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BOLOGNA UNIVERSITY |
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| FACULTY OF SCIENCES MM.FF.NN | ||
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Prof. Gabriele Giovannini phone: (+39) 051-2095716 fax : (+39) 051-2095700 email: ggiovannini@ira.cnr.it RESEARCH INTERESTS: At present main fields of research are the study in the radio band of radio galaxies at very high angular resolution (milliarcsecond) with the Very Long Baseline Interferometry technique (VLBI) and the observation and study of low brightness extended sources connected to clusters of galaxies (Halos and Relics). 1. Radio Galaxies properties at parsec resolution: The study of the parsec scale properties of radio galaxies is crucial to obtain information on the nature of their central engine, and provides the basis ofthe current unified theories, which suggest that the appearance of active galactic nuclei strongly depends on orientation. To this aim, we undertook a project of observations of a complete sample of radio galaxies selected from the B2 and 3CR catalogs. Final results have been published in 2001. For a deeper study on this topic we recently selected a second sample with all the B2 and 3CR radio sources present in the same sky region of the first sample and z 0.1 (i.e. no constrain on the core flux density). This sample consists of 95 sources. At present we have obtained detailed observations on 54/95 sources. Preliminary results show that the jet Lorentz factor is between 3 and 10, and that highly relativistic parsec scale jets have been found regardless of radio source power. Sources with a different kpc scale morphology, and total radio power have pc scale jets moving at the same velocity. Single interesting sources have been studied in detail. Moreover a homogeneous sample of nearby BL-Lac sources have been selected and it is under study with VLA and VLBI observations to understand pc scale jet physical properties in low power radio sources.
2. Non thermal emission in Clusters of Galaxies: In some clusters of Galaxies diffuse radio sources, which cannot be obviously associated with the individual galaxies, are present, thus demonstrating the existence of non-thermal processes in the ICM. These source are named radio halos or relics according to their position with respect to the cluster center and to their properties. Their synchrotron radio emission implies magnetic fields of the order of 0.1-1 microGauss, and relativistic particles of Lorentz factor >>1000. The importance of these sources is that they are large scale features, which are related to other cluster properties in the optical and X-ray domain, and are thus directly connected to the cluster history and evolution. Halos and relics are found in clusters which have recently undergone a merger event, thus leading to the idea that they originate from particle acceleration in cluster merger turbulence and shocks. The formationand evolution of these sources is however still under debate: radio emitting electrons could be reaccelerated cosmic rays, or accelerated from the thermal population, or could be produced as a result of the interaction between cosmic-ray protons and the ICM (secondary electrons models).
MAIN COLLABORATORS: Bill Cotton (NRAO - Charlottesville - USA) Daniele Dallacasa (Astronomy Dept. Bologna) Luigina Feretti (IRA - CNR Bologna) Marcello Giroletti (PhD - Astronomy Dept. Bologna) Federica Govoni (Astronomy Dept. Bologna) Lucas Lara (Granada University) Greg Taylor (NRAO Socorro, USA) Tiziana Venturi (IRA - CNR Bologna)
Some published papers in the last 5 yrs:
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| Last update: 30/06/2003 |
http://urania.bo.astro.it/giovannini.htm |
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