As an ideally symmetrical regime we assume that central engine ejects the same volumes of radio emitting matter – hereafter called ‘plasmons’ – into two opposite directions. The plasmons have the identical velocities and evolution and are small. We assume that each plasmon on one side has its corresponding twin on the opposite side of the structure. Since in fact observations do not reveal any symmetrical structures we must include into our model some mechanism to reproduce an asymmetry. It is our assumption that such asymmetry is due to the fact that the observer sees the plasmons at their different evolutionary ages and that their velocity vectors have different directions. We are looking for the functions which describe differences between the twins. These functions give us differences in brightness and expected positions of the twins and may be used for interchanging their elements. This exchange leads to obtaining new structure. If this new structure is identical to the original one, then the functions correctly describe the differences between the two sides of the structure (Paper 1).

We assume that two continuous, supersonic jets of plasma advance into a uniform surrounding medium of constant density and pressure. In terms of fluid dynamics their propagation is described by the kinetic model suitable for high Mach number flows, which likely occur in edge-brightened powerful radio sources. In this approximation the jet flowing energy is dominated by the bulk energy of thermal material. The end of the jet enters the undisturbed ambient medium and forms a front shock, where the supplied bulk energy is in situ transferred to relativistic particles and magnetic field.

In studying the dynamical evolution of radio galaxies, I find that the dynamical ages of the sources are older than the ages inferred from spectral breaks, typically by a factor ≃ 10. This suggests to me that the spectral ages are misleading.

The structure of the quasar 3C 345 is studied at λ = 49cm. The core has a low-frequency cut off spectrum and α ≃ 3. The brightest knot is in the nearest part of the jet. The cocoon wall absorbs low-frequency emission and changes the polarization orientation, RM = 3500 rad m–2, B|| ≃ 100 μG at the core region.

Here are reported new successful results of analysis for jet in the strong radial magnetic field of an active galactic nuclei, suggested in.

We have developed a new set of techniques for extracting information from maps of synchrotron emission. Some of these methods are used to determine the shape of the spectrum and then to isolate the contributions of the number and energy of relativistic electrons and the local magnetic field strength to the total intensity images. These are discussed in Katz-Stone, Rudnick & Anderson (1993), Katz-Stone & Rudnick (1994), and Rudnick, Katz-Stone & Anderson, (1994). Here, we describe a method - called spectral tomography - to remove confusion from various features along the line of sight. We find that both structural and spectral confusion are commonplace, and therefore our dynamical and radiative models of extragalactic sources need significant revision.

The WEsterbork Northern Sky Survey (WENSS) is a large–sky survey being carried out at 92 and 49 cm with the Westerbork Synthesis Radio Telescope (WSRT). At 92 cm WENSS will cover the sky north of declination +30° (an area of 10,000 square degrees) to a limiting (5σ) flux density of about 15-20 mJy. Both linear and circular polarization data is obtained. The polarization images have a noise level of about 2 mJy (lσ). The spatial resolution at 92 cm is about 1′. At 49 cm about one fifth of this area will be covered to somewhat lower flux density and with twice the resolution. The resulting catalogue will contain about 250,000 sources at 92 cm and 30,000 sources at 49 cm.

The VLA FIRST survey is now in its second year. We have completed mapping over 1500 deg2 of the North Galactic Cap and present here the catalog of the 138,000 radio sources detected therein. We discuss the statistics of this new catalog including the two-point angular correlation function for all radio emitters, present our optical identification of 24,000 sources using the APM catalog, and report followup studies on radio variability, X-ray source identification, and our bright quasar sample.

Early large scale radio surveys of the sky were made with instruments with poor imaging quality and were limited to measuring positions and brightnesses of discrete sources. In recent decades radio interferometric arrays have dramatically increased their speed, sensitivity and ability to image the sky and several large scale radio surveys are currently being made with imaging instruments. One of these surveys is discussed in this paper.

During 1990, the Parkes radio telescope made a new, deep survey of the southern sky at 4850 MHz (the PMN Survey: see e.g. Griffith and Wright, 1993; Wright et al., 1994). The declination coverage of the survey was from δ = −87° to +10°. The flux limit of the survey was around 30 mJy, although dependent on declination. This survey increased the number of known, southern radio sources by a factor of about 6 to over 65,000.

DRAGNs (Double Radio sources Associated with Galactic Nuclei, Leahy 1991) are the class of powerful extragalactic radio sources thought to be produced by the interaction of a jet with the ambient medium. They exhibit strong cosmological evolution in comoving number density; at z ≃ 2 the “classical double” FR II DRAGNs were ≃ 1000 times as common as they are now (Dunlop & Peacock 1990).

To understand this, systematic studies of complete DRAGN samples at low and high z and differing levels of flux density are required, in order to resolve the P – z ambiguity. The Distant DRAGNs Survey is a long-term project to image with the VLA and MERLIN, matched samples of DRAGNs at high redshift.

We have collected multi-waveband (radio, optical and X-ray) data for a complete sample of southern radio sources. The sample includes 88 objects selected from the Wall & Peacock (1985) catalogue that is complete down to S2.7GHz = 2 Jy, δ < 10° and the z < 0.7. This database (Tadhunter et al. (1993), Morganti et ai. (1993), and Siebert et al. these Proceedings) provides an important tool for investigating the nature of anisotropies and orientation effects in AGN and the physical causes of the correlation between their emission at different frequencies.

Most known galaxies at high redshifts have been found by concentrating on ultra steep spectrum (α≳l) sources in low frequency radio surveys (eg. Rottgering et al., 1994; McCarthy et al., 1990). We have been carrying out a systematic study of a large and complete sample from the 408 MHz Molonglo Reference Catalogue which is not biased by any spectral index criterion. Containing 558 sources, defined by S408 ≥ 0.95 Jy; −30° < δ < −20° and the RA ranges of 20h 20m to 06h00m and 09h20m to 14h00m, our sample is about 3 times larger in size and 5 times deeper in flux density than the well studied 3CRR sample.

The use of radio sources to identify the most distant object in the Universe has been proved to be a very successful approach in observational cosmology. Studies of high flux, powerful 3CR and 1-Jy galaxies show dramatic evidence for color and luminosity evolution, reaching to look-back times 80% of the Hubble time. In order to disentangle the selection effect, correlation with redshift, and correlation with radio power, it is necessary to obtain well defined, complete samples of radio galaxies at a large range of redshifts, and with a wide baseline of radio power. We need the identifications of complete samples in the flux range of a factor 10 smaller than 3CR sample. The B3VLA sample (Vigotti et al. 1989) is a subset of 1050 sources selected in restricted areas at high galactic latitudes from the B3 survey, which is complete down to S(408 MHz) = 100 mJy. For the B3VLA sample detailed VLA maps were obtained at 1.4 GHz using A, C and D arrays. We are conducting a long-term effort to provide optical ID's and redshifts for well-defined, complete subsamples of the B3VLA survey (Djorgovski et al. 1990, Vigotti et al. 1990, Thompson et al., 1994), a similar effort is being conducted independently by others. We present here the “status of the art” for the B3VLA sample: a new low flux sample of 124 QSS selected at meter wavelenghts, a sample of 194 radio galaxies (77 with measured redshift) and a sample of 732 Empty Fields (EF : no optical counterpart on POSS I plate).

In two strips of 22° × 1° and 5° × 1° near the SGP Vettolani et al. (1993, IA U Symposium 161, “Astronomy from Wide Field Imaging”, H.T. MacGillivray ed., Reidel, in press) have made a deep redshift survey as an ESO Key Project. All the galaxies down to bJ ≃ 19.4 were observed with the OPTO-PUS multi-fiber spectrograph on the 3.6 m telescope in La Silla, yielding 3348 redshifts. The survey has a typical depth of z = 0.1. It fully samples the optical luminosity function down to B = −15 and various galaxy populations (e.g. normal galaxies, LSBDs and BCDs) are present. Interestingly, emission lines (OII, Hβ, OIII) have been found in a large fraction of the galaxy spectra (≃ 40%), suggesting strong evolution of the galaxy population in terms of enhanced star formation.

The Marano Field (centered at α(2000)=03h 15m 09s δ(2000)= −55° 13′ 57″) is a deep ROSAT field (flux limit ≃ 4 × 10–15 erg cm–2 s–1), which has been entirely covered by ESO 3.6 m plates and in the inner part by deep CCD exposures. In order to follow up these data in other wavelength regions, deep radio observations of this field have been carried out with the Australia Telescope Compact Array (ATCA) at 1.370 and 2.378 GHz. The minimum reached rms noise value is ≃42 μJy at both frequencies. 80 and 45 sources form complete samples above 5.5 σlocal level at 1.370 and 2.378 GHz respectively, in a square area of ≃0.34 sq. deg. Almost all of the sources detected at 2.378 GHz have been detected also at 1.370 GHz.

Using phase-referencing, the coherent integration time of VLBI observations can be substantially increased, permitting observations of weaker (≃mJy) target sources (see e.g. Beasley & Conway 1995). The position of a source can also be accurately measured relative to a reference source, allowing absolute and proper-motion measurements, optical-radio image alignment, and alignment of images made at different frequencies.

The VSOP (VLBI Space Observatory Programme) mission is being developed by the Institute of Space and Astronautical Science (ISAS), in close collaboration with the National Astronomical Observatory (NAO) of Japan. NASA and NRAO of the USA are key collaborating institutions, and most radio-telescopes world-wide will participate in some VSOP observations.

In September 1996 the first dedicated VLBI spacecraft, VSOP, will be launched. This Japanese spacecraft operating in conjunction with ground-based VLBI arrays such as the EVN or VLBA will enable observers to routinely undertake VLBI observations with maximum baseline lengths of 2.6 Earth diameters and a resolution of 55 μas at the highest operating frequency of 22 GHz. In this paper we present a brief overview of the imaging capability of the VSOP mission together with an example of an imaging simulation.