational Lens B1608+656: III. A Significant Improvement in the Precision of the Time Delay MeasurementsAug 22 2002The gravitational lens CLASS B1608+656 is the only four-image lens system for which all three independent time delays have been measured. This makes the system an excellent candidate for a high-quality determination of H_0 at cosmological distances. However, ... More
A time-delay determination from VLA light curves of the CLASS gravitational lens B1600+434Jan 31 2000We present Very Large Array (VLA) 8.5-GHz light curves of the two lens images of the Cosmic Lens All Sky Survey (CLASS) gravitational lens B1600+434. We find a nearly linear decrease of 18-19% in the flux densities of both lens images over a period of ... More
The dichotomy of dark matter fraction and total mass density slope of galaxies over five dex in massFeb 26 2019We analyse the mass density distribution in the centres of galaxies across a mass range of about five orders of magnitude. Using high-quality spiral-galaxy rotation curves and infrared photometry from the SPARC database, we conduct a systematic study ... More
Stars and dark matter in the spiral gravitational lens 2237+0305Dec 03 2008Nov 29 2009We construct a mass model for the spiral lens galaxy 2237+0305, at redshift z_l=0.04, based on gravitational-lensing constraints, HI rotation, and new stellar-kinematic information, based on data taken with the ESI spectrograph on the 10m Keck-II Telescope. ... More
Evidence For A Mild Steepening And Bottom-Heavy IMF In Massive Galaxies From Sodium And Titanium-Oxide IndicatorsApr 17 2012Jun 11 2012We measure equivalent widths (EW) - focussing on two unique features (NaI and TiO2) of low-mass stars (<0.3M\odot) - for luminous red galaxy spectra from the the Sloan Digital Sky Survey (SDSS) and X-Shooter Lens Survey (XLENS) in order to study the low-mass ... More
Radio counterpart of the lensed sub-mm emission in the cluster MS0451.6-0305: new evidence for the merger scenarioOct 07 2009SMM J04542-0301 is an extended (~1 arcmin) sub-mm source located near the core of the cluster MS0451.6-0305. It has been suggested that part of its emission arises from the interaction between a LBG and two EROs at z~2.9 that are multiply-imaged. However, ... More
Measuring gravitational lens time delays using low-resolution radio monitoring observationsMar 19 2014Obtaining lensing time delay measurements requires long-term monitoring campaigns with a high enough resolution (< 1 arcsec) to separate the multiple images. In the radio, a limited number of high-resolution interferometer arrays make these observations ... More
The dark matter halos of spheroidal galaxies and clusters of galaxiesNov 03 2003We describe the first results from two observational projects aimed at measuring the amount and spatial distribution of dark matter in distant early-type galaxies (E/S0s) and clusters of galaxies. At the galaxy scale, the Lenses Structure and Dynamics ... More
A New Generation of Cool White Dwarf Atmosphere Models. III. WD J2356$-$209: Accretion of a Planetesimal with an Unusual CompositionFeb 08 2019WD J2356$-$209 is a cool metal-polluted white dwarf whose visible spectrum is dominated by a strong and broad sodium feature. Although discovered nearly two decades ago, no detailed and realistic analysis of this star had yet been realized. In the absence ... More
Massive Dark-matter halos and Evolution of Early-type Galaxies to z=1Jan 19 2004May 01 2004(Shortened) The combination of lensing and stellar dynamics breaks the mass-anisotropy degeneracy and provides stringent constraints on the mass distribution in early-type (E/S0) galaxies out to z~1. We present the combined results from the five field ... More
Strong Gravitational Lensing with SKASep 04 2004The advent of new observational facilities in the last two decades has allowed the rapid discovery and high-resolution optical imaging of many strong lens systems from galaxy to cluster scales, as well as their spectroscopic follow-up. Radio telescopes ... More
Detection of a Dark Substructure through Gravitational ImagingOct 05 2009Oct 11 2009We report the detection of a dark substructure through direct gravitational imaging - undetected in the HST-ACS F814W image - in the gravitational lens galaxy of SLACS SDSSJ0946+1006 (the "Double Einstein Ring"). The detection is based on a Bayesian grid ... More
The signature of substructure on gravitational lensing in the LCDM cosmological modelJun 11 2003May 13 2004We present a study of the lens properties of quadruply imaged systems, lensed by numerically simulated galaxies. We investigate a simulated elliptical and disc galaxy drawn from high resolution simulations of galaxy formation in a concordance $\Lambda$CDM ... More
Are the total mass density and the low-mass end slope of the IMF anti-correlated?May 27 2015We conduct a detailed lensing, dynamics and stellar population analysis of nine massive lens early-type galaxies (ETGs) from the X-Shooter Lens Survey (XLENS). Combining gravitational lensing constraints from HST imaging with spatially-resolved kinematics ... More
The X-Shooter Lens Survey - I. Dark-Matter Domination and a Salpeter-type IMF in a Massive Early-type GalaxyMar 24 2011Jul 15 2011We present the first results from the X-shooter Lens Survey (XLENS): an analysis of the massive early-type galaxy SDSS J1148+1930 at redshift z=0.444. We combine its extended kinematic profile -derived from spectra obtained with X-shooter on the ESO VLT- ... More
Constrained Least Squares for Extended Complex Factor AnalysisApr 02 2018For subspace estimation with an unknown colored noise, Factor Analysis (FA) is a good candidate for replacing the popular eigenvalue decomposition (EVD). Finding the unknowns in factor analysis can be done by solving a non-linear least square problem. ... More
Radio Interferometric Calibration Using The SAGE AlgorithmDec 08 2010Feb 16 2011The aim of the new generation of radio synthesis arrays such as LOFAR and SKA is to achieve much higher sensitivity, resolution and frequency coverage than what is available now, especially at low frequencies. To accomplish this goal, the accuracy of ... More
A radio-microlensing caustic crossing in B1600+434?Apr 19 2000First, we review the current status of the detection of strong `external' variability in the CLASS gravitational B1600+434, focusing on the 1998 VLA 8.5-GHz and 1998/9 WSRT multi-frequency observations. We show that this data can best be explained in ... More
The Hubble Constant from the Gravitational Lens B1608+656Jun 11 2003Aug 20 2003We present a refined gravitational lens model of the four-image lens system B1608+656 based on new and improved observational constraints: (i) the three independent time-delays and flux-ratios from VLA observations, (ii) the radio-image positions from ... More
Inference of the Cold Dark Matter substructure mass function at z=0.2 using strong gravitational lensesMay 14 2014Jun 04 2014We present the results of a search for galaxy substructures in a sample of 11 gravitational lens galaxies from the Sloan Lens ACS Survey. We find no significant detection of mass clumps, except for a luminous satellite in the system SDSS J0956+5110. We ... More
Highly-magnified, Multiply-imaged radio counterparts of the Sub-mm Starburst Emission in the Cluster-Lens MS0451.6-0305Mar 17 2006Nov 20 2006Previous authors have reported the detection of intrinsically faint sub-mm emission lensed by the cluster MS0451.6-0305. They suggest that this emission arises from a merging system composed of a Ly-break galaxy and a pair of extremely red objects which ... More
The inner mass power spectrum of galaxies using strong gravitational lensing: beyond linear approximationOct 09 2017In the last decade the detection of individual massive dark matter sub-halos has been possible using potential correction formalism in strong gravitational lens imaging. Here we propose a statistical formalism to relate strong gravitational lens surface ... More
A Unifying Framework for Self-consistent Gravitational Lensing and Stellar Dynamics Analyses of Early-Type GalaxiesJan 12 2007Sep 28 2007Gravitational lensing and stellar dynamics are two independent methods, based solely on gravity, to study the mass distributions of galaxies. Both methods suffer from degeneracies, however, that are difficult to break. In this paper, we present a new ... More
The internal structure of the lens PG1115+080: breaking degeneracies in the value of the Hubble ConstantSep 30 2002We combine lensing, stellar kinematic and mass-to-light ratio constraints to build a two-component (luminous plus dark) mass model of the early-type lens galaxy in PG1115+080. We find a total mass density profile steeper than r^-2, effectively rho r^-gamma' ... More
Polarization leakage in epoch of reionization windows: III. Wide-field effects of narrow-field arraysJun 02 2017Leakage of polarized Galactic diffuse emission into total intensity can potentially mimic the 21-cm signal coming from the epoch of reionization (EoR), as both of them might have fluctuating spectral structure. Although we are sensitive to the EoR signal ... More
Measuring H_0 with CLASS B1608+656: The Second Season of VLA MonitoringSep 24 1999The four-component gravitational lens CLASS B1608+656 has been monitored with the VLA for two seasons in order to search for time delays between the components. These time delays can be combined with mass models of the lens system to yield a measurement ... More
B0218+357: Time Delays and New MERLIN/VLA 5GHz Maps of the Einstein RingSep 22 1999This poster presents a new 5 GHz combined MERLIN/VLA map of B0218+357 which shows for the first time believable substructure in the Einstein ring. This will now be exploited for further constraints on the model which presently dominates the error on the ... More
SHARP - I. A high-resolution multi-band view of the infra-red Einstein ring of JVAS B1938+666Jun 08 2012We present new mass models for the gravitational lens system B1938+666, using multi-wavelength data acquired from Keck adaptive optics (AO) and Hubble Space Telescope (HST) observations. These models are the first results from the Strong-lensing at High ... More
Gravitational detection of a low-mass dark satellite at cosmological distanceJan 17 2012The mass-function of dwarf satellite galaxies that are observed around Local Group galaxies substantially differs from simulations based on cold dark matter: the simulations predict many more dwarf galaxies than are seen. The Local Group, however, may ... More
SHARP - V. Modelling gravitationally-lensed radio arcs imaged with global VLBI observationsJul 15 2018We present milliarcsecond (mas) angular resolution observations of the gravitationally lensed radio source MG J0751+2716 (at z=3.2) obtained with global Very Long Baseline Interferometry (VLBI) at 1.65 GHz. The background object is highly resolved in ... More
The X-shooter Lens Survey - II. Sample presentation and spatially resolved kinematicsJul 08 2015We present the X-shooter Lens Survey (XLENS) data. The main goal of XLENS is to disentangle the stellar and dark matter content of massive early-type galaxies (ETGs), through combined strong gravitational lensing, dynamics and spectroscopic stellar population ... More
Probing a massive radio galaxy with gravitational lensingDec 07 2007The gravitational lens system CLASS B2108+213 has two lensed images separated by 4.56 arcsec. Such a wide image separation suggests that the lens is either a massive galaxy, or is composed of a group of galaxies. To investigate the structure of the lensing ... More
Time delay for the gravitational lens system B0218+357Nov 18 1998Measurement of the time delay between multiple images of a gravitational lens system is potentially an accurate method of determining the Hubble constant over cosmological distances. One of the most promising candidates for an application of this technique ... More
Radio Monitoring Campaigns of Six Strongly Lensed QuasarsOct 24 2014We observed six strongly lensed, radio-loud quasars (MG 0414+0534, CLASS B0712+472, JVAS B1030+074, CLASS B1127+385, CLASS B1152+199, and JVAS B1938+666) in order to identify systems suitable for measuring cosmological parameters using time delays between ... More
The role of luminous substructure in the gravitational lens system MG 2016+112Oct 29 2008Mar 31 2009MG 2016+112 is a quadruply imaged lens system with two complete images A and B and a pair of merging partial images in region C as seen in the radio. The merging images are found to violate the expected mirror symmetry. This indicates an astrometric anomaly ... More
Dark Matter Contraction and the Stellar Content of Massive Early-type Galaxies: Disfavoring "Light" Initial Mass FunctionsJul 14 2010We use stellar dynamics, strong lensing, stellar population synthesis models, and weak lensing shear measurements to constrain the dark matter (DM) profile and stellar mass in a sample of 53 massive early-type galaxies. We explore three DM halo models ... More
The initial mass function of early-type galaxiesNov 17 2009We determine an absolute calibration of the initial mass function (IMF) of early-type galaxies, by studying a sample of 56 gravitational lenses identified by the SLACS Survey. Under the assumption of standard Navarro, Frenk & White dark matter halos, ... More
Chromatic effects in the 21 cm global signal from the cosmic dawnJun 10 2013The redshifted 21 cm brightness distribution from neutral hydrogen is a promising probe into the cosmic dark ages, cosmic dawn, and re-ionization. LOFAR's Low Band Antennas (LBA) may be used in the frequency range 45 MHz to 85 MHz (30>z>16) to measure ... More
Observational constraints on the sub-galactic matter-power spectrum from galaxy-galaxy strong gravitational lensingMar 15 2018Constraining the sub-galactic matter-power spectrum on 1-10 kpc scales would make it possible to distinguish between the concordance $\Lambda$CDM model and various alternative dark-matter models due to the significantly different levels of predicted mass ... More
A method for efficient measurement of gravitational lens time delaysNov 30 2010The Hubble constant value is currently known to 10% accuracy unless assumptions are made for the cosmology (Sandage et al. 2006). Gravitational lens systems provide another probe of the Hubble constant using time delay measurements. However, current investigations ... More
The fundamental plane of evolving red nuggetsJan 11 2017We present an exploration of the mass structure of a sample of 12 strongly lensed massive, compact early-type galaxies at redshifts $z\sim0.6$ to provide further possible evidence for their inside-out growth. We obtain new ESI/Keck spectroscopy and infer ... More
2016+112: A Gravitationally Lensed Type-II QuasarJun 29 2001Jan 02 2002A single-screen model of the gravitational lens system 2016+112 is proposed, that explains recent Hubble Space Telescope} (HST) infrared (NICMOS-F160W) observations and new high-resolution European VLBI Network (EVN) 5-GHz radio observations, presented ... More
Radio Microlensing: Past, Present & Near FutureNov 01 2000Strongly correlated non-intrinsic variability between 5 and 8.5 GHz has been observed in one of the lensed images of the gravitational lens B1600+434. These non-intrinsic (i.e. `external') variations are interpreted as `radio-microlensing' of relativistic ... More
Gravitational lensing statistics with extragalactic surveys. II. Analysis of the Jodrell Bank-VLA Astrometric SurveyApr 13 1999We present constraints on the cosmological constant $\lambda_{0}$ from gravitational lensing statistics of the Jodrell Bank-VLA Astrometric Survey (JVAS). Although this is the largest gravitational lens survey which has been analysed, cosmological constraints ... More
Cool White Dwarfs Revisited -- New Spectroscopy and PhotometryAug 07 2003Oct 08 2003In this paper we present new and improved data on 38 cool white dwarfs identified by Oppenheimer et al. 2001 (OHDHS) as candidate dark halo objects. Using the high-res spectra obtained with LRIS, we measure radial velocities for 13 WDs that show an H ... More
The non-universality of the low-mass end of the IMF is robust against the choice of SSP modelJan 06 2014Feb 14 2015We perform a direct comparison of two state-of-the art single stellar population (SSP) models that have been used to demonstrate the non-universality of the low-mass end of the Initial Mass Function (IMF) slope. The two public versions of the SSP models ... More
Testing Convolutional Neural Networks for finding strong gravitational lenses in KiDSJul 12 2018Oct 01 2018Convolutional Neural Networks (ConvNets) are one of the most promising methods for identifying strong gravitational lens candidates in survey data. We present two ConvNet lens-finders which we have trained with a dataset composed of real galaxies from ... More
Reionisation & Cosmic Dawn Astrophysics from the Square Kilometre Array: Impact of Observing StrategiesJun 19 2019Interferometry of the cosmic 21-cm signal is set to revolutionise our understanding of the Epoch of Reionisation (EoR) and the Cosmic Dawn (CD). The culmination of ongoing efforts will be the upcoming Square Kilometre Array (SKA), which will provide tomography ... More
The impact of primordial supersonic flows on early structure formation, reionization and the lowest-mass dwarf galaxiesNov 17 2010Dec 09 2010Tseliakhovich & Hirata recently discovered that higher-order corrections to the cosmological linear-perturbation theory lead to supersonic coherent baryonic flows just after recombination (i.e. z~1020), with rms velocities of ~30 km/s relative to the ... More
Dissecting the 3D structure of elliptical galaxies with gravitational lensing and stellar kinematicsSep 15 2014The combination of strong gravitational lensing and stellar kinematics provides a powerful and robust method to investigate the mass and dynamical structure of early-type galaxies. We demonstrate this approach by analysing two massive ellipticals from ... More
Optimal core baseline design and observing strategy for probing the astrophysics of reionization with the SKASep 10 2015With the first phase of the Square Kilometre Array (SKA1) entering into its final pre-construction phase, we investigate how best to maximise its scientific return. Specifically, we focus on the statistical measurement of the 21 cm power spectrum (PS) ... More
Bulk Flows and End of the Dark Ages with the SKAJan 16 2015The early Universe is a precious probe of the birth of primordial objects, first star formation events and consequent production of photons and heavy elements. Higher-order corrections to the cosmological linear perturbation theory predicts the formation ... More
The stellar IMF determined in early-type galaxies from a non-degenerate set of optical line indicesMay 13 2013Nov 28 2013We investigate the optical spectral region of spectra of 1000 stars searching for IMF-sensitive features to constrain the low-mass end of the initial mass function (IMF) slope in elliptical galaxies. We use the MILES stellar library in the wavelength ... More
LEDDB: LOFAR Epoch of Reionization Diagnostic DatabaseFeb 18 2013One of the key science projects of the Low-Frequency Array (LOFAR) is the detection of the cosmological signal coming from the Epoch of Reionization (EoR). Here we present the LOFAR EoR Diagnostic Database (LEDDB) that is used in the storage, management, ... More
The new gravitational lens system B1030+074Feb 02 1998We report the discovery of a new double image gravitational lens system B1030+074 which was found during the Jodrell Bank - VLA Astrometric Survey (JVAS). We have collected extensive radio data on the system using the VLA, MERLIN, the EVN and the VLBA ... More
Everything you ever wanted to know about the JVAS gravitational lens system B1030+074 but were afraid to askSep 28 1999We present an overview of all the observations (radio - VLA, MERLIN, VLBA,EVN - and optical - WFPC2 and NICMOS -) that were initially used to confirm the gravitational lens nature of the double JVAS system B1030+074. Since the 1.56 arcsec system showed ... More
High resolution imaging of the anomalous flux-ratio gravitational lens system CLASS B2045+265: Dark or luminous satellites?Nov 07 2006Mar 16 2007The existence of flux-ratio anomalies between fold and cusp images in galaxy-scale strong-lens systems has led to an interpretation based on the presence of a high mass-fraction of cold-dark-matter (CDM) substructures around galaxies, as predicted by ... More
The Structure & Dynamics of Massive Early-type Galaxies: On Homology, Isothermality and Isotropy inside one Effective RadiusJun 08 2009Aug 12 2009Based on 58 SLACS strong-lens early-type galaxies with direct total-mass and stellar-velocity dispersion measurements, we find that inside one effective radius massive elliptical galaxies with M_eff >= 3x10^10 M_sun are well-approximated by a power-law ... More
SHARP - IV. An apparent flux ratio anomaly resolved by the edge-on disc in B0712+472Jan 23 2017Apr 27 2017Flux ratio anomalies in quasar lenses can be attributed to dark matter substructure surrounding the lensing galaxy and, thus, used to constrain the substructure mass fraction. Previous applications of this approach infer a substructure abundance that ... More
Finding Strong Gravitational Lenses in the Kilo Degree Survey with Convolutional Neural NetworksFeb 24 2017Aug 23 2017The volume of data that will be produced by new-generation surveys requires automatic classification methods to select and analyze sources. Indeed, this is the case for the search for strong gravitational lenses, where the population of the detectable ... More
The Sloan Lens ACS Survey. X. Stellar, Dynamical, and Total Mass Correlations of Massive Early-type GalaxiesJul 16 2010We use stellar masses, photometry, lensing, and velocity dispersions to investigate empirical correlations for the final sample of 73 early-type lens galaxies (ETGs) from the SLACS survey. The traditional correlations (Fundamental Plane [FP] and its projections) ... More
The Sloan Lens ACS Survey. VIII. The relation between environment and internal structure of early-type galaxiesJun 05 2008Oct 06 2008We study the relation between the internal structure of early-type galaxies and their environment using 70 strong gravitational lenses from the Sloan ACS Lens Survey. The Sloan database is used to determine two measures of overdensity of galaxies around ... More
Keck spectroscopy of CLASS gravitational lensesFeb 04 2004We present the optical spectra of four newly discovered gravitational lenses from the Cosmic Lens All-Sky Survey (CLASS). These observations were carried out using the Low Resolution Imaging Spectrograph on the W. M. Keck-I Telescope as part of a program ... More
The Sloan Lens ACS Survey. IX. Colors, Lensing and Stellar Masses of Early-type GalaxiesNov 12 2009We present the current photometric dataset for the Sloan Lens ACS (SLACS) Survey, including HST photometry from ACS, WFPC2, and NICMOS. These data have enabled the confirmation of an additional 15 grade `A' (certain) lens systems, bringing the number ... More
Redshift of the Einstein Ring in MG1549+305Jun 02 2003A deep spectrum taken with the Echelle Spectrograph and Imager (ESI) at the Keck II Telescope as part of the Lenses Structure and Dynamics (LSD) Survey reveals the redshifts of the extremely red source of the radio Einstein Ring in the gravitational lens ... More