Sarah Jeffreson (Aus)
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 and thus is an essential quantity for determining the galactic star formation rate (SFR). Cloud evolution can be influenced by a complex interplay between a wide variety of physical mechanisms, ranging from galactic dynamics to small-scale turbulence and feedback. However, previous theories have predicted cloud lifetimes based on just one mechanism of cloud evolution, relevant only in a fraction of the parameter space spanned by observable galactic properties. This 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 present a comprehensive theory for molecular cloud lifetimes which takes into account the diversity of observed cloud properties, dependent on the time-scales of evolution set by their environment. Our analytic theory combines the rate of gravitational collapse, spiral-arm crossings, cloud-cloud collisions, epicyclic perturbations and galactic shear to span the entire parameter space of galactic properties that may feasibly be observed. The resulting analytic predictions depend only upon five observable properties, accessible through measurements of the rotation curve, surface density and velocity dispersion of the host galaxy. We are currently making the first comparison of our predicted cloud lifetimes to observed cloud lifetimes for a sample of galaxies, derived via the statistical method presented in Kruijssen & Longmore 2014. We are also working to produce the first set of comparisons of our theory to hydrodynamic simulations performed using the moving-mesh code AREPO (Springel 2010).
Supervisor: Diederik Kruijssen (ARI)