Lensed Arcs Research Articles

TEGLIE: Transformer encoders as strong gravitational lens finders in KiDS

Context.With the current and upcoming generation of surveys, such as the Legacy Survey of Space and Time (LSST) on theVera C. RubinObservatory and theEuclidmission, tens of billions of galaxies will be observed, with a significant portion (~105) exhibiting lensing features. To effectively detect these rare objects amidst the vast number of galaxies, automated techniques such as machine learning are indispensable.Aims.We applied a state-of-the-art transformer algorithm to the 221 deg2of the Kilo Degree Survey (KiDS) to search for new strong gravitational lenses (SGLs).Methods.We tested four transformer encoders trained on simulated data from the Strong Lens Finding Challenge on KiDS data. The best performing model was fine-tuned on real images of SGL candidates identified in previous searches. To expand the dataset for fine-tuning, data augmentation techniques were employed, including rotation, flipping, transposition, and white noise injection. The network fine-tuned with rotated, flipped, and transposed images exhibited the best performance and was used to hunt for SGLs in the overlapping region of the Galaxy And Mass Assembly (GAMA) and KiDS surveys on galaxies up toz= 0.8. Candidate SGLs were matched with those from other surveys and examined using GAMA data to identify blended spectra resulting from the signal from multiple objects in a GAMA fiber.Results.Fine-tuning the transformer encoder to the KiDS data reduced the number of false positives by 70%. Additionally, applying the fine-tuned model to a sample of ~5 000 000 galaxies resulted in a list of ~51 000 SGL candidates. Upon visual inspection, this list was narrowed down to 231 candidates. Combined with the SGL candidates identified in the model testing, our final sample comprises 264 candidates, including 71 high-confidence SGLs; of these 71, 44 are new discoveries.Conclusions.We propose fine-tuning via real augmented images as a viable approach to mitigating false positives when transitioning from simulated lenses to real surveys. While our model shows improvement, it still does not achieve the same accuracy as previously proposed models trained directly on galaxy images from KiDS with added simulated lensing arcs. This suggests that a larger fine-tuning set is necessary for a competitive performance. Additionally, we provide a list of 121 false positives that exhibit features similar to lensed objects, which can be used in the training of future machine learning models in this field.

TEMPLATES: Characterization of a Merger in the Dusty Lensing SPT0418–47 System

We present JWST and Atacama Large Millimeter/submillimeter Array (ALMA) imaging for the lensing system SPT0418−47, which includes a strongly lensed, dusty, star-forming galaxy at redshift z = 4.225 and an associated multiply imaged companion. The JWST NIRCam and MIRI imaging observations presented in this paper were acquired as part of the Early Release Science program Targeting Extremely Magnified Panchromatic Lensed Arcs and Their Extended Star formation (TEMPLATES). This data set provides robust mutiwavelength detections of stellar light in both the main (SPT0418A) and companion (SPT0418B) galaxies, while the ALMA detection of [C ii] emission confirms that SPT0418B lies at the same redshift as SPT0418A. We infer that the projected physical separation of the two galaxies is 4.42 ± 0.05 kpc. We derive total magnifications of μ = 29 ± 1 and μ = 4.1 ± 0.7 for SPT0418A and SPT0418B, respectively. We use both prospector and cigale to derive stellar masses. We find that SPT0418A has a stellar mass of M*=3.4−0.6+1.1×1010M⊙ from prospector or M * = 1.5 ± 0.3 × 1010 M ⊙ from cigale. The stellar mass ratio of SPT0418A and SPT0418B is roughly between 4 and 7 ( 4.2−1.6+1.9 for prospector and 7.5 ± 3.7 for cigale). We see evidence of extended structure associated with SPT0418A that is suggestive of a tidal feature. These features, along with the close projected proximity, imply that the system is interacting. Interestingly, the star formation rates and stellar masses of both galaxies are consistent with the main sequence of star-forming galaxies at this epoch, indicating that this ongoing interaction has not noticeably elevated the star formation levels.

Detecting low-mass perturbers in cluster lenses using curved arc bases

ABSTRACT Strong gravitationally lensed arcs produced by galaxy clusters have been observationally detected for several decades now. These strong lensing constraints provided high-fidelity mass models for cluster lenses that include substructure down to $10^{9{-}10}\, \mathrm{M}_\odot$. Optimizing lens models, where the cluster mass distribution is modelled by a smooth component and subhaloes associated with the locations of individual cluster galaxies, has enabled deriving the subhalo mass function, providing important constraints on the nature and granularity of dark matter. In this work, we explore and present a novel method to detect and measure individual perturbers (subhaloes, line-of-sight haloes, and wandering supermassive black holes) by exploiting their proximity to highly distorted lensed arcs in galaxy clusters, and by modelling the local lensing distortions with curved arc bases. This method offers the possibility of detecting individual low-mass perturber subhaloes in clusters and haloes along the line of sight down to a mass resolution of $10^8\, \mathrm{M}_\odot$. We quantify our sensitivity to low-mass perturbers ($M\sim 10^{7{-}9}\, \mathrm{M}_\odot$) in clusters (M ∼ 1014–15 M⊙), by creating realistic mock data. Using three lensed images of a background galaxy in the cluster SMACS J0723, taken by JWST, we study the retrieval of the properties of potential perturbers with masses $M=10^{7{-}9}\, \mathrm{M}_\odot$. From the derived posterior probability distributions for the perturber, we constrain its concentration, redshift, and ellipticity. By allowing us to probe lower mass substructures, the use of curved arc bases can lead to powerful constraints on the nature of dark matter as discrimination between dark matter models appears on smaller scales.

Constraining the multi-scale dark-matter distribution in CASSOWARY 31 with strong gravitational lensing and stellar dynamics

We study the inner structure of the group-scale lens CASSOWARY 31 (CSWA 31) by adopting both strong lensing and dynamical modeling. CSWA 31 is a peculiar lens system. The brightest group galaxy (BGG) is an ultra-massive elliptical galaxy atz = 0.683 with a weighted mean velocity dispersion ofσ = 432 ± 31 km s−1. It is surrounded by group members and several lensed arcs probing up to ≃150 kpc in projection. Our results significantly improve on previous analyses of CSWA 31 thanks to the new HST imaging and MUSE integral-field spectroscopy. From the secure identification of five sets of multiple images and measurements of the spatially resolved stellar kinematics of the BGG, we conduct a detailed analysis of the multi-scale mass distribution using various modeling approaches, in both the single and multiple lens-plane scenarios. Our best-fit mass models reproduce the positions of multiple images and provide robust reconstructions for two background galaxies atz = 1.4869 andz = 2.763. Despite small variations related to the different sets of input constraints, the relative contributions from the BGG and group-scale halo are remarkably consistent in our three reference models, demonstrating the self-consistency between strong lensing analyses based on image position and extended image modeling. We find that the ultra-massive BGG dominates the projected total mass profiles within 20 kpc, while the group-scale halo dominates at larger radii. The total projected mass enclosed withinReff = 27.2 kpc is 1.10−0.04+0.02 × 1013M⊙. We find that CSWA 31 is a peculiar fossil group, strongly dark-matter dominated toward the central region, and with a projected total mass profile similar to higher-mass cluster-scale halos. The total mass-density slope within the effective radius is shallower than isothermal, consistent with previous analyses of early-type galaxies in overdense environments.

Massive Molecular Gas Reservoir in a Luminous Submillimeter Galaxy during Cosmic Noon

Abstract We present multiband observations of an extremely dusty star-forming lensed galaxy (HERS1) at z = 2.553. High-resolution maps of HST/WFC3, SMA, and ALMA show a partial Einstein ring with a radius of ∼3″. The deeper HST observations also show the presence of a lensing arc feature associated with a second lens source, identified to be at the same redshift as the bright arc based on a detection of the [N ii] 205 μm emission line with ALMA. A detailed model of the lensing system is constructed using the high-resolution HST/WFC3 image, which allows us to study the source-plane properties and connect rest-frame optical emission with properties of the galaxy as seen in submillimeter and millimeter wavelengths. Corrected for lensing magnification, the spectral energy distribution fitting results yield an intrinsic star formation rate of about 1000 ± 260 M ⊙ yr−1, a stellar mass M * = 4.3 − 1.0 + 2.2 × 10 11 M ⊙ , and a dust temperature T d = 35 − 1 + 2 K. The intrinsic CO emission line (J up = 3, 4, 5, 6, 7, 9) flux densities and CO spectral line energy distribution are derived based on the velocity-dependent magnification factors. We apply a radiative transfer model using the large velocity gradient method with two excitation components to study the gas properties. The low-excitation component has a gas density n H 2 = 10 3.8 ± 0.6 cm−3 and kinetic temperature T k = 18 − 5 + 7 K, and the high-excitation component has n H 2 = 10 3.1 ± 0.4 cm−3 and T k = 480 − 220 + 260 K. Additionally, HERS1 has a gas fraction of about 0.19 ± 0.14 and is expected to last 100 Myr. These properties offer a detailed view of a typical submillimeter galaxy during the peak epoch of star formation activity.

Combining strong and weak lensing estimates in the Cosmos field

We present a combined cosmic shear analysis of the modeling of line-of-sight distortions on strongly lensed extended arcs and galaxy shape measurements in the COSMOS field. We develop a framework to predict the covariance of strong lensing and galaxy shape measurements of cosmic shear on the basis of the small scale matter power-spectrum. The weak lensing measurement is performed using data from the COSMOS survey calibrated with a cloning scheme using the Ultra Fast Image Generator UFig [1]. The strong lensing analysis is performed by forward modeling the lensing arcs with a main lensing deflector and external shear components from the same Hubble Space Telescope imaging data set. With a sample of three strong lensing shear measurements we present a 2-sigma detection of the cross-correlation signal between the two complementary measurements of cosmic shear along the identical line of sight. With large samples of lenses available with the next generation ground and space based observatories, the covariance of the signal of the two probes with large samples of lenses allows for systematic checks, cross-calibration of either of the two measurement and the measurement of the small scale shear power-spectrum.

The Velocity Dispersion Function for Quiescent Galaxies in Nine Strong-lensing Clusters

Abstract We measure the central stellar velocity dispersion function for quiescent galaxies in a set of nine northern clusters in the redshift range 0.18 < z < 0.29 and with strong lensing arcs in Hubble Space Telescope images. The velocity dispersion function links galaxies directly to their dark matter halos. From dense SDSS and MMT/Hectospec spectroscopy, we identify 222–463 spectroscopic members in each cluster. We derive physical properties of cluster members including redshift, , and central stellar velocity dispersion and we include a table of these measurements for 3419 cluster members. We construct the velocity dispersion functions for quiescent galaxies with > 1.5 and within R 200. The cluster velocity dispersion functions all show excesses at σ ≳ 250 km s−1 compared to the field velocity dispersion function. The velocity dispersion function slope at large velocity dispersion (σ > 160 km s−1) is steeper for more massive clusters, consistent with the trend observed for cluster luminosity functions. The spatial distribution of galaxies with large velocity dispersion at radii larger than R 200 further underscores the probable major role of dry mergers in the growth of massive cluster galaxies during cluster assembly.

Understanding the large inferred Einstein radii of observed low-mass galaxy clusters

ABSTRACT We assess a claim that observed galaxy clusters with mass ${\sim}10^{14} \mathrm{\, M_\odot }$ are more centrally concentrated than predicted in lambda cold dark matter (ΛCDM). We generate mock strong gravitational lensing observations, taking the lenses from a cosmological hydrodynamical simulation, and analyse them in the same way as the real Universe. The observed and simulated lensing arcs are consistent with one another, with three main effects responsible for the previously claimed inconsistency. First, galaxy clusters containing baryonic matter have higher central densities than their counterparts simulated with only dark matter. Secondly, a sample of clusters selected because of the presence of pronounced gravitational lensing arcs preferentially finds centrally concentrated clusters with large Einstein radii. Thirdly, lensed arcs are usually straighter than critical curves, and the chosen image analysis method (fitting circles through the arcs) overestimates the Einstein radii. After accounting for these three effects, ΛCDM predicts that galaxy clusters should produce giant lensing arcs that match those in the observed Universe.

Image simulations for gravitational lensing withskylens

We present the latest version of the ray-tracing simulation code Skylens, which can be used to develop image simulations that reproduce strong lensing observations by any mass distribution with a high level of realism. Improvements of the code with respect to previous versions include the implementation of the multi-lens plane formalism, the use of denoised source galaxies from the Hubble eXtreme Deep Field, and the simulation of substructures in lensed arcs and images, based on a morphological analysis of bright nearby galaxies. Skylens can simulate observations with virtually any telescope. We present examples of space- and ground-based observations of a galaxy cluster through the Wide Field Channel on the Advanced Camera for Surveys of the Hubble Space Telescope, the Near Infrared Camera of the James Webb Space Telescope, the Wide Field Imager of the Wide Field Infrared Survey Telescope, the Hyper Suprime Camera of the Subaru telescope, and the Visible Imaging Channel of the Euclid space mission.

Discovery of eight lensing clusters of galaxies

Clusters of galaxies have a huge mass which can act as gravitational lenses. Galaxies behind clusters can be distorted by the lenses to form arcs in images. Herein a search was done for giant lensed arcs using the SDSS data. By visually inspecting SDSS images of newly identified clusters in the SDSS DR8 and Stripe 82 data, we discover 8 strong lensing clusters together with additional 3 probable and 6 possible cases. The lensed arcs show bluer colors than the member galaxies of clusters. The masses and optical luminosities of galaxy clusters interior to the arcs are calculated. The mass-to-light ratios are found to be in the range of a few tens of M⊙/L⊙, consistent with the distribution of previously known lensing clusters.

Gravitational lensing in WDM cosmologies: the cross-section for giant arcs

The nature of the dark sector of the Universe remains one of the outstanding problems in modern cosmology, with the search for new observational probes guiding the development of the next generation of observational facilities. Clues come from tension between the predictions from {\Lambda}CDM and observations of gravitationally lensed galaxies. Previous studies showed that galaxy clusters in the {\Lambda}CDM are not strong enough to reproduce the observed number of lensed arcs. This work aims to constrain the warm dark matter cosmologies by means of the lensing efficiency of galaxy clusters drawn from these alternative models. The lensing characteristics of two samples of simulated clusters in the warm dark matter ({\Lambda}WDM) and cold dark matter ({\Lambda}CDM) cosmologies have been studied. The results show that even though the CDM clusters are more centrally concentrated and contain more substructures, the WDM clusters have slightly higher lensing efficiency than their CDM counterparts. The key difference is that WDM clusters have more extended and more massive subhaloes than CDM analogues. These massive substructures significantly stretch the critical lines and caustics and hence they boost the lensing efficiency of the host halo. Despite the increase in the lensing efficiency due to the contribution of massive substructures in the WDM clusters, this is not enough to resolve the arc statistics problem.

Strong lensing analysis of PLCK G004.5–19.5, aPlanck-discovered cluster hosting a radio relic atz= 0.52

The recent discovery of a large number of galaxy clusters using the Sunyaev-Zel'dovich (SZ) effect has opened a new era on the study of the most massive clusters in the Universe. Multi-wavelength analyses are required to understand the properties of these new sets of clusters, which are a sensitive probe of cosmology. We aim at a multi-wavelength characterization of PLCK G004.5$-$19.5, one of the most massive X-ray validated SZ effect-selected galaxy clusters discovered by the Planck satellite. We have observed PLCK G004.5$-$19.5 with GMOS on Gemini South for optical imaging and spectroscopy, and performed a strong lensing analysis. We also searched for associated radio emission in published catalogs. An analysis of the optical images confirms that this is a massive cluster, with a dominant central galaxy (the BCG) and an accompanying red sequence of galaxies, plus a $14''$-long strong lensing arc. Longslit pectroscopy of 6 cluster members shows that the cluster is at $z=0.516\pm0.002$. We also targeted the strongly lensed arc, and found $z_{\rm arc}=1.601$. We use LensTool to carry out a strong lensing analysis, from which we measure a median Einstein radius $\theta_E(z_s=1.6)\simeq30''$ and estimate an enclosed mass $M_E=2.45_{-0.47}^{+0.45}\times10^{14}\,M_\odot$. By extrapolating an NFW profile we find a total mass $M_{500}^{SL}=4.0_{-1.0}^{+2.1}\times10^{14}M_\odot$. Including a constraint on the mass from previous X-ray observations yields a slightly higher mass, $M_{500}^{SL+X}=6.7_{-1.3}^{+2.6}\times10^{14}M_\odot$, marginally consistent with the value from strong lensing alone. High-resolution radio images from TGSS at 150~MHz reveal that PLCK G004.5$-$19.5 hosts a powerful radio relic on scales $\lesssim500$ kpc. Emission at the same location is also detected in low resolution images at 843~MHz and 1.4~GHz. This is one of the higher redshift radio relics known to date.

CLASH: Photometric redshifts with 16 HST bands in galaxy cluster fields

The Cluster Lensing And Supernovae survey with Hubble (CLASH) is an Hubble Space Telescope (HST) Multi-Cycle Treasury program observing 25 massive galaxy clusters. CLASH observations are carried out in 16 bands from UV to NIR to derive accurate and reliable estimates of photometric redshifts. We present the CLASH photometric redshifts and study the photometric redshift accuracy of the arcs in more detail for the case of MACS1206.2-0847. We use the publicly available Le Phare and BPZ photometric redshift codes on 17 CLASH galaxy clusters. Using Le Phare code for objects with StoN>=10, we reach a precision of 3%(1+z) for the strong lensing arcs, which is reduced to 2.4%(1+z) after removing outliers. For galaxies in the cluster field the corresponding values are 4%(1+z) and 3%(1+z). Using mock galaxy catalogues, we show that 3%(1+z) precision is what one would expect from the CLASH photometry when taking into account extinction from dust, emission lines and the finite range of SEDs included in the photo-z template library. We study photo-z results for different aperture photometry and find that the SExtractor isophotal photometry works best. Le Phare and BPZ give similar photo-z results for the strong lensing arcs as well as galaxies of the cluster field. Results are improved when optimizing the photometric aperture shape showing an optimal aperture size around 1" radius giving results which are equivalent to isophotal photometry. Tailored photometry of the arcs improve the photo-z results.

Constraints on cosmological models from strong gravitational lensing systems

Strong lensing has developed into an importantastrophysical tool for probing both cosmology and galaxies (theirstructure, formation, and evolution). Using the gravitationallensing theory and cluster mass distribution model, we try tocollect a relatively complete observational data concerning theHubble constant independent ratio between two angular diameterdistances Dds/Ds from various large systematic gravitationallens surveys and lensing by galaxy clusters combined with X-rayobservations, and check the possibility to use it in the future ascomplementary to other cosmological probes. On one hand, stronglygravitationally lensed quasar-galaxy systems create such a newopportunity by combining stellar kinematics (central velocitydispersion measurements) with lensing geometry (Einstein radiusdetermination from position of images). We apply such a method to acombined gravitational lens data set including 70 data points fromSloan Lens ACS (SLACS) and Lens Structure and Dynamics survey(LSD). On the other hand, a new sample of 10 lensing galaxy clusterswith redshifts ranging from 0.1 to 0.6 carefully selected fromstrong gravitational lensing systems with both X-ray satelliteobservations and optical giant luminous arcs, is also used toconstrain three dark energy models (ΛCDM, constant w andCPL) under a flat universe assumption. For the full sample (n = 80)and the restricted sample (n = 46) including 36 two-image lenses and10 strong lensing arcs, we obtain relatively good fitting values ofbasic cosmological parameters, which generally agree with theresults already known in the literature. This results encouragesfurther development of this method and its use on larger samplesobtained in the future.

SOUTHERN COSMOLOGY SURVEY. II. MASSIVE OPTICALLY SELECTED CLUSTERS FROM 70 SQUARE DEGREES OF THE SUNYAEV–ZEL'DOVICH EFFECT COMMON SURVEY AREA

We present a catalog of 105 rich and massive ($M>3\times10^{14}M_{\sun}$) optically-selected clusters of galaxies extracted from 70 square-degrees of public archival griz imaging from the Blanco 4-m telescope acquired over 45 nights between 2005 and 2007. We use the clusters' optically-derived properties to estimate photometric redshifts, optical luminosities, richness, and masses. We complement the optical measurements with archival XMM-Newton and ROSAT X-ray data which provide additional luminosity and mass constraints on a modest fraction of the cluster sample. Two of our clusters show clear evidence for central lensing arcs; one of these has a spectacular large-diameter, nearly-complete Einstein Ring surrounding the brightest cluster galaxy. A strong motivation for this study is to identify the massive clusters that are expected to display prominent signals from the Sunyaev-Zeldovich Effect (SZE) and therefore be detected in the wide-area mm-band surveys being conducted by both the Atacama Cosmology Telescope and the South Pole Telescope. The optical sample presented here will be useful for verifying new SZE cluster candidates from these surveys, for testing the cluster selection function, and for stacking analyzes of the SZE data.

The lensing efficiencies of MACS X-ray-selected versus RCS optically selected galaxy clusters

The statistics of strongly lensed arcs in samples of galaxy clusters provide information on cluster structure that is complementary to that from individual clusters. However, samples of clusters that have been analyzed to date have been either small, heterogeneous, or observed with limited angular resolution. We measure the lensed-arc statistics of 97 clusters imaged at high angular resolution with the Hubble Space Telescope, identifying lensed arcs using two automated arc detection algorithms. The sample includes similar numbers of X-ray selected (MACS) and optically selected (RCS) clusters, and spans cluster redshifts in the range 0.2 < z < 1. We compile a catalogue of 42 arcs in the X-ray selected subsample and 7 arcs in the optical subsample. All but five of these arcs are reported here for the first time. At 0.3 < z < 0.7, the X-ray selected clusters have a significantly higher mean frequency of arcs, 1.2+/-0.2 per cluster, versus 0.2+/-0.1 in the optical sample. The strikingly different lensing efficiencies indicate that X-ray clusters trace much larger mass concentrations, despite the similar optical luminosities of the X-ray and optical clusters. The mass difference is supported also by the lower space density of the X-ray clusters, and by the small Einstein radii of the few arcs in the optical sample. Higher-order effects, such as differences in concentration or substructure, may also contribute.

XMMU J100750.5+125818: a strong lensing cluster atz= 1.082

We report on the discovery of the X-ray luminous cluster XMMU J100750.5+125818 at redshift 1.082 based on 19 spectroscopic members, which displays several strong lensing features. SED modeling of the lensed arc features from multicolor imaging with the VLT and the LBT reveals likely redshifts ~2.7 for the most prominent of the lensed background galaxies. Mass estimates are derived for different radii from the velocity dispersion of the cluster members, M_200 ~ 1.8 10^{14} Msun, from the X-ray spectral parameters, M_500 ~ 1.0 10^{14} Msun, and the largest lensing arc, M_SL ~ 2.3 10^{13} Msun. The projected spatial distribution of cluster galaxies appears to be elongated, and the brightest galaxy lies off center with respect to the X-ray emission indicating a not yet relaxed structure. XMMU J100750.5+125818 offers excellent diagnostics of the inner mass distribution of a distant cluster with a combination of strong and weak lensing, optical and X-ray spectroscopy.

The Third Image of the Large-Separation Lensed Quasar SDSS J1029+2623

We identify a third image in the unique quasar lens SDSS J1029+2623, the second known quasar lens produced by a massive cluster of galaxies. The spectrum of the third image shows similar emission and absorption features but has a redder continuum than the other two images, which can be explained by differential extinction or microlensing. We also identify several lensed arcs. Our observations suggest a complicated structure of the lens cluster at z ≈ 0.6. We argue that the three lensed images are produced by a naked cusp on the basis of successful mass models, the distribution of cluster member galaxies, and the shapes and locations of the lensed arcs. Lensing by a naked cusp is quite rare among galaxy-scale lenses but is predicted to be common among large-separation lensed quasars. Thus the discovery can be viewed as support for an important theoretical prediction of the standard cold dark matter model.

Automated Search for Gravitational Lensing Arcs and Interacting Galaxies in the Red Sequence Survey

AbstractWe have developed a robust and efficient algorithm to identify gravitational lensing arcs and interacting galaxies. The algorithm has been applied to the Red Sequence Survey II (RCS II) data, and we demonstrate a few examples here.

The kinematical structure of gravitationally lensed arcs

In this paper the expected properties of the velocity fields of strongly lensed arcs behind galaxy clusters are investigated. The velocity profile along typical lensed arcs is determined by ray tracing light rays from a model source galaxy through parametric cluster toy-models consisting of individual galaxies embedded in a dark cluster halo. We find that strongly lensed arcs of high redshift galaxies show complex velocity structures that are sensitive to the details of the mass distribution within the cluster, in particular at small scales. From fits to the simulated imaging and kinematic data we demonstrate that reconstruction of the source velocity field is in principle feasible: two dimensional kinematic information obtained with Integral Field Units (IFU's) on large ground based telescopes in combination with adaptive optics will allow the reconstruction of rotation curves of lensed high redshift galaxies. This makes it possible to determine the mass-to-light ratios of galaxies at redshifts z>1 out to about 2-3 scale lengths with better than about 20% accuracy. We also discuss the possibilities of using two dimensional kinematic information along the arcs to give additional constraints on the cluster lens mass models.