Molecular outflows in starburst nuclei

Recent observations have detected molecular outflows in a few nearby starburst nuclei. We discuss the physical processes at work in such an environment in order to outline a scenario that can explain the observed parameters of the phenomenon, such as the molecular mass, speed and size of the outflows. We show that outflows triggered by OB associations, with N-OB >= 10(5) (corresponding to a star formation rate (SFR)>= 1 M-circle dot yr(-1) in the nuclear region), in a stratified disc with mid-plane density n(0) similar to 200-1000 cm(-3) and scaleheight z(0) >= 200(n(0)/10(2) cm (3)) (3/5) pc, can form molecules in a cool dense and expanding shell. The associated molecular mass is >= 10(7) M-circle dot at a distance of a few hundred pc, with a speed of several tens of km s(-1). We show that an SFR surface density of 10 <= Sigma(SFR) <= 50 M-circle dot yr(-1) kpc(-2) favours the production of molecular outflows, consistent with observed values.