Extragalactic Relativistic Jets and Nuclear Regions in Galaxies

Substantial progress achieved during the past decade in studies of active galactic nuclei (see [25] for a review of recent results) has brought an increasingly wider recognition of the ubiquity of relativistic outflows (jets) in galactic nuclei [5, 43] turning them into an effective probe of nuclear regions in galaxies [21]. Emission properties, dynamics, and evolution of an extragalactic jet are intimately connected to the characteristics of the supermassive black hole, accretion disk and broad-line region in the nucleus of the host galaxy [25]. The jet continuum emission is dominated by non-thermal synchrotron and inverseCompton radiation [40]. The synchrotron mechanism plays a more prominent role in the radio domain, and the properties of the emitting material can be assessed using the turnover point in the synchrotron spectrum [20], synchrotron self-absorption [19], and free-free absorption in the plasma [12, 42]. High-resolution radio observations access directly the regions where the jets are formed [11], and trace their evolution and interaction with the nuclear environment [30]. Evolution of compact radio emission from several hundreds of extragalactic relativistic jets is now systematically studied with dedicated monitoring programs and large surveys using very long baseline interferometry (such as the 15GHz VLBA survey [13] and MOJAVE [18]). These studies, combined with optical and X-ray studies, yield arguably the most detailed picture of the galactic nuclei. Presented below is a brief summary of recent