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 COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses

Image Lens Source Observer Quasar time delays, H 0 and galaxy mass profile Geometry (plus Ho)Radial (mass) profile of the lens

Quasar lensing requires: High-accuracy astrometry (a few milli-arcsec)High-accuracy astrometry (a few milli-arcsec) Detailed mapping of the light distribution in the lensDetailed mapping of the light distribution in the lens Image of the lensed host galaxy of the quasarImage of the lensed host galaxy of the quasar Accurate measurement the time delaysAccurate measurement the time delays Image deconvolution of HST images is extensively used but: Lack of PSF stars in the small HST field of viewLack of PSF stars in the small HST field of view PSF distortions across the fieldPSF distortions across the field Colour dependence of the PSFColour dependence of the PSF Quasar time delays, H 0 and galaxy mass profile HST Ground

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

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

WFI 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)

WFI Vuissoz et al epochs ! Sampling ~ 4 days 3 full years

WFI 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.

WFI Shifted curves Vuissoz et al. 2008

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

WFI “Ingredients” for the modeling: G1 and G2, plus group, plus external shear

WFI Non parametric modeling Twisting of the mass contours Dynamical perturbation from group ?

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

Going beyond HST resolution An iterative PSF construction algorithm is devised: Start with a TinyTim PSF (Krist & Hook)Start with a TinyTim PSF (Krist & Hook) Carry out a first deconvolutionCarry out a first deconvolution Remove extended sources in the imageRemove extended sources in the image Estimate a new PSF on the point sources in the dataEstimate a new PSF on the point sources in the data Deconvolve againDeconvolve again Do this a few times until the residuals are acceptableDo 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

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

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

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

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

For the concordance cosmology lenses appear to split in two groups: isothermal lenses isothermal lenses lenses with a steeper-than-isothermal inner (15 kpc) mass profile 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. 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 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 interpret the time delays

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