The Role of Gas In Maintaining Quasi-Steady Spiral Structure In Stellar Disks

TL;DR

This study uses high-resolution simulations to show that gas-star dynamical coupling sustains long-lived spiral structures in stellar disks of isolated galaxies, contrasting with more rapid dissipation without gas.

Contribution

It demonstrates that the dynamical interaction between gas and stars, facilitated by angular momentum transfer, maintains quasi-steady spiral structures in stellar disks.

Findings

Gas presence prolongs spiral structure lifetime.

Dissipative gas induces azimuthal phase shift, supporting spiral persistence.

Results consistent across different star formation timescales.

Abstract

We study the dynamical evolution of spiral structure in the stellar disks of isolated galaxies using high resolution Smoothed Particle Hydrodynamics (SPH) simulations that treat the evolution of gas, stars, and dark matter self-consistently. We focus this study on the question of self-excited spiral structure in the stellar disk and investigate the dynamical coupling between the cold, dissipative gaseous component and the stellar component. We find that angular momentum transport from the gas to the stars inside of corotation leads to a roughly time-steady spiral structure in the stellar disk. To make this point clear, we contrast these results with otherwise identical simulations that do not include a cold gaseous component that is able to cool radiatively and dissipate energy, and find that spiral structure, when it is incipient, dies out more rapidly in simulations that do not include gas. We also employ a standard star formation prescription to convert gas into stars and find that our results hold for typical gas consumption time scales that are in accord with the Kennicutt-Schmidt relation. We therefore attribute the long-lived roughly time steady spiral structure in the stellar disk to the dynamical coupling between the gas and the stars and the resultant torques that the self-gravitating gaseous disk is able to exert on the stars due to an azimuthal phase shift between the collisionless and dissipative components.