Evolution of Supernova Remnants in a Cloudy Multiphase Interstellar Medium

TL;DR

This study uses high-resolution 3D hydrodynamical simulations to explore how supernova remnants evolve in a complex, cloudy interstellar medium, revealing differences from uniform models and emphasizing the roles of energy loss and thermal conduction.

Contribution

It provides the first detailed 3D simulation analysis of SNRs in a two-phase cloudy medium, highlighting the importance of energy sinks and the limitations of previous 1D models.

Findings

SNRs in a cloudy medium sweep up more mass than in uniform media.

Energy loss due to cooling in cold clouds reduces hot gas and momentum.

Thermal conduction alters internal structure but has little impact on overall dynamics.

Abstract

We investigate the evolution of supernova remnants (SNRs) in a two-phase cloudy medium by performing a series of high-resolution (up to $\Delta x\approx0.01\,\mathrm{pc}$), 3D hydrodynamical simulations including radiative cooling and thermal conduction. We aim to reach a resolution that directly captures the shock-cloud interactions for the majority of the clouds initialized by the saturation of thermal instability. In comparison to the SNR in a uniform medium with the volume filling warm medium, the SNR expands similarly (following $\propto t^{2/5}$) but sweeps up more mass as the cold clouds contribute before shocks in the warm medium become radiative. However, the SNR in a cloudy medium continuously loses energy after shocks toward the cold clouds cool, resulting in less hot gas mass, thermal energy, and terminal momentum. Thermal conduction has little effect on the dynamics of the SNR but smooths the morphology and modifies the internal structure by increasing the density of hot gas by a factor of $\sim 3-5$. The simulation results are not fully consistent with many previous 1D models describing the SNR in a cloudy medium including a mass loading term. By direct measurement in the simulations, we find that, apart from the mass source, the energy sink is also important with a spatially flat cooling rate $\dot{e}\propto t^{-11/5}$. As an illustration, we show an example 1D model including both mass source and energy sink terms (in addition to the radiative cooling in the volume filling component) that better describes the structure of the simulated SNR.