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 \squareforqed \arcmin each in three wavelengths windows centered on \lambda \simeq 700 , 820 , and 920 nm , and reaches to a typical limiting line flux of 3 \times 10 ^ { -20 } W m ^ { -2 } .
This is the deepest emission line survey covering a field of several 100 \squareforqed \arcmin .
Galaxies between z = 0.25 and z = 1.4 are detected by prominent emission lines ( from H \alpha to [ O ii ] 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 H \alpha ( 92 galaxies ) , [ O iii ] 500.7 ( 124 galaxies ) , or [ O ii ] 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 .
Although the relative [ O iii ] emission line strength depends on excitation and metallicity and shows strong variation , the mean line ratios yield SFR [ O iii ] values consistent with the SFR evolution .
Our results substantiates the indications from previous studies ( based on small galaxy samples ) that the SFR decreases by a factor of \sim 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 \dot { \rho } _ { SFR } \propto \exp ( - t _ { lookback } / 2.6 Gyr ) .
This decrease of the SFR with time follows an exponential law which is compatible with the decreasing galaxy merger rate as expected from model calculations .
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 .