  Recent work in galaxy formation has enlightened the important role of baryon
physics, to solve the main problems encountered by the standard theory at the
galactic scale, such as the galaxy stellar mass functions, or the missing
satellites problem. The present work aims at investigating in particular the
role of the cold and dense molecular phase, which could play a role of gas
reservoir in the outer galaxy discs, with low star formation efficiency.
Through TreeSPH simulations, implementing the cooling to low temperatures, and
the inclusion of the molecular hydrogen component, several feedback
efficiencies are studied, and results on the gas morphology and star formation
are obtained. It is shown that molecular hydrogen allows some slow star
formation (with gas depletion times of about 5 Gyr) to occur in the outer parts
of the discs. This dense and quiescent phase might be a way to store a
significant fraction of dark baryons, in a relatively long time-scale, in the
complete baryonic cycle, connecting the galaxy discs to hot gaseous haloes and
to the cosmic filaments.
