What Controls Star Formation in Galaxies?

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This investigation evaluates the relative importance different physical processes during molecular cloud and star formation. Overall, this improves our understanding of the dynamics of molecular cloud formation and of how external flows and internal massive star formation act to disperse or destroy them again. It tests whether star formation rates are governed by molecular cloud formation due to high pressure in a disk's mid-plane, or by gravitational instability of the combination of gas and stars. Related problems are the lifetimes and star formation efficiency in molecular clouds. Dr. Mac Low and his team use the FLASH adaptive mesh refinement (AMR) simulation code that can handle the modeling of the most important physical processes important to star formation models. These include effects of supernova explosions; self gravity; differential rotation in the shearing sheet approximation; ionizing, dissociating, and non-ionizing but heating radiation from point sources; magnetic fields; molecular chemistry in two different levels of approximation; an approximation to radiative cooling in optically thin and thick regions; a fixed stellar gravitational potential to maintain vertical stratification; the full galactic fountain; and sink particles emitting both radiation and stellar jets and winds. The models are done so that effects are integrated into a multiscale model of star formation covering scales ranging from 0.5 kiloparsec down to 100 Astronomical Units. The results help to distinguish between the "high midplane pressure" and the "gravitational instability" models. Thus, self-consistent numerical models follow the assembly of giant molecular clouds and the results of star formation within them. The team evaluates the relative importance of these processes by parameter studies using the fully resolved version of these models with full chemistry.This research program is an international collaboration between the Museum and the Institute for Theoretical Astrophysics of the University of Heidelberg. It will also support the training of a graduate student. Results from this research are also incorporated into the exhibition and education program of the American Museum of Natural History, including the Hayden Planetarium.