Kai+Noeske

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.