EVOLUTION OF THE RATE AND MODE OF STAR FORMATION IN GALAXIES SINCE z=0.7

We present the star formation rate (SFR) and starburst fraction (SBF) for a sample of field galaxies from the Inamori-Magellan Areal Camera and Spectrograph Cluster Building Survey intermediate-redshift cluster survey. We use [O II] and Spitzer 24 mu m fluxes to measure SFRs, and 24 mu m fluxes and H delta absorption to measure SBFs, for both our sample and a present-epoch field sample from the Sloan Digital Sky Survey and Spitzer Wide-area Infrared Extragalactic survey. We find a precipitous decline in the SFR since z = 1, in agreement with other studies, as well as a corresponding rapid decline in the fraction of galaxies undergoing long-duration moderate-amplitude starbursts. We suggest that the change in both the rate and mode of star formation could result from the strong decrease since z = 1 of gas available for star formation.