Starbursts driven by central gas compaction

TL;DR

This study investigates the mechanisms behind starburst galaxies, revealing that both gas compaction and galaxy interactions or instabilities drive their intense star formation, with different processes dominating based on galaxy mass.

Contribution

It provides a detailed analysis of starburst triggers, highlighting the roles of gas compaction, galaxy interactions, and gravitational instabilities across different galaxy masses.

Findings

Starburst galaxies have higher molecular gas fractions and shorter depletion times.

Gas compaction in control galaxies leads to starbursts within ~70 Myr.

Massive galaxies often experience interaction-driven starbursts, while low-mass galaxies are triggered by gravitational instabilities.

Abstract

Starburst (SB) galaxies are a rare population of galaxies with star formation rates (SFRs) greatly exceeding those of the majority of star-forming galaxies with similar stellar mass. It is unclear whether these bursts are the result of either especially large gas reservoirs or enhanced efficiencies in converting gas into stars. Tidal torques resulting from gas-rich galaxy mergers are known to enhance the SFR by funneling gas towards the centre. However, recent theoretical works show that mergers do not always trigger a SB and not all SB galaxies are interacting systems, raising the question of what drives a SB. We analyse a large sample of SB galaxies and a mass- and redshift-matched sample of control galaxies, drawn from the FIREbox cosmological volume at z=0-1. We find that SB galaxies have both larger molecular gas fractions and shorter molecular depletion times than control galaxies, but similar total gas masses. Control galaxies evolve towards the SB regime by gas compaction in their central regions, over timescales of about 70 Myr, accompanied by an increase in the fraction of ultra-dense and molecular gas. The driving mechanism behind the SB varies depending on the mass of the galaxy. Massive (Mstar > 1e10 Msun) galaxies undergoing intense, long-lasting SBs are mostly driven by galaxy interactions. Conversely, SBs in non-interacting galaxies are often triggered by a global gravitational instability, that can result in a breathing mode in low-mass galaxies.