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[more ▼]Assuming that (i) damped Ly-alpha absorbers (DLAs) arise in present-day-like spiral galaxies which are immersed in isothermal dark matter halos, (ii) that these galaxies obey the Tully-Fisher sigma/sigma_* = (L/L_*)^1/alpha_TF and the Holmberg R_L/R_* = (L/L_*)^alpha_H relations, and (iii) that they follow the Schechter luminosity distribution, we describe how their observed number density (dN/dz), distribution of column density (f(N)) as well as inferred cosmological density of HI (Omega_HI) derived from DLA surveys are affected by gravitational lensing (GL). The by-pass' effect causes the lines-of-sight (LOSs) towards background QSOs to avoid the central parts of galaxies and reduces their effective cross-section for absorption; the amplification bias' leads observers to select QSOs whose LOSs preferentially cross galaxies close to their Einstein radius. As a consequence, the determination of the quantities dN/dz, f(N) and Omega_HI from DLA surveys does not only depend on the redshift z and luminosity L of galaxies responsible for the absorbers but also on the column density profile of HI within the galaxies and on the redshift z_q and magnitude b_q of the background QSOs. For most of the existing surveys using b_q <~ 19 QSOs, the amplification bias dominates the combined effect resulting in a slight overestimate of dN/dz, f(N) and Omega_HI. We mainly find that observational strategies presently used to produce high-z DLA surveys result in avoiding the signature of significant GL effects: following our model, we determine that an overestimate of Omega_HI by more than 10% is unlikely for the z > 1.7 existing surveys, but may reach ~= 35% for the low redshift ones. However, we show that, in the absence of extinction by dust and micro-lensing effects, surveys ideally designed to enhance GL effects, i.e. to search for DLAs at z ~ 0.5 in front of very bright (b_q ~= 16), high-z (z_q > 1) QSOs, may lead 1) to overestimate by up to ~= 90% the number of DLAs per unit redshift; 2) to bias the survey towards high HI column density systems so that it could contain up to 4 times as many such systems, thus 3) to overestimate by up to ~= 170% the cosmological density of gas associated with those DLAs. Identification of the galaxies responsible for the DLAs may be severely biased towards luminous galaxies if 2/alpha_TF - alpha_H>0 this latter effect is greatly increased for log N_HI > 21 DLAs. Hence, GL effects on the quantities derived from surveys for z ~ 0.5 DLAs are of the same order, but of opposite direction, as the effects of extinction by dust (cf. Fall & Pei, 1993). However, the GL and dust extinction effects do not compensate each other: combining them in a consistent way is necessary to interpret existing DLA surveys. Furthermore, the effects due to micro-lensing should be simultaneously taken into account. We intend to report the results on the complex interplay between macro-lensing, micro-lensing and dust in a subsequent paper. We briefly present statistical tests specifically designed to check whether GL affects existing DLA surveys, and assuming that extinction by dust is negligible. We only find indications of GL effects for the z < 1 ones which, if confirmed, might even be stronger than predicted by our model. We show that an independent work on the same subject by Bartelmann & Loeb (1996) incorrectly treats the inclination effects for the intervening galaxies, thus undermining some of their main results and conclusions. [less ▲]Detailed reference viewed: 17 (2 ULg) Gravitational lensing in quasar samplesClaeskens, Jean-François ; Surdej, Jean in Astronomy and Astrophysics Review (2002), 10(4), 263-311The first cosmic mirage was discovered approximately 20 years ago as the double optical counterpart of a radio source. This phenomenon had been predicted some 70 years earlier as a consequence of General ... [more ▼]The first cosmic mirage was discovered approximately 20 years ago as the double optical counterpart of a radio source. This phenomenon had been predicted some 70 years earlier as a consequence of General Relativity. We present here a summary of what we have learnt since. The applications are so numerous that we had to concentrate on a few selected aspects of this new field of research. This review is focused on strong gravitational lensing, i.e. the formation of multiple images, in QSO samples. It is intended to give the reader an up-to-date status of the observations and to present an overview of its most interesting potential applications in cosmology and astrophysics, as well as numerous important results achieved so far. The first section follows an intuitive approach to the basics of gravitational lensing and is developed in view of our interest in multiply imaged quasars. The astrophysical and cosmological applications of gravitational lensing are outlined in Sect. 2 and the most important results are presented in Sect. 5. Sections 3 and 4 are devoted to the observations. Finally, conclusions are summarized in the last section. We have tried to avoid duplication with existing (and excellent) introductions to the field of oravitational lensing. For this reason, we did not concentrate on the individual properties of specific lens models, as these are already well presented in Narayan and Bartelmann (1996) and on a more intuitive ground in Refsdal and Surdej (1994). Wambsganss (1998) proposes a broad view on gravitational lensing, in astronomy; the reviews by Fort and Mellier (1994) and Hattori et al. (1999) deal with lensing by galaxy clusters, microlensing in the Galaxy and the local group is reviewed by Paczynski (1996) and a general panorama on weak lensing is given by Bartelmann and Schneider (1999) and Mellier (1999). The monograph on the theory of gravitational lensing by Schneider, Ehlers and Falco (1992) also remains a reference in the field. [less ▲]Detailed reference viewed: 20 (9 ULg) Gravitational lensing search for dark matter halosBiernaux, Judith Conference (2014, November 19)Detailed reference viewed: 13 (4 ULg) Gravitational lensing statistics based on a large sample of highly luminous quasarsSurdej, Jean ; Claeskens, Jean-François ; Crampton, D. et alin Astronomical Journal (The) (1993), 105Results on gravitational lensing statistics applied to a sample of 469 highly luminous quasars are reported. The objects were directly imaged, either from the ground under optimal seeing conditions, or ... [more ▼]Results on gravitational lensing statistics applied to a sample of 469 highly luminous quasars are reported. The objects were directly imaged, either from the ground under optimal seeing conditions, or using the HST. We have derived values for the effectiveness parameter F of galaxies, modeled by means of singular isothermal spheres, to produce macrolensed images of distant quasars, and upper limits on the density parameter Omega(L) of compact objects with masses between 10 exp 10 and 10 exp 12 solar masses. Adopting H(0)= 50 km/s/Mpc, Omega(0)= 1, and Lambda = 0, we find that at the 99.7 percent confidence level, F is between 0.005 and 0.478 and that Omega(L) is less than 0.02. A critical discussion of these results is presented. Finally, comparing the efficiencies of ground-based and space instruments used to search for gravitational lens systems among highly luminous quasars, we conclude that for the near future, ground-based direct imaging characterized by a good dynamical range still constitutes the best observational strategy. [less ▲]Detailed reference viewed: 22 (10 ULg) Gravitational lensing statistics based on a large sample of highly luminous quasars observed with ground-based telescopes and HSTSurdej, Jean ; Claeskens, Jean-François ; Crampton, D. et alin Benvenuti, Piero; Schreier, Ethan J (Eds.) Proceedings of a ST-ECF/STScI Workshop "Science with the Hubble Space Telescope" (1992)We present here some recent results on gravitational lensing statistics as applied to a sample of 470 highly luminous quasars.Detailed reference viewed: 9 (4 ULg) Gravitational lensing studies with the 4-m International Liquid Mirror Telescope (ILMT)Jean, C.; Claeskens, J *-F; Surdej, Jean Poster (1999, October 01)A 4-m International Liquid Mirror Telescope (ILMT) is being built in the north of Chile by an international consortium and will become operational in two years from now. We present here a short ... [more ▼]A 4-m International Liquid Mirror Telescope (ILMT) is being built in the north of Chile by an international consortium and will become operational in two years from now. We present here a short description of the telescope as well as estimates of the microlensing, macrolensing and weak lensing effects expected from a deep, multicolor imaging survey made with such a telescope. [less ▲]Detailed reference viewed: 7 (1 ULg) Gravitational lensing studies with the 4-m International Liquid Mirror Telescope (ILMT) (poster contribution)Jean, C.; Claeskens, Jean-François ; Surdej, Jean in Brainerd, T. G.; Kochanek, C. S. (Eds.) Proceedings of the Conference "Gravitational lensing: recent progress and future goals" (2001, October 01)A 4-m International Liquid Mirror Telescope (ILMT) is being built in the north of Chile by an international consortium and will become operational in two years from now. We present here a short ... [more ▼]A 4-m International Liquid Mirror Telescope (ILMT) is being built in the north of Chile by an international consortium and will become operational in two years from now. We present here a short description of the telescope as well as estimates of the microlensing, macrolensing and weak lensing effects expected from a deep, multicolor imaging survey made with such a telescope. [less ▲]Detailed reference viewed: 17 (6 ULg) The 'Gravitational Lensing' BibliographyPospieszalska-Surdej, Anna ; Surdej, Jean ; Veron, P.in Kochanek, C. S.; Hewitt, Jacqueline N (Eds.) Astrophysical applications of gravitational lensing, Proceedings of the 173rd Symposium of the International Astronomical Union (1996)Not AvailableDetailed reference viewed: 20 (8 ULg) Gravitational Lensing, Dark Matter and the Optical Gravitational Lens ExperimentSurdej, Jean ; Claeskens, Jean-François ; Delacroix, Christian et alin Matagne, N.; Cugnon, Joseph; Lansberg, Jean-Philippe (Eds.) American Institute of Physics Conference Proc. Volume 1038 (2008, August 01)After briefly reviewing the history of gravitational lensing, we recall the basic principles of the theory. We then describe and use a simple optical gravitational lens experiment which has the virtue of ... [more ▼]After briefly reviewing the history of gravitational lensing, we recall the basic principles of the theory. We then describe and use a simple optical gravitational lens experiment which has the virtue of accounting for all types of image configurations observed so far among the presently known gravitational lens systems. Finally, we briefly present the 4m International Liquid Mirror Telescope project in the context of a photometric monitoring of multiply imaged quasars. [less ▲]Detailed reference viewed: 109 (29 ULg) Gravitational lensing, rapport invitéSurdej, Jean Conference (2005)Detailed reference viewed: 17 (3 ULg) Gravitational settling in pulsating subdwarf B stars and their progenitorsHu, Haili; Glebbeek, E.; Thoul, Anne et alin Astronomy and Astrophysics (2010), 511Context. Diffusion of atoms can be important during quiescent phases of stellar evolution. Particularly in the very thin inert envelopes of subdwarf B stars, diffusive movements will considerably change ... [more ▼]Context. Diffusion of atoms can be important during quiescent phases of stellar evolution. Particularly in the very thin inert envelopes of subdwarf B stars, diffusive movements will considerably change the envelope structure and the surface abundances on a short timescale. Also, the subdwarfs will inherit the effects of diffusion in their direct progenitors, namely giants near the tip of the red giant branch. This will influence the global evolution and the pulsational properties of subdwarf B stars.