The CADIS search for Lyman-α galaxies

The Calar Alto Deep Imaging Survey (CADIS) [5] combines a deep emission line survey employing an imaging Fabry-Perot-Interferometer (F-lim = 3 x 10(-20) Wm(-2)) with a moderately deep multi-band survey (400 less than or equal to lambda less than or equal to 2300nm, R-lim similar or equal to 24). One of its major goals is the search for Ly-alpha galaxies in three redshift windows around z similar or equal to 4.8, 5.7 and 6.6. Six extragalactic fields of 11 x 11square' each are surveyed. About 300 emission line galaxies are detected in every field, greater than or similar to 98% of them being foreground galaxies at z < 1.4. The Ly-(alpha) candidates are selected by means of the absence of flux below the Lyman limit (B-band "dropouts") and the non-detection of secondary emission lines. In this way foreground contamination is kept less than or similar to 50%. Although spectroscopic verification is still pending, the candidate lists alone place upper limit to the abundance of Ly-alpha galaxies. From the comparison with Ly-alpha surveys at z similar or equal to 3.5 we conclude that bright Ly-alpha galaxies become such rare beyond z = 5 that a non-evolving population seems virtually excluded.