A STUDY OF GRAVITATIONAL LENS CHROMATICITY USING GROUND-BASED NARROWBAND PHOTOMETRY

We present high-resolution CCD images (FWHM ≈ 0.6 – 0.7) of the compact gravitational lens system B0218+35.7 obtained at the Nordic Optical Telescope. Using aperture and point spread function photometry, we detect the two closely separated (335 mas) components A and B as well as the lensing galaxy. In the optical B seems to be very much brighter than A, in contrast to the radio structure. This suggests that most of the light from A is absorbed in the lensing galaxy, possibly by a giant molecular cloud located in the line of sight to component A. The lensing galaxy appears to be a late-type galaxy at a small inclination. For future variability studies, we present calibrated photometry of the system and its immediate surroundings, even though the relative faintness of A will make it difficult to obtain an optical time delay even with the Hubble Space Telescope.

We report the discovery of a new gravitational lens system from the CLASS survey. Radio observations with the VLA, the WSRT and MERLIN show that the radio source B0850+054 is comprised of two compact components with identical spectra, a separation of 0.7 arcsec and a flux density ratio of 6:1. VLBA observations at 5 GHz reveal structures that are consistent with the gravitational lens hypothesis. The brighter of the two images is resolved into a linear string of at least six sub-components whilst the weaker image is radially stretched towards the lens galaxy. UKIRT K-band imaging detects an 18.7 mag extended object, but the resolution of the observations is not sufficient to resolve the lensed images and the lens galaxy. Mass modelling has not been possible with the present data and the acquisition of high-resolution optical data is a priority for this system.

We report the discovery of a new gravitational lens system. This object, ULAS J234311.93-005034.0, is the first to be selected by using the new UKIRT Infrared Deep Sky Survey (UKIDSS), together with the Sloan Digital Sky Survey (SDSS). The ULAS J234311.93-005034.0 system contains a quasar at redshift 0.788 which is doubly imaged, with separation 1.4 arcsec. The two quasar images have the same redshift and similar, though not identical, spectra. The lensing galaxy is detected by subtracting point spread functions from R-band images taken with the Keck telescope. The lensing galaxy can also be detected by subtracting the spectra of the A and B images, since more of the galaxy light is likely to be present in the latter. No redshift is determined from the galaxy, although the shape of its spectrum suggests a redshift of about 0.3. The object's lens status is secure, due to the identification of two objects with the same redshift together with a lensing galaxy. Our imaging suggests that the lens is found in a cluster environment, in which candidate arc-like structures, that require confirmation, are visible in the vicinity. Further discoveries of lenses from the UKIDSS survey are likely as part of this programme, due to the depth of UKIDSS and its generally good seeing conditions.

view Abstract Citations (100) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Do the Redshifts of Gravitational Lens Galaxies Rule Out a Large Cosmological Constant? Kochanek, Christopher S. Abstract The distribution of lens galaxy redshifts in known gravitational lens systems is an extremely powerful means of discriminating between some cosmologies. Standard cosmologies are 5-10 times more probable than flat large cosmological constant cosmologies with λ_0_ >~ 0.9 based on the existing small sample. A few additional gravitational lens systems produced by isolated galaxies with known source and lens redshifts would settle the question, because the probability of the redshift distribution in an Einstein-de Sitter universe agreeing with the flat λ_0_ >~ 0.9 models drops faster than proportional to (0.5)^N^, where N is the number of systems. The uncertainties in the mass distribution of galaxies are larger than the differences between standard FRW {OMEGA}_0_ = 0 to {OMEGA}_0_ = 1 models. If we confine ourselves to Einstein-de Sitter cosmologies, we can predict redshifts for several of the lenses in which they are not currently known. If we model the lens galaxies as ellipticals, then the predicted redshifts of the lens galaxy for the gravitational lenses PG 1115+080 and 1413+117 are z_L_= 0.37+/-0.18 (0.48 +/- 0.22) and Z_L_ = 0.68 +/- 0.33, (0.92+/-0.40) where the errors correspond to one standard deviation in the redshift probability distribution, and the two sets of ranges correspond to σ_m_ = σ or σ_m_ = (3/2)^1/2sigma, where σ_m_ is the velocity dispersion characteristic of the mass distribution, and σ is the measured velocity dispersion. Publication: The Astrophysical Journal Pub Date: January 1992 DOI: 10.1086/170845 Bibcode: 1992ApJ...384....1K Keywords: Cosmology; Galaxies; Gravitational Lenses; Red Shift; Astronomical Models; Einstein Equations; Astrophysics; COSMOLOGY: GRAVITATIONAL LENSING; COSMOLOGY: OBSERVATIONS; GALAXIES: DISTANCES AND REDSHIFTS full text sources ADS | data products SIMBAD (9) NED (5)

Quadruple gravitational lens systems offer the possibility of measuring time delays for image pairs, microlensing effects, and extinction in distant galaxies. Observations of these systems may be used to obtain estimates of H_o and to study the various mass components of lens galaxies at high redshifts. With HST, we have observed the reddest known gravitational lens system, MG 0414+0534. We used WFPC2/PC1 to obtain deep, high-resolution images with two filters, F675W and F814W. We present a detailed analysis of all of the components, as well as macrolens models. Our main results are: (1) confirmation that MG 0414+0534 is inescapably a gravitational lens system; (2) discovery of a blue arc connecting the 3 brightest images of the QSO central core; (3) accurate positions and apparent brightnesses for all 4 known images of the QSO central core and for the lens galaxy G; (4) a good representation of the brightness distribution of G by elliptical isophotes with a De Vaucouleurs profile, characteristic of an elliptical galaxy; (5) models that consist of simple elliptical potentials and account qualitatively, not quantitatively, for the HST image positions, arc morphology and radio flux ratios for the images of the QSO central core; (6) a possible new test to distinguish between reddening in the host galaxy of the QSO and in the lens galaxy, based on future accurate measurements of spatial variations in the color of the arc; and (7) the suggestion that microlensing is a plausible cause for the differences between the radio and optical flux ratios for the brightest images, A1 and A2. Further observations and measurements such as of the redshift of the lens galaxy, can be used fruitfully to study microlensing for this system.

The effect of extremely low frequency primordial gravitational wave with arbitrary direction of propagation on a gravitational lens system in expanding universe is investigated. From the point of view of real astrophysical lens model, singular isothermal sphere lens model is adopted in the gravitational lens system. The results show that, under the perturbation from extremely low frequency primordial gravitational wave, time delay in the gravitational lens system is very sensitive to extremely low frequency primordial gravitational wave and could strongly deviate from that deduced from theoretical model. This means that the strongly deviated time delay could be the imprint of extremely low frequency primordial gravitational wave on gravitational lens system, indicating that gravitational lens system could be used as a long baseline detector to detect extremely low frequency primordial gravitational wave.

Strong gravitational lensing is a powerful technique for probing galaxy mass distributions and for measuring cosmological parameters. We present a pixelated approach to modeling simultaneously the lens potential and source intensity of strong gravitational lens systems with extended source-intensity distributions. For systems with sources of sufficient extent such that the separate lensed images are connected by intensity measurements, the accuracy in the reconstructed potential is solely limited by the quality of the data. We apply this potential reconstruction technique to deep HST observations of B1608+656, a four-image gravitational lens system formed by a pair of interacting lens galaxies. We present a comprehensive Bayesian analysis of the system that takes into account the extended source-intensity distribution, dust extinction, and the interacting lens galaxies. Our approach allows us to compare various models of the components of the lens system, which include the point-spread function (PSF), dust, lens galaxy light, source-intensity distribution, and lens potential. Using optimal combinations of the PSF, dust, and lens galaxy light models, we successfully reconstruct both the lens potential and the extended source-intensity distribution of B1608+656. The resulting reconstruction can be used as the basis of a measurement of the Hubble constant. We use our reconstruction of the gravitational potential to study the relative distribution of mass and light in the lensing galaxies. We find that the mass-to-light ratio for the primary lens galaxy is (2.0+/-0.2)h M_{\sun} L_{B,\sun}^{-1} within the Einstein radius 3.9 h^{-1} kpc, in agreement with what is found for noninteracting lens galaxies at the same scales. (Abridged)

Previous observations of the environments of the lensing galaxies in gravitational lens systems suggest that many of the lensing galaxies are associated with small groups of galaxies. As a result, we have begun a coordinated program to study the local environments of all known gravitational lens systems. In this paper, we present results on the gravitational lens system CLASS B0712+472, which has previously measured source and lens redshifts of (zl, zs) = (0.4060, 1.339). Although we have not found a galaxy group associated with the primary lensing galaxy, we have found a foreground group that is spatially coincident with the lens system. Based on multiobject spectroscopy taken at the Keck 10 m telescope, we have confirmed 10 group members with a mean redshift of = 0.2909. The resulting velocity dispersion and estimated virial mass are 306 km s-1 and 3.0 × 1013 h-1 M⊙, respectively, for (Ωm, ΩΛ) = (0.2, 0.0). The dynamical properties of this moderate-redshift group are completely consistent with the range of values found in nearby groups of galaxies. Five of the group members are red elliptical-like galaxies, while the remaining five are active star-forming galaxies. Based on the spectroscopic results and the publicly available Hubble Space Telescope imaging of nine group members, we find that the early-type fraction is 40%. We estimate that the effect of this foreground group on the gravitational lensing potential of B0712+472 is small, producing an external shear that is only a few percent, although the shear could be larger if the group centroid is significantly closer to the lens system than it appears to be.

We present narrowband images of the gravitational lens system Q~2237+0305 made with the Nordic Optical Telescope in eight different filters covering the wavelength interval 3510-8130 \AA. Using point-spread function photometry fitting we have derived the difference in magnitude versus wavelength between the four images of Q~2237+0305. At $\lambda=4110$ \AA, the wavelength range covered by the Str\"omgren-v filter coincides with the position and width of the CIV emission line. This allows us to determine the existence of microlensing in the continuum and not in the emission lines for two images of the quasar. Moreover, the brightness of image A shows a significant variation with wavelength which can only be explained as consequence of chromatic microlensing. To perform a complete analysis of this chromatic event our observations were used together with Optical Gravitational Lensing Experiment light curves. Both data sets cannot be reproduced by the simple phenomenology described under the caustic crossing approximation; using more realistic representations of microlensing at high optical depth, we found solutions consistent with simple thin disk models ($r_{s}\varpropto \lambda^{4/3}$); however, other accretion disk size-wavelength relationships also lead to good solutions. New chromatic events from the ongoing narrow band photometric monitoring of Q~2237+0305 are needed to accurately constrain the physical properties of the accretion disk for this system.

This study is based on a monitoring of the two components (A and B) of the gravitational lens system QSO 0957+561. The V-band and R-band observations were made with the Nordic Optical Telescope (Roque de los Muchachos Observatory, La Palma, Spain). We have obtained the light curves of the two components in both filters, as well as the corresponding magnification ratios. Finally, we explain the V-band and R-band magnification ratios through two different physical processes taking place in the lens galaxy: microlensing and extinction.

We present observations of CLASS B2108+213, the widest separation gravitational lens system discovered by the Cosmic Lens All-Sky Survey. Radio imaging using the VLA at 8.46 GHz and MERLIN at 5 GHz shows two compact components separated by 4.56 arcsec with a faint third component in between which we believe is emission from a lensing galaxy. 5-GHz VLBA observations reveal milliarcsecond-scale structure in the two lensed images that is consistent with gravitational lensing. Optical emission from the two lensed images and two lensing galaxies within the Einstein radius is detected in Hubble Space Telescope imaging. Furthermore, an optical gravitational arc, associated with the strongest lensed component, has been detected. Surrounding the system is a number of faint galaxies which may help explain the wide image separation. A plausible mass distribution model for CLASS B2108+213 is also presented.

After some preliminary observations in 1990, a program was started in 1991 at the Nordic Optical Telescope (NOT) on the island of La Palma for monitoring mainly four well known gravitational lens systems: QSO0142-100, QSO0957+561, QS01413+117 and QSO2237+0305 (The Einstein Cross). Here we report results from the monitoring of the Einstein Cross. During the four year period the Monitor Program was active (1990-1993) we gathered 55 high quality observations of this well known lens system. In addition we have collected 32 more observations in 1994 and a further four so far in 1995, a total of 91 new observations of the Einstein Cross.Here we report results from the monitoring of the Einstein Cross. During the four year period the Monitor Program was active (1990–1993) we gathered 55 high quality observations of this well known lens system. In addition we have collected 32 more observations in 1994 and a further four so far in 1995, a total of 91 new observations of the Einstein Cross.

The Gravitational Lenses International Time Project (GLITP) collaboration observed the first gravitational lens system (QSO 0957+561) from 2000 February 3 to March 31. The daily VR observations were made with the 2.56-m Nordic Optical Telescope at Roque de los Muchachos Observatory, La Palma, Spain. We have derived detailed and robust VR light curves of the two components Q0957+561A and Q0957+561B. In spite of the excellent sampling rate, we have not found evidence in favour of true daily variability. With respect to variability on time-scales of several weeks, we measure VR gradients of about -0.8 mmag d - 1 in Q0957+561A and +0.3 mmag d - 1 in Q0957+561B. The gradients are very probably originated in the far source. Thus, adopting this reasonable hypothesis (intrinsic variability), we compare them to the expected gradients during the evolution of a compact supernova remnant at the redshift of the source quasar. The starburst scenario is roughly consistent with some former events, but the new gradients do not seem to be caused by supernova remnant activity.

After some preliminary observations in 1990, a program was started in 1991 at the Nordic Optical Telescope (NOT) on the island of La Palma for monitoring mainly four well known gravitational lens systems: QS00142−100, QS00957+561, QS01413+117 and QS02237+0305 (The Einstein Cross).

We present the first automated spectroscopic search for disk-galaxy lenses, using the Sloan Digital Sky Survey database. We follow up eight gravitational lens candidates, selected among a sample of ~40000 candidate massive disk galaxies, using a combination of ground-based imaging and long-slit spectroscopy. We confirm two gravitational lens systems: one probable disk galaxy, and one probable S0 galaxy. The remaining systems are four promising disk-galaxy lens candidates, as well as two probable gravitational lenses whose lens galaxy might be an S0 galaxy. The redshifts of the lenses are z_lens ~ 0.1. The redshift range of the background sources is z_source ~ 0.3 - 0.7. The systems presented here are (confirmed or candidate) galaxy-galaxy lensing systems, that is, systems where the multiple images are faint and extended, allowing an accurate determination of the lens galaxy mass and light distributions without contamination from the background galaxy. Moreover, the low redshift of the (confirmed or candidates) lens galaxies is favorable for measuring rotation points to complement the lensing study. We estimate the rest-frame total mass-to-light ratio within the Einstein radius for the two confirmed lenses: we find M_tot/L_I = 5.4 +- 1.5 within 3.9 +- 0.9 kpc for SDSS J081230.30+543650.9, and M_tot/L_I = 1.5 +- 0.9 within 1.4 +- 0.8 kpc for SDSS J145543.55+530441.2 (all in solar units). Hubble Space Telescope or Adaptive Optics imaging is needed to further study the systems.