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The apparent change in the composition of the parent optical objects of radio sources around 1 mJy (at 1.4 GHz) is now well established, although there is still some debate about the relative importance of classical radio galaxies and star-forming galaxies at sub-mJy levels (see e.g. Gruppioni et al. 1999, MNRAS, 304, 199; Prandoni et al. 2001, A&A, 369, 787). It is clear, however, that at μJy levels star-forming galaxies are dominant (see Fomalont et al. 1997, ApJ, 475, L5; Haarsma et al. 2000, ApJ, 544, 641).

We present radio observations at 610 MHz, 330 MHz and 235 MHz, carried out with the Giant Metrewave Radio Telescope (GMRT, Pune, India) of three clusters of galaxies at different merging stages. The purpose of our work is to investigate the connection between cluster merger parameters (i.e. masses, ages, impact parameter) and the formation of radio halos and relic sources.

Over the last five decades, AGN studies have produced a number of spectacular examples of synergies and multifaceted approaches in astrophysics. The field of AGN research now spans the entire spectral range and covers more than twelve orders of magnitude in the spatial and temporal domains. The next generation of astrophysical facilities will open up new possibilities for AGN studies, especially in the areas of high-resolution and high-fidelity imaging and spectroscopy of nuclear regions in the X-ray, optical, and radio bands. These studies will address in detail a number of critical issues in AGN research such as processes in the immediate vicinity of supermassive black holes, physical conditions of broad-line and narrow-line regions, formation and evolution of accretion disks and relativistic outflows, and the connection between nuclear activity and galaxy evolution.

After four years of dedicated service from the new generation of X-ray telescopes, XMM-Newton and Chandra, as well as results obtained from various multiwavelength observations, we are at a good point to revisit the topic of AGN physics. This proceeding will review the basic open questions posed by earlier X-ray missions which have now been answered, as well as address new questions which still require further investigation. The topics critically discussed will include: the physics of the innermost region of AGN, the nature of sharp spectral drops in the high-energy spectra of NLS1s, as well as new aspects of Seyfert unification.

We discuss the potential of the SKA for doing deep surveys considering the limitations of sensitivity and confusion resulting from the expected high source density and finite source size. Array dimensions of several thousand or more may be needed to reduce confusion below the thermal noise.

The European VLBI Network (EVN) is in the process of establishing an e-VLBI array in which the radio telescopes and the EVN correlator at JIVE are connected in real-time, via high-speed national fibre optic networks and the pan-European research network, GÉANT. This paper reports on recent test results, including the production of the first real-time e-VLBI astronomical image. In a parallel and related development, the field-of-view of VLBI is also expanding by many orders of magnitude, and the first results of deep, wide-field surveys capable of detecting many sources simultaneously are summarised. The detection of sources as faint as 10 microJy should soon be possible in the era of “Mk5” and e-VLBI.

The H·E·S·S· (High Energy Stereoscopic System) Phase-I is comprised of four Imaging Atmospheric Cherenkov Telescopes (IACTs) for observation of galactic and cosmic sources of Very High Energy (VHE) gamma rays, with a significant improvement in sensitivity and a detection threshold below that of previous IACTs. Observations of Active Galactic Nuclei (AGNs) since the start of operations in June 2002 are presented, in particular for PKS 2155-304 and Mkn 421, along plans for Phase-II.

More than 40 years since the discovery of the AGNs, there are still fundamental questions related to the nature of these intriguing objects. In particular, the accretion processes onto their super-massive black holes and the mechanisms through which their relativistic jets are formed, accelerated and collimated are still not well understood. Great effort has been made during the last decade to push the mm-VLBI technique to progressively shorter wavelengths, offering the best tool to observe the innermost regions of the jets and study the physics involved in their behaviour.

I explore a possibility to measure the gravitational redshift (GR) effect in the gravitational field of massive central nuclei residing in active galaxies (AGN). The activity of central nuclei is associated with the bipolar jet ejection of relativistic plasma which produces strong radio emission. I consider the behavior of the flux density variations of the jet plasma as a result of GR effect, and I discuss possibilities to detect the GR effect from the relativistic jets of compact AGN with present and future radio facilities.

Preparation of Space VLBI (SVLBI) mission titled RADIOASTRON (see ) requires, particularly, the developing of new software methods for data processing. We present the method. Maps of 2 sources from the RADIOASTRON listing had been observed with VLBA in 2 and 8 GHz bands simultaneously are demonstrated. We have used the MFS method to reconstruct 5 GHz images of these sources.