Star formation in field galaxies since z=1: a quiescent,
mass-dependent history from the deepest surveys


I review results from the recent deep multi-wavelength surveys, which
have revealed a relatively complete picture of star formation (SF) in
field galaxies out to z=1. In that redshift range, star-forming
galaxies show a defined relation between SF rate (SFR) and stellar
mass ("main sequence"). The discovery that SF follows strong
systematics with mass and z opens new prospects to understand
galaxy-wide star formation prior to quenching processes.

The width and zeropoint evolution of the main sequence imply that SF
evolved predominantly through a gradual decline of SFR. The increase
of SFR with z mostly witnesses earlier stages of that gradual decline.
Other than previously assumed, brief SF episodes ("starbursts") play a
secondary role that hardly evolves.

We find that the observed mass-dependence of SF histories
("downsizing") includes at least two components, longer decline
timescales, and a systematically later onset of major star formation,
in less massive galaxies. I present a model that parametrizes this
behaviour, can be used to measure the mass dependence of SF
timescales, and serve as a reference SF history for observational
work, and to test and calibrate theoretical concepts. The main
sequence also provides a baseline against which the effects of
e.g. galaxy collisions and envoronmental density on SF can be
measured. I present new studies that exploit these possibilities.