SELF-REGULATED STAR-FORMATION IN CHEMODYNAMICAL MODELS OF GALAXIES

We study numerically and analytically the evolution of galactic stella r and gaseous components in a closed-box model that includes the energ etics of the star-forming gas. The gas is heated mainly by massive sta rs (UV-radiation, stellar winds). The stellar birth function depends o n the density (g), but also on the temperature of the gas. This descri bes the fact that the star-forming molecular fraction is smaller in ho t 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 sta r-formation rate is a quadratic Schmidt-type law (SFR proportional to g(2)), independent of the assumed form and parameters of the stellar b irth function. An analysis of the local and global stability shows tha t this behaviour is stable against disturbances in the state of the in terstellar medium as well as against reasonable changes in the paramet rizations of the star-formation or heating processes. While at low or high gas densities the system reaches the equilibrium directly, at int ermediate densities (10(-3.5) - 10(-1)M.pc(-3)) it performs strongly d amped oscillations. In any case, the system settles into equilibrium w ithin a short time (the cooling time of the gas), and evolves almost e xclusively in equilibrium.