Star formation on GMC and galactic scales

The rate of star formation in star-forming disks is slow compared to the dynamical time, at least on kiloparsec scales, a result known as the Kennicutt-Schmidt relation. Candidates for opposing the force of self-gravity and thereby reducing the rate of star formation include magnetic fields, large scale turbulence, and feedback effects from newly formed stars (including thermal gas pressure, shocked stellar winds, radiation pressure, and supernovae). I will present analytic and numerical work showing that large scale turbulence does not limit the rate of star formation in regions where the virial parameter is less than a few. The theory provides an explanation for deviations from Larson's law (the size-linewidth relation) in massive star forming regions: a substantial fraction of the potential energy of the accreting gas is converted to turbulent kinetic energy. The theory predicts that inside the radius at which the stellar (or stellar cluster) gravity dominates, the turbulent velocity will {it increase} with decreasing radius. The theory predicts that the star formation rate in gravitationally bound GMCs (in the Milky Way, those with masses in excess of 1 million solar masses) increases linearly with time. I will also present the results of cosmological simulations showing that feedback from stars can reproduce the Kennicutt-Schmidt relation.

Speaker: Norm Murray (CITA)