The Formation of Galaxy Disks

Abstract

Galaxy disk formation must incorporate the multiphase nature of the interstellar medium. The resulting two-phase structure is generated and maintained by gravitational instability and supernova energy input, which yield a source of turbulent viscosity that is able to effectively compete in the protodisk phase with early angular momentum loss of the baryonic component via dynamical friction in the dark halo. Provided that star formation occurs on the viscous drag time-scale, this mechanism provides a means of accounting for disk sizes and radial profiles. The star formation feedback is self-regulated by turbulent gas pressure-limited percolation of the supernova remnant-heated hot phase, but can run away in gas-rich protodisks to generate compact starbursts. A simple analytic model is derived for a Schmidt-like global star formation law in terms of the cold gas volume density.