Self-regulated star-formation in chemodynamical models of galaxies

J.Köppen, Ch.Theis, G.Hensler

ABSTRACT We study numerically and analytically the evolution of galactic stellar and gaseous components in a closed-box model that includes the energetics of the star-forming gas. The gas is heated mainly by massive stars (UV-radiation, stellar winds). The stellar birth function depends on the density (g), but also on the temperature of the gas. This describes the fact that the star-forming molecular fraction is smaller in hot and warm gas than in cold clouds. This negative feed-back causes the system to exhibit a strong self-regulation, quite independent of the parametrizations of the basic processes. The resultant equilibrium star-formation rate is a quadratic Schmidt-type law (SFR propto g**2), independent of the assumed form and parameters of the stellar birth function. An analysis of the local and global stability shows that this behaviour is stable against disturbances in the state of the interstellar medium as well as against reasonable changes in the parametrizations of the star-formation or heating processes. While at low or high gas densities the system reaches the equilibrium directly, at intermediate densities (3000 - 0.1 Msun/pc**3) it performs strongly damped oscillations. In any case, the system settles into equilibrium within a short time (the cooling time of the gas), and evolves almost exclusively in equilibrium.