Abstract

Contributed Talk - Splinter MassiveStars

Tuesday, 10 September 2024, 15:15   (S23)

Confronting Observations with Simulations - Blister-Type HII Regions

Sebastian Vider, Stefanie Walch-Gassner
Universität zu Köln, I. Physikalisches Institut

Massive stars regulate star formation by various feedback mechanisms. They heat up and expel gas and disrupt their parental molecular cloud, stopping ongoing star formation in the process. Supernovae are often considered to be the main feedback mechanism, but they only start happening a few Myr after the first massive star is born. Pre-SN feedback can already long before that inject large amounts of energy into the MC and drive outflows or even disrupt the MC. The most important pre-SN feedback mechanisms are ionizing radiation, stellar wind, and radiation pressure. Where either one can, depending on the environment and length scale, be the dominant mechanism. Both observations and simulations of HII regions help us understand the importance of feedback and the interplay between the different mechanisms. Recent observations of the 158 μm [CII] line find fast-expanding HII bubbles with velocities faster than the isothermal sound speed of the ionized gas. This can not be explained by a d-type expansion into a uniform medium, so it is concluded that the stellar wind has to be the dominant driver of the expansion. We propose another possibility supported by hydro-dynamical simulations: a HII region breaking out of a dense part of the MC. A simple model of this so-called blister-type HII region reproduces many features of the observations: (1) The fast expansion is traced by [CII] emission and not by emission lines from the CO isotopologues. (2) The expansion arc in the PV diagram has a smaller extent than the HII region. (3) The fast-moving gas is moving towards the observer. (4) We find an expansion speed of about 13 km/s. (5) The strongest emission comes from the wings of the arc.