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(abridged) Gravitationally lensed quasars can be used as powerfulcosmological and astrophysical probes. We can (i) infer the Hubble constantbased on the time-delay technique, (ii) unveil substructures along the l.o.s.toward distant galaxies, and (iii) compare the shape and the slope of baryonsand dark matter distributions in galaxies. To reach these goals, we needhigh-accuracy astrometry and morphology measurements of the lens. In this work,we first present new astrometry for 11 lenses with measured time delays. UsingMCS deconvolution on NIC2 HST images, we reached an astrometric accuracy ofabout 1-2.5 mas and an accurate shape measurement of the lens galaxy. Second,we combined these measurements with those of 14 other systems to present newmass models of these lenses. This led to the following results: 1) In 4double-image quasars, we show that the influence of the lens environment on thetime delay can easily be quantified and modeled, hence putting these lenseswith high priority for time-delay determination. 2) For quadruple-imagequasars, the difficulty often encountered in reproducing the image positions tomilli-arcsec accuracy (astrometric anomaly) is overcome by explicitly includingthe nearest visible galaxy in the model. However, one anomalous system(J1131-1231) does not show any luminous perturber in its vicinity, and threeothers (WFI2026-4536, WFI2033-4723, and B2045+265) have problematic modeling.These 4 systems are the best candidates for a pertubation by a dark mattersubstructure. 3) We find a significant correlation between the PA of the lightand of the mass distributions in lensing galaxies. In contrast with otherstudies, we find that the ellipticity of the light and of the mass alsocorrelate well, suggesting that the overall spatial distribution of matter isnot very different from the baryon distribution in the inner \sim 5 kpc oflensing galaxies.

astronomy and astrophysics

COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses X.  Modeling based on high-precision astrometry of a sample of 25 lensed quasars:  consequences for ellipticity, shear, and astrometric anomalies