What powers the starburst activity of NGC 1068? Star-driven gravitational instabilities caught in the act

Abstract

We explore the role that gravitational instability plays in NGC 1068, a nearby Seyfert galaxy that exhibits unusually vigorous starburst activity. For this purpose, we use the Romeo-Falstad disc instability diagnostics and data from the BIMA Survey of Nearby Galaxies, the Sloan Digital Sky Survey and the Spectrographic Areal Unit for Research on Optical Nebulae. Our analysis illustrates that NGC 1068 is a gravitationally unstable 'monster'. Its starburst disc is subject to unusually powerful instabilities. Several processes, including feedback from the active galactic nucleus and starburst activity, try to quench such instabilities from inside out by depressing the surface density of molecular gas across the central kpc, but they do not succeed. Gravitational instability 'wins' because it is driven by the stars via their much higher surface density. In this process, stars and molecular gas are strongly coupled, and it is such a coupling that ultimately triggers local gravitational collapse/fragmentation in the molecular gas.