5 Conclusion

We have reported the spectra and the main properties of 90 EL objects, 80 of which are newly discovered. Seventy-one objects belong to a well defined sample of Radio-Emitting X-ray sources, the REX catalog (Caccianiga et al. 1999). The majority of the objects presented here show broad (FWHM>1000 km s^-1) emission lines in the optical spectrum while only 9% are type 2 sources, i.e. Narrow Emission line objects. Except for three sources, all the objects presented in this paper are AGNs (QSOs, Seyfert galaxies, emission line radiogalaxies). The sample contains two high redshift (z=3.47 and 3.49) radio-loud AGNs.

We have then studied the general properties of the 226 AGNs discovered so far in the REX sample, including sources identified from literature. We have analyzed their radio properties (compactness and slope) as deduced from the NVSS data. On average, we select a similar number of SS and FS radio sources despite the fact that the selection has been done by using a relatively low frequency (1.4 GHz) radio catalog. At this frequency, we would have expected a dominance of SS AGNs. The large number of FS AGNs found in this sample is probably due to the presence of the X-ray constraint that favors the selection of compact FS sources. On the other side, the presence of a radio limit favors the selection of RL AGNs. In fact, the majority of these sources ($\sim$88%) is radio loud while only a small percentage ($\sim$10%, Della Ceca et al. 1994) of such objects is expected in a purely X-ray selected survey.

Acknowledgements

We are grateful to the staff at the UH (Hawaii, U.S.A.), ESO (La Silla, Chile) and UNAM (San Pedro Martir, Mexico) telescopes for their support during the observing runs. This research was partially supported by the Italian Space Agency (ASI), by the European Commission, TMR Programme, Research Network Contract ERBFMR XCT96-0034 "CERES", by the FCT under grant PRO15132/1999 and by the Italian Ministry for University and Research (MURST) under grant Cofin98-02-32. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.