We present the results of a program of monitoring structure changes in the radio core of the quasar 3C 279 (z = 0.538) using VLBI. In all, nine hybrid maps have been made from observations at frequencies of 5, 11, and 22 GHz, during the period 1981–1985. The VLBI structure shows many similarities with other ‘superluminal’ radio sources, e.g. 3C 273 (Unwin et al. 1985), such as alignment with a kiloparsec-scale jet, a one-sided spectral distribution, and superluminal motion. The proper motion measured from our observations is v/c ≈ 2, only one quarter of the previously published rate.

Since 1977 we have been engaged on a project to survey the milliarcsecond structure and internal motions of a complete, unbiased sample of 65 radio sources (Pearson and Readhead 1984). One of the goals of the project was to discover more superluminal sources and find out how common they are. The sample contains three established superluminal sources (3C 179, 3C 345, and BL Lacertae); so far we have discovered three new superluminal quasars (0850+581, 1642+690, and 1928+738), and a fourth (3C 216) that may be superluminal. Thus at least six out of the 65 sources are superluminal, and we expect to find more as our observations proceed.

8 station VLBI maps of the nuclear jets in 3C309.1 and 3C380 reveal complex, bent, structures which seem hard to reconcile with the concept of ballistic outflow. Together with the observation of “flaring” in the MERLIN/EVN map of the 3C309.1 jet the maps point strongly to the jets being confined fluid flows.

We present a status report on a project to study structural changes in a sample of radio cores associated with quasars with extended double lobes. Of six objects observed, so far two (3C 179 and 3C 263) are superluminal and two more (3C 268.4 and 1951+49) are possible superluminal candidates.

An intercontinental VLBI experiment at 327 MHz involving the Ooty Radio Telescope and telescopes at Jodrell Bank, Westerbork, Torun and Crimea was carried out during December 8–12, 1983. The purpose of the experiment was to (i) establish the feasibility of performing MKII VLBI observations from India and (ii) to study the low frequency structure of nearby galaxies, quasars and some other well known radio sources at metre wavelengths. The sources observed were NGC 262, 315, 1052, 1068, 1265, 1275, 4151, 4486, 7674 and 3C 120; PKS 1055+018, 1148−001 and CTA 102; 3C 237 and SS 433. The bright NGC galaxies chosen were selected from an Interplanetary Scintillation survey of 150 nearby galaxies (Bagri and Ananthakrishnan 1983); they were found to have a flux density greater than about 0.2 Jy in subarcsec components at 327 MHz and have high frequency VLBI observations. The quasars chosen are amongst the most compact sources known at metrewavelengths. The other objects were the well known sources which have been studied extensively at higher frequencies.

The variable BL Lac objects OJ 287 and B2 (1308+326) have been observed using the Ooty Synthesis Radio Telescope (OSRT) at 327 MHz. Preliminary analysis of one of them, namely OJ 287 indicates that flux variations of ∼ 20% on a time scale of few hours to few days could be present, but this needs to be confirmed by a larger data base.

Modern radio maps usually allow quasars to be recognized from their radio morphology alone. Most have strong central components, double lobed outer structure and one-sided jets connecting the inner and outer structures. The physics of the sources is poorly understood. The observed bending of the jets, the high minimum pressures observed, and the required energy supply to the lobes are major problems. However, the outstanding problem regarding the extended structure is whether or not this morphology is produced by special relativistic effects or the intrinsic activity level and physics of the radio sources.

The mapping at kpc-scale resolution of the radio sources associated with quasars is fascinating, since it provides us with morphological information on a population of objects during 1010.3 y evolution of the universe, as well as information on a possible epoch dependence of the influence of the ambient medium on the properties of these objects.

Slit spectra have shown optical emission line gas in the vicinity of the radio jet and the north radio lobe of PKS 0812+020. Velocities up to −1000 km/s with respect to the central quasar are seen in the north lobe. The [OII] emission strength becomes comparable to the [OIII] near the north lobe, as would be expected from acceleration by shocks. We suggest this acceleration occurs by interaction with the radio-emitting jet.

We present new VLA observations of this complex low redshift quasar, which was previously modelled as a precessing twin-jet nucleus. A new 2cm map fails to show the predicted curvature near the nucleus. B and C configuration maps have been obtained, to study the halo of the source. These results suggest that the radio source is not very old, and appears to have undergone two major changes of orientation in its < 107 year history.

We have observed 20 classical double radio galaxies and quasars with MERLIN at 151 MHz. We discuss the systematic variation of the bridge structures with radio power and the nature of the identification.

The radio source B2 1320+299 is associated with a 20m QSO. Apart from the core component, it has two outer components on the same side of the QSO; it was therefore classified as of the one-sided (‘D2’) type. The radio structure is unusual in that the three slightly non-collinear components are apparently unconnected and the projected linear size for any plausible redshift is large for a ‘D2’ source (Feretti et al. 1982, Astron. Astrophys.115, 423). The radio structure has now been mapped with the VLA (λ20 & 6 cm, B array and λ20, 6 & 2 cm, A array; Figs.1a, b).

For a complete sample of 42 sources, defined over a narrow flux density range around 0.25 Jy at 408 MHz, properties related to size and nuclear radio emission are discussed and compared with the 3CR sample.

We have investigated a possible relationship between the radio structure of quasars and their absorption line systems with velocities, V, in the range 3000–18000 km s−1 and find a marginal trend for such quasars to have compact radio structures (Swarup et al. 1986).

Relativistic motion has been established with a certain degree of confidence only on VLBI scales, but its application to larger scales has encountered severe difficulties (see e.g. De Young, 1984).

A few years ago we presented evidence for large scale radio structures around most superluminal radio sources (Schilizzi and de Bruyn, 1983). The extended emission is relatively faint and, in at least two cases (3C120 and 30345), exhibits a rather complex morphology. Although the sample was small, the conclusion seemed inescapable that the largest angular sizes (LAS) of the superluminals do not permit a large deprojection factor due to foreshortening, without making these sources exceptionally large intrinsically. That is to say, they would be exceptional within the context of the unified scheme (US) which interprets superluminal sources as favourably oriented, strongly beamed, core components of classical double radio sources. To save the US, we concluded that the ejection axes of these sources must undergo a large (≥ 30°) change of direction in the period between the creation of the outer and inner emission regions. Superluminality would then be a temporary phase (although possibly recurrent) in the lifespan of a large fraction of the parent population of classical doubles.

Redshift distributions of almost complete samples of steep as well as flat-spectrum radio quasars are investigated. It is found that flat-spectrum (core-dominated) quasars contain a higher fraction of high redshifts (z ≳ 1.4) compared to steep-spectrum ones. The difference can be understood in the ‘unified scheme’ in which the two types of quasars differ only in the orientation of their jet axes with respect to the observer.

The ‘superluminal’ motion observed in the cores of radio sources such as 3C273 is now accepted as evidence of relativistic motion within a few parsecs of the centre, but it is less clear whether such speeds persist out to kiloparsec scales. The one-sidedness of such sources is often cited as evidence of relativistic Doppler beaming, but could equally be intrinsic. New MERLIN maps of 3C273 at 151 MHz and 408 MHz have been made with dynamic range of 4.103:1 and 104:1 respectively. These show that (i) there is an extended region or lobe to the south of the main jet; (ii) the radio emission of the jet is continuous from the core to beyond the limit of the optical jet; (iii) no counter-component can be found in the opposite direction to the jet. The ridge-line of the jet shows a ‘wiggle’, the wavelength of which decreases by a factor of 6 along its length. This is interpreted as a deceleration of the bulk flow along the jet.

Here we present two main results that relate properties of quasar IR-to-UV spectra to the fraction of radio flux density in the compact core.

We selected 16 core-dominated sources based on two criteria. (1) They have a core-jet VLBI morphology. (2) Previous observations at lower resolution indicated that there was extended structure on scales of ≥1″. The sources were observed in the A configuration of the VLA at 6 and 2 cm with typical resolutions of ∼0.″45 and ∼0.″15 respectively. Contour plots of total intensity with E vectors superposed (length proportional to fractional polarization) of four sources with jets are shown in Figure 1.