Filamentary Hierarchies and Superbubbles II: Impact of superbubbles and galactic dynamics on filament formation and fragmentation

TL;DR

This study examines how galactic shear, supernovae, magnetic fields, and superbubbles influence filament formation, stability, and fragmentation in a simulated Milky Way-like galaxy, revealing the dominant factors and regional differences.

Contribution

It provides a detailed analysis of the roles of various galactic phenomena on filament dynamics and introduces new insights into the influence of magnetic fields and pressure ratios.

Findings

Magnetic fields significantly stabilize filaments.

Outer disk filaments are more affected by shear.

Filaments with low pressure ratio tend to be gravitationally supercritical.

Abstract

Large scale phenomena in spiral galaxies such as shear, supernovae, and magnetic fields all contribute to the formation and subsequent evolution of filamentary structure and star formation within them. In this paper, we analyze the properties and dynamics of filaments in a simulated Milky Way-like galaxy from Zhao et al. 2024. Using filament and superbubble structure analysis codes, we investigate the roles of galactic shear, supernovae and superbubbles, and magnetic fields on the stability and fragmentation of filaments. We find that local shear has little effect on filament stability and the largest structures at outer radii of the disk may be more likely to be dissipated by shear than supernovae. Filaments are largely parallel to the magnetic field, which plays a significant role in filament stability. By measuring the ratio of surface pressure on a filament to that on its central spine, $\chi_f=P_{surf}/P_{central}$, we find that filaments with $\chi_f \le 1$ are dominated by their own self gravity and have a strong tendency to be gravitationally supercritical, whereas those with $\chi_f > 1$ are either transitory or in the act of being formed. Finally, we investigate the role of ISM pressure on filament dynamics and stability as a function of galactic radius, finding considerable changes in filament stability and the accompanying star formation rates in the inner versus outer regions of the disk.