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To date, PMN J2134-0419 (at a redshift z=4.33) is the second most distant quasar known with a milliarcsecond-scale morphology permitting direct estimates of the jet proper motion. Based on two-epoch observations, we constrained its radio jet proper motion using the very long baseline interferometry (VLBI) technique. The observations were conducted with the European VLBI Network (EVN) at 5 GHz on 1999 November 26 and 2015 October 6. We imaged the central 10-pc scale radio jet emission and modeled its brightness distribution. By identifying a jet component at both epochs separated by 15.86 yr, a proper motion of mu=0.035 +- 0.023 mas/yr is found. It corresponds to an apparent superluminal speed of beta_a=4.1 +- 2.7 c . Relativistic beaming at both epochs suggests that the jet viewing angle with respect to the line of sight is smaller than 20 deg, with a minimum bulk Lorentz factor Gamma=4.3. The small value of the proper motion is in good agreement with the expectations from the cosmological interpretation of the redshift and the current cosmological model. Additionally we analyzed archival Very Large Array observations of J2143-0419 and found indication of a bent jet extending to ~30 kpc., 7 pages, 3 figures, 2 tables, accepted for publication in MNRAS

The Square Kilometre Array (SKA) will be the world’s largest and most sensitive radio telescope. It will address fundamental unanswered questions about our Universe including how the first stars and galaxies formed after the Big Bang, how dark energy is accelerating the expansion of theUniverse, the role of magnetism in the cosmos, the nature of gravity, and the search for life beyond Earth. This project envisages the construction of 133 15-m antennas in South Africa and 131072 log-periodic antennas in Australia, together with the associated infrastructure in the two desert sites. In addition, the SKA is an exemplar Big Data project, with data rates of over 10 Tbps being transported from the telescope to HPC/HTC facilities.

The Square Kilometre Array (SKA) will be an ultrasensitive radio telescope, built to further the understanding of the most important phenomena in the Universe, including some pertaining to the birth and eventual death of the Universe itself. Over the next few years, the SKA will make the transition from an early formative to a well-defined design. This paper outlines how the scientific challenges are translated into technical challenges, how the application of recent technology offers the potential of affordably meeting these challenges, and how the choices of technology will ultimately be made. The SKA will be an array of coherently connected antennas spread over an area about 3000 km in extent, with an aggregate antenna collecting area of up to 106 m 2 at centimeter and meter wavelengths. A key scientific requirement is the ability to carry out sensitive observations of the sky over large areas (surveys). The ldquosurvey speedrdquo of the SKA will be enabled by the application of the most up-to-date signal-processing technology available. The SKA science impact will be widely felt in astroparticle physics and cosmology, fundamental physics, galactic and extragalactic astronomy, solar system science, and astrobiology.

This paper summarizes some of the ongoing projects on the CORALZ sample, the first statistically complete sample of young radio galaxies. The low redshift of the sources in the sample (z < 0.16) makes them excellent targets for a comprehensive and homogeneous follow-up in virtually all bands of the electromagnetic spectrum. Here we report on the almost completed radio continuum observations which confirm the relatively young ages of the sources in the CORALZ sample. The radio spectra in addition with new measurements at 250 GHz indicate a large fraction of sources with excess mm-emission, probably due to radiation of cold dust. These sources are also excellent candidates for detection ofmolecular gas, which we have traced through CO observations in the 3-mm band in several cases. Additional molecules as H2O or OH are being observed. The atomic gas content is disclosed by H I absorption observations (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper presents a new sample of Compact Radio sources at Low Redshift (CORALZ), which is used to study the onset and evolution of young radio-loud active galactic nuclei (AGN) and their environments. The CORALZ sample consists of 28 sources, of which 17 form a ∼95 per cent statistically complete sample with S 1.4GHz >100 mJy and 0 < 2 arcsec, over the redshift range 0.005 < z < 0.16. The sample is selected from the Very Large Array (VLA) FIRST 1.4-GHz radio survey over an area of sky of 2850 deg 2 , cross-correlated with the APM Palomar Sky Survey (APM/POSS-I) catalogue. In contrast to most previous studies of young radio-loud AGN, no selection has been made on radio spectral characteristics. This is to enable investigation of the relation between radio spectra and morphologies, orientation and Doppler boosting in young radio sources, in an unbiased way. Remarkably, more than 90 per cent of the sources in the complete CORALZ sample are classified as Gigahertz Peaked Spectrum (six) or Compact Steep Spectrum (10) sources, and only one object shows indication of strong flux density variability. Several projects are under way to study this unique sample in detail, including investigation of the optical host galaxies and their emission line characteristics, radio morphologies and dynamical evolution, and the neutral hydrogen distribution and kinematics in absorption towards these strong compact radio sources.

We have determined the central velocity dispersion and surface brightness profiles for a sample of powerful radio galaxies in the redshift range 0.06

Compact Steep Spectrum (CSS) sources are known to show strong optical line emission (Gelderman & Whittle 1994) which is generally considered to be due to the interaction between the radio jet and the ISM. This argument is strengthened by the HST observations of Axon et al. (2000) which show this emission is frequently associated with the radio jet. Previous observations of the CSS quasar 3C 138 (Cotton et al. 1997) have shown that the bulk of the jet has very low amounts of Faraday rotation whereas the inner jet shows very high Faraday rotation (≈−5000 rad m −2 ). The inner jet is dominated by moving components which allows observing the fine scale of the Faraday screen as the components move behind it. We report the results of such a monitoring campaign which indicated that there is structure in the Faraday screen on the pc and possibly sub pc scale. Motions of the polarized component slowed dramatically during the course of these observations, limiting the region probed. The observations also strongly suggest that the polarized emission from the inner jet is seen through limited holes in a dense Faraday screen. In this case, the observed variations in Faraday rotation are possibly the result of jet-ISM interactions.

This paper describes the selection of a new southern/equatorial sample of Gigahertz Peaked Spectrum (GPS) radio galaxies, and subsequent optical CCD imaging and spectroscopic observations using the ESO 3.6m telescope. The sample consists of 49 sources with -40 20 degrees, and S(2.7GHz)>0.5 Jy, selected from the Parkes PKSCAT90 survey. About 80% of the sources are optically identified, and about half of the identifications have available redshifts. The R-band Hubble diagram and evolution of the host galaxies of GPS sources are reviewed.

Three high redshift radio galaxies, 1345+245 (4C 24.28, $z=2.889$), 1809+407 (4C 40.36, $z=2.267$) and 2349+289 (4C 28.58, $z=2.905$) were observed with VLBI at 327 MHz giving an angular resolution of $\simeq$40–100 mas and yielding images with the off-source noise level of 3$\sigma \simeq 3.5$ mJy/beam. On the centiarcsecond scale, the three sources are each characterized by two components with asymmetry both in flux density and in size. The compact components in the VLBI maps correspond to the hot spots in the VLA maps. No radio cores have been detected. The physical parameters for the components derived are consistent with a model in which shocks accelerate electrons in the hotspots.

A functional description is given of the new 16-station MarkIV VLBI data processor for the European VLBI Network. The data processor can operate in many configurations including sensitive continuum modes, line modes with unprecedented spectral resolution, and wide field imaging and pulsar gating modes. The EVN-MarkIV processor was developed by an international European/U.S. consortium. Several similar processors are deployed in both Europe and in the U.S.

Space very long baseline interferometry (VLBI) observations of the quasar 3C216 with the VLBI Space Observatory Programme (VSOP) reveal that the parsec scale structure of the source can be well described by compact jet models developed for interpreting the core region of radio-loud active galactic nuclei (AGN). The measured brightness temperature of T_(b) = 7.9*10^{11} K is comparable to the inverse Compton limit, from which we determine a lower limit of delta ~ 3.17 for the Doppler-boosting factor. The apparent transvers velocity of the superluminal component is beta_(app) = (3.0+-0.2) h^{-1} asuming a constant velocity, but deceleration of the jet material cannot be excluded from our data. A combination of the above values indicates that the viewing angle of the core-jet to the line-of-sight is less than 18.4 degrees, and the jet Lorentz-factor exceeds 3.16. The observed small size of the source is probably caused by both interaction with the interstellar medium, and a projection effect., 6 pages, 3 figures, accepted for publication by PASJ

We have analysed HALCA and global VLBI data for 2021+614, the first of eleven GPS quasars and galaxies to be observed by HALCA. We show that 2021+614 is a compact symmetric object of overall size ∼40 pc, and confirm that the speed of separation of the two dominant lobes is approximately one tenth of the speed of light. Its apparent age of less than 1000 years provides additional support for the contention that compact symmetric radio objects associated with galaxies are young radio sources and the possible precursors of the classical FR1 or FR2 radio galaxies.

Young radio-loud active galactic nuclei form an important tool to investigate the evolution of extragalactic radio sources. In this paper we present a summary of our recent work on the CORALZ sample of young radio sources at low redshift. We have found strong evidence that the radio spectral turnovers in GPS and CSS sources are caused by synchrotron selfabsorption (SSA): the CORALZ sources follow the well established relation between radio spectral peak frequency and largest angular size, but with significantly smaller sizes at any particular peak frequency, compared to more powerful and more distant GPS/CSS sources, as expected from SSA theory combined with simple self-similar evolution models. Current models that invoke free-free absorption (FFA) to explain the spectral turnovers in GPS and CSS sources can not easily explain the relatively small angular sizes found for the CORALZ sources. We therefore conclude that, although FFA may play a role in some sources, the radio spectral turnovers in GPS and CSS radio sources are generally caused by SSA (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We have analysed VSOP and global VLBI data at 5 GHz and VLBA + Effelsberg data at 15 GHz for 2021+614. By identifying the core as being between two bright hotspots, we show that 2021+614 is a compact symmetric object of size ∼40 pc. From comparison with earlier observations we deduce an apparent age of ≲375 yr for 2021+614. This provides additional support for the contention that compact symmetric radio objects associated with galaxies are in fact young radio sources and the possible precursors of the classical FR I or FR II radio galaxies.

We present results of VLBA observations of SS433 at two epochs at 5, 8.4, and 15 GHz. The AU-scale region of the source is resolved and shows the familiar quasi-symmetric core-jet structures. But at another epoch, the maps show bright knots ejected a few days before the observation, while the core-complex disappeared. The bright jet components are completely depolarised with fractional polarization less than 0.5%. We also present the first VLBI image of SS433 at 22 GHz.

A sample of 47 faint Gigahertz Peaked Spectrum (GPS) radio sources selected from the Westerbork Northern Sky Survey (WENSS, Rengelink et al. 1997), has been imaged in the optical and near infrared, resulting in an identification fraction of 87%. The R-I and R-K colours of the faint optical counterparts are as expected for passively evolving elliptical galaxies, assuming that they follow the R band Hubble diagram as determined for radio-bright GPS galaxies. We have found evidence that the radio spectral properties of the GPS quasars are different from those of GPS galaxies: The observed distribution of radio spectral peak frequencies for GPS sources optically identified with bright stellar objects (presumably quasars) is shifted compared with GPS sources identified with faint or extended optical objects (presumably galaxies), in the sense that a GPS quasar is likely to have a higher peak frequency than a GPS galaxy. This means that the true peak frequency distribution is different for the GPS galaxies and quasars, because the sample selection effects are independent of optical identification. The correlation between peak frequency and redshift as has been suggested for bright sources has not been found in this sample; no correlation exists between R magnitude (and therefore redshift) and peak frequency for the GPS galaxies. We therefore believe that the claimed correlation is actually caused by the dependence of the peak frequency on optical host, because the GPS galaxies are in general at lower redshifts than the quasars. The difference in the peak frequency distributions of the GPS galaxies and quasars is further evidence against the hypothesis that they form a single class of object., LaTeX, 12 pages. Accepted by MNRAS. For Fig. 8 and more info, see http://www.ast.cam.ac.uk/~snellen

The Westerbork Northern Sky Survey (WENSS) has been used to select a sample of Gigahertz Peaked Spectrum (GPS) radio sources at flux densities one to two orders of magnitude lower than bright GPS sources investigated in earlier studies. Sources with inverted spectra at frequencies above 325 MHz have been observed with the WSRT at 1.4 and 5 GHz and with the VLA at 8.6 and 15 GHz to select genuine GPS sources. This has resulted in a sample of 47 GPS sources with peak frequencies ranging from ~500 MHz to >15 GHz, and peak flux densities ranging from ~40 to ~900 mJy. Counts of GPS sources in our sample as a function of flux density have been compared with counts of large scale sources from WENSS scaled to 2 GHz, the typical peak frequency of our GPS sources. The counts can be made similar if the number of large scale sources at 2 GHz is divided by 250, and their flux densities increase by a factor of 10. On the scenario that all GPS sources evolve into large scale radio sources, these results show that the lifetime of a typical GPS source is ~250 times shorter than a typical large scale radio source, and that the source luminosity must decrease by a factor of ~10 in evolving from GPS to large scale radio source. However, we note that the redshift distributions of GPS and large scale radio sources are different and that this hampers a direct and straightforward interpretation of the source counts. Further modeling of radio source evolution combined with cosmological evolution of the radio luminosity function for large sources is required., LaTeX, 15 pages, 8 figs. To be published in A&AS. For more info see http://www.ast.cam.ac.uk/~snellen

Radio supernovae are rare events among supernovae, usually taking place in distant galaxies. In recent years, great progress has been made in the study of radio supernovae with high angular resolution, due to advances in the VLBI technique and to the lucky occurrence of the powerful supernova SN 1993J in M81 only 3.6 Mpc distant. Its spatial structure has been unveiled and its expansion rate determined at 3.6 cm. Here we present new preliminary VLBI results on the expansion of this supernova at 6 and 13 cm. We resolve the shell at both wavelengths. The size estimates at 6 cm indicate a lower expansion rate than previously estimated. This may be the first evidence of deceleration.

The Westerbork Northern Sky Survey (WENSS) has been used to select a population of Gigahertz Peaked Spectrum (GPS) sources with flux densities one or two orders of magnitude lower than previous samples. We present preliminary VLBI observations of this new GPS sample.

The Russian Academy of Sciences and Federal Space Agency, together with the participation of many international organizations, worked toward the launch of the RadioAstron orbiting space observatory with its onboard 10-m reflector radio telescope from the Baikonur cosmodrome on July 18, 2011. Together with some of the largest ground-based radio telescopes and a set of stations for tracking, collecting, and reducing the data obtained, this space radio telescope forms a multi-antenna ground-space radio interferometer with extremely long baselines, making it possible for the first time to study various objects in the Universe with angular resolutions a million times better than is possible with the human eye. The project is targeted at systematic studies of compact radio-emitting sources and their dynamics. Objects to be studied include supermassive black holes, accretion disks, and relativistic jets in active galactic nuclei, stellar-mass black holes, neutron stars and hypothetical quark stars, regions of formation of stars and planetary systems in our and other galaxies, interplanetary and interstellar plasma, and the gravitational field of the Earth. The results of ground-based and inflight tests of the space radio telescope carried out in both autonomous and ground-space interferometric regimes are reported. The derived characteristics are in agreement with the main requirements of the project. The astrophysical science program has begun., 54 pages, 11 figures; published by Astronomicheskij Zhurnal (in Russian) and Astronomy Reports (in English)

The Square Kilometre Array (SKA) is the future centimeter- and meter-wavelength telescope with a sensitivity about 50 times higher than present instruments. Its Key Science Projects are (a) Astrobiology including planetary formation within protoplanetary disks; (b) Testing theories of gravitation using an array of pulsars to search for gravitational waves and relativistic binaries to probe the strong-field regime; (c) The origin and evolution of cosmic magnetism, both within the Galaxy and in intergalactic space, via an all-sky grid of magnetic field measurements; (d) The end of the Dark Ages, involving searches for a neutral hydrogen signature, the first supermassive black holes, and the first metal-rich systems; and (e) A hydrogen census to a redshift z greater than or equal to 1 from which to study the evolution of galaxies, dark matter, and dark energy. The SKA will operate at wavelengths from 1.2 cm to 3 m (0.1-25 GHz), providing milliarcsecond resolution at the shortest wavelengths. Its instantaneous field of view will be about 1° (20 cm wavelength), with many simultaneous beams on the sky. The Reference Design is composed of a large number of small dish antennas, building upon an original US proposal. In order to obtain these capabilities at a reasonable cost, significant engineering investments are being made in antennas, wideband feeds and receivers, and signal processing; aperture arrays (phased feeds) are also being investigated in Europe for the lower frequencies. Candidate sites are in Argentina, Australia, China, and South Africa, with a short list of acceptable sites anticipated late in 2006.

Young radio-loud active galactic nuclei form an important tool to investigate the evolution of extragalactic radio sources. To study the early phases of expanding radio sources, we have constructed CORALZ, a sample of 25 compact ($��, Accepted for publication in A&A. 21 pages, 14 figures

We present high-resolution observations carried out at 18-cm wavelength with MERLIN and the European VLBI Network (EVN) on eight compact steep-spectrum (CSS) sources from the 3CR catalogue (3C43, 186, 190, 286, 299, 318, 346, 454). The typical resolution achieved on maps made with combined data is ≤ 30 mas. The relationships between compact features on these maps with low-brightness extended regions seen in the MERLIN data alone can be found. Prominent jets were found in seven sources, enabling us to discuss the properties of jets for the 3CR sample of CSS sources in general

IVS is under study in ESA as a second generation space VLBI observatory. The mission concept calls for a 25 m diameter radio telescope in space funded by the principal space agencies. Orbiting the Earth and observing in concert with the established ground-based VLBI arrays in Europe, USA, USSR and Australia, IVS will provide high quality images of galactic and extragalactic radio sources at wavelengths spanning the radio band from decimetres to millimetres with resolution as high as 10 micro arcseconds and sensitivity equal to those of ground-based images. New features of IVS compared to the first generation missions are: a more than order of magnitude increase in sensitivity; an order of magnitude increase in maximum angular resolution; extension of the wavelength range to the millimetre band; and the capability to operate as a stand-alone radio telescope enabling it to explore new frontiers in spectral line and microwave background research, in particular the distribution of galactic molecular oxygen and Compton scattering of the microwave background by foreground cluster gas.

Gigahertz Peaked Spectrum (GPS) radio galaxies are generally thought to be the young counterparts of classical extended radio sources. Statistically complete samples of GPS sources are vital for studying the early evolution of radio-loud AGN and the trigger of their nuclear activity. The 'Parkes half-Jansky' sample of GPS radio galaxies is such a sample, representing the southern counterpart of the 1998 Stanghellini sample of bright GPS sources. As a first step of the investigation of the sample, the host galaxies need to be identified and their redshifts determined. Deep R-band VLT-FORS1 and ESO 3.6m EFOSC II images and long slit spectra have been taken for the unidentified sources in the sample. We have identified all twelve previously unknown host galaxies of the radio sources in the sample. Eleven have host galaxies in the range 21.0 < Rc < 23.0, while one object, PKS J0210+0419, is identified in the near infrared with a galaxy with Ks = 18.3. The redshifts of 21 host galaxies have been determined in the range 0.474 < z < 1.539, bringing the total number of redshifts to 39 (80%). Analysis of the absolute magnitudes of the GPS host galaxies show that at z > 1 they are on average a magnitude fainter than classical 3C radio galaxies, as found in earlier studies. However their restframe UV luminosities indicate that there is an extra light contribution from the AGN, or from a population of young stars., Accepted for publication in A&A. 14 pages, 8 figures

1 Istituto di Radioastronomia del CNR, Via P. Gobetti 101, I-40129 Bologna, Italy 2 Radioastronomisches Institut der Universitat Bonn, Auf dem Hugel 71, D-53121 Bonn, Germany 3 Sterrewacht Leiden, PO Box 9513, NL-2300 RA Leiden, The Netherlands 4 Int. SKA Project Office, Postbus 2, NL-7990 AA Dwingeloo, The Netherlands 5 Institute for Astronomy, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, United Kingdom

LOFAR (Low Frequency Array) is an innovative radio telescope optimized for the frequency range 30-240 MHz. The telescope is realized as a phased aperture array without any moving parts. Digital beam forming allows the telescope to point to any part of the sky within a second. Transient buffering makes retrospective imaging of explosive short-term events possible. The scientific focus of LOFAR will initially be on four key science projects (KSPs): 1) detection of the formation of the very first stars and galaxies in the universe during the so-called epoch of reionization by measuring the power spectrum of the neutral hydrogen 21-cm line (Shaver et al. 1999) on the ~5' scale; 2) low-frequency surveys of the sky with of order $10^8$ expected new sources; 3) all-sky monitoring and detection of transient radio sources such as gamma-ray bursts, x-ray binaries, and exo-planets (Farrell et al. 2004); and 4) radio detection of ultra-high energy cosmic rays and neutrinos (Falcke & Gorham 2003) allowing for the first time access to particles beyond 10^21 eV (Scholten et al. 2006). Apart from the KSPs open access for smaller projects is also planned. Here we give a brief description of the telescope., 2 pages, IAU GA 2006, Highlights of Astronomy, Volume 14, K.A. van der Hucht, ed

The EVN is currently in the midst of an ambitious upgrade programme. The hardware and software developments in progress are briefly summarized, and changes in operational practice and user support are also described.

3C286 (1328+307) is a powerful radio source identified with a quasar at z=0.849. There is a foreground galaxy responsible for an H I absorption line system at z=0.6922 (Brown & Roberts 1973), centered approximately 2.″5 to the southeast of 3C286. The radio source has a steep spectrum (α = −0.61, Sv ∝ vα between 1.4 and 15 GHz) which turns over at about 100 MHz. Subarcsecond resolution radio images show a misaligned triple structure, dominated by the central component (Spencer et al. 1989) which accounts for at least 95% of the total flux density at all frequencies. 3C286 is one of the strongest extragalactic sources in polarized emission (0.84 Jy at 5 GHz and 1.41 Jy at 1.4 GHz) and with a rotation measure close to 0 rad m–2 (Rudnick and Jones 1983). Hence the observed orientation of the electric field vector is essentially independent of frequency.

[1] The Mark 4 VLBI correlator is a station-based system designed to process data from up to 16 stations at an aggregate data rate of 1 Gbps/station. It is compatible with data recorded on Mark 3A, Mark 4, and VLBA tape-based data-acquisition systems, as well as the new disc-based Mark 5 system which also supports both real-time and quasi-real-time data-transmission over high-speed networks. The system incorporates an XF algorithm implemented in a custom-VLSI chip that can be flexibly configured to cross-correlate VLBI data from one to four baselines of a single 2-bits/sample channel at 64 Mbps/channel/station. Each chip also incorporates integral phase generators, rotators and vernier-delay management circuitry. Each of the sixteen Correlator Boards in the system contains 32 correlator chips and can process up to 8192 complex lags that can be flexibly traded off between baselines, lags and channels. Innovative algorithms allow station-model information to be injected periodically into the data stream from each channel of each station to drive the correlation process. The correlator control software allows up to four independent multistation scans to be processed simultaneously to significantly improve processing efficiency.

We carried out VLA observations in A configuration at 74 MHz of a new sample of faint Compact Steep-Spectrum (CSS) radio sources as part of a comprehensive project to study the nature and evolution of peaked-spectrum radio sources. In conjunction with higher frequency spectral information this has enabled us to determine the peak frequency and peak flux density of the spectral turnover for 35 faint CSS radio sources. Spectra are presented. An analysis is given of the quality of the images and their suitability for integrated intensity measurements of the CSS radio sources.

The main-line OH masers around 4 AGB stars have been observed with the NRAO Very Long Baseline Array (VLBA) at 8 epochs over a period of 2.5 years. Using a phase referencing technique, the position of the most compact maser spot of each star was monitored with respect to two extragalactic reference sources. For U Her and W Hya, we observe the most blue-shifted maser spot, while for R Cas and S CrB we only detect a compact red-shifted maser spot. We managed to determine an accurate proper motion and parallax for U Her, R Cas and S CrB, while additional motion of the compact blue-shifted maser of W Hya is shown to possibly be related to the stellar pulsation. The motion and radio position are compared with the stellar trajectory and absolute optical position determined by the Hipparcos satellite. For U Her and W Hya, the most blue-shifted maser is consistent with the amplified stellar image. The new distances are compared with several published P--L relations, and in this respect the VLBI distances seem an improvement upon the Hipparcos distances., Comment: 13 pages, 12 figures; accepted by A&A

GPS and CSS radio sources are the objects of choice to investigate the evolution of young radio-loud AGN. Previous investigations, mainly based on number counts and source size distributions, indicate that GPS/CSS sources decrease significantly in radio power when evolving into old, extended objects. We suggest this is preceded by a period of increase in radio luminosity, which lasts as long as the radio source is confined within the core-radius of its host galaxy. We have selected a sample of nearby compact radio sources, unbiased by radio spectrum, to determine their radio luminosity function, size distribution, dynamical ages, and emission line properties in a complete and homogeneous way. First results indicate that the large majority of objects (>80%) exhibit classical GPS/CSS radio spectra, and show structures consistent with the being compact double, or compact symmetric objects. This sample provides and ideal basis to further test and constrain possible evolution scenarios, and to investigate the relation between radio spectra and morphologies, orientation and Doppler boosting in samples of young radio-loud AGN, in an unbiased way., LaTeX, 8 pages, 3 figs: Accepted by Publications of the Astronomical Society of Australia, as part of the proceedings of the 3rd GPS/CSS workshop, eds. T. Tzioumis et al

We present and discuss observations made with MERLIN and VLBI at 1.7 and 5 GHz of the two CSS quasars 3C 43 and 3C 298. They show quite different morphologies, the former being a very distorted triple radio source, the latter a small FRII type object. Relativistic effects and structural distortions are discussed. Source ages are evaluated to be of the order of ~10^5 years, therefore 3C 43 and 3C 298 can be considered fairly ''young'' radio sources. Some inference is also derived on the properties of the medium surrounding the radio emitting regions in these sub-galactic objects, whose density could be as low as 10^-3 cm^-3., Comment: 14 pages, A&A accepted

We present VLBI and MERLIN data at 1.66 and 4.99 GHz on the central component coincident with the nucleus of the giant radio galaxy, 3C236. The nuclear radio structure is composed of two complexes of emission which are resolved on scales from 1 milli-arcsec (mas) to 1 arcsec. Oscillations with an amplitude of about 5 degrees can be seen in the compact radio structure. Spectral index distributions are plotted at angular resolutions of 10 and 25 mas and allow us to identify the core component in the south-east emission complex. Re-examination of the HST WFPC-2 image of 3C236 by de Koff et al. (2000), shows that the normal to the dust disk in the nucleus is ~30 degrees from the plane of the sky and within 12 degrees of parallel to the overall orientation of the radio source. We suggest that the radio axis is also at an angle of ~30 degrees to the plane of the sky and that the north-west jet is on the approaching side. This orientation implies an overall size of 4.5 Mpc (H_o = 75 km/s/Mpc, q_o = 0.5) for 3C236. The coincidence of a dust feature and the south-east compact jet, within the astrometric errors, leads us to suggest that the dust may be in the form of a cloud encountered by the jet in the first ~400 pc of its journey out from the nucleus. One-sided emission at 5 GHz on 1 mas scales would suggest that the jets are ejected initially at, 11 pages, 9 figures, accepted for Astronomy and Astrophysics

We present spectroscopic observations of a sample of faint Gigahertz Peaked Spectrum (GPS) radio sources drawn from the Westerbork Northern Sky Survey (WENSS). Redshifts have been determined for 19 (40%) of the objects. The optical spectra of the GPS sources identified with low redshift galaxies show deep stellar absorption features. This confirms previous suggestions that their optical light is not significantly contaminated by AGN-related emission, but is dominated by a population of old (>9 Gyr) and metal-rich (>0.2 [Fe/H]) stars, justifying the use of these (probably) young radio sources as probes of galaxy evolution. The optical spectra of GPS sources identified with quasars are indistinguishable from those of flat spectrum quasars, and clearly different from the spectra of Compact Steep Spectrum (CSS) quasars. The redshift distribution of the GPS quasars in our radio-faint sample is comparable to that of the bright samples presented in the literature, peaking at z ~ 2-3. It is unlikely that a significant population of low redshift GPS quasars is missed due to selection effects in our sample. We therefore claim that there is a genuine difference between the redshift distributions of GPS galaxies and quasars, which, because it is present in both the radio-faint and bright samples, can not be due to a redshift-luminosity degeneracy. It is therefore unlikely that the GPS quasars and galaxies are unified by orientation, unless the quasar opening angle is a strong function of redshift. We suggest that the GPS quasars and galaxies are unrelated populations and just happen to have identical observed radio-spectral properties, and hypothesise that GPS quasars are a sub-class of flat spectrum quasars., LaTeX, 13 pages. Accepted by MNRAS. For related papers see http://www.ast.cam.ac.uk/~snellen

This triennium began with an action to re-create the Terms of Reference for the Working Group Global VLBI (WG-GV). These had been lost over the years since the Group was established in 1990. Fortunately, the personal archive of one long-term member yielded a copy of the original memorandum by R. D. Ekers, which was found to coincide quite well with current practice and areas of interest. New Terms of Reference, based on modern conditions, were drafted and accepted by both IAU and URSI.

GPS sources are the objects of choice to study the initial evolution of extragalactic radio sources, since it is most likely that they are the young counterparts of large scale radio sources. Correlations found between their peak frequency, peak flux density and angular size provide strong evidence that synchrotron self absorption is the cause of the spectral turnovers, and indicate that young radio sources evolve in a self-similar way. The difference in redshift distribution between young and old radio sources must be due to a difference in slope of their luminosity functions, and we argue that this slope is strongly affected by the luminosity evolution of the individual sources. A luminosity evolution scenario is proposed in which GPS sources increase in luminosity and large scale radio sources decrease in luminosity with time. It is shown that such a scenario agrees with the local luminosity function of GPS galaxies., Late, 6 pages, 2 figs. To appear in the proceedings of EVN/JIVE Symposium No 4, New Astronomy Reviews (eds. Garrett et al.). For related papers, see http://www.ast.cam.ac.uk/~snellen

Gigahertz Peaked Spectrum (GPS) radio galaxies are generally thought to be the young counterparts of classical extended radio sources and live in massive ellipticals. GPS sources are vital for studying the early evolution of radio-loud AGN, the trigger of their nuclear activity, and the importance of feedback in galaxy evolution. We study the Parkes half-Jansky sample of GPS radio galaxies of which now all host galaxies have been identified and 80% has their redshifts determined (0.122 < z < 1.539). Analysis of the absolute magnitudes of the GPS host galaxies show that at z > 1 they are on average a magnitude fainter than classical 3C radio galaxies. This suggests that the AGN in young radio galaxies have not yet much influenced the overall properties of the host galaxy. However their restframe UV luminosities indicate that there is a low level of excess as compared to passive evolution models., To appear in the proceedings of "Formation and Evolution of Galaxy Bulges", IAUS 245; M. Bureau, E. Athanassoula & B. Barbuy, eds

A new four-image gravitational lens system, B0712+472, has been discovered during the Cosmic Lens All-Sky Survey. This system consists of four flat-spectrum radio images that are also seen on a Hubble Space Telescope (HST) image, together with the lensing galaxy. We present MERLIN, VLA and VLBA maps and WHT spectra of the system as well as the HST images. The light distribution of the tensing galaxy is highly elongated and so too is the mass distribution deduced from modelling. We suggest a redshift of similar to 1.33 for the lensed object the lens redshift will require further investigation. The discovery of this new system further increases the ratio of four-image to two-image lens systems currently known, exacerbating problems of required ellipticity of matter distributions in lensing galaxies.

We have discovered a new gravitational lens in the Cosmic Lens All-Sky Survey (CLASS). B2045+265 is a four-image system with a maximum separation of 1.9 arcsec. A fifth radio component is detected, but its radio spectrum and its positional coincidence with infrared emission from the lensing galaxy strongly suggests that it is the radio core of the lensing galaxy. This implies that the B2045+265 system consists of a flat-spectrum radio source being lensed by another flat-spectrum radio source. Infrared images detect the lensed images of the background source and the lensing galaxy. The lensed images have relative positions and flux densities that are consistent with those seen at radio wavelengths. Spectra of the system reveal a lens redshift of z_l=0.8673 and a source redshift of z_s=1.28. The image splitting and system redshifts imply that the projected mass inside the Einstein radius of the lensing galaxy is M_E=4.7x10^{11} h^{-1} M_sun. An estimate of the light emitted inside the Einstein radius gives a mass-to-light ratio in the rest frame B band of (M/L_B)_E = 20 h (M/L_B)_sun. Both the mass and mass-to-light ratio are higher than what is seen in nearby Sa galaxies. In fact, the implied rotation velocity for the lensing galaxy is two to three times higher than what is seen in nearby spirals. The large projected mass inside the Einstein ring radius may be the result of a significant amount of dark matter in the system, perhaps from a compact group of galaxies; however, it may also arise from a misidentification of the source redshift. A simple model of the gravitational potential of the lens reproduces the image positions well, but further modeling is required to satisfy the constraints from the image flux density ratios. With further observations and modeling, this lens may yield an estimate of H_0., Comment: 18 pages, 15 figures. Accepted for publication in the Astronomical Journal (Feb 1999)

We report the discovery of the most complex arcsec-scale radio gravitational lens system yet known. B1933+503 was found during the course of the CLASS survey and MERLIN and VLA radio maps reveal up to 10 components. Four of these are compact and have flat spectra; the rest are more extended and have steep spectra. The background lensed object appears to consist of a flat spectrum core (quadruply imaged) and two compact "lobes" symmetrically disposed relative to the core. One of the lobes is quadruply imaged while the other is doubly imaged. An HST observation of the system with the WFPC2 shows a galaxy with an axial ratio of 0.5, but none of the images of the background object are detected. A redshift of 0.755 has been measured for the lens galaxy., Comment: 7 pages, 8 postscript figures, uses mn.sty and psfig.tex. To appear in MNRAS