Star forming rates between z=0.25 and z=1.2 from the CADIS emission line survey

The emission line survey within the Calar Alto Deep Imaging Survey (CADIS) detects emission line galaxies by a scan with an imaging Fabry-Perot interferometer. It covers 5 fields of > 100 square arcmin each in three wavelengths windows centered on lambda ~ 700, 820, and 920nm, and reaches to a typical limiting line flux of 3 x 10^(-20) W m^(-2). This is the deepest emission line survey covering a field of several 100 square arcmin. Galaxies between z = 0.25 and z = 1.4 are detected by prominent emission lines (from Halpha to [OII]372.7) falling into the FP scans. Additional observations with a dozen medium band filters allow to establish the line identification and thus the redshift of the galaxies to better than sigma(z) =0.001. On the basis of a total of more than 400 emission line galaxies detected in Halpha (92 galaxies), [OIII]500.7 (124 galaxies), or [OII]372.7 (222 galaxies) we measure the instantaneous star formation rate (SFR) in the range 0.24 < z < 1.21. With this purely emission line selected sample we are able to reach much fainter emission line galaxies than previous, continuum-selected samples. Thus completeness corrections are much less important. Our results substantiates the indications from previous studies (based on small galaxy samples) that the SFR decreases by a factor of ~20 between z = 1.2 and today. In fact, for a Omega(m) = 0.3, Omega(Lambda) = 0.7 cosmology, we find an exponential decline rho(SFR) proportional to exp(-lookback_time) / 2.6Gyr). The inferred SF density is in perfect agreement with that deduced from the FIR emission of optically selected galaxies which is explained by a large overlap between both populations. We show that self-consistent extinction corrections of both our emission lines and the UV continua lead to consistent results for the SF density.