Weak lensing studies with GOODS/ACS fields

The main goal of this thesis is to improve current understanding of structure formation in the universe at z ∼ 1--2 through weak lensing studies with the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) data, obtained as part of the Great Observatories Origin Deep Survey (GOODS) project.; In this thesis, we present a uniform approach to describes light propagation in both isotropic universe and weakly perturbed universe to discuss the effects of gravitational lensing, apply it to two prime applications of gravitational lensing to cosmology; lensing by dark matter halos and lensing by the large-scale structure, investigate the expected weak lensing effects from the applications and discuss how the effects can be measured through galaxy shape.; We describe how galaxy shapes are measured from the GOODS data. We present preliminary measurements of galaxy-galaxy lensing and detection of cosmic shear. We detect a clear galaxy-galaxy lensing signal for lens galaxies at z ∼ 0.5 at projected separations ranging from 10" to 200". The detected shear is compatible with ground-based measurements obtained for low-redshift galaxies. We also detect a clear cosmic shear signal using source galaxies at z ∼ 1.0. The detected shear is generally consistent with other observations that measured sigma8 ≃ 0.7.