Self-Perpetuating Spiral Arms in Disk Galaxies

TL;DR

This paper demonstrates through high-resolution simulations that density inhomogeneities like molecular clouds can generate long-lasting spiral arms in disk galaxies via non-linear swing amplification, challenging previous linear models.

Contribution

It shows that non-linear effects allow spiral structures to persist long after initial perturbations, providing new insights into galaxy morphology formation.

Findings

Giant molecular clouds induce spiral arms through swing amplification.

Non-linear responses significantly alter spiral arm formation and longevity.

Ragged spiral structures can survive long after perturbations are gone.

Abstract

The causes of spiral structure in galaxies remain uncertain. Leaving aside the grand bisymmetric spirals with their own well-known complications, here we consider the possibility that multi-armed spiral features originate from density inhomogeneities orbiting within disks. Using high-resolution N-body simulations, we follow the motions of stars under the influence of gravity, and show that mass concentrations with properties similar to those of giant molecular clouds can induce the development of spiral arms through a process termed swing amplification. However, unlike in earlier work, we demonstrate that the eventual response of the disk can be highly non-linear, significantly modifying the formation and longevity of the resulting patterns. Contrary to expectations, ragged spiral structures can thus survive at least in a statistical sense long after the original perturbing influence has been removed.