Radiation-pressure-driven dust waves inside bursting interstellar bubbles

Abstract

Massive stars drive the evolution of the interstellar medium through their radiative and mechanical energy input. After their birth, they form bubbles of hot gas surrounded by a dense shell. Traditionally, the formation of bubbles is explained through the input of a powerful stellar wind, even though direct evidence supporting this scenario is lacking. Here we explore the possibility that interstellar bubbles seen by the Spitzer- and Herschel space telescopes, blown by stars with log(L/L_sun) < 5.2, form and expand due to the thermal pressure accompanying ionization of the surrounding gas. We show that density gradients in the natal cloud or a puncture in the swept up shell lead to an ionized gas flow through the bubble into the general interstellar medium, which is traced by a dust wave near the star, demonstrating the importance of radiation pressure during this phase. Dust waves provide a natural explanation for the presence of dust inside H II bubbles, offer a novel method to study dust in H II regions and provide direct evidence that bubbles are relieving their pressure into the ISM through a champagne flow, acting as a probe of the radiative interaction of a massive star with its surroundings. We create a parameter space connecting the ambient density, the ionizing source luminosity, and the position of the dust wave, while using the well-studied H II bubbles RCW 120 and RCW 82 as benchmarks of our model. Finally, we briefly examine the implications of our study for the environments of super star clusters formed in UltraLuminous InfraRed Galaxies (ULIRGs), merging galaxies and the early Universe, which occur in very luminous and dense environments and where radiation pressure is expected to dominate the dynamical evolution.