Photometric calibration of the MegaCam imager. Analysis of the SnDICE data. ; Calibration photométrique de l'imageur MegaCam. Analyse des données SnDICE.

version finale ; Photometric calibration of wide field imagers is becoming a crucial issue in various cosmological measurements, such as the measurement of the cosmological parameters with type Ia supernovæ. To achieve the accuracy level of 0.1% required by future surveys, several collaborations are studying new instrumental calibration strategies as alternative to the traditional stellar calibration. The LPNHE Cosmology Group is working on the SnDICE project. SnDICE is an innovative and very stable illumination system installed at the Canada-France-Hawaii Telescope to calibrate the MegaCam imager and monitor its performances. The goal is to demonstrate the feasibility of an instrumental photometric absolute calibration with an accuracy at least of 0.1%. In the first part of this thesis, an introduction to the basic concepts is given. The cosmological standard model and the principal probes studied in order to constrain it are presented, before moving to the description of MegaCam and SNDIce. The second part is devoted to the modeling of the MegaCam optics and to the geometrical model allowing to know the relative orientations of the imager and the SnDICE light source in the dome. These two models have been implemented in a ray-tracing soft- ware developed within the CERN ROOT framework in order to simulate the focal plan illumination. This simulation allows one to disentangle the direct light from the secondary contributions due to reflections within the optics of the wide field corrector. Finally the application of the developed tools to the first analysis of the SnDICE calibration poses is presented, discussing the determination of the MegaCam rM passband. ; L'étalonnage photométrique des imageurs grand champ est à ce jour la principale limitation pour plusieurs mesures de cosmologie, parmi lesquelles celle des paramètres cosmologiques à l'aide des supernovæ de type Ia. Afin d'obtenir l'exactitude de l'ordre de 0.1% nécessaire pour les relevés futurs, les collaborations actives dans ce domaine explorent la ...