Long-Lived Spiral Structure for Galaxies with Intermediate Size Bulges

TL;DR

This study uses N-body simulations to explore long-lived spiral structures in disk galaxies with intermediate-sized bulges, revealing conditions that support persistent two-arm spiral waves lasting several billion years.

Contribution

It demonstrates that galaxies with certain bulge-to-disk ratios and high Toomre Q parameters can sustain long-lived spiral modes, highlighting the role of bulge mass and Q-barriers in spiral longevity.

Findings

Long-lasting two-arm spirals last for about 5 Gyr.

High Q parameters and lighter disks favor persistent spiral modes.

Bulge mass around 10% is associated with long-lived spirals.

Abstract

Spiral structure in disk galaxies is modeled with nine collisionless N-body simulations including live disks, halos, and bulges with a range of masses. Two of these simulations make long-lasting and strong two-arm spiral wave modes that last for $\sim5$ Gyr with constant pattern speed. These two had a light stellar disk and the largest values of the Toomre $Q$ parameter in the inner region at the time the spirals formed, suggesting the presence of a Q-barrier to wave propagation resulting from the bulge. The relative bulge mass in these cases is about 10\%. Models with weak two-arm spirals had pattern speeds that followed the radial dependence of the Inner Lindblad Resonance.