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I present a comprehensive view of star formation since z~1 in massive
field galaxies. For ~3000 galaxies in the "All Wavelength Extended Groth
Strip Survey" (AEGIS), we combine UV-to-IR star formation rate tracers,
stellar masses, quantitative HST morphologies and rest-frame photometry.
Galaxies segregate into a fiducial star-forming population, and red and
dead galaxies or LINER candidates. The majority of star-forming galaxies
form a distinct "Main Sequence", with a narrow range of star formation
rates at a given mass and redshift. The range of star formation (1) limits
the amplitude of episodic star formation; (2) constrains the effect of
major mergers; (3) shows that a gradual decrease of star formation in
most galaxies dominated since z~1, not a decrease of strong starbursts;
(4) shows Luminous Infrared galaxies at z~1 to be mostly normal star-forming
galaxies, not strong bursts. This gradual decrease of star formation can
be reproduced by a model of gas exhaustion with timescales increasing to
less massive galaxies, quantifying mass depencencies of star formation
histories. The data and models also indicate a new picture of "staged
galaxy formation", where the onset of major star formation shifts to lower
redshifts for less massive galaxies.
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