Impact of the external radiation field on the structure and evolution of supernova remnants

TL;DR

This study uses 1D hydrodynamical simulations to explore how external radiation fields affect supernova remnant evolution, revealing distinct behaviors based on radiation shielding levels and their impact on remnant structure.

Contribution

It provides the first systematic analysis of external radiation field effects on SNR evolution, highlighting the role of UV shielding in shaping remnant morphology and thermal properties.

Findings

Unshielded cases develop an isothermal shock with a thickening shell.

Shielded cases form a thin, cold, dense shell during evolution.

Luminosity distribution varies with shielding, being more uniform in unshielded scenarios.

Abstract

We carry out 1D hydrodynamical simulations of the evolution of a spherically symmetric supernova remnant (SNR) subject to an external radiation field (ERF) that influences the cooling and heating rates of the gas. We consider homogeneous media with ambient hydrogen number densities $n_{\rm H,0}$ of $0.1$ and $1$ cm$^{-3}$ permeated by an average radiation field including the cosmic microwave, extragalactic, and Galactic backgrounds, attenuated by an effective column density $N_{\rm H,eff}$ from $10^{18}$ to $10^{21}$~cm$^{-2}$. Our results may be classified into two broad categories: at low $N_{\rm H,eff}$, the ERF presents little absorption in the ultraviolet (ionising) regime, and all the 'unshielded' cases feature an equilibrium temperature $T_{eq} \sim 7000$~K below which the ambient gas cannot cool further. In this scenario, the SNR develops a nearly isothermal shock profile whose shell becomes thicker over time. At higher $N_{\rm H,eff}$, the ERF is heavily absorbed in the UV range, yielding a roughly constant heating function for temperatures $\lesssim 10^4$ K. These `shielded' cases develop a thin, cold and dense shell throughout their evolution. Energy and momentum injection to the medium do not change significantly between both scenarios, albeit luminosity is higher and more uniformly distributed over the shell for unshielded SNR.