The Parker Instability with Cosmic Ray Streaming

TL;DR

This paper analyzes how different cosmic ray transport models, especially streaming, influence the stability of stratified galactic systems, revealing that streaming significantly destabilizes the system and impacts cosmic ray feedback.

Contribution

It provides the first stability analysis of the Parker Instability incorporating cosmic ray streaming, highlighting its destabilizing effect compared to other transport models.

Findings

Cosmic ray streaming severely destabilizes the Parker Instability.

Decreased cosmic ray compressibility stabilizes the system.

3D systems are more unstable over larger wavelength ranges.

Abstract

Recent studies have found that cosmic ray transport plays an important role in feedback processes such as star formation and the launching of galactic winds. Although cosmic ray buoyancy is widely held to be a destabilizing force in galactic disks, the effect of cosmic ray transport on the stability of stratified systems has yet to be analyzed. We perform a stability analysis of a stratified layer for three different cosmic ray transport models: decoupled (Classic Parker), coupled with $\gamma_c=4/3$ but not streaming (Modified Parker), and finally coupled with streaming at the Alfv\'{e}n speed. When the compressibility of the cosmic rays is decreased the system becomes much more stable, but the addition of cosmic ray streaming to the Parker Instability severely destabilizes it. Through comparison of these three cases and analysis of the work contributions for the perturbed quantities of each system, we demonstrate that cosmic ray heating of the gas is responsible for the destabilization of the system. We find that a 3D system is unstable over a larger range of wavelengths than the 2D system. Therefore, the Parker Instability with cosmic ray streaming may play an important role in cosmic ray feedback.