Institution(s): 1. Caltech
The ISM is a chaotic, highly nonlinear system in which super-sonic turbulence, gravity, accretion, and "feedback" play critical roles. Yet there is remarkable regularity in certain properties. I'll discuss how many observed properties of the ISM can be understood as a fundamental consequence of super-sonic turbulence in a rapidly cooling, self-gravitating medium. In doing so, I'll show how analytic methods used in cosmology to describe the formation of large-scale structure can be applied to understand the origins of structure in the ISM, including the mass function and structural properties of giant molecular clouds, the stellar initial mass function, the clustering of star formation, and the formation of planets via "direct collapse" (gravitational instability). This can be used to study time-dependent evolution of structure even in highly non-linear systems, allowing us to understand many emergent properties of simulations with turbulence and gravity. In particular this provides a rigorous, natural explanation for the universality of these mass functions, the translation from the core mass function to the stellar IMF, and the structure of the ISM. It also makes natural predictions for IMF evolution in other galaxies, which can provide a unique insight into these physics.