Mathematics – Logic
Scientific paper
Aug 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...430..533d&link_type=abstract
The Astrophysical Journal, vol. 430, no. 2, pt. 1, p. 533-544
Mathematics
Logic
55
Active Galactic Nuclei, Cosmic X Rays, Galactic Evolution, Galactic Radio Waves, Radio Emission, Astronomical Models, Continuums, Cosmology, Luminosity, Red Shift
Scientific paper
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 alpharo approximately 0.35. A bimodal distribution is observed also in samples of optically selected AGNs, making this characteristics a general property of the total AGN population. This feature allows us to split, almost unambiguously, the EMSS AGN sample into radio-loud (RL: alpharo greater than 0.35: 43 objects) and radio-quiet (RQ: alpharo less than 0.35: 363 objects) objects. An abrupt change in the radio properties of the X-ray selected AGN population is observed at MB approximately -24: in the optically bright subsample (30 + or - 4)% of the objects are RL, while in the optically faint subsample (3 + or - 1)% of the obejcts are RL. This difference is statistically confirmed at a high confidence level by the comparison of the alpharo distributions of the two subsamples. These results have been compared with those obtained from a compilation of optically selected AGNs. The G(greater than alpharo) distributions for optically and X-ray selcted optically faint (MB greater than -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 approximately 2.5 times larger than among the optically selected ones. We have determined, for the first time, the X-ray luminosity funcitons (XLF) at different redshifts, the cosmological evolution and the de-evolved 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 de-evolved XLF of the two classes appears to be different and a flattening of the XLF of the RL subsample is visible for Lx (Z =zero) less than or approximately 3 x 1044 ergs/s. 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 de-evolved 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 approximately 9% for fx approximately 5 x 10-12 ergs/sq cm/s to approximately 13% for fx approximately 2 x 10-13 /sq cm/s, and then decreases to approximately 2.5% for fx approximately 2 x 10-15 ergs/sq cm/s. Recent deep radio observations of a deep ROSAT field seem to be in agreement with our calculations.
della Ceca Roberto
Griffiths Richard
Lamorani Giovanni
Maccacaro Tommaso
Setti Giancarlo
No associations
LandOfFree
The properties of X-ray selected active galactic nuclei. 3: The radio-quiet versus radio-loud samples does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The properties of X-ray selected active galactic nuclei. 3: The radio-quiet versus radio-loud samples, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The properties of X-ray selected active galactic nuclei. 3: The radio-quiet versus radio-loud samples will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1494156