• high-redshift galaxies
• Gravitational lensing

Faint galaxies are the main responsible for the onset of reionization and the early metal enrichment. Because of their low luminosity, such objects are difficult to observe, even with the most powerful telescopes. Gravitational lensing (GL) represents a powerful tool to investigate the properties of faint objects: indeed, a foreground cluster can magnify the emitted flux of a background faint galaxy by a factor mu=5-100.
In this context, theoretical studies of GL are fundamental to interpret and guide observations, in view of the launch of new instruments as James Webb Space Telescope (JWST). The aim of this Thesis is to study the effects of strong lensing from a theoretical perspective, reconstructing the images of lensed galaxies and inferring their properties. We developed a software that allows the user to define a source and a lens, and to produce the resulting lensed image. The code has been successfully benchmarked against analytical models for sources and lenses.
As a relevant application of our developed tool, we have studied the case of two galaxies observed at redshift z=3.222 (Vanzella et al. 2017) and z=6.143 (Vanzella et al. 2018) that are highly magnified (mu = 10-70) by MACS J0416.1-2403, a z=0.397 cluster. As lens and source we have used respectively a state-of-the-art lens model (Caminha et al. 2017) and a zoom-in cosmological hydrodynamical simulation of a high-redshift galaxy (Pallottini et al. 2017), combined with radiative transfer models calculating the continuum emission. We manage to obtain lensed images with positions and magnification factors that are compatible with the available photometric observations (e.g. F435W, F606W, F814W, H, J, Y). We conclude by assessing the possibility of studying galaxies in the Epoch of Reionization (z=6) in detail with JWST. We find that in a typical cluster region the estimated mu spans the range [2;50], with a probability of 20% of observing a highly magnified galaxy; using our fiducial galaxy simulation, about 6 strongly magnified z=6 galaxies are expected in the cluster area, with lensed images that can be spatially resolved with the capabilities of JWST.