A multi-wavelength view of Active Galactic Nuclei with an emphasis on gamma-rays

Abstract

Active Galactic Nuclei (AGN) are remarkable astronomical sources emitting over the whole electromagnetic spectrum, with different bands providing unique windows on distinct sub-structures and their related physics. AGN come in a large number of types only partially related to intrinsic differences. I highlight here the most important AGN classes, namely jetted and non-jetted, radiatively efficient and inefficient, and face-on and edge-on, the source types selected by different bands together with the most important selection effects and biases, and the underlying emission processes, emphasising the gamma-ray band. I then conclude with a look at some open issues in AGN research and at the main new astronomical facilities, which will provide us with new data to tackle them.

Invited talk at the 7th Heidelberg International Symposium on High-Energy Gamma-Ray Astronomy, July 4-8, 2022, Barcelona, Spain. 13 pages, 1 figure. To appear in Proceedings of Science