Constraining the Cosmological Parameters using Strong Lensing

We investigate the potentiality of using strong lensing clusters to constrain the cosmological parameters Omega_m and Omega_lambda. The existence of a multiple image system with known redshift allows, for a given (Omega_m, Omega_lambda) cosmology, absolute calibration of the total mass deduced from lens modelling. Recent Hubble Space Telescope (HST) observations of galaxy clusters reveal a large number of multiple images, which are predicted to be at different redshifts. If it is possible to measure spectroscopically the redshifts of many multiple images then one can in principle constrain (Omega_m,Omega_lambda) through ratios of angular diameter distances, independently of any external assumptions. For a regular/relaxed cluster observed by HST with 3 multiple image systems, each with different spectroscopic redshifts, we show by analytic calculation that the following uncertainties can be expected: Omega_m=0.30 +/- 0.11, Omega_lambda=0.70 +/- 0.23 or Omega_m=1.00 +/- 0.17, Omega_lambda=0.00 +/- 0.48 for the two most popular world models. Numerical tests on simulated data confirm these good constraints, even in the case of more realistic cluster potentials, such as bimodal clusters, or when including perturbations by galaxies. To investigate the sensitivity of the method to different mass profiles, we also use an analytic ``pseudo-elliptical'' Navarro, Frenk & White profile in the simulations. These constraints can be improved if more than 3 multiple images with spectroscopic redshifts are observed, or by combining the results from different clusters. Some prospects on the determination of the cosmological parameters with gravitational lensing are given.Comment: Revised Version. 15 pages, 18 figures and 6 table

Probing the Universe with Weak Lensing

Gravitational lenses can provide crucial information on the geometry of the Universe, on the cosmological scenario of formation of its structures as well as on the history of its components with look-back time. In this review, I focus on the most recent results obtained during the last five years from the analysis of the weak lensing regime. The interest of weak lensing as a probe of dark matter and the for study of the coupling between light and mass on scales of clusters of galaxies, large scale structures and galaxies is discussed first. Then I present the impact of weak lensing for the study of distant galaxies and of the population of lensed sources as function of redshift. Finally, I discuss the potential interest of weak lensing to constrain the cosmological parameters, either from pure geometrical effects observed in peculiar lenses, or from the coupling of weak lensing with the CMB.Comment: To appear Annual Review of Astronomy and Astrophysiscs Vol. 37. Latex and psfig.sty. Version without figure, 54 pages, 73Kb. Complete version including 13 figures (60 pages) available on ftp.iap.fr anonymous account in /pub/from_users/mellier/AnnualReview ; file ARAAmellier.ps.gz 1.6 M

Physical properties of two low-luminosity z ~ 1.9 galaxies behind the lensing cluster AC 114

We present VLT/ISAAC near-infrared spectroscopy of two gravitationally-lensed z ~ 1.9 galaxies, A2 and S2, located behind the cluster AC 114. Thanks to large magnification factors, we have been successful in detecting rest-frame optical emission lines in star-forming galaxies 1 to 2 magnitudes fainter than in previous studies of Lyman break galaxies (LBGs) at z ~ 3. From the Ha luminosity, we estimate star formation rates (SFRs) which are 7 to 15 times higher than those inferred from the UV continuum flux at 1500 ang without dust extinction correction. The behavior of S2 and A2 in terms of O/H and N/O abundance ratios are very different, and they are also different from typical LBGs at z ~ 3. S2 is a low-metallicity object (Z ~ 0.03 Zsun) with a low N/O ratio, similar to those derived in the most metal-poor nearby HII galaxies. In contrast, A2 is a high-metallicity galaxy (Z ~ 1.3 Zsun) with a high N/O abundance ratio, similar to those derived in the most metal-rich starburst nucleus galaxies. The virial masses, derived from emission-line widths, are 0.5 and 2.4 x 10^10 Msun, for S2 and A2 respectively. Thanks to the gravitational amplification, the line profiles of S2 are spatially resolved, leading to a velocity gradient of +- 240 km/s, which yields a dynamical mass of ~ 1.3 x 10^10 Msun within the inner 1 kpc radius. Combining these new data with the sample of LBGs at z ~ 3, we conclude that these three galaxies exhibit different physical properties in terms of SFRs, abundance and mass-to-light ratios, and reddening. High-redshift galaxies of different luminosities could thus have quite different star formation histories (abridged version).Comment: 11 pages, 8 figures. Accepted for publication in A&

An ISOCAM survey through gravitationally lensing galaxy clusters

ISOCAM was used to perform a deep survey through three gravitationally lensing clusters of galaxies. Nearly seventy sq. arcmin were covered over the clusters A370, A2218 and A2390. We present maps and photometry at 6.7 & 14.3 microns, showing a total of 145 mid-IR sources and the associated source counts. The 15 micron counts reach the faintest level yet recorded. All sources have counterparts in the optical or near-IR. Models of the clusters were used to correct for the effects of lensing, which increases the sensitivity of the survey. Seven of fifteen SCUBA sources were detected at 15 microns. Five have redshift between 0.23 & 2.8, with a median of 0.9. The field sources were counted to a lensing-corrected sensitivity of 30 microJy at 15 microns, and 14 microJy at 7 microns. The counts, corrected for completeness, contamination by cluster sources and lensing, confirm and extend findings of an excess by a factor of ten in the 15 micron population with respect to source models with no evolution. Source redshifts are mostly between 0.4 and 1.5. For the counts at 7 microns, integrating from 14 microJy to 460 microJy, we resolve 0.49+/-0.2 nW.m^(-2).sr^(-1) of the infrared background light (IBL) into discrete sources. At 15 microns we include the counts from other ISOCAM surveys to integrate from 30 microJy to 50 mJy, two to three times deeper than unlensed surveys, to resolve 2.7+/-0.62 nW.m^(-2).sr^(-1) of the IBL. These values are 10% and 55%, respectively, of the upper limit to the IBL, derived from photon-photon pair production of the TeV gamma rays from BL-Lac sources on the IBL photons. However, recent detections of TeV gamma rays from the z=0.129 BL Lac H1426+428 suggest that the 15 micron background reported implies substantial absorption of TeV photons from that source.Comment: 35 pages, 17 figures, to appear in Astronomy and Astrophysics, full paper with high-resolution figures available at http://www.iso.vilspa.esa.es/science/pub/2003