The formation of the exponential disk in spiral galaxies

Abstract

The authors propose a mechanism for the formation of the exponential stellar disk distribution in spiral galaxies. It is assumed that the gas which falls in to form the disk behaves like an accretion disk which evolves on a viscous time scale tv and forms stars on a time scale t*. The authors demonstrate that if tv ≈ t* the resulting stellar disk has an exponential distribution independent of the disk rotation law and of the assumed viscosity prescription. They comment briefly on why the viscous and star formation time scales might be related.