External pressure-triggering of star formation in a disc galaxy: a template for positive feedback

TL;DR

This paper investigates how external pressure from active galactic nuclei can positively influence star formation in disc galaxies, showing that moderate over-pressurisation significantly boosts star formation and causes gas fragmentation.

Contribution

It demonstrates through hydrodynamical simulations that external pressure can trigger starburst activity and destabilize galaxy discs, providing a new perspective on positive feedback mechanisms.

Findings

Moderate external pressure increases galaxy star formation rates by an order of magnitude.

External pressure causes disc instability and gas fragmentation.

Results resemble observed high-redshift galaxy behaviors.

Abstract

Feedback from active galactic nuclei (AGN) has often been invoked both in simulations and in interpreting observations for regulating star formation and quenching cooling flows in massive galaxies. AGN activity can, however, also over-pressurise the dense star-forming regions of galaxies and thus enhance star formation, leading to a positive feedback effect. To understand this pressurisation better, we investigate the effect of an ambient external pressure on gas fragmentation and triggering of starburst activity by means of hydrodynamical simulations. We find that moderate levels of over-pressurisation of the galaxy boost the global star formation rate of the galaxy by an order of magnitude, turn stable discs unstable, and lead to significant fragmentation of the gas content of the galaxy, similar to what is observed in high redshift galaxies.