Multi-wavelength Properties of Active Galactic Nuclei

Dear Colleagues,

The multi-wavelength study of active galactic nuclei (AGNs) dates back to the 1970s, when the need to obtain observations taken "at the same time and at different wavelengths" started to emerge. At the very beginning, radio and optical data were the main windows through which to investigate these extragalactic sources. The advent of both space- and ground-based facilities allowed us to investigate almost the entire electromagnetic spectrum, spanning about 20 orders of magnitude in energy.

Multi-wavelength studies of AGNs allow us to probe different physical structures of these sources, from the boundaries of central black holes to kiloparsec scales typical of emerging jets.

The present Special Issue aims to discuss some of the currently open questions on AGNs from a multi-wavelength point of view, including both observational and theoretical results. Potential topics include but are not limited to the following:

• Is there a consensus on what a jetted source looks like?
• How do we investigate the central black hole? What if it is a binary structure?
• How does a jet form and propagate, and what does it look like at different wavelengths?
• How do we investigate AGN winds?
• How can different wavelengths probe different AGN structures?
• What can we infer from theoretical modelling from the spectral energy distribution?
• How can AGNs probe fundamental physics?
• How do we exploit AGN multi-wavelength catalogues?
• How will new facilities allow us to shed light on AGN controversies?

Prof. Stefano Vercellone
Guest Editor

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