Speaker
Bram Ochsendorf
(Leiden Observatory)
Description
Massive stars drive the evolution of the interstellar medium of galaxies and its observational characteristics through their radiative and mechanical energy input. It has been thought that fast stellar winds from massive stars sweep up the ambient gas to form 'bubbles' of hot gas, surrounded by dense shells of ionized and neutral gas. Infrared surveys of the Milky Way have revealed that bubble H II regions dominate the morphology of the disk of the Galaxy. However, there is no direct evidence that mechanical energy input from winds is driving the evolution of these regions. In this talk, I will show that instead interstellar bubbles form and expand due to the thermal pressure accompanying ionization of the surrounding gas and that this phase ends when the bubble is punctured, leading to an ionized gas flow into the general interstellar medium (a champagne flow). Infrared observations of bubbles reveal 'dust waves' near their stars, demonstrating the importance of radiation pressure on dust during this phase. We have analyzed the dust wave in the photo-evaporation flow in IC 434 and the Horsehead nebula, where radiation pressure from the nearby star has stalled the dust but the gas flows along unhindered. Our study demonstrates that dust waves allow us to study the properties and role of dust inside H II regions and to directly trace the radiative interaction of massive stars with the evacuating flow and the dynamical evolution of interstellar bubbles. I will emphasize that the evolution of super star clusters formed in UltraLuminous InfraRed Galaxies (ULIRGs), merging galaxies and the early Universe occurs in very luminous and dense environments, where radiation pressure will dominate the dynamical evolution and the study presented here provides the tool to quantify this interaction.
Author
Bram Ochsendorf
(Leiden Observatory)