Molecular outflows in starburst nuclei

TL;DR

This paper models molecular outflows in starburst nuclei, showing they can form in dense, stratified disks with high star formation rates, explaining observed outflow properties.

Contribution

It presents a physical scenario for molecular outflows driven by OB associations in starburst nuclei, linking outflow characteristics to specific environmental conditions.

Findings

Outflows can form molecules in cool, dense shells expanding from starburst regions.

High star formation rates and dense stratified disks are conducive to molecular outflow formation.

Predicted outflow velocities and masses align with observations.

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 $N_{OB}\ge 10^5$ (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.