A Dynamical Model for the Formation of Gas Rings and Episodic Starbursts Near Galactic Centres

TL;DR

This paper presents a dynamical model explaining how gas accumulates and triggers episodic starbursts near galactic centers, driven by bar-induced angular momentum transport and changes in the rotation curve.

Contribution

The model links gas dynamics, turbulence, and rotation curve transitions to episodic star formation in galactic centers, providing a unified explanation for observed phenomena.

Findings

Gas is driven inward by acoustic instabilities within the bar's resonance.

Gas accumulation occurs around 100 pc from the galactic center, matching observations.

Starburst episodes have a characteristic timescale of 10-20 Myr.

Abstract

We develop a simple dynamical model for the evolution of gas in the centres of barred spiral galaxies, using the Milky Way's Central Molecular Zone (CMZ, i.e., the central few hundred pc) as a case study. We show that, in the presence of a galactic bar, gas in a disc in the central regions of a galaxy will be driven inwards by angular momentum transport induced by acoustic instabilities within the bar's inner Lindblad resonance. This transport process drives turbulence within the gas that temporarily keeps it strongly gravitationally stable and prevents the onset of rapid star formation. However, at some point the rotation curve must transition from approximately flat to approximately solid body, and the resulting reduction in shear reduces the transport rates and causes gas to build up, eventually producing a gravitationally-unstable region that is subject to rapid and violent star formation. For the observed rotation curve of the Milky Way, the accumulation happens $\sim 100$ pc from the centre of the Galaxy, in good agreement with the observed location of gas clouds and young star clusters in the CMZ. The characteristic timescale for gas accumulation and star formation is of order $10-20$ Myr. We argue that similar phenomena should be ubiquitous in other barred spiral galaxies.