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 $N_{OB}\ge 10^5$(correspondingtoastarformationrate(SFR)$\ge 1$M$_{\odot}$yr$^{-1}$inthenuclearregion),inastratifieddiskwithmid-planedensity$n_0\sim 200\hbox{–}1000$cm$^{-3}$andscaleheight$z_0\ge 200 (n_0/10^2 , {\rm cm}^{-3})^{-3/5}$ pc, can form molecules in a cool dense and expanding shell. The associated molecular mass is $\ge {10}^7$ M${}_{\odot }$ at a distance of a few hundred pc, with a speed of several tens of km s${}^{-1}$. We show that a SFR surface density of $10\le {\mathrm{\Sigma }}_{SFR}\le 50$ M${}_{\odot }$ yr${}^{-1}$ kpc${}^{-2}$ favours the production of molecular outflows, consistent with observed values.