THE CAMBRIDGE-CAMBRIDGE ROSAT SERENDIPITY SURVEY .3. VLA OBSERVATIONSAND THE EVOLUTION OF RADIO-QUIET AND RADIO-LOUD OBJECTS

We present the results of the VLA radio observations at 1.475 GHz (20 cm) of the active galactic nuclei (AGN) in the Cambridge-Cambridge ROS AT Serendipity Survey (CRSS), a sample of 123 faint X-ray sources with f(x)(0.5-2.0 keV) greater than or equal to 2 x 10(-14) erg s(-1) cm(- 2). Of the 80 AGN in the sample, seven show radio emission at the 5 si gma level and only two (2.5(-1.7)(+4.0) per cent) qualify as radio-lou d (RL) objects (alpha(10) greater than or equal to 20.35). This result , compared with 13 per cent RL in the Einstein Observatory Extended Me dium Sensitivity Survey (EMSS) sample of AGN [flux limit f(x)(0.3-3.5 keV) similar to 2 x 10(-13) erg s(-1) cm(-2)], confirms that the fract ion of X-ray-selected RLAGN drops rapidly as the X-ray flux limit is l owered. Combining the CRSS AGN sample with that extracted from the EMS S we study the X-ray luminosity function (XLF) and evolutionary proper ties for radio-quiet (RQ) and RLAGN separately. We find that the RQ an d RLAGN populations show the same cosmological evolution within the er rors. In fact, when the luminosity evolution is parametrized with a po wer law of the form L(x)(z) = L(x)*(0)(1+z)(k), we find k = 2.43 +/- 0.26 and 2.71 +/- 0.10 for RL and RQAGN populations respectively. In a ddition, the shapes of the de-evolved XLFs of the two classes appear t o be different at both the low-luminosity (L(x) < 10(44) erg s(-1)) an d high-luminosity ends, These results are robust for different cosmolo gical models (using q(0) = 0.0 and 0.5) and for different values of th e threshold alpha(10) used to distinguish between RQ and RL objects. F inally, we find that the differences in the shapes of the XLFs of RQ a nd RL AGN can be explained by introducing an X-ray beaming model to se parate the observed X-ray luminosity of radio quasars into relativisti cally beamed and isotropic contributions.