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 $N_{OB}\ge
10^5$ (corresponding to a star formation rate (SFR)$\ge 1$ M$_{\odot}$
yr$^{-1}$ in the nuclear region), in a stratified disk with mid-plane density
$n_0\sim 200\hbox{--}1000$ cm$^{-3}$ and scale height $z_0\ge 200 (n_0/10^2 \,
{\rm cm}^{-3})^{-3/5}$ 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 $10 \le \Sigma_{SFR} \le 50$ M$_\odot$ yr$^{-1}$ kpc$^{-2}$
favours the production of molecular outflows, consistent with observed values.
