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 a bove the Galactic plane. One version of this model had been used earli er to study the effect of heavy element loss from spiral galaxies on t he chemical evolution of the intergalactic medium. Here, the primary e mphasis is on investigations of the star formation history. Varying th e 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 luminosit y. There is a phase of enhanced star formation in the early stages of evolution of massive galaxies. Taking into account the absorption of o ptical radiation by dust grains makes it possible to explain certain o bserved characteristics of the luminosity evolution, in particular, th e absence of bursts in optical luminosity in disk galaxies at the init ial period of intense star formation. The possibility of reconstructin g the star-formation history and galactic luminosity from observations of galaxies at different redshifts z is discussed. If selection effec ts are accurately taken into account, the model makes it possible to c onstruct specific evolutionary scenarios that are consistent with the observations. Factors responsible for the deviation of the evolution o f the average luminosity from the luminosity history in individual gal axies are discussed.