Multiarm spirals on the periphery of disc galaxies

TL;DR

This paper investigates multiarm spiral patterns in disc galaxies, proposing that rapid gas cooling and giant molecular cloud formation lead to multiarm spirals via swing amplification, differing from traditional secular instability models.

Contribution

It introduces a new mechanism linking fast gas cooling and molecular cloud formation to multiarm spiral structures in galaxies.

Findings

Multiarm spirals can form due to rapid gas cooling within 50 Myr.

Giant molecular clouds induce multiarm spirals through swing amplification.

The process occurs on a timescale ten times shorter than secular instability.

Abstract

Spiral patterns in some disc galaxies have two arms in the centre, and three or more arms on the periphery. The same result is also obtained in numerical simulations of stellar and gaseous discs. We argue that such patterns may occur due to fast cooling of the gas, resulting in formation of giant molecular clouds. The timescale of this process is 50 Myr, the factor of 10 shorter than of ordinary secular instability. The giant molecular clouds give rise to multiarm spirals through the mechanism of swing amplification.