How radiation affects superbubbles: Through momentum injection in early phase and photo-heating thereafter

TL;DR

This study uses hydrodynamic simulations to analyze how radiation and winds from massive star clusters influence superbubble evolution, highlighting the roles of radiation pressure, heating, cooling, and ambient medium properties.

Contribution

It provides a detailed analysis of radiation's impact on superbubbles, including the relative importance of radiation pressure and thermal pressure, and explores parameter space effects on bubble structure.

Findings

Radiation pressure exceeds thermal pressure before 1 Myr.

Hot gas cavity size is insensitive to dust opacity.

Superbubbles retain up to 10% of input energy in dense environments.

Abstract

Energetic winds and radiation from massive star clusters push the surrounding gas and blow superbubbles in the interstellar medium (ISM). Using 1-D hydrodynamic simulations, we study the role of radiation in the dynamics of superbubbles driven by a young star cluster of mass $10^{6}$ M$_{\odot}$. We have considered a realistic time evolution of the mechanical power as well as radiation power of the star cluster, and detailed heating and cooling processes. We find that the ratio of the radiation pressure on the shell (shocked ISM) to the thermal pressure ($\sim10^{7}$ K) of the shocked wind region is almost independent of the ambient density, and it is greater than unity before $\lesssim 1$ Myr. We explore the parameter space of density and dust opacity of the ambient medium, and find that the size of the hot gas ($\sim$ 10$^{7}$ K) cavity is insensitive to the dust opacity ($\sigma_{d}\approx(0.1-1.5)\times 10^{-21}$ cm$^{2}$), but the structure of the photoionized ($\sim10^4$ K) gas depends on it. Most of the radiative losses occur at $\sim10^{4}$ K, with sub-dominant losses at $\lesssim 10^3$ K and $\sim10^{6}-10^{8}$ K. The superbubbles can retain as high as $\sim 10\%$ of its input energy, for an ambient density of $10^{3}\,m{\rm_{H}\,cm^{-3}}$. We discuss the role of ionization parameter and recombination-averaged density in understanding the dominant feedback mechanism. Finally, we compare our results with the observations of 30 Doradus.