On the evolution of the star formation rate in disk galaxies

A model for the chemical evolution of a disk galaxy is presented. The model reproduces all the basic parameters of our own Galaxy, including, for the first time, the correlation between metallicity and height above the Galactic plane. One version of this model had been used earlier to study the effect of heavy element loss from spiral galaxies on the chemical evolution of the intergalactic medium. Here, the primary emphasis is on investigations of the star formation history. Varying the basic parameters of the model-the mass and radius of the galaxy-and incorporating a delay in the onset of star formation make it possible to model different scenarios for the evolution of a galaxy's luminosity. There is a phase of enhanced star formation in the early stages of evolution of massive galaxies. Taking into account the absorption of optical radiation by dust grains makes it possible to explain certain observed characteristics of the luminosity evolution, in particular, the absence of bursts in optical luminosity in disk galaxies at the initial period of intense star formation. The possibility of reconstructing the star-formation history and galactic luminosity from observations of galaxies at different redshifts z is discussed. If selection effects are accurately taken into account, the model makes it possible to construct specific evolutionary scenarios that are consistent with the observations. Factors responsible for the deviation of the evolution of the average luminosity from the luminosity history in individual galaxies are discussed.