Feathering Instability of Spiral Arms. II. Parameter Study

TL;DR

This study investigates the feathering instability in galactic spiral arms through a parameter analysis, revealing how self-gravity and magnetic fields influence the formation and spacing of feathering structures, aligning with observations of galaxies like M51.

Contribution

It provides a detailed linear stability analysis of feathering instability considering self-gravity and magnetic fields, expanding understanding of spiral arm substructures.

Findings

Self-gravity shifts spiral shocks downstream and increases growth rates.

Magnetic fields suppress velocity fluctuations but do not significantly affect growth rates.

Feather spacing at maximum growth rate matches observational data (~530 pc in M51).

Abstract

We report the results of a parameter study of the feathering stability in the galactic spiral arms. A two-dimensional razor-thin magnetized self-gravitating gas disk with an imposed two-armed stellar spiral structure is considered. Using the formulation developed previously by Lee and Shu, a linear stability analysis of the spiral shock is performed in a localized Cartesian geometry. Results of the parameter study of the base state with a spiral shock are also presented. The single-mode feathering instability that leads to growing perturbations may explain the feathering phenomenon found in nearby spiral galaxies. The self-gravity of the gas, characterized by its average surface density, is an important parameter which 1) shifts the spiral shock further downstream; 2) increases the growth rate and decreases the characteristic spacing of the feathering structure due to the instability. On the other hand, while the magnetic field suppresses the velocity fluctuation associated with the feathers, it does not strongly affect their growth rate. Using a set of typical parameters of the grand-design spiral galaxy M51 at 2 kpc from the center, the spacing of the feathers with the maximum growth rate is found to be 530 pc, which agrees with the previous observational studies.