Many galaxies have been detected at high redshift since the late nineties thanks to their strong Lyman-alpha emission line. These objects, knows as Lyman-alpha Emitters, allow us to probe galaxies in the first two Gigayears of the Universe. Although a large amount of detections, their statistical and physical properties are still poorly constrained. Indeed, observations are difficult to interpret, mainly due to line transfer effects in the interstellar mediaum and gas kinematics. In addition to observations, theoretical efforts are needed to reach a better understanding of the properties of these objects, their role in the scenario of hierarchical formation of galaxies, and their link with the other main high redshift galaxy population, the so-called Lyman Break galaxies. In this thesis, we model Lyman-alpha Emitters in the cosmological context with an original method. The hierarchical galaxy formation process is described with the GALICS model, which couples a N body simulation of Dark Matter, with semi-analytic prescriptions to model galaxy physics. GALICS can predict the physical properties of a large sample of mock galaxies between z~3 and 7. Lyman-alpha properties are computed thanks to the coupling of GALICS with a library of numerical tranfser models, generated with the MCLya code. With this approach, Lyman-alpha photons escape fractions and line profiles can be predicted, taking into account resonnant scattering effects and gas kinematics. We find a strong dispersion of the escape fraction with respect to the star formation rate of the galaxies. The model predictions are in good agreement with most of the observationnal data, especially the Lyman-alpha luminosity functions between z~3 and 7. The model is able to reproduce UV properties of UV and Lyman-alpha selected galaxies. We find that Lyman-alpha Emitters have moderate mass on average and display asymetric line profiles, as it is shown by the observations. In particular, we predict a strong abundance of faint Lyman-alpha Emitters. These objects will be a main target of the forthcoming MUSE instrument that will be installed at VLT. In order to help preparing future surveys with MUSE, mock fields of Lyman-alpha Emitters have been created with our model to make predictions, especially in terms of number counts and cosmic variance.
