view Abstract Citations (68) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Properties of X-Ray-selected Active Galactic Nuclei. III. The Radio-quiet versus Radio-loud Samples della Ceca, Roberto ; Lamorani, Giovanni ; Maccacaro, Tommaso ; Wolter, Anna ; Griffiths, Richard ; Stocke, John T. ; Setti, Giancarlo Abstract Using a sample of 406 active galactic nuclei (AGNs), extracted from the Einstein Observatory Extended Medium Sensitivity Survey (EMSS), for which complete radio information exists, we present and discuss some properties of the radio-loud and radio-quiet objects, and compare them with those of radio-observed, optically selected AGNs. The radio to optical spectral index of the EMSS AGN sample shows a bimodal distribution with a minimum at α_ro_~0.35. A bimodal distribution is observed also in samples of optically selected AGNs, making this characteristic a general property of the total AGN population. This feature allows us to split, almost unambiguously, the EMSS AGN sample into radio-loud (RL: α_ro_ > 0.35: 43 objects) and radio-quiet (RQ: α_ro_ < 0.35:363 objects) objects. An abrupt change in the radio properties of the X-ray selected AGN population is observed at M_B_ ~ -24: in the optically bright subsample (30 +/- 4)% of the objects are RL, while in the optically faint subsample (3 +/- 1)% of the objects are RL. This difference is statistically confirmed at a high confidence level by the comparison of the α_ro\_ distributions of the two subsamples. These results have been compared with those obtained from a compilation of optically selected AGNs. The G(> α_ro_) distributions for optically and X-ray selected optically faint (M_B_ > - 24) AGN are not statistically different. On the contrary, the same distributions for optically bright AGNs are statistically different at a high confidence level. As expected from previous results, the fraction of RL AGNs among optically bright X-ray selected AGNs is ~2.5 times larger than among the optically selected ones. We have determined, for the first time, the X-ray luminosity functions (XLF) at different redshifts, the cosmological evolution and the devolved XLF of radio-quiet and radio-loud objects separately. There is no evidence that the evolutionary properties of radio-loud objects differ significantly from those of radio-quiet ones: the best-fit evolution parameter of the RL AGNs is higher than, but consistent within errors with, that of the RQ AGNs. On the contrary, the shape of the devolved XLF of the two classes appears to be different and a flattening of the XLF of the RL subsample is visible for L_x_(z = 0) <~ 3 x 10^44^ ergs s^-1^. Similar results were obtained, in the optical domain, from an analysis of the radio properties of the PG sample, the only sizeable complete sample of optically selected AGNs with full radio information. This measured difference adds to the already significant number of reasons for postulating the two distinct classes of AGNs: RL and RQ. Using the devolved XLF and the best-fit evolution parameters for the two classes of AGN, we have computed the expected fraction of RL objects as a function of the X-ray flux: this fraction ranges from ~9% for f_x_ ~5 x 10^12^ ergs cm^-2^ s^-1^, to ~13% for f_x_~2 x 10^-13^ ergs cm^-2^ s^-1^, and then decreases to ~2.5% for f_x_~ 2 x 10^-15^ ergs cm^-2^ s^- 1^. Recent deep radio observations of a deep ROSAT field seem to be in agreement with our calculations. Publication: The Astrophysical Journal Pub Date: August 1994 DOI: 10.1086/174428 Bibcode: 1994ApJ...430..533D Keywords: Active Galactic Nuclei; Cosmic X Rays; Galactic Evolution; Galactic Radio Waves; Radio Emission; Astronomical Models; Continuums; Cosmology; Luminosity; Red Shift; Astrophysics; GALAXIES: ACTIVE; GALAXIES: EVOLUTION; GALAXIES: LUMINOSITY FUNCTION; MASS FUNCTION; GALAXIES: NUCLEI; RADIO CONTINUUM: GALAXIES; X-RAYS: GALAXIES full text sources ADS | data products SIMBAD (11) Related Materials (3) Part 1: 1991ApJ...374..117M Part 2: 1992ApJ...389..491D Part 4: 1996ApJ...465..650D