Nuclei Of Radio Galaxies Research Articles

The Milliarcsecond Structure of Radio Galaxies and Quasars

Hybrid maps of the nuclei of radio galaxies and quasars show a variety of morphologies. Among compact sources, two structures are common: an asymmetric, “core-jet” morphology (eg, 3C 273), and an “equal double” morphology with two separated, similar components (eg, CTD 93). The nuclei of extended, double radio galaxies generally have a core-jet morphology with the jet directed toward one of the outer components.

VLBI Mapping of the Nuclei of Radio Galaxies and Quasars

It is now possible, by means of VLBI hybrid mapping, to make maps of radio sources with a resolution of ~ 1 milliarcsecond. This enables us for the first time to compare the morphologies of the small- and large-scale structures of extragalactic radio sources, and they are strikingly different.

OPTICAL SPECTRA OF THE NUCLEI OF RADIO GALAXIES WITH RADIO JETS.

ABSTRACT Emission-line optical spectra have been measured for several radio galaxies with radio jets, including the giant radio galaxies 3C 236 and NGC 6251. The emission lines in all these objects are relatively weak and correspond to a lower average degree of ionization than in typical narrow-line radio galaxies.

The Large Scale Structure of Extra-Galactic Radio Sources (>1 Arcsecond)

Current data on the structures of extended extragalactic radio sources are reviewed. The major technique used to study such sources is aperture synthesis. Thus the review begins with a brief description of the techniques used in aperture synthesis and the advantages and disadvantages of the method.Section 2 contains a discussion of the source properties which can be derived from multi-wavelength aperture synthesis observations of an individual radio source. The following Sections 3 and 4 describe the general morphological characteristics of extended extragalactic radio sources. Some recent observations from the Westerbork radio telescope are used to illustrate these properties. Finally, Section 5 attempts to relate both morphological characteristics and integrated source parameters directly to activity within the nuclei of radio galaxies and quasars.

The Continuous Optical Spectra of Active Nuclei

The optical continuum properties of the nuclei of radio galaxies, Seyfert galaxies, N systems, BL Lac Objects, and QSOs are reviewed. The observations are in the main consistent with the hypothesis of contributions in varying degrees for a stellar component and a small non-thermal source. The presence of dust strongly influences the continuum spectrum and polarization in the case of Seyferts. The observations have not as yet led to an understanding of the nature of the non-thermal continuum source but offer prospects of so doing.

Observational model of the ionized gas in Seyfert and radio-galaxy nuclei

Equivalent widths of the total emission-line Hbeta in Seyfert 1, Seyfert 2, and intermediate-type Seyfert galaxies, expressed in terms of the featureless continuum, all have approximately the same frequency distribution. This suggests that the energy-input mechanism to both the narrow-line, low-density gas and the broad-line, high-density gas is photoionization by the featureless continuum. The reason for the weakness of the narrow emission lines in extreme Seyfert 1 galaxies is then the absorption of most of the ionizing photons in the dense gas near the central source. The statistics of line widths can be fitted by a model in which the dense gas has typical rotational velocity 5000 km/sec and typical turbulent velocity 2000 km/sec. A model is proposed in which the dense gas forms a rotating, turbulent disk with dimension approximately 0.1 pc and height/diameter approximately 2/5. Seyfert 2 galaxies are objects with little dense gas, and intermediate-type Seyfert galaxies are objects in which the dense gas is optically thin to ionizing radiation at least along the poles. Most radio galaxies have strong narrow emission lines, suggesting that escape of radio plasma can only occur where some ionizing photons can also escape from the dense gas. Other predictions, implications, and tests of this model are discussed.

Observations of the Structure of Radio Sources in the 3C Catalogue--IV. Correlation Diagrams and the Evolution of Radio Sources

The radio structures of a complete sample of 200 radio sources from the Revised 3C catalogue are now available with a resolution of |${23}^{\prime{}\prime}\,\times\,{23}^{\prime{}\prime}\,\text{cosec}\,\delta$| from recent observations at 1407 MHz with the One-Mile telescope at Cambridge. These results are taken together with other data from long baseline interferometry and studies of interplanetary scintillation to derive correlation diagrams of radio luminosity against surface brightness and of radio luminosity against total linear size at 178 MHz and 1407 MHz. Particular attention is given to the proper selection of sources at different frequencies and the selection effects which can influence the correlation diagrams. It is shown that these correlation diagrams are well determined from the present data. Since the diagrams represent a complete sample of sources it is possible to make quantitative comparison between theories of the evolution of radio sources and the observations. A general procedure has been developed for testing theories in which the components of radio sources are ejected from the nuclei of radio galaxies and QSO's. In this analysis it is essential to incorporate the effects of cosmological evolution, which can considerably change the appearance of the predicted diagrams. It is shown that it is possible to account for a large part of the dispersion in the correlation diagrams as being due to the fact that sources are observed at different stages in their evolution.