Fakultät für Physik und Astronomie
STEPHEN PHILLIPS hostreviews.co.uk / UNSPLASH

A general theory for the lifetimes of giant molecular clouds under the influence of galactic dynamics

Sarah Jeffreson

The giant molecular cloud (GMC) lifetime provides an upper bound on the local time-scale for star-formation, linking cloud-scale and sub cloud-scale physics to galaxy-scale trends in the star formation rate. Conversely, the galactic environment plays an important role in setting the cloud lifetime, leading to a complex interplay of physical mechanisms over a range of scales in the interstellar medium (ISM), from galactic dynamics to small-scale turbulence and feedback. Previous theories of GMC lifetimes have made predictions based on just one mechanism of cloud evolution, relevant only in a fraction of Galactic and extragalactic star-forming environments. That approach is inconsistent with recent observations, which show that a diverse range of entities are observationally-identifiable as clouds, and reveal environmentally-driven correlations between their gravitational boundedness and the galaxy-scale star formation rate. I present an analytic theory for GMC lifetimes, dependent on the large-scale dynamical environment of the ISM, including its local gravitational stability, cloud-cloud collisions, epicyclic perturbations, galactic shear, and interaction with galactic bars and spiral arms. Our analytic predictions depend on just five observable properties, accessible through measurements of the rotation curve, surface density and velocity dispersion of the host galaxy, and are applicable over a wide range of redshifts. In this contribution, I will present predicted cloud lifetimes and properties across a range of galactic dynamical environments. I will compare these results to hydrodynamic simulations performed using the moving-mesh code Arepo, where the influence of dynamics is combined with sub-cloud physics such as supernova feedback, HII-region feedback, and ISM chemistry. These theoretical and numerical results are consistent with pioneering observational results currently obtained with ALMA. Together, this combination of analytic, numerical and observational results show that the galactic dynamic environment plays a crucial role in determining GMC lifecycles and thus the star formation rates of their host galaxies.

ITA "blackboard" Colloquium
17 Jun 2019, 11:15
Philosophenweg, 12, 106

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