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

Abstract

Energetic winds and radiation from massive star clusters push the surrounding gas and blow superbubbles in the interstellar medium (ISM). Using 1D hydrodynamic simulations, we study the role of radiation in the dynamics of superbubbles driven by a young star cluster of mass 106 M⊙. 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 (∼107 K) of the shocked-wind region is almost independent of the ambient density, and it is greater than unity before ≲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 (∼107 K) cavity is insensitive to the dust opacity [σd ≈ (0.1–1.5) × 10−21 cm2], but the structure of the photoionized (∼104 K) gas depends on it. Most of the radiative losses occur at ∼104 K, with sub-dominant losses at ≲103 K and ∼106–108 K. The superbubbles can retain as high as ∼10 per cent of its input energy, for an ambient density of 103 mH 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.