Giant Luminous Arcs Research Articles

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.

Combining optical and X-ray observations of galaxy clusters to constrain cosmological parameters

Galaxy clusters present unique advantages for cosmological study. Here we collect a new sample of 10 lensing galaxy clusters with X-ray observations to constrain cosmological parameters. The redshifts of the lensing clusters lie between 0.1 and 0.6, and the redshift range of their arcs is from 0.4 to 4.9. These clusters are selected carefully from strong gravitational lensing systems which have both X-ray satellite observations and optical giant luminous arcs with known redshifts. Giant arcs usually appear in the central region of clusters, where mass can be traced with luminosity quite well. Based on gravitational lensing theory and a cluster mass distribution model, we can derive a ratio using two angular diameter distances. One is the distance between lensing sources and the other is that between the deflector and the source. Since angular diameter distance relies heavily on cosmological geometry, we can use these ratios to constrain cosmological models. Moreover, X-ray gas fractions of galaxy clusters can also be a cosmological probe. Because there are a dozen parameters to be fitted, we introduce a new analytic algorithm, Powell's UOBYQA (Unconstrained Optimization By Quadratic Approximation), to accelerate our calculation. Our result demonstrates that this algorithm is an effective fitting method for such a continuous multi-parameter constraint. We find an interesting fact that these two approaches are separately sensitive to ΩΛ and ΩM. By combining them, we can get reasonable fitting values of basic cosmological parameters: ΩM = 0.26+0.04−0.04, and ΩΛ = 0.82+0.14−0.16.

Strong gravitational lensing: relativity in action

AbstractDeflection of light by gravity was predicted by Einstein's Theory of General Relativity and observationally confirmed in 1919. In the following decades, various aspects of the gravitational lens effect were explored theoretically, among them measuring the Hubble constant from multiple images of a background source, making use of the magnifying effect as a gravitational telescope, or the possibility of a “relativistic eclipse” as a perfect test of GR. Only in 1979, gravitational lensing became an observational science when the first doubly imaged quasar was discovered. Today lensing is a booming part of astrophysics and cosmology. A whole suite of strong lensing phenomena have been investigated: multiple quasars, giant luminous arcs, Einstein rings, quasar microlensing, and galactic microlensing. The most recent lensing application is the detection of extrasolar planets. Lensing has contributed significant new results in areas as different as the cosmological distance scale, mass determination of galaxy clusters, physics of quasars, searches for dark matter in galaxy halos, structure of the Milky Way, stellar atmospheres and exoplanets. A guided tour through some of these applications will illustrate how gravitational lensing has established itself as a very useful universal astrophysical tool.

Gravitational lensing as a powerful astrophysical tool: Multiple quasars, giant arcs and extrasolar planets

In the 25 years since the discovery of the first double quasar Q0957+561, gravitational lensing has established itself as a valuable tool in many branches of astronomy. Fields as different as galactic structure, cosmology, or extrasolar planets benefit from the gravitational lensing effect. This article starts with a brief historic reflection, then the basics of light deflection are reviewed. Observable lensing effects and a few examples of strong lensing phenomena are shown. In the main part four applications of ''strong'' lensing will be presented and discussed: The determination of the Hubble constant from time delay measurements in multiple quasars; it is argued that this method of determining H0 is competitive with other methods by now. The lensing-derived values of H0 are on the low side. Microlensing of quasars– the effects of compact stellar-mass objects on the apparent brightness – allows us to constrain the quasar size and the occurrence of dark matter objects. The frequency of giant luminous arcs strongly depends on the high mass end of the galaxy cluster distribution. Recent investigations show that arc statistics is in agreement with the concordance cosmological model. Searching for extrasolar planets is one of the most recent applications of gravitational lensing. The first detection shows that the method works well. This planet-search method is complementary to other programs and has the potential to detect exo-planets with lower masses than other ground-based techniques. An outlook is provided on the prospects of gravitational lensing in the next few years. In particular the magnification effect on faint high-redshift sources will be used for the investigation of the early universe, and the detection of low-mass extrasolar planets will provide a valuable sample for statistical evaluations of the frequency of exoplanets.

Gravitational lensing as a powerful astrophysical tool: Multiple quasars, giant arcs and extrasolar planets

AbstractIn the 25 years since the discovery of the first double quasar Q0957+561, gravitational lensing has established itself as a valuable tool in many branches of astronomy. Fields as different as galactic structure, cosmology, or extrasolar planets benefit from the gravitational lensing effect. This article starts with a brief historic reflection, then the basics of light deflection are reviewed. Observable lensing effects and a few examples of strong lensing phenomena are shown. In the main part four applications of ''strong'' lensing will be presented and discussed: The determination of the Hubble constant from time delay measurements in multiple quasars; it is argued that this method of determining H0 is competitive with other methods by now. The lensing‐derived values of H0 are on the low side. Microlensing of quasars– the effects of compact stellar‐mass objects on the apparent brightness – allows us to constrain the quasar size and the occurrence of dark matter objects.The frequency of giant luminous arcs strongly depends on the high mass end of the galaxy cluster distribution. Recent investigations show that arc statistics is in agreement with the concordance cosmological model. Searching for extrasolar planets is one of the most recent applications of gravitational lensing. The first detection shows that the method works well. This planet‐search method is complementary to other programs and has the potential to detect exo‐planets with lower masses than other ground‐based techniques.An outlook is provided on the prospects of gravitational lensing in the next few years. In particular the magnification effect on faint high‐redshift sources will be used for the investigation of the early universe, and the detection of low‐mass extrasolar planets will provide a valuable sample for statistical evaluations of the frequency of exoplanets.

The Lensed Arc Production Efficiency of Galaxy Clusters: A Comparison of Matched Observed and Simulated Samples

We compare the statistical properties of giant gravitationally lensed arcs produced in matched simulated and observed cluster samples. The observed sample consists of 10 X-ray selected clusters at redshifts z ~ 0.2 imaged with HST by Smith et al. The simulated dataset is produced by lensing the Hubble Deep Field, which serves as a background source image, with 150 realizations (different projections and shifts) of five simulated z = 0.2 clusters from a LambdaCDM N-body simulation. The real and simulated clusters have similar masses, the real photometric redshift is used for each background source, and all the observational effects influencing arc detection in the real dataset, including light from cluster galaxies, are simulated in the artificial dataset. We develop, and apply to both datasets, an objective automatic arc-finding algorithm. We find consistent arc statistics in the real and in the simulated sample, with an average of ~ 1 detected giant (length to width ratio >= 10) arc per cluster and ~ 0.2 giant luminous (R<22.3 mag) arc per cluster. Thus, taking into account a realistic source population and observational effects, the clusters predicted by LambdaCDM have the same arc-production efficiency as the observed clusters. If, as suggested by other studies, there is a discrepancy between the predicted and the observed total number of arcs on the sky, it must be the result of differences between the redshift dependent cluster mass functions, and not due to differences in the lensing efficiency of the most massive clusters.

Determining cosmological parameters from X-ray measurements of strong lensing clusters

We discuss a new method which is potentially capable of constraining cosmological parameters using observations of giant luminous arcs in rich X-ray clusters of galaxies. The mass profile and the mass normalization of the lenses are determined from X-ray measurements. The method also allows to probe the amount and equation of state of the dark energy in the universe. The analysis of a preliminary sample of 6 luminous, relatively relaxed clusters of galaxies strongly favours an accelerating expansion of the universe. Under the assumption that the dark energy is in the form of a cosmological constant, the data provide an estimate of �0 = 1.1 with a statistical error of ±0.2. Including the constraint of a flat universe and an equation of state for the dark energy wX > 1, we obtain M0 = 0.10±0.10 and wX = 0.84±0.14. Relaxing the prior on wX, we find that the null energy condition is satisfied at the 3-σ confidence level.

Weak Gravitational Lensing by a Sample of X‐Ray–luminous Clusters of Galaxies. III. Serendipitous Weak Lensing Detections of Dark and Luminous Mass Concentrations

In the course of a weak gravitational lensing survey of 39 clusters of galaxies,covering a total sky area of ~1 square degree, we have serendipitously discovered mass concentrations in the fields of A1705 and A1722 which are most probably not associated with the main cluster target. By combining weak lensing information with two-color galaxy photometry in fields centered on our sample clusters, we identify a new cluster candidate at z~0.5 in the field of A1705. This cluster candidate also displays strong lensing in the form of a giant luminous arc. The new mass concentration in the field of A1722 also seems to be associated with an optically luminous cluster of galaxies at z~0.5, but in this case there is some evidence for additional structures along the line of sight that may contribute to the lensing signal. A third cluster, A959, has a dark sub-clump which shows interesting morphological evidence in the mass map for being associated with the main cluster. This is the first case where there is any significant evidence for a physical association between a dark sub-clump (discovered from weak lensing) and a normal cluster. Analysis of archival X-ray data shows that the three new mass concentrations are not firmly detected in X-rays and that they are X-ray underluminous.

Gravitational Microlensing of Giant Luminous Arcs: a Test for Compact Dark Matter in Clusters of Galaxies

AbstractThe true nature of dark matter in the universe still eludes us. This paper discusses a new test for the detection of stellar mass compact dark matter in galaxy clusters by observing its gravitational lensing influence on the surface brightness of giant luminous arcs. If dark matter is in the form of stellar mass compact objects, then the extremes of such variability are accessible to a monitoring campaign with the Hubble Space Telescope. With the advent of the Next Generation Space Telescope, cluster dark matter in the form of compact objects will induce a ubiquitous ‘shimmering’ of the giant arcs.

Detection of iron emission line from the galaxy cluster including the distant radio galaxy 3C220.1

We detected an emission line feature at 4 keV in the X-ray spectrum of a sky region including the distant radio galaxy 3C220.1( z = 0.62) obtained with ASCA. The line energy is 6.1 7.0 keV (90% confidence) in the rest frame of 3C220.1. Within the present statistics, the observed spectra are consistent with two different models; a non-thermal model consisting of a power-law continuum plus a 6.4 keV iron emission line, and a Raymond-Smith thin-thermal emission model of k T ∼ 6keV with a metal abundance of ∼ 0.5 solar. However, the large (∼ 500 eV) equivalent width of the line indicates that a significant fraction of the X-ray emission is likely to arise from the hot intracluster gas associating the galaxy cluster including 3C220.1. The spectral parameters of the thermal emission are consistent with the luminosity-temperature relation of nearby clusters and the mass estimates from the giant luminous arc.

Galaxy cluster masses from arc statistics based on ROSAT/HRI data

We examine the expected number of giant luminous arcs (GLAs) for Le Fèvre et al. arc survey sample using two spherically symmetric lens models in which free parameters are determined from ROSAT/HRI X-ray data. We conclude that spherically symmetric models cannot reproduce the observed number of giant luminous arcs in the sample.

Detection of Iron emission line from the galaxy cluster including the distant radio galaxy 3C220.1

We detected an emission line feature at 4 keV in the X-ray spectrum of a sky region including the distant radio galaxy 3C220.1(z=0.62) obtained with ASCA. The line energy is 6.1 - 7.0 keV (90% confidence) in the rest frame of 3C220.1. Within the present statistics, the observed spectra are consistent with two different models; a non-thermal model consisting of a power-law continuum plus a 6.4 keV iron emission line, and a Raymond-Smith thin-thermal emission model of kT ~6 keV with a metal abundance of ~0.5 solar. However, the large (~500 eV) equivalent width of the line indicates that a significant fraction of the X-ray emission is likel y to arise from the hot intracluster gas which associates the galaxy cluster including 3C220.1. The spectral parameters of the thermal emission is consistent with the luminosity-temperature relation of nearby clusters and the mass estimates from the giant luminous arc.

Detection of Iron emission line from the galaxy cluster including the distant radio galaxy 3C220.1

We detected an emission line feature at 4 keV in the X-ray spectrum of a sky region including the distant radio galaxy 3C220.1(z=0.62) obtained with ASCA. The line energy is 6.1 - 7.0 keV (90% confidence) in the rest frame of 3C220.1. Within the present statistics, the observed spectra are consistent with two different models; a non-thermal model consisting of a power-law continuum plus a 6.4 keV iron emission line, and a Raymond-Smith thin-thermal emission model of kT ~6 keV with a metal abundance of ~0.5 solar. However, the large (~500 eV) equivalent width of the line indicates that a significant fraction of the X-ray emission is likel y to arise from the hot intracluster gas which associates the galaxy cluster including 3C220.1. The spectral parameters of the thermal emission is consistent with the luminosity-temperature relation of nearby clusters and the mass estimates from the giant luminous arc.

Gravitational Lensing in Astronomy.

Deflection of light by gravity was predicted by General Relativity and observationally confirmed in 1919. In the following decades, various aspects of the gravitational lens effect were explored theoretically. Among them were: the possibility of multiple or ring-like images of background sources, the use of lensing as a gravitational telescope on very faint and distant objects, and the possibility of determining Hubble’s constant with lensing. It is only relatively recently, (after the discovery of the first doubly imaged quasar in 1979), that gravitational lensing has became an observational science. Today lensing is a booming part of astrophysics.In addition to multiply-imaged quasars, a number of other aspects of lensing have been discovered: For example, giant luminous arcs, quasar microlensing, Einstein rings, galactic microlensing events, arclets, and weak gravitational lensing. At present, literally hundreds of individual gravitational lens phenomena are known.Although still in its childhood, lensing has established itself as a very useful astrophysical tool with some remarkable successes. It has contributed significant new results in areas as different as the cosmological distance scale, the large scale matter distribution in the universe, mass and mass distribution of galaxy clusters, the physics of quasars, dark matter in galaxy halos, and galaxy structure. Looking at these successes in the recent past we predict an even more luminous future for gravitational lensing.Electronic Supplementary MaterialSupplementary material is available for this article at 10.12942/lrr-1998-12.

Discovery of X‐Ray Emission from the Distant Lensing Cluster of Galaxies Cl 2236−04 atz= 0.552

X-ray emission from the distant lensing cluster Cl 2236-04 at z = 0.552 was discovered by ASCA and ROSAT/HRI observations. If the spherical symmetric mass distribution model of the cluster is assumed, the lensing estimate of the cluster mass is a factor of 2 higher than that obtained from X-ray observations as reported for many distant clusters. However, the elliptical and clumpy lens model proposed by Kneib and coworkers is surprisingly consistent with the X-ray observations, assuming that the X-ray-emitting hot gas is isothermal and in a hydrostatic equilibrium state. The existence of the cooling flow in the central region of the cluster is indicated by the short central cooling time and the excess flux detected by ROSAT/HRI compared to the ASCA flux. However, it is shown that, even if the Cl 2236-04 has a cooling flow in the central region, the temperature measured by ASCA, which is the mean emission-weighted cluster temperature in this case, should not be different from the virial temperature of the cluster. Therefore, we conclude that the effects of the clumpiness and nonzero ellipticity in the mass distribution of the cluster are essential to explain the observed feature of the giant luminous arc, and in this cluster there is no discrepancy between strong lensing and X-ray estimation of the cluster mass.

Non-parametric reconstruction of cluster mass distribution from strong lensing: modelling Abell 370

We describe a new non-parametric technique for reconstructing the mass distribution in galaxy clusters with strong lensing, i.e., from multiple images of background galaxies. The observed positions and redshifts of the images are considered as rigid constraints and through the lens (ray-trace) equation they provide us with linear constraint equations. These constraints confine the mass distribution to some allowed region, which is then found by linear programming. Within this allowed region we study in detail the mass distribution with minimum mass-to-light variation; also some others, such as the smoothest mass distribution. The method is applied to the extensively studied cluster Abell 370, which hosts a giant luminous arc and several other multiply imaged background galaxies. Our mass maps are constrained by the observed positions and redshifts (spectroscopic or model-inferred by previous authors) of the giant arc and multiple image systems. The reconstructed maps obtained for \a370 reveal a detailed mass distribution, with substructure quite different from the light distribution. The method predicts the bimodal nature of the cluster and that the projected mass distribution is indeed elongated along the axis defined by the two dominant cD galaxies. But the peaks in the mass distribution appear to be offset from the centres of the cDs. We also present an estimate for the total mass of the central region of the cluster. This is in good agreement with previous mass determinations. The total mass of the central region is M=(2.0-2.7) 10^14 Msun/h50, depending on the solution chosen.

Testing Cosmological Models by Gravitational Lensing. I. Method and First Applications

Gravitational lensing directly measures mass density fluctuations along the lines of sight to very distant objects. No assumptions need to be made concerning bias, the ratio of fluctuations in galaxy density to mass density. Hence, lensing is a very useful tool for studying the universe at low to moderate redshifts. We describe in detail a new method for tracing light rays from redshift zero through a three-dimensional mass distribution to high redshift. As an example, this method is applied here to a standard cold dark matter universe. We obtain a variety of results, some of them statistical in nature, others from rather detailed case studies of individual lines of sight. Among the statistical results are the frequency of multiply imaged quasars, the distribution of separation of multiple quasars, and the redshift distribution of lenses, all as functions of quasar redshift. We find effects ranging from very weak lensing to highly magnified multiple images of high-redshift objects, which for extended background sources (i.e., galaxies) range from slight deformation of shape to tangentially aligned arclets to giant luminous arcs. Different cosmological models differ increasingly with redshift in their predictions of mass (and thus gravitational potential) distributions. Our ultimate goal is to apply this method to a number of cosmogonic models and to eliminate some models for which the gravitational lensing properties are inconsistent with those observed.

Non-parametric reconstruction of cluster mass distribution from strong lensing: modelling Abell 370

We describe a new non-parametric technique for reconstructing the mass distribution in galaxy clusters with strong lensing, i.e. from multiple images of background galaxies. The observed positions and redshifts of the images are considered as rigid constraints, and through the lens (ray-trace) equation they provide us with linear constraint equations. These constraints confine the mass distribution to some allowed region, which is then found by linear programming. Within this allowed region we study in detail the mass distribution with minimum mass-to-light variation, and also some other distributions, such as the smoothest mass distribution. The method is applied to the extensively studied cluster Abell 370, which hosts a giant luminous arc and several other multiply imaged background galaxies. Our mass maps are constrained by the observed positions and redshifts (spectroscopic or model-inferred by previous authors) of the giant arc and multiple-image systems. The reconstructed maps obtained for Abell 370 reveal a detailed mass distribution, with substructure quite different from the light distribution. The method predicts the bimodal nature of the cluster, and that the projected mass distribution is indeed elongated along the axis defined by the two dominant cD galaxies. However, the peaks in the mass distribution appear to be offset from the centres of the cDs. We also present an estimate for the total mass of the central region of the cluster. This is in good agreement with previous mass determinations. The total mass of the central region is M=(2.0–2.7)×1014 M⊙h−150, depending on the solution chosen.

Weak Gravitational Lensing—The Need for Surveys

Light rays from distant sources are deflected if they pass near an intervening matter inhomogeneity. This gravitational lens effect is responsible for the well-established lens systems like multiple-imaged QSOs, (radio) ‘Einstein’ rings, the giant luminous arcs in clusters of galaxies, and the flux variations of stars in the LMC and the Galactic bulge seen in the searches for compact objects in our Galaxy. These types of lensing events are nowadays called ‘strong lensing,’ to distinguish it from the effects discussed here: light bundles are not only deflected as a whole, but distorted by the tidal gravitational field of the deflector. This image distortion can be quite weak and can then not be detected in individual images. However, since we are lucky to live in a Universe where the sky is full of faint distant galaxies, this distortion effect can be discovered statistically. This immediately implies that weak lensing requires excellent and deep images so that image shapes (and sizes) can be accurately measured and the number density be as high as possible to reduce statistical uncertainties. Weak gravitational lensing can be defined as using the faint galaxy population to measure the mass and/or mass distribution of individual intervening cosmic structures, or the statistical properties of their mass distribution, or to detect them in the first place, independent of the physical state or nature of the matter, or the luminosity of these mass concentrations. In addition, weak lensing can be used to infer the redshift distribution of the faintest galaxies. After introducing the necessary concepts, I will list the main applications of weak lensing and discuss some of them in slightly more detail, stressing the need for very deep and wide-field images of the sky taken with instruments of excellent image quality.

Detailed Lensing Properties of the MS 2137−2353 Core and Reconstruction of Sources fromHubble Space TelescopeImagery

A deep HST image of the core of the cluster of galaxies MS 2137-2353 has revealed detailed morphological structures in two arc systems, which are modeled and well reproduced. An analysis of the lensing properties of the dark matter component indicates that the cluster could have a mass distribution almost as simple as a single elliptical mass distribution, with ellipticity and angular orientation similar to those in visible and X-ray light. This suggests that MS 2137-2353 is a relaxed cluster at z = 0.313. The predicted density profile (ρ ~ r-1.75 ± 0.09, with rc ≤ 17 h−150 kpc) within 150 h−150 kpc, implies a M/L ratio increasing with the radius, and could be in agreement with predictions from standard CDM simulations. Two faint sources (unlensed magnitude R = 23.5 and 25.6) at the same redshift are aligned with the cluster core and are responsible for the arc systems. They have been reconstructed with details as small as 0015 (or 120 h−150 pc in the source assumed at z = 1), and show complex morphology, which for one source could be related to a close interacting pair and/or to dust. They also show strong signs of star formation, indicated by compact H II regions away from their centers. Because magnification factors of the giant luminous arc are large, our method can even resolve the size of a giant H II region at z ~ 1.