Identification of active galaxies behind the Coma cluster of galaxies

mie describe the results of an efficient survey to identify bright B less t han or similar to 18 active galactic nuclei (AGN) within approximate to 4 d egrees (4.7 h(-1) Mpc projected radius) of the centre of the Coma cluster o f galaxies. The candidates have been carefully selected either as unresolve d UV-excess objects with no detected proper motion, or from identifications on objective-prism plates including a few ROSAT sources. A global success rate larger than 30% is achieved. Low-resolution spectra are presented for the extragalactic objects identified in the course of the survey: the sampl e contains 16 emission-line objects, a BL Lac candidate and an elliptical g alaxy. The AGNs of this list are unique targets to study the association of the Lyman-alpha forest with large-scale structures and galactic haloes at low redshift, to search for warm gas within the Coma cluster and nearby fil aments, and for optical monitoring to detect the microlensing variability p roduced by the baryonic dark matter in the cluster.