Sarah Jeffreson (Australia)
s.jeffreson @ uni-heidelberg.de
Which physical processes drive the evolution of giant molecular clouds?
The molecular cloud lifetime provides an upper bound on the local time-scale for star formation, making it an essential quantity in determining the star formation rate. 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, from galactic dynamics to small-scale turbulence and feedback. Previous theories have predicted cloud lifetimes based on just one mechanism of cloud evolution, relevant in only a fraction of nearby star-forming environments. That approach is inconsistent with recent observations, which show that a diverse range of entities are observationally-identifiable as clouds, with a correspondingly large spread of virial parameters and states of gravitational boundedness. We have developed an analytic theory for the molecular cloud lifetime, independent of theoretical assumptions about its size, structure, mode of gravitational collapse and gravitational boundedness. Within this theory, the cloud lifetime depends on the large-scale dynamics of the ISM, including those processes that may trigger star formation, such as local gravitational instability, spiral-arm crossings, cloud-cloud collisions and epicyclic perturbations, as well as the quenching effects of galactic shear. Our analytic predictions depend upon 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. We have predicted cloud lifetimes across a variety of galactic environments, which will soon be compared to observed cloud lifetimes from an ongoing ALMA survey of nearby galaxies. We are currently producing the first set of comparisons of our theory to hydrodynamic simulations performed using the moving-mesh code Arepo. Together, this combination of analytic, numerical and observational results show that all environmental evolutionary mechanisms need to be accounted for when aiming to understand the lifecycle of molecular clouds and the star formation within them.
Please visit my website at http://wwwstaff.ari.uni-heidelberg.de/jeffreson/
Supervisor: Diederik Kruijssen (ARI)