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P. J. McCarthy (Carnegie Obs.), GDDS Team
We examine the cosmic star formation rate density (SFRD) as a function of stellar mass over the redshift range from 0.5 to 2 using the Gemini Deep Deep Survey. The star formation density in the most massive galaxies was six times higher at z = 2 than it is today. The massive galaxy SFRD declines steeply with time and reached its present level at z ~ 1. The star formation density in intermediate mass galaxies peaks at redshifts near 1.5 and declined to its present-day value at z ~0.5. The characteristic growth time, a guage of the contribution of observed star formation to a galaxy's final stellar mass, provides complimentary evidence that the most massive galaxies transition from a burst phase to a more quiescent mode of star formation at z ~2. Evidence of this burst phase in the intermediate mass population is seen in the high incidence of strong balmer line galaxies in our mass selected sample.
Our star formation rate density study and age-dating of the oldest high-mass galaxies strongly favor downsizing in the star formation rate. The most massive galaxies in our sample formed at high redshifts while the lowest mass galaxies continued to build up their stellar mass through star formation over much of cosmic time.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.