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  • 1
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    Spectroscopy and high-resolution imaging of the gravitational lens SDSS J1206+4332 (2016)
    Oxford University Press
    Details
    Publication Date: 2016-04-07
    Description: We present spectroscopy and laser guide star adaptive optics (LGSAO) images of the doubly imaged lensed quasar SDSS J1206+4332. We revise the deflector redshift proposed previously to z d = 0.745, and measure for the first time its velocity dispersion = (290 ± 30) km s –1 . The LGSAO data show the lensed quasar host galaxy stretching over the astroid caustic thus forming an extra pair of merging images, which was previously thought to be an unrelated galaxy in seeing limited data. Owing to the peculiar geometry, the lens acts as a natural coronagraph on the broad-line region of the quasar so that only narrow $\left.\mathrm{C {\scriptscriptstyle III}}\right]$ emission is found in the fold arc. We use the data to reconstruct the source structure and deflector potential, including nearby perturbers. We reconstruct the point-spread function (PSF) from the quasar images themselves, since no additional point source is present in the field of view. From gravitational lensing and stellar dynamics, we find the slope of the total mass density profile to be ' = –log /log r = 1.93 ± 0.09. We discuss the potential of SDSS J1206+4332 for measuring a time-delay distance (and thus H 0 and other cosmological parameters), or as a standard ruler, in combination with the time-delay published by the COSMOGRAIL collaboration. We conclude that this system is very promising for cosmography. However, in order to achieve competitive precision and accuracy, an independent characterization of the PSF is needed. Spatially resolved kinematics of the deflector would reduce the uncertainties further. Both are within the reach of current observational facilities.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 2
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    Radio monitoring campaigns of six strongly lensed quasars (2015)
    Oxford University Press
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    Publication Date: 2015-04-23
    Description: We 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 their multiple images. These systems are in standard two- and four-image configurations, with B1938 having a faint secondary pair of images. Two separate monitoring campaigns were carried out using the Very Large Array (VLA) and upgraded VLA. Light curves were extracted for each individual lensed image and analysed for signs of intrinsic variability. While it was not possible to measure time delays from these data, 2 -based and structure function tests found evidence for variability in a majority of the light curves. B0712 and B1030 had particularly strong variations, exhibiting linear flux trends. These results suggest that most of these systems should be targeted with follow-up monitoring campaigns, especially B0712 and B1030. We estimate that we can measure time delays for these systems with precisions of 0.5–3.5 d using two more seasons of monitoring.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    Discovery of two gravitationally lensed quasars in the Dark Energy Survey (2015)
    Agnello, A., Treu, T., Ostrovski, F., Schechter, P. L., Buckley-Geer, E. J., Lin, H., Auger, M. W., Courbin, F., Fassnacht, C. D., Frieman, J., Kuropatkin, N., Marshall, P. J., McMahon, R. G., Meylan, G., More, A., Suyu, S. H., Rusu, C. E., Finley, D., Abbott, T., Abdalla, F. B., Allam, S., Annis, J., Banerji, M., Benoit-Levy, A., Bertin, E., Brooks, D., Burke, D. L., Rosell, A. C., Kind, M. C., Carretero, J., Cunha, C. E., D'Andrea, C. B., da Costa, L. N., Desai, S., Diehl, H. T., Dietrich, J. P., Doel, P., Eifler, T. F., Estrada, J., Neto, A. F., Flaugher, B., Fosalba, P., Gerdes, D. W., Gruen, D., Gutierrez, G., Honscheid, K., James, D. J., Kuehn, K., Lahav, O., Lima, M., Maia, M. A. G., March, M., Marshall, J. L., Martini, P., Melchior, P., Miller, C. J., Miquel, R., Nichol, R. C., Ogando, R., Plazas, A. A., Reil, K., Romer, A. K., Roodman, A., Sako, M., Sanchez, E., Santiago, B., Scarpine, V., Schubnell, M., Sevilla-Noarbe, I., Smith, R. C., Soares-Santos, M., Sobreira, F., Suchyta, E., Swanson, M. E. C., Tarle, G., Thaler, J., Tucker, D., Walker, A. R., Wechsler, R. H., Zhang, Y.
    Oxford University Press
    Details
    Publication Date: 2015-10-03
    Description: We present spectroscopic confirmation of two new gravitationally lensed quasars, discovered in the Dark Energy Survey (DES) and Wide-field Infrared Survey Explorer ( WISE ) based on their multiband photometry and extended morphology in DES images. Images of DES J0115–5244 show a red galaxy with two blue point sources at either side, which are images of the same quasar at z s  = 1.64 as obtained by our long-slit spectroscopic data. The Einstein radius estimated from the DES images is 0.51 arcsec. DES J2146–0047 is in the area of overlap between DES and the Sloan Digital Sky Survey (SDSS). Two blue components are visible in the DES and SDSS images. The SDSS fibre spectrum shows a quasar component at z s  = 2.38 and absorption by Mg  ii and Fe  ii at z l  = 0.799, which we tentatively associate with the foreground lens galaxy. Our long-slit spectra show that the blue components are resolved images of the same quasar. The Einstein radius is 0.68 arcsec, corresponding to an enclosed mass of 1.6  x  10 11 M . Three other candidates were observed and rejected, two being low-redshift pairs of starburst galaxies, and one being a quasar behind a blue star. These first confirmation results provide an important empirical validation of the data mining and model-based selection that is being applied to the entire DES data set.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Galaxy structure from multiple tracers - II. M87 from parsec to megaparsec scales (2016)
    Oxford University Press
    Details
    Publication Date: 2016-01-22
    Description: Following a number of conflicting studies of M87's mass profile, we undertake a dynamical analysis of multiple tracer populations to constrain its mass over a large radius range. We combine stellar kinematics in the central regions with the dynamics of 612 globular clusters out to 200 kpc and satellite galaxies extending to scales comparable with the virial radius. Using a spherical Jeans analysis, we are able to disentangle the mass contributions from the dark and baryonic components and set constraints on the structure of each. Assuming isotropy, we explore four different models for the dark matter halo and find that a centrally cored dark matter distribution is preferred. We infer a stellar mass-to-light ratio *, v = 6.9 ± 0.1 – consistent with a Salpeter-like initial mass function (IMF) – and a core radius r c = 67 ± 20 kpc. We then introduce anisotropy and find that, while the halo remains clearly cored, the radial stellar anisotropy has a strong impact on both *, v and the core's radius; here we find $\Upsilon _{\star ,v} = 3.50_{-0.36}^{+0.32}$ – consistent with a Chabrier-like IMF – and $r_c = 19.00_{-8.34}^{+8.38}$  kpc. Thus, the presence of a core at the centre of the dark halo is robust against anisotropy assumptions, while the stellar mass and core size are not. We are able to reconcile previously discrepant studies by showing that modelling the globular cluster data alone leads to the very different inference of a super-NFW cusp, thus highlighting the value of multiple-population modelling, and we point to the possible role of M87's AGN and the cluster environment in forming the central dark matter core.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Inference of the cold dark matter substructure mass function at z = 0.2 using strong gravitational lenses (2014)
    Oxford University Press
    Details
    Publication Date: 2014-06-19
    Description: We present the results of a search for galaxy substructures in a sample of 11 gravitational lens galaxies from the Sloan Lens ACS Survey by Bolton et al. We find no significant detection of mass clumps, except for a luminous satellite in the system SDSS J0956+5110. We use these non-detections, in combination with a previous detection in the system SDSS J0946+1006, to derive constraints on the substructure mass function in massive early-type host galaxies with an average redshift 〈 z lens 〉  ~ 0.2 and an average velocity dispersion 〈 eff 〉  ~ 270 km s –1 . We perform a Bayesian inference on the substructure mass function, within a median region of about 32 kpc 2 around the Einstein radius (〈 R ein 〉  ~ 4.2 kpc). We infer a mean projected substructure mass fraction f = $0.0076_{-0.0052}^{+0.0208}$ at the 68 per cent confidence level and a substructure mass function slope α 〈 2.93 at the 95 per cent confidence level for a uniform prior probability density on α. For a Gaussian prior based on cold dark matter (CDM) simulations, we infer f = $0.0064^{+0.0080}_{-0.0042}$ and a slope of α = $1.90^{+0.098}_{-0.098}$ at the 68 per cent confidence level. Since only one substructure was detected in the full sample, we have little information on the mass function slope, which is therefore poorly constrained (i.e. the Bayes factor shows no positive preference for any of the two models). The inferred fraction is consistent with the expectations from CDM simulations and with inference from flux ratio anomalies at the 68 per cent confidence level.
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    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Testing metallicity indicators at z ~ 1.4 with the gravitationally lensed galaxy CASSOWARY 20 (2014)
    Oxford University Press
    Details
    Publication Date: 2014-04-15
    Description: We present X-shooter observations of CASSOWARY 20 (CSWA 20), a star-forming (SFR ~ 6 M yr –1 ) galaxy at z  = 1.433, magnified by a factor of 11.5 by the gravitational lensing produced by a massive foreground galaxy at z  = 0.741. We analysed the integrated physical properties of the H ii regions of CSWA 20 using temperature- and density-sensitive emission lines. We find the abundance of oxygen to be ~1/7 of solar, while carbon is ~50 times less abundant than in the Sun. The unusually low C/O ratio may be an indication of a particularly rapid time-scale of chemical enrichment. The wide wavelength coverage of X-shooter gives us access to five different methods for determining the metallicity of CSWA 20, three based on emission lines from H ii regions and two on absorption features formed in the atmospheres of massive stars. All five estimates are in agreement, within the factor of ~2 uncertainty of each method. The interstellar medium (ISM) of CSWA 20 only partially covers the star-forming region as viewed from our direction; in particular, absorption lines from neutrals and first ions are exceptionally weak. We find evidence for large-scale outflows of the ISM with speeds of up 750 km s –1 , similar to the values measured in other high- z galaxies sustaining much higher rates of star formation.
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    Topics: Physics
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  • 7
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    Cosmological constraints from the double source plane lens SDSSJ0946+1006 (2014)
    Oxford University Press
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    Publication Date: 2014-07-19
    Description: We present constraints on the equation of state of dark energy, w , and the total matter density, M , derived from the double-source-plane strong lens SDSSJ0946+1006, the first cosmological measurement with a galaxy-scale double-source-plane lens. By modelling the primary lens with an elliptical power-law mass distribution, and including perturbative lensing by the first source, we are able to constrain the cosmological scaling factor in this system to be β –1  = 1.404 ± 0.016, which implies $\Omega _{\mathrm{M}}= 0.33_{-0.26}^{+0.33}$ for a flat cold dark matter (CDM) cosmology. Combining with a cosmic microwave background prior from Planck , we find w = $-1.17^{+0.20}_{-0.21}$ assuming a flat w CDM cosmology. This inference shifts the posterior by 1 and improves the precision by 30 per cent with respect to Planck alone, and demonstrates the utility of combining simple, galaxy-scale multiple-source-plane lenses with other cosmological probes to improve precision and test for residual systematic biases.
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    Topics: Physics
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  • 8
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    A precise extragalactic test of General Relativity (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-06-22
    Description: Einstein’s theory of gravity, General Relativity, has been precisely tested on Solar System scales, but the long-range nature of gravity is still poorly constrained. The nearby strong gravitational lens ESO 325-G004 provides a laboratory to probe the weak-field regime of gravity and measure the spatial curvature generated per unit mass, . By reconstructing the observed light profile of the lensed arcs and the observed spatially resolved stellar kinematics with a single self-consistent model, we conclude that = 0.97 ± 0.09 at 68% confidence. Our result is consistent with the prediction of 1 from General Relativity and provides a strong extragalactic constraint on the weak-field metric of gravity.
    Keywords: Astronomy, Physics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 9
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    Reconstructing the lensing mass in the Universe from photometric catalogue data (2013)
    Oxford University Press
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    Publication Date: 2013-05-21
    Description: High precision cosmological distance measurements towards individual objects such as time delay gravitational lenses or Type Ia supernovae are affected by weak lensing perturbations by galaxies and groups along the line of sight. In time delay gravitational lenses, ‘external convergence’, ext , can dominate the uncertainty in the inferred distances and hence cosmological parameters. In this paper we attempt to reconstruct ext , due to line of sight structure, using a simple halo model. We use mock catalogues from the Millennium Simulation, and calibrate and compare our reconstructed P( ext ) to ray-traced ext ‘truth’ values; taking into account realistic uncertainties on redshift and stellar masses. We find that the reconstruction of ext provides an improvement in precision of ~50 per cent over galaxy number counts. We find that the lowest ext lines of sight have the best constrained P( ext ). In anticipation of future samples with thousands of lenses, we find that selecting the third of the systems with the highest precision ext estimates gives a subsample of unbiased time delay distance measurements with (on average) just 1 per cent uncertainty due to line of sight external convergence effects. Photometric data alone are sufficient to pre-select the best-constrained lines of sight, and can be done before investment in light-curve monitoring. Conversely, we show that selecting lines of sight with high external shear could, with the reconstruction model presented here, induce biases of up to 1 per cent in time delay distance. We find that a major potential source of systematic error is uncertainty in the high-mass end of the stellar mass–halo mass relation; this could introduce ~2 per cent biases on the time delay distance if completely ignored. We suggest areas for the improvement of this general analysis framework (including more sophisticated treatment of high-mass structures) that should allow yet more accurate cosmological inferences to be made.
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    Topics: Physics
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  • 10
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    SHARP - III. First use of adaptive-optics imaging to constrain cosmology with gravitational lens time delays (2016)
    Oxford University Press
    Details
    Publication Date: 2016-09-02
    Description: Accurate and precise measurements of the Hubble constant are critical for testing our current standard cosmological model and revealing possibly new physics. With Hubble Space Telescope ( HST ) imaging, each strong gravitational lens system with measured time delays can allow one to determine the Hubble constant with an uncertainty of ~7 per cent. Since HST will not last forever, we explore adaptive-optics (AO) imaging as an alternative that can provide higher angular resolution than HST imaging but has a less stable point spread function (PSF) due to atmospheric distortion. To make AO imaging useful for time-delay-lens cosmography, we develop a method to extract the unknown PSF directly from the imaging of strongly lensed quasars. In a blind test with two mock data sets created with different PSFs, we are able to recover the important cosmological parameters (time-delay distance, external shear, lens-mass profile slope, and total Einstein radius). Our analysis of the Keck AO image of the strong lens system RXJ 1131–1231 shows that the important parameters for cosmography agree with those based on HST imaging and modelling within 1 uncertainties. Most importantly, the constraint on the model time-delay distance by using AO imaging with 0.09 arcsec resolution is tighter by ~50 per cent than the constraint of time-delay distance by using HST imaging with 0.09 arcsec when a power-law mass distribution for the lens system is adopted. Our PSF reconstruction technique is generic and applicable to data sets that have multiple nearby point sources, enabling scientific studies that require high-precision models of the PSF.
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    Topics: Physics
    Published by Oxford University Press
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