Contribution to the Study of the Quasar Unification Model on the Basis of Polarimetry and Gravitational Microlensing

Quasars are among the most luminous and the most distant objects in the Universe. Consequently they are particularly interesting to probe its originand to understand its evolution. However, the huge distances at which theseobjects are generally found prevent us from resolving their central regionsso that we cannot directly check the validity of the geometrical as well asthe dynamical models accounting for their observational properties (spectralenergy distribution, line profiles, presence or absence of radio jets etc). Inour thesis, we use two indirect observational techniques in order to constrainthe existing models.These techniques which are particularly sensitive to the geometrical structureof the quasar emission regions are polarimetry and gravitational microlensing.In the first part of our thesis we study the correlation betweenthe direction of the linear polarization and the orientation of the host galaxy/extended emission that we determined on the basis of high resolutionHST images. We show how this study enables us to bring new clues favoringthe existence of a unification model for the Type 1 and Type 2 quasars.In the second part, we show how gravitational microlensing allows toconstrain the geometry and size of the regions at the origin of the broadabsorption lines observed in the spectrum of 10 to 20 % of quasars. Forthis purpose we build a radiative transfer code allowing to simulate the lineprofiles produced in a variety of realistic wind models. These models arethen used to study the variations of line profiles induced by the transit of agravitational microlens. This technique is finally applied to the case of thequasar H1413+117 in order to determine the geometry of the regions whichproduce the broad absorption lines.