Contributed Talk - Splinter Stars
Thursday, 16 September 2021, 09:40 (virtual Stars)
Identifying Molecular Superbubbles in Nearby Galaxies using PHANGS-ALMA 12CO (2-1)
Elizabeth Watkins, Kathryn Kreckel
Superbubbles are extreme regions of expanding gas, important for redistributing energy, turbulence and material throughout galaxies. They provide a vital mechanism for maintaining the baryonic cycle within galaxies. Molecular superbubbles trace younger stages of evolution making them ideal for constraining early feedback processes, however molecular gas observations containing velocity information covering entire galaxies with sub-100 pc scales are needed. With the wide coverage (89 galaxies) and high angular resolution (~50 pc) provided in the PHANGS-ALMA CO (J=2-1) survey, for the first time, we can characterise the properties for a significant sample of molecular superbubbles in nearby galaxies. To understand how well CO constrains superbubble properties (e.g. mass, age), we compare with properties measured within PHANGS-HST and PHANGS-MUSE. We find a robust sample of 31 molecular superbubbles with clear superbubble signatures (shells, central clusters, kinematics) and measure their radii and expansion velocities using CO. Using a fully radiative, wind-driven expansion model, we estimate the dynamic age of the bubbles as a proxy for the age of the cluster and use the kinetic energy of the molecular gas to estimate the cluster mass needed to power the expansion. When compared to their optical HST counterpoints, we find that while the cluster masses agree very well, the HST ages are 0.68 times smaller. This offset is likely a result of neglecting the contribution of supernovae, resulting in an underestimate of the energy injection. These molecular superbubbles inform supernova studies, gas clearing times, propagating star formation and chemical enrichment of galaxies, important processes needed to understand what sets the observed star formation rates in galaxies.