Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995mnras.277.1463c&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 277, Issue 4, pp. 1463-1476.
Astronomy and Astrophysics
Astronomy
21
Surveys, Galaxies: Active, Galaxies: Nuclei, Quasars: General, Radio Continuum: Galaxies, X-Rays: Galaxies
Scientific paper
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 ROSAT Serendipity Survey (CRSS), a sample of 123 faint X-ray sources with f_x(0.5-2.0 keV)>=2x10^-^14 erg s^-^1 cm^-^2. Of the 80 AGN in the sample, seven show radio emission at the 5sigma level and only two (2.5^+^4.0_-_1.7 per cent) qualify as radio-loud (RL) objects (alpha_ro>=0.35). This result, compared with 13 per cent RL in the Einstein Observatory Extended Medium Sensitivity Survey (EMSS) sample of AGN [flux limit f_x(0.3-3.5 keV)~2x10^-^13 erg s^-^1 cm^-^2], confirms that the fraction of X-ray-selected RL AGN drops rapidly as the X-ray flux limit is lowered. Combining the CRSS AGN sample with that extracted from the EMSS we study the X-ray luminosity function (XLF) and evolutionary properties for radio-quiet (RQ) and RL AGN separately. We find that the RQ and RL AGN populations show the same cosmological evolution within the errors. In fact, when the luminosity evolution is parametrized with a power 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 RQ AGN populations respectively. In addition, the shapes of the de-evolved XLFs of the two classes appear to be different at both the low-luminosity (L_x<10^44 erg s^-^1) and high-luminosity ends. These results are robust for different cosmological models (using q_0=0.0 and 0.5) and for different values of the threshold a_ro used to distinguish between RQ and RL objects. Finally, we find that the differences in the shapes of the XLFs of RQ and RL AGN can be explained by introducing an X-ray beaming model to separate the observed X-ray luminosity of radio quasars into relativistically beamed and isotropic contributions.
Boyle Brian J.
Ciliegi Paolo
Elvis Martin
Maccacaro Tomasso
McMahon Richard G.
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