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Laboratoire d’Astrophysique Ecole Polytechnique Fédérale de Lausanne Switzerland

Laboratoire d’Astrophysique Ecole Polytechnique Fédérale de Lausanne Switzerland. Strong gravitational lensing as a tool for studying galaxy formation and cosmology. Frédéric Courbin For the COSMOGRAIL collaboration Bologna, January 2008.

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Laboratoire d’Astrophysique Ecole Polytechnique Fédérale de Lausanne Switzerland

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  1. Laboratoire d’Astrophysique Ecole Polytechnique Fédérale de Lausanne Switzerland Strong gravitational lensing as a tool for studying galaxy formation and cosmology Frédéric Courbin For the COSMOGRAIL collaboration Bologna, January 2008 COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses http://www.cosmograil.net

  2. Image Source Observer Lens Quasar time delays, H0 and galaxy mass profile Geometry (plus Ho) Radial (mass) profile of the lens

  3. Quasar time delays, H0 and galaxy mass profile Quasar lensing requires: • High-accuracy astrometry (a few milli-arcsec) • Detailed mapping of the light distribution in the lens • Image of the lensed host galaxy of the quasar • Accurate measurement the time delays Image deconvolution of HST images is extensively used but: • Lack of PSF stars in the small HST field of view • PSF distortions across the field • Colour dependence of the PSF HST Ground

  4. Example of a lensed quasar: RX J1131-123 HST / ACS 1.2 m Euler (La Silla) 3 arcsec (Sluse et al. 2006, A&A 449, 539, including data from CASTLEs)

  5. COSMOGRAIL telescopes Liverpool 2m Robotic Telescope Euler (Chile) Mercator (La Palma) 2 x 1.2m telescopes Uzbek 1.5m Telescope 2m Himalayan Chandra Telescope Switzerland: G. Meylan F. Courbin C. Vuissoz A. Eigenbrod G. Burki D. Sluse P. Saha Belgium: P. Magain V. Chantry E. Eulaers L. Le Guillou H. Van Winckel C. Waelkens India: T. Prabhu D. Sahu C.S. Stalin Uzbekistan: M. Ibrahimov I. Asfandiyarov UK: S. Dye S. Warren

  6. WFI 2033-4723 Rather wide angular separation (2-3 arcsec) Photometry using MCS deconvolution (Magain, Courbin, Sohy, 1998, ApJ 494, 472) 1.2 m Euler (deconvolved) image FWHM = 0.35 arcsec HST ACS image (from CASTLEs)

  7. WFI 2033-4723 219 epochs ! Sampling ~ 4 days 3 full years Vuissoz et al. 2008

  8. WFI 2033-4723 Time delays measured from 3 different methods (Vuissoz et al. 2008) : B-A = 35.5 ± 1.4 days (3.8%), most of the error is shot noise B-C = 63.7 ± 3.4 days (5.0%), most of the error comes from systematics Slow microlensing is negligible, fast microlensing (scales of weeks) is not.

  9. WFI 2033-4723 Shifted curves Vuissoz et al. 2008

  10. WFI 2033-4723 Detailed HST-NICMOS (F160W) imaging (from CASTLE): • Light profile of the lens (best fit: de Vaucouleurs) • Astrometry to 3 mas accuracy including systematics • Faint Einstein ring

  11. WFI 2033-4723 Non parametric modeling Twisting of the mass contours Dynamical perturbation from group ?

  12. WFI 2033-4723 • Twisted mass iso-contours, suggesting gravitational perturbation • When the time delays are not fitted, all models agree with the data: isothermal, de Vaucouleurs, NFW • When the time delays are used, the best mass model is a central de Vaucouleur plus NFW dark matter halo • The twisting of the mass contours and the steep mass profile of the lens in WFI 2033-4723 suggest the lens is a satellite rather than a central galaxy of a group.

  13. Going beyond HST resolution An iterative PSF construction algorithm is devised: • Start with a TinyTim PSF (Krist & Hook) • Carry out a first deconvolution • Remove extended sources in the image • Estimate a new PSF on the point sources in the data • Deconvolve again • Do this a few times until the residuals are acceptable Magain, Courbin, Gillon, et al. 2007, A&A 461, 373 Chantry & Magain 2007, A&A 470, 467 -> For more details

  14. 1 arcsec Going beyond HST resolution Example of application to NICMOS images of the « cloverleaf » Original F160W image

  15. Going beyond HST resolution Example of application to NICMOS images of the « cloverleaf » Modifications applied to the PSF after each deconvolution step Chantry & Magain 2007, A&A 470, 467

  16. 1 arcsec Going beyond HST resolution Example of application to NICMOS images of the « cloverleaf » New résolution is 0.05 arcsec Chantry & Magain 2007, A&A 470, 467 (+ see poster)

  17. Going beyond HST resolution: the double Einstein ring in SDSS 0924+02 HST (F555W+F814W+F160W) Deconvolved (Eigenbrod et al. 2006, A&A 451, 747; data from CASTLEs)

  18. For the concordance cosmology lenses appear to split in two groups: • isothermal lenses • lenses with a steeper-than-isothermal inner (15 kpc) mass profile Most lenses are in groups, often dominated by a brighter member. Numerical simulations show that galaxies in groups, that have steep mass profiles are satellite galaxies, and that the steep profile is transient (e.g. Dobke, King & Fellhauer 2007). -> The time delay technique allows to infer the details of the inner structure of galaxies in a range of environments -> Estimate Ho independent of standard candles by “stacking” lenses -> provided there exist sufficiently high resolution images to interpret the time delays

  19. COSMOGRAIL papers so far I: Simulated light curves Eigenbrod et al. 2005, A&A 436, 25 II: The double Einstein ring in SDSS J0924+02 Eigenbrod et al. 2006, A&A 451, 747 III: Deep VLT spectroscopy of 7 lensed quasars Eigenbrod et al. 2006, A&A 451, 759 IV: Non parametric modeling of cosmograil objects Saha et al. 2006, A&A 450, 461 V: First time delay measurement Vuissoz et al. 2007, A&A 464, 845 IV: Deep VLT spectroscopy of 8 lensed quasars Eigenbrod et al. 2007, A&A 465, 51 VII: First high-accuracy time delay (~3%) Vuissoz et al. 2008

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