Mass Transport and Turbulence in Gravitationally Unstable Disk Galaxies. I: The Case of Pure Self-Gravity

TL;DR

This study uses high-resolution simulations to show that gravitational instability alone can generate turbulence and mass transport in disk galaxies, potentially explaining observed galaxy properties without feedback.

Contribution

It demonstrates that gravity-driven turbulence can sustain velocity dispersions and mass inflow rates comparable to observations, without including star formation feedback.

Findings

Gravity alone drives significant turbulence in galaxy disks.

Mass transport rates are sufficient to fuel star formation.

Turbulence levels match those observed in nearby galaxies.

Abstract

The role of gravitational instability-driven turbulence in determining the structure and evolution of disk galaxies, and the extent to which gravity rather than feedback can explain galaxy properties, remains an open question. To address it, we present high resolution adaptive mesh refinement simulations of Milky Way-like isolated disk galaxies, including realistic heating and cooling rates and a physically motivated prescription for star formation, but no form of star formation feedback. After an initial transient, our galaxies reach a state of fully-nonlinear gravitational instability. In this state, gravity drives turbulence and radial inflow. Despite the lack of feedback, the gas in our galaxy models shows substantial turbulent velocity dispersions, indicating that gravitational instability alone may be able to power the velocity dispersions observed in nearby disk galaxies on 100 pc scales. Moreover, the rate of mass transport produced by this turbulence approaches $\sim 1$ $M_\odot$ yr$^{-1}$ for Milky Way-like conditions, sufficient to fully fuel star formation in the inner disks of galaxies. In a companion paper we add feedback to our models, and use the comparison between the two cases to understand what galaxy properties depend sensitively on feedback, and which can be understood as the product of gravity alone. All of the code, initial conditions, and simulation data for our model are publicly available.