Thermal instability and multiphase dynamics in the ISM with polybaric pressure effects

TL;DR

This study uses 2D simulations to explore thermal instability in the interstellar medium, revealing how anisotropic pressure and magnetic fields influence the multiphase structure and evolution of the ISM.

Contribution

It introduces a multi-fluid flux-corrected transport simulation incorporating polybaric pressure and magnetic fields to analyze ISM thermal instability.

Findings

Magnetic field strength marginally affects overall evolution.

Pressure anisotropy significantly alters phase fractions.

Results align with observational data on ISM phases.

Abstract

In this work, we have carried out a two-dimensional (2D) simulation of thermal instability (TI) in interstellar matter (ISM), considering it to be a weakly ionised inviscid plasma with radiation loss. We carry out the simulation using our multi-fluid flux-corrected transport (mFCT) code, which incorporates a background magnetic field and anisotropic pressure. The anisotropic pressure is modelled with a polybaric pressure model. The findings of our analysis are consistent with the contemporary status of knowledge about the multiphase nature of the ISM, with volume and mass fractions of the various components of the ISM, that is, warm, cold, and unstable neutral matter (UNM) in the ranges reported by various numerical and observational analyses. Though the strength of the background magnetic field only marginally affects the overall evolution, the ratio of the parallel and perpendicular pressures can considerably alter the mass and volume fractions of the three phases, which can affect the overall evolution of the TI in the long run.