Thermal condensation with polybaric pressure

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 ionized inviscid plasma with radiation loss. We carry out the simulation with the help of our multi-fluid flux-corrected transport (mFCT) code which incorporates a background magnetic field and anisotropic pressure. The anisotropic pressure is modeled with a polybaric pressure model (Stasiewicz 2004). We find that the resultant turbulent state of the interstellar matter (ISM), driven purely by time-dependent heating and cooling with polybaric pressure is similar in nature to the one driven by external forcing such as by supernova feedback. This demonstrates the universal nature of the turbulence in ISM, which is largely isobaric and incompressible. The findings of our analysis is 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 analysis.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.