One of the most luminous radio jet sources known is 4C 32.69, identified with a z=0.67 QSO. It has previously been mapped at 5 GHz by Potash and Wardle (1980, PW hereafter). Here a 1.4 GHz VLA map of comparable resolution is presented and compared to the earlier map.

How is energy transported out from the central engine in quasars and radio galaxies to the distant radio lobes? This problem has been around since the early discovery of classical double radio sources, and is still not answered in detail. The idea of relativistic beams was first suggested by Martin Rees as a means of transporting plasma out of the nucleus (Rees, 1971, Blandford and Rees, 1974). This idea gained support first from the discovery of hot spots in the radio lobes of these large classical double sources, and later by observations of the beams themselves in radio galaxies. As more jets were observed, it became obvious that they were often curved, serpentine, or even sharply bent. This behavior has been modeled as precession of the central nozzle (Bridle et al., 1976, Ekers et al., 1978), as nuclear refraction (Henriksen et al., 1981), as a growing plasma instability (Hardee, 1981) and as various combinations of the above. At the present time, it seems safest to conclude that there are some examples of each of these processes known.

Bridle (this volume) has summarized the overall characteristics of the jets found in numerous low-luminosity and some high-luminosity radio sources. Previous observations made with the partially completed VLA at wavelengths of 6 and 20 cm indicated that 3C449 was an archetypal radio source obeying all the “rules” summarized by Bridle. New observations with the VLA of the polarization structure at 6 and 20 cm have destroyed this simple picture and identify 3C449 as a “rogue” jet source.

NGC 6251, a 14th mag elliptical galaxy, was shown by Waggett et al. (1977) to have large-scale radio emission features with a total angular extent of ∼ 1.1°, which corresponds to a projected linear size of about 1.7 Mpc (HO = 75 km s−1 Mpc−1). A bright radio jet links a central core source embedded in NGC 6251 to the extended emission on the northwest side of the galaxy.

The remarkable continuum arms in the spiral galaxy NGC 4258 are suggestive of some form of ejection from the nucleus of this galaxy (Van der Kruit, Oort and Mathewson, 1972). To summarize the observations (see Oort, Figure 2, this volume), the “anomalous spiral arms” are clearly distinct from the normal spiral arms, although wound in the same sense; there is a sharp gradient of the continuum emission on the leading edge of the arms, and an indication that the arms split on the western side; the arms go directly into the nucleus and coincide with Hα emitting filaments (Courtes, Viton and Veron, 1965).

The new Jodrell Bank Multi-Telescope-Radio-Link Interferometer system (MTRLI) began operating in January 1980 with four telescopes and with its full complement of six telescopes in December 19 80. The location of the telescopes and the baseline lengths (in km) thus obtained are shown in Fig. 1. However, before describing some of the exciting new results it has yielded on high luminosity radio sources it is important to outline the capabilities of the instrument since the maps are produced in a rather different way to those from conventional synthesis instruments.

High resolution (1′→0′.1) maps of the outer complexes of some “well formed” powerful radio sources suggest that we can now distinguish two physically distinct types of outer hotspots. We denote them as type “A” and “B” and describe them as follows: Type A hotspots, illustrated in Figure 1, occur at the outer leading edge, and have a cusp-like, or otherwise elongated shape. This strongly suggests that their shape and energy density are determined by the ram-pressure interaction between the end of a beam or momentum flux “pipeline”, and the ambient i.g.m. Magnetic fields appear well-ordered along the cusp (Laing, 1981). The surface brightness of well-resolved Type A hotspots leads to a velocity of advance (Va) which is typically 103→104 (ρ−1ig-27)km/s (ignoring the ion energy).

Compact hot-spots in luminous extragalactic radio sources are often double on the scale of a few kpc (Laing 1981a). Examples are shown in Figures 1–3; the maps were made with the A and B configurations of the VLA. The general features are as follows:

1. (a) It is usually possible to recognize a compact, “active” subcomponent within a radio lobe. This has a size of <1 kpc and may only contain a small fraction of the total flux of the hot-spot. It need not be at the leading edge.

2. (b) More diffuse regions are often grossly offset from the source axis (e.g. 3C 196). In some cases, there is apparent inversion symmetry about the optical identification.

3. (c) The characteristic morphology of a diffuse subcomponent is best illustrated by the eastern hot-spot of 3C 20, which is limb-brightened, with a circumferential magnetic field. The bright edge is on the side furthest away from the compact subcomponent.

4. (d) The polarization structure in the diffuse subcomponents, like that in most extended radio lobes, can be explained if the magnetic field has been sheared so as to be tangential to the surface, but is otherwise random (Laing 1980; 1981b).

5. (e) The most obvious explanation for the multiple structure is that the compact subcomponents represent the points of impact on the surrounding gas of twin beams from the associated galactic nucleus; if these alter their direction, then diffuse remnants may be formed. This idea would be consistent with the inversion symmetry seen, for example, in 3C 196.

6. (f) A problem with this model is posed by the detailed morphology of the diffuse subcomponents: why should the bright limb be opposite the compact subcomponent, rather than at the leading edge of the source? An alternative picture, in which the diffuse subcomponents are formed by material escaping from the active regions, should also be considered.

I want to make two points:

1. 1. Observations suggest that the hot-spots move about either because the beam precesses (e.g. Ekers et al. 1978; Lonsdale & Morrison 1980) or more discontinuously, as in sources like 3C351 that have multiple hot-spots (Laing 1981). The natural interpretation is that the hot-spot at the end of the beam slides over the inner surface of a ‘cavity’ filled with very hot dilute ex-hot-spot material (Scheuer 1974), extending the cavity at various places at different times. Such a ‘dentist's drill’ model has various consequences:

   1. (i) The mean speed (length/age) at which the cavity elongates may be considerably smaller than the instantaneous speed V of the hot-spot, estimated in the customary way from pressure balance:

   2. (ii) Remark (i) raises the possibility that giant radio sources have become so long because their jets are unusually constant in direction. NGC6251, which is over 2 Mpc long, has a jet whose direction has not wavered by more than a few degrees in ∼ 107 years (Saunders et al. 1981).

   3. (iii) We should not be surprised by sources whose hot-spots lie some way behind the extreme ends of the source; this may merely mean that the beam at present impinges on one side of the ‘cavity’. 3C285 is a typical example; a more persuasive case is the Np component of 3C219 (Perley et al. 1980).

2. 2. Most of the radio emission of most really powerful radio sources comes from their hot spots. Contrariwise, straightforward equipartition calculations on models lead to at least as much emission from the ‘cavity’ as from the hot-spots (Scheuer 1974). While there are several possible explanations, one in particular is suggested by Laing's (1981) extensive data on 40 sources. He lists the synchrotron lifetimes in the hot-spots for electrons radiating at 15 GHz, and while these exceed the light crossing times, they do so by only one or two orders of magnitude. One expects flow through the hot spots at some fairly small fraction of the speed of light; the synchrotron loss cutoff in the hot-spot is then expected to appear in the mm or infra-red region. Expansion of the hot-spot material into the cavity shifts the loss cutoff to a much lower frequency. If the expansion is adiabatic (certainly an oversimplification) the ratio of loss cutoff frequencies is equal to the ratio of energy densities. We cannot use this relationship directly in the more interesting cases, as we cannot estimate the energy density (or even the size) of a ‘cavity’ that we cannot observe. However, we can estimate the cutoff frequency within the hot-spots (for some assumed streaming speed), and Figure 1 shows that the most powerful hot-spots have loss cutoff frequencies in the 10–100 GHz range, implying cutoff frequencies in the ‘cavity’ that could well be below 1 GHz.

Most radio sources are two-sided, like Cygnus A. A minority, however, are one-sided, and the first-known and brightest example is 3C273 (see Fig. 1), a high-luminosity QSO, showing ‘super-luminal’ proper motions in the core. The explanation of such one-sided sources may follow one of two lines (and it seems that both schools of thought are represented at the present meeting): on the one hand, the ejection of material from the central object may truly be one-sided, while on the other hand the ejection may be two-sided but at a relativistic speed, so that the receding half is hidden by Doppler beaming.

The predictions of a scheme which attributes the observed differences between flat and steep spectrum quasars to projection and the effects of relativistic beaming are explored. We conclude that the statistical properties of quasars are entirely consistent with such a scheme provided the mean Lorentz factor in the central components of quasars is ∼5.

The two-kpc steep-spectrum radio core in the giant radio galaxy 3C 236 has been mapped with 0′.1 resolution using the VLA. The core morphology is substantially different from other radio cores and suggests that the flow of energy from the galactic nucleus may be continuous on one side and “blobby” on the other side.

As part of the VLA calibration program, 404 small angular size sources have been observed in the “A” array at both 6 and 20 cm with resulting resolutions of 0.4′ and 1.2′ respectively. Use of self-calibration techniques has allowed a search for associated extended structure to a level of ∼0.3% of the peak. Here we report preliminary analysis of the results.

The hotspot in the eastern lobe of the nearby giant radio galaxy DA240 (z=0.0356) provides a rare opportunity to examine the detailed polarization structure of a hotspot. Maps have been made with the Cambridge 5-km telescope at 2.7 and 5.0 GHz. The 5.0-GHz maps are shown in Figs 1 and 2. The main characteristics are: (a) The hotspot has an overall size in the 2.7-GHz map of 10×18 kpc2. It blends smoothly at its outer edge into the background of the extended lobe. The 5.0 GHz total intensity map shows a yet more compact region (subcomponent A). It has not been fully resolved in the direction of the minor axis and has a size <1×2.5 kpc2. There is a second much weaker and diffuse region (subcomponent B). Both subcomponents are superimposed on a broad plateau of emission. The hotspot has spectral index α(0.61–5.0)=0.52, minimum total energy Emin=3×1056 ergs and equipartition magnetic field Beq=2×10−5 G, values typical of other hotspots, although its projected distance from the nucleus is very large (0.65 Mpc);

Observations of sample of Markarian Seyferts with the VLA indicate that a large fraction possess linear radio structure on a scale of a few hundred parsecs to a few kiloparsecs. The radio components generally straddle the optical nucleus and several sources are simple doubles. Similar structures are seen in the classical Seyferts NGC 1068, 4151, and 5548. NGC 4151 is probably best interpreted as a jet. A few sources (e.g. Mark 315, NGC 7469) exhibit diffuse, non-aligned radio structure on a scale similar to that of the linear sources. The radio axis in linear sources is misaligned with respect to the rotation axis of the galaxy disc by a large angle. The linear sources are discussed in terms of a model of a supersonic beam or jet which is “disrupted” by interaction with interstellar gas in the inner part of the galaxy (often a spiral). Two aspects of this interaction are emphasised. Firstly, the curved shape of the radio sources in NGC 1068 and NGC 4151 is ascribed to beam bending by the ram pressure of the rotating interstellar medium. Simple models of this process are shown to be consistent with the observations. Secondly, it is suggested that the broadened forbidden lines in Seyferts originate in part from interstellar gas accelerated outwards by the beam. This picture accounts for some of the empirical correlations found between radio and optical forbidden line properties.

A survey has been carried out at Jodrell Bank of the continuum radio emission from nearby galaxies. The objects include normal galaxies, Seyfert galaxies and others with nuclei active at optical and radio wavelengths.

Weak radio emission from the type 1.5 Seyfert galaxy NGC 5548 has been mapped with high resolution at the VLA at both 1465 and 4885 MHz. The galaxy contains the largest (5.9 kpc) triple radio source known in a Seyfert galaxy. The central component of that triple is unresolved (<0.39×0.15 kpc) and has a flatter spectrum than the well-resolved outer lobes. In addition, the field surrounding NGC 5548 and two of the sources in that field have been mapped at 1465 MHz; the field sources are unlikely to be physically associated with NGC 5548.

The two radio galaxies 0326+39 and 1321+31 are both part of a complete sample of low luminosity radio galaxies which was obtained by identifying B2 radio sources with galaxies from the Zwicky Catalogue. Both sources have a very symmetrical double jet, like many other sources of the sample (Ekers et al. 1981a).

Markarian 8, a clumpy irregular galaxy (Casini et al. 1979), was observed with the VLA at 20 cm (Mar. 19, 1981; 26 ant.) and 6 cm wavelengths (June 12, 1980; 18 ant.) The structure is alike at the two wavelengths, consisting of 3 distinct clumps imbedded in a diffuse envelope of about 40 arcsec extent. Figure 1 shows the 6 cm structure. At higher resolution the clumps break up into several components. The 20 cm structure is shown in Figure 2, which also compares the optical and radio morphologies. There is excellent general agreement, suggesting a common origin of emission in the clumps.

We commonly refer to the central “object” in extra-galactic radio sources as the “engine” that is the root cause of many radio source characteristics. We frequently ask, COULD “engines” at the cores of extra-galactic sources: (1) be compact objects with accretion disks; (2) eject well-collimated supersonic jets; (3) show relativistic effects in ejected material; (4) produce twin-jets; (5) produce one-sided jets; and (6) initiate highly polarized synchrotron radiation sources? SS433 is a binary star system with radio and optical jets that is relevant because it is a “little engine that could”, and does, do all of these things. Further, we can observe changes in SS433 on time scales from hours to several months, and these data allow one to study evolution of jets in a more thorough fashion than is possible for extra-galactic sources.