Unification scheme of radio galaxies and quasars falsified by their observed size distributions

Abstract

In the currently popular orientation-based unified scheme, a radio galaxy appears as a quasar when its principal radio-axis happens to be oriented within a certain cone opening angle around the observer's line of sight. Due to geometrical projection, the observed sizes of quasars should therefore appear smaller than those of radio galaxies. We show that this simple, unambiguous prediction of the unified scheme is not borne out by the actually observed angular sizes of radio galaxies and quasars. Except in the original 3CR sample, based on which the unified scheme was proposed, in other much larger samples no statistically significant difference is apparent in the size distributions of radio galaxies and quasars. The population of low-excitation radio galaxies with apparently no hidden quasars inside, which might explain the observed excess number of radio galaxies at low redshifts, cannot still account for the absence of any foreshortening of the sizes of quasars at large redshifts. On the other hand from infrared and X-ray studies there is evidence of hidden quasar within a dusty torus in many RGs, at $z>0.5$. It seems difficult how to reconcile this with the absence of foreshortening of quasar sizes at even these redshifts, and perhaps one has to allow that the major radio axis may not have anything to do with the optical axis of the torus. Otherwise to resolve the dichotomy of radio galaxies and quasars, a scheme quite different from the present might be required.

arXiv comment32 pages; 7 figures, 2 tables

References in corpus (10)

• First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Determination of Cosmological Parameters
• Unified Schemes for Radio-Loud Active Galactic Nuclei
• The active nuclei of z<1.0 3CRR radio sources
• Spitzer Reveals Hidden Quasar Nuclei in Some Powerful FR II Radio Galaxies
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• Far Infrared Observations of Radio Quasars and FR II Radio Galaxies
• Dust emission from 3C radio galaxies and quasars: New ISO observations favour the unified scheme
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• Mid-infrared spectroscopy of high-redshift 3CRR sources
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Cited by in corpus (10)

• The Tiered Radio Extragalactic Continuum Simulation (T-RECS)
• Modelling the luminosities and sizes of radio galaxies: radio luminosity function at z = 6
• A Uniformly Selected, All-Sky, Optical AGN Catalog
• An optical spectroscopic survey of the 3CR sample of radio galaxies with z<0.3. V. Implications for the unified model for FRIIs
• The orientation dependence of quasar spectral energy distributions
• Does Size Matter? The Underlying Intrinsic Size Distribution of Radio Sources and Implications for Unification by Orientation
• Discordance of the unified scheme with observed properties of quasars and high-excitation galaxies in the 3CRR sample
• Incongruity of the unified scheme with a 3CRR-like equatorial strong-source sample
• Dependence of Fanaroff--Riley break of radio galaxies on luminosity and redshift
• Unified models revisited I: modelling the effect of source geometry on radio galaxy/quasar unification