Molecular Hydrogen MAGIE

Spitzer space telescope spectroscopy reveal a new class of galaxies with enhanced molecular hydrogen (H2) line emission, but where star formation is strongly suppressed. This is in sharp contrast with what is observed in standard star forming galaxies. These sources are all in active phases of galaxy evolution (galaxy interactions, AGN feedback, gas accretion in galaxy clusters, etc.). Why is H2 present in violent phases of galaxy evolution? How is the H2 emission powered? Why is the H2 gas inefficient at forming stars? What can we learn from these ''H2 galaxies'' about galaxy formation? This thesis addresses these questions, and discuss the theoretical and observational perspectives of this work (in particular Herschel and JWST).