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 ) 5.2, form and expand because of the thermal pressure that accompanies the 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, which demonstrates 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 interstellar medium through a champagne flow, acting as a probe of the radiative interaction of a massive star with its surroundings. We explore 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, 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.

Wind bubbles within H ii regions around slowly moving stars

“…In any case, we can conclude that the H ii region should be < ∼ 0.4 Myr old. Ochsendorf et al (2014) proposed a model in which a strong…”

“…Ochsendorf et al (2014) interpret these arcs (based on the original idea by van Buren & McCray 1988) as emission from dust grains that have decoupled from the gas and are deflected away from the ionizing stars by their radiation pressure. An alternative interpretation -that the arcs delineate the edge of a stellar wind bubble within a larger H ii regionhas not so far been explored with multidimensional simulations.…”

“…Pressure and density gradients in the ISM generate asymmetric H ii regions (Champagne flows, Tenorio-Tagle 1979), and this model was recently applied to RCW 120 by Ochsendorf et al (2014) to explain the asymmetry implied by the mid-IR arcs. Stellar motion also provides a pressure asymmetry that produces asymmetric stellar wind bubbles (Weaver et al 1977;Mac Low et al 1991;Arthur & Hoare 2006) and H ii region bubbles (Raga 1986;Mackey et al 2013).…”

Detecting stellar-wind bubbles through infrared arcs in H ii regions

“…Some H  regions do show a central decrement in emission near the ionizing star (e.g., N49; Watson et al 2008) in these tracers, but others do not (e.g., RCW 120; Ochsendorf et al 2014b;Torii et al 2015). This can be understood if some SWBs fill only a small fraction of the H  region along the line of sight (so that the fractional decrement is small), but we then need more sensitive tracers to detect these SWBs.…”

“…• 11636 in RCW 120 (Ochsendorf et al 2014b; Paper I), an arc within the H  region RCW 82 (Ochsendorf et al 2014b), around σ Ori within IC 434 (Ochsendorf et al 2014a), around λ Ori , an almost-complete ring in N49 (Watson et al 2008), an arc within G31.165-00.127 , and various arcs in the sample of Paladini et al (2012). We have excluded from this list arcs around runaway stars that are definitely bow shocks (e.g., Gvaramadze et al 2012).…”