THE ROSAT AGN CONTENT OF THE 87GB 5-GHZ SURVEY - BULK PROPERTIES OF PREVIOUSLY OPTICALLY IDENTIFIED SOURCES

The cross - correlation of the source list from the ROSAT All - Sky Su rvey with the 5 GHz Green Bank survey yields a list of 2127 objects. A bout two thirds of them are optically unidentified. The majority of th e objects with known optical counterparts are quasars and radio galaxi es, most of them detected in X-rays for the first time. In this paper we present a list of the previously optically identified objects with their main characteristics and discuss their general (bulk) properties . We find strong correlations between luminosities in the radio, optic al, and X-ray bands which differ for quasars and radio galaxies. The f raction of flat radio spectrum sources increases with redshift and app roximately 95% of all sources above z = 2 are of that type. In the rel atively large group of blazars, radio selected BL Lacs and highly pola rized quasars show very similar properties while X-ray selected BL Lac s have markedly different X-ray to radio flux ratios. The sample is la rge enough and of sufficiently high quality to reveal clearly various detection biases and selection effects which strongly influence the ph ysical interpretation of the correlations. Radio follow - up observati ons for the determination of the morphological and spectral properties as well as environmental conditions are needed for a statistically re liable study of the sample. The very large group of sources with low r adio fluxes remains to be optically identified.