Sensitivity of the star formation rate to the interstellar gas abundance of heavy elements

The critical pressure required to produce the thermal instability in the interstellar gas is approximately inversely proportional to the heavy-element abundance. A model for the rate of star formation is presented which is based upon this relationship plus the assumption that star formation accompanies the formation of interstellar gas clouds of high density. This physical model is equivalent to the model of metal-enhanced star formation hypothesized by Talbot and Arnett to explain the paucity of stars with low metal abundance. The model presented here is shown to agree with the following observations: the mass fraction remaining in the form of interstellar gas; the U, Th, Re, Os, Pu, and I radioactive chronologies; the metal abundance of disk stars formed throughout the Galaxy's history, including spatial variations at a given epoch; the efficiency of star formation; and both a mass-to-light ratio and a supernova rate which are compatible with those of the Galaxy. The rate of star formation per unit area of the disk varies with the areal density of the interstellar gas in such a way as to simulate a power law with an exponent of 1.7 to 2.3. The scale height of disk stars decreases with time in a manner consistent with observations. Subject headings: galactic structure - interstellar matter - nucleosynthesis - star formation