Cosmological Constraints From Strong Gravitational Lensing

In 1998, two supernovae groups reported that our Universe is undergoing a late time accelerated expansion, to reveal the nature of this late time accelerated expansion has be-come one of the most important issue of modern cosmology in this century. There are two approaches to interpret this phenomenon at present, the dark energy hypothesis and a modi-fication to general relativity at large scales. Researchers who focus on the former one believe that a negative pressure of dark energy provides a motivation for the accelerated expansion. In addition, the latest observations show that normal matter that makes up stars and galax-ies contributes just 4% of the universe, dark matter which determines the evolution of the Universe, occupies 28%, while dark energy, a mysterious force thought to be responsible for accelerating expansion of the Universe, accounts for 68%. Therefore, the dark sectors deter-mine the evolution of the Universe, this consequence inspires the theorist to put forward a variety of dark energy models. ?CDM model as a simplest promotion for the fiducial ACDM model has a significant research value. In order to constraint the cosmological models, more cosmological probe is necessary. Strong gravitational lensing systems as a new star is being more and more extensive attention. Nowadays the strong gravitational lensing systems com-plied from many surveys have accumulated to 118. To study their cosmic constraint on dark energy models is a very meaningful work.The main work in this thesis is to constraint the ?CDM model with a constant equation of state by using 118 strong gravitational lensing systems. Via Markov Chain Mote Carlo (MCMC), we got a compact parameter space, verified the dependence between cosmological parameters and strong gravitational lensing models, and studied the influence of two param-eterisations of ?. Concretely, this thesis is divided into three chapters, and the main work of us is in Chapter 3. In Chapter 1, we will give a brief introduction of the background knowledge of cosmology including the background dynamical evolution equations, the con-cept of cosmological redshift and angular diameter distance. Subsequently, several common cosmological model is introduced. In Chapter 2, we talk about the basic theory of strong gravitational lensing. Firstly, lens galaxies are supposed can be represented by the SIS model, then we further discussed a more general model where the mass density of a lens to follow a general power-law. In Chapter 3, we study the cosmic constraint to ?CDM model via 118 strong gravitational lensing systems complied from SLACS, BELLS, LSD and SL2S surveys, where the ratio between two angular diameter distances Dobs= D(zl, zs)/D(0, zs) is taken as a cosmic observable. Via MCMC method, the posterior distribution of the model parameters space is obtained. Finally, the summary and outlook are presented in the last chapter.