Molecular outflows in starburst nuclei

Abstract

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 NOB ≥ 105 (corresponding to a star formation rate (SFR)≥1 M⊙ yr−1 in the nuclear region), in a stratified disc with mid-plane density n0 ∼ 200–1000 cm−3 and scaleheight z0 ≥ 200(n0/102 cm−3)−3/5 pc, can form molecules in a cool dense and expanding shell. The associated molecular mass is ≥107 M⊙ 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 ≤ ΣSFR ≤ 50 M⊙ yr−1 kpc−2 favours the production of molecular outflows, consistent with observed values.